LWS
Keyword Interface

Contents


Introduction

The present document describes the LWS keyword library and implicitly all of the functionality of the LWS instrument. In addition to describing the internal control of the LWS instrument, it also describes the manner in which the LWS team expects to be able to control (or interact with) all of the external interfaces, DCS, telescope chopper, IRE electronics, etc.


Basic Keyword Interface Design

In order for the LWS interface to look as uniform as possible with existing Keck software, we will make the LWS/IRE keyword interface part of the KTL keyword library and support KTL show, modify, and xshow commands. This design is essentially as described in Keck Software Document 45: LWS Host Software Design (Lupton, 1994). Also, BCE will be using qckMon calls to implement the Collect-Structure interface and these qckMon calls use a keyword-like structure so that mapping KTL keywords onto the qckMon software will be relatively straight forward.

Hence to be specific, the LWS can be run exclusively through its keywords using show and modify commands (e.g., show -service lws graraw, to show the raw motor position of the grating motor). In each of these cases, BCE supplies an RPC server and the LWS team supplies the KTL to RPC client-side translation layer. For the data acquisition software, BCE hasl written a data acquisition server that uses qckMon calls to access the Timing Generator and Co-Adder programs and the LWS project has written a data acquisition control program that uses KTL keywords to communicate to the BCE data acquisition RPC server. The current document describes the LWS/IRE keywords. Before going on to describe each of the keywords in detail, we would like to point out that there are two distinct types of keywords in the LWS keyword library. There are the so called "normal" keywords and there are the "cached" keywords. The cached keywords are for informational purposes only. In other words, setting the values of cached keyword causes no change in the status of the LWS instrument. An example of a cached keyword is objname (object name) or photondc (photon duty cycle). The values of these keywords are simply stored for informational purposes, perhaps to be written to a data file or to be displayed on the instrument control GUI. If a keyword is a cached keyword, this is indicated in the first line of the subsection describing the keyword.


Data File Specification Keywords

objname.a ­ ObjectName ­ string ­ read/write ­ cached
This keyword specifies the name of the object being observed for recording in the data header.
Keyword values: Character string.

outdir.a ­ OutputDirectory ­ string ­ read/write ­ normal
This keyword specifies output directory path for the data file.
Keyword values: Character string.

outfile.a ­ OutputFile ­ string ­ read/write ­ normal
This keyword specifies the name of the output data file.
Keyword values: Character string.

frameno.a ­ FrameIndexNumber ­ string ­ read/write ­ normal
This keyword specifies the index number of the data frame.
Keyword values: Character string.


Exposure Time Keywords

objtime ­ ObjectTime ­ double ­ read/write ­ cached
This keyword is used to specify the integration time that is to be spent on the object.
Keyword values: Units of this keyword are seconds.

exptime ­ ExposureTime ­ double ­ read/write ­ cached
This keyword specifies the total duration of the exposure.
Keyword values: Units of this keyword are seconds. This keyword gives the total exposure time required to ensure the specified value of objtime taking into account an equivalent exposure time on the sky and the observational inefficiencies.


Observing Mode Configuration Keywords

The fundamental apects of the LWS that need to be controlled in a routine manner by an observer are related to controlling the exposure time, the observing mode, and data archiving. Since certain aspects of the detector (e.g., pixel saturation) and chopping and nodding interact directly with each other and the efficiency of the observation, these aspects must also be controllable at some level by the observer. In this section we shall define keywords directly related to issues.

Observing Parameters

The fundamental parameters that an observer will normally control are given in the table ``Observing Parameters''. From these fundamental parameters all of the other related LWS and IRE keywords are derived.

Once the fundamental observing parameters are specified, all the dependent keywords can be calculated. Also, some of the specified values of the fundamental keywords must be reset in order to make them consistent with integer number of detector frames, chop cycles, and nod cycles, etc. The manner in which the dependent keyword values are calculated depends on the obsmode . These calculations will be described next.

Calculation of Dependent Keywords Values

chop-nod Mode:
To calculate the dependent keyword values in chop-nod mode, traverse the following equations once. (Note: certain fundamental keywords get recalculated. At each step, use the most current value of each keyword.)

where the function "CEILING" means to pick the next highest integer, and the function "ROUND" means to pick the closest integer.

Chop Mode:

Nod Mode:

Stare Mode:

Exposure Control Keywords

backrow.a ­ BackgroundRow ­ integer ­ read/write ­ normal
This keyword indicates the central row of the 3x3 pixel grid for the background measurement.
Keyword values: Dimensionless row number. Valid values lie in the range [1,96].

backcol.a ­ BackgroundColumn ­ integer ­ read/write ­ normal
This keyword indicates the central column of the 3x3 pixel grid for the background measurement.
Keyword values: Dimensionless column number. Valid values lie in the range [1,96].

backgrnd.a ­ Background ­ double ­ read only ­ normal
This keyword indicates the fraction of full well the detectors are running at. This keyword has its value updated every time the coadders read out. The value presented in average value of a 3×3 grid of adjacent pixels in the center of the good portion of the array.
Keyword values: The value of this keyword is a fraction in the range [0,1].

pxlev.a ­ PixelLevel ­ double ­ read only ­ normal
This keyword indicates the average fraction of the ADC range for pixel reads in the 3×3 grid of background monitor pixels.
Keyword values: Dimensionless pixel ADC level. Valid values lie in the range [0.0,1.0].

rslev.a ­ ResetLevel ­ double ­ read only ­ normal
This keyword indicates the average fraction of the ADC range for reset reads in the 3×3 grid of background monitor pixels.
Keyword values: Dimensionless pixel ADC level. Valid values lie in the range [0,4095].

endut ­ EndUT ­ string ­ read/write ­ cached
This read-only keyword indicates the ending time of the current exposure in UT.
Keyword values: The output units are time expressed as an ASCII string; e.g., hh:mm:ss.

Basic Observing Configuration

obsmode ­ ObservationMode ­ string ­ read/write ­ normal
This keyword specifies the observing mode.
Keyword values:
  • chop-nod = chop-nod mode
  • chop = chop mode
  • nod = nod mode
  • stare = star mode

savefreq ­ SaveFrequency ­ double ­ read/write ­ cached
The frequency at which data is saved to media.
Keyword values: The dimensions of this keywords is Hz. The valid ranges of this keywords are: ??

chpbeams ­ ChopperBeams ­ integer ­ read/write ­ cached
This keyword specifies the number of chop positions (either 1 or 2). In the LWS FITS structure, the value of this keyword defines NAXIS3. This keyword belongs to the LWS keyword library.
Keyword values:
  • 1 = Single chop beam. Used in staring mode and nod mode
  • 2 = Double chop beam. Used in chop and chop/nod mode.

chpdelay ­ ChopperDelay ­ double ­ read/write ­ cached
This keyword specifies how long the data collection program should wait after a chop move before considering the data to be valid. This keyword belongs to the LWS chopper keyword library.
Keyword values: Units: dimensionless, number of frames.

irefreq ­ IREFrequency ­ double ­ read/write ­ cached
This keyword specifies the frequency at which the IRE sends chop trigger signals to the chopping secondary mirror. A copy of the value of this keyword should be copied into the CARA chopper keyword library via chpfreq. This keyword belongs to the IRE keyword library .
Keyword values: The units of this keyword are Hz.

nodbeams ­ NodBeams ­ integer ­ read/write ­ cached
This keyword indicates the number of nod positions (either 1 or 2). In the LWS FITS structure, the value of this keyword defines NAXIS5.
Keyword values:
  • 1 = Single nod beam. Used in staring and chop modes.
  • 2 = Double nod beams. Used in nod and chop/nod modes.

nodtime ­ NodTme ­ double ­ read/write ­ cached
This keyword specifies the time spent is a nod position; i.e., 1/2 the nod period.
Keyword values: The units are seconds.

noddelay ­ NodDelay ­ double ­ read/write ­ cached
This keyword specifies the nominal length of time that the LWS data collection program will wait before the nod motion settles to its final resting position.
Keyword values: The units are seconds.

Sector Wheel Motor Control Keywords

secmode ­ SectorWheelMode ­ string ­ read/write ­ normal
This keyword specifies the chopper mode.
Keyword values:
  • off = chopper off
  • sector = sector wheel is the source of chopping
  • secondary = chopping secondary is the chopper.

secbeam0 ­ SectorWheelBeam0 ­ enumerate ­ read/write ­ normal
The default sector wheel beam position. Sector wheel chopping alternates between this beam position and secbeam1 . Note, these beam positions are read into the motor controllers only when secmode is set. So to change these values, secmode must be set to off, then secbeam0 and secbeam1 can be set. Then set secmode back to sector .
Keyword values:
  • open = The detector looks out unobstructed--same as home position (secraw=0).
  • mirror = The detector looks at shiny blade blade (secraw=-67).
  • transparent = The detector looks at a blackened blade (secraw=267).

secbeam1 ­ SectorWheelBeam1 ­ enumerate ­ read/write ­ normal
This keyword specifies what position on the sector wheel the detector will look at in beam position 1 (sector wheel chopping occurs between beam position 0 and beam position 1). Note, these beam positions are read into the motor controllers only when secmode is set. So to change these values, secmode must be set to off, then secbeam0 and secbeam1 can be set. Then set secmode back to sector .
Keyword values: The default value for this keyword is ``blocked''. Valid values for secbeam1 are the same as for secbeam0 --see above.

sectellm ­ SectorWheelTellMotor ­ string ­ write only ­ normal
Keyword used to send an arbitrary ASCII string to the sector wheel stepper motor.
Keyword values: Arbitrary ASCII control string automatically prefaced by the sector wheel motor number. Convenient strings to remember:
  • ST0 ­ turn motor controller on; i.e., modify -service lws sectellm=ST0
  • ST1 ­ turn motor controller off.
Note: Turning motor power off and on will not reset counter, but motor is likely to move to nearest pole.

sechome ­ SectorWheelHome ­ Boolean ­ write only ­ normal
Boolean keyword to home the sector wheel stepper motor.
Keyword values: Setting this keyword value to ``t'' mean to home the sector wheel motor.

secraw ­ SectorWheelRaw ­ integer ­ read only ­ normal
Integer keyword that reports the raw motor step position of the sector wheel. To actually move the sector wheel, use the keyword secdel--see below.
Keyword values: Any valid long integer value is acceptable. One revolution of the sector wheel is 2000 steps (micro-step mode).

secdel ­ SectorWheelDelta ­ integer ­ write only ­ normal
Integer keyword that allows one to change the raw motor step position of the sector wheel. To reade the sector wheel position, use the keyword secdel (see above).
Keyword values: Any valid long integer value is acceptable. (See, however, the keyword secbeam0 for valid beam position values.

Duty Cycle keywords

savedc ­ SaveDutyCycle ­ double ­ read/write ­ cached
Save duty cycle due to the non-zero value of saveovhd.
Keyword values: Dimensionless fraction.
chpdc ­ ChopperDutyCycle ­ double ­ read/write ­ cached
This read only keyword indicates what duty cycle (or efficiency) has been achieved by the chopper; i.e., valid data time in each beam position divided by the total time. This keyword belongs to the CARA chopper keyword library .
Keyword values: Dimensionless fraction.
noddc ­ NodDutyCycle ­ double ­ read/write ­ cached
This read only keyword specifies the nod duty cycle (or efficiency) obtained; i.e., nod data valid time divided by the total time.
Keyword values: Dimensionless fraction.
photondc ­ PhotonDutyCycle ­ double ­ read/write ­ cached
This keyword indicates the total duty cycle (or efficiency) of collecting photons both on and off source, including all over-heads due to detector timing, chopper inefficiency, and nodding inefficiency, etc.
Keyword values: Dimensionless fraction.


Basic Lightpath Configuration Keywords

Window Flipper Control Keywords

windowin ­ WindowIn ­ Boolean ­ read/write ­ normal
This keyword specifies whether or not the 10 µm window is in.
Keyword values: A value of ``t'' indicates the 10 µm window is in. A value of ``f'' indicates that the 10 µm window is out of the beam and the LWS operating mode is suitable for 20 µm data collection.

wintellm ­ WindowTellMotor ­ string ­ write only ­ normal
Keyword used to send an arbitrary ASCII string to the window flipper stepper motor.
Keyword values: Arbitrary ASCII control string automatically prefaced by the window stepper motor number.
Convient strings to remember:
  • ST0 ­ Turn motor controller on; i.e., modify -service lws wintellm=ST0
  • ST1 ­ Turn motor controller off.
Note: Turning motor power off and on will not reset counter, but motor is likely to move to nearest pole.

apname ­ ApertureName ­ string ­ read/write ­ normal
Indicates name of aperture in place, or the name of the aperture which the aperture mechanism should place in the beam.
Keyword values:
  • pixels_2 ­ Two pixel wide slit
  • pixels_4 ­ Four pixel wide slit
  • pixels_6 ­ Six pixel wide slit
  • open ­ Wide open aperture for imaging
  • home ­ Move to home position without slow seeking of position and re-zeroing of apraw, etc.
  • dark ­ Move to a position between aperture openings for dark frame.

apos ­ AperturePosition ­ integer ­ read/write ­ normal
Indicates the position of the aperture in units of the aperture position number.
Keyword values: There are 4 valid aperture positions. Current assignments of the aperture positions are:
  • 0: Home position (apname=home)
  • 1: Open (apname=open)
  • 2: Two pixel wide slit (apname=pixels_2)
  • 3: Dark (apname=dark)
  • 4: Four pixel wide silt (apname=pixels_4)
  • 5: Six pixel wide slit (apname=pixels_6)

apraw ­ ApertureRawSteps ­ integer ­ read/write ­ normal
Indicates the position of the aperture wheel in raw number of steps CW from the home (apraw =0) position.
Keyword values: Valid values of apraw lie in the range of [0, 599999]. The home position is defined to be at apraw=0.

apangle ­ ApertureAngle ­ double ­ read/write ­ normal
Indicates the position angle of the aperture wheel.
Keyword values: Input units: degrees. Internal units: radians. Valid input values of apangle lie in the range of [0, 360.0). The home position is defined to be at apangle=0.0

aptellm ­ ApertureTellMotor ­ string ­ write only ­ normal
Keyword used to send an arbitrary ASCII command string to the aperture stepper motor.
Keyword values: Arbitrary ASCII command string automatically prefaced with the aperture motor number.
Convient strings to remember:
  • ST0 ­ Turn motor controller on; i.e., modify -service lws aptellm=ST0
  • ST1­ Turn motor controller off.
Note: Turning motor power off and on will not reset counter, but motor is likely to move to nearest pole.

aphome ­ ApertureHome ­ Boolean ­ write only ­ normal
This keyword is used to move to the home position for the aperture wheel and to zero apraw, apangle, and apos. Note that before aphome can be used, the internal home microswitch must be connected to the motor controller. This is done by setting msrelay=closed. After the home position is reached, the microswitch must be disconnected for low noise operation. This is done by setting msrelay=open.
Keyword values: Valid values of this Boolean are ``t'' and ``f''. Note that setting aphome=t causes a slow seek of the home position and resetting of the values of apraw, apos, and apangle. To move to the home position without resetting the position counter, use apname=home.

Filter Wheel Keywords

filname ­ FilterName ­ string ­ read/write ­ normal
This keyword is used to move the filter wheel to a specified filter.
Keyword values: There are 16 valid filter wheel positions--see filpos description for value values.

filpos ­ FilterPosition ­ integer ­ read/write ­ normal
Indicates the position of the filter wheel in units of the 16 basic viable filter positions as opposed to the current filter name assignments.
Keyword values: Current assignments of the filter positions to filters are:

Pos Name filraw Description
0 Home 0 Home position
1 12.5 6000 OCLI Silicate ``S'' filter, 11.9 to 13.0 µm
2 11.7 43,500 OCLI Silicate ``R'' filter, 11.1 to 12.2 µm
3 10.4 81,000 OCLI Silicate ``Q'' filter, 9.7 to 10.7 µm
4 9.9 118,500 OCLI Silicate ``P'' filter, 9.3 to 10.2 µm
5 8.9 156,000 OCLI Silicate ``O'' filter, 8.3 to 9.2 µm
6 8.0 193,500 OCLI Silicate ``N'' filter, 7.5 to 8.2 µm
7 10.3 231,000 W10692, 9.8 to 10.8 µm filter
8 open 268,500 OPEN
9 L 306,000 Standard ``L'' filter, 3.5 to 4.15 µm
10 M 343,500 Standard ``M'' filter, 4.4 to 5.0 µm
11 open1 381,000 22.2 to 23.41 µm
12 17.9 418,500 16.9 to 18.9 µm
13 18.7 456,000 Q2, 18.4 to 18.9 µm filter
14 Nwide 493,500 W10527-8, 7 to 14 µm
15 spec20 531,000 6.942 µm cut-on long pass filter
16 spec10 568,500 13.712 µm cut-on long pass filter

filraw ­ FilterRawPosition ­ integer ­ read/write ­ normal
Indicates the position of the filter wheel in raw motor steps CW from the home (filraw=0) position.
Keyword values: Valid positions of filraw lie in the range [0, 599999]. The home position is defined to be filraw=0.

filangle ­ FilterAngle ­ double ­ read/write ­ normal
Indicates the position angle of the filter wheel.
Keyword values: Input units: degrees. Internal units: radians. Valid input values of filangle lie in the range [0, 360.0). The home position is defined to have filangle=0.0.

filtellm ­ FilterTellMotor ­ string ­ write only ­ normal
Keyword used to send an arbitrary ASCII command string to the filter stepper motor.
Keyword values: Arbitrary ASCII command string automatically prefaced with the filter motor number.
Convient strings to remember:
  • ST0 ­ Turn motor controller on; i.e., modify -service lws filtellm=ST0
  • ST1 ­ Turn motor controller off.
Note: Turning motor power off and on will not reset counter, but motor is likely to move to nearest pole.

filhome
This keyword is used to move to the home position for the filter wheel and to zero filraw, filangle, and filpos. Note that before filhome can be used, the internal home microswitch must be connected to the motor controller. This is done by setting msrelay=closed. After the home position is reached, the microswitch must be disconnected for low noise operation. This is done by setting msrelay=open.
Keyword values: Valid values of this Boolean are ``t'' and ``f''. Note that setting filhome=t causes a slow seek of the home position and resetting of the values of filraw, filpos, and filangle. To move to the home position without resetting the position counter, use filname=home.

Spectroscopic Mode Keywords

alphac ­ AlphaCenter ­ double ­ read/write ­ normal
This keyword specifies the angle between the input beam and the input beam to detector angle; i.e., . Thus twice alphac is the angle between the input beam and the dector beam (beam to the center of the detector).
Keyword values: The dimensions of this keyword are radians.

dgamma ­ DGamma ­ double ­ read/write ­ normal
This keyword specifies the half angular size of the array; i.e., .
Keyword values: The dimensions of this keyword are radians.

dhigh ­ DHigh ­ double ­ read/write ­ normal
This keyword specifies the grating groove separation, d, for the high resolution grating.
Keyword values: The dimension of this keyword is microns.

dlow ­ DLow ­ double ­ read/write ­ normal
This keyword specifies the grating groove separation, d, for the low resolution grating.
Keyword values: The dimension of this keyword is microns.

zposhigh ­ ZeroPositionHigh ­ integer ­ read/write ­ normal
This keyword specifies the zero offset position in motor steps for the high resolution grating (see calculation of grapos from other keywords; e.g., cenlam, below).
Keyword values: This keyword is the dimensionless number of stepper motor steps.

zposlow ­ ZeroPositionLow ­ integer ­ read/write ­ normal
This keyword specifies the zero offset position in motor steps for the low resolution grating (see, for example, the calculation of graraw in the definition of grapos below).
Keyword values: This keyword is the dimensionless number of stepper motor steps.

zposimg ­ ZeroPositionImaging ­ integer ­ read/write ­ normal
This keyword specifies the zero offset position in motor steps for the imaging mirror on the mirror/grating turret.
Keyword values: This keyword is the dimensionless number of stepper motor steps.

graname ­ GratingName ­ string ­ read/write ­ normal
This keyword is use to specify any of a number of preset positions for the grating/mirror turret mechanism. Spectroscopic keyword name values start with ``H'' or ``L'' for high or low resolution modes. The next digit is the order number. This is followed by a dash (i.e., ``-''), then the set wavelength (to the nearest 1/100th of a micron) of the grating to be placed in the center of the detector array. (To position an arbitrary wavelength at the start, center, or end of the array use the keywords startlam, cenlam, endlam, grating, and order.) Wavelengths have been selected to cover the full spectral range of the window with 16 pixel overlap in the 10 and 20 micron windows and 38 pixel overlap in the 5 micron window (the 5 micron window still only requires very few settings).
Keyword values: Valid keyword values are listed below in the accompanying tables. (Numbered entries range from short wavelengths--low numbered entries, to progressively longer wavelengths--larger numbered entries). Besides the keyword values listed in the tables below, graname can take on the value graname = home which will move to the grating home position without slow seeking of the home switch and re-zeroing of filraw, etc.

The appropriate values of graraw can be calculated from the central wavelengths of the preset filter positions by use of the following formulae:

	  ,
	  
where for d the appropriate value of either dhigh or dlow must be selected and for the appropriate value of zposhigh or zposlow must be used depending on whether the high or low resolution gratings are used.

graname cenlam
[µm]
Bandpass
Filter
Imaging Mode
imaging N/A
Low Resolution Mode
L3-3.50 3.50 L
L3-4.00 4.00
L3-4.50 4.50 M
L3-5.00 5.00
L3-5.50 5.50
High Resolution Mode
H5-3.50 3.50 L
H5-3.55 3.55
H5-3.60 3.60
H5-3.65 3.65
H5-3.70 3.70
H5-3.75 3.75
H5-3.80 3.80
H5-3.85 3.85
H5-3.90 3.90
H5-3.95 3.95
H5-4.00 4.00
H5-4.05 4.05
H5-4.10 4.10
H5-4.15 4.15
H3-4.53 4.53 M
H3-4.60 4.60
H3-4.67 4.67
H3-4.74 4.74
H3-4.80 4.80
H3-4.87 4.87
H3-4.94 4.94
H3-5.00 5.00
Low Resolution Mode
L1-8.00 8.00 spec10
L1-9.00 9.00
L1-10.00 10.00
L1-11.00 11.00
L1-12.00 12.00
L1-13.00 13.00
High Resolution Mode
H2-7.61 7.61 Nwide
H2-7.84 7.84
H2-8.06 8.06
H2-8.28 8.28
H2-8.50 8.50
H2-8.72 8.72
H2-8.94 8.94
H2-9.15 9.15
H2-9.37 9.37
H2-9.58 9.58
H2-9.79 9.79
H2-9.99 9.99
H2-10.20 10.20
H2-10.40 10.40
H2-10.61 10.61
H2-10.80 10.80
H2-11.00 11.00
H2-11.20 11.20
H2-11.39 11.39
H2-11.58 11.58
H2-11.77 11.77
H2-11.96 11.96
H2-12.14 12.14
H2-12.33 12.33
H2-12.51 12.51
H2-12.68 12.68
H2-12.86 12.86
H2-13.03 13.03
H2-13.21 13.21
H2-13.38 13.38
Low Resolution Mode
L1-20.00 20.00 spec20
High Resolution Mode
H1-15.23 15.23 spec20
H1-15.68 15.68
H1-16.13 16.13
H1-16.57 16.57
H1-17.01 17.01
H1-17.45 17.45
H1-17.88 17.88
H1-18.31 18.31
H1-18.73 18.73
H1-19.16 19.16
H1-19.58 19.58
H1-19.99 19.99
H1-20.40 20.40
H1-20.81 20.81
H1-21.21 21.21
H1-21.61 21.61
H1-22.00 22.00
H1-22.40 22.40
H1-22.78 22.78
H1-23.16 23.16
H1-23.54 23.54
H1-23.92 23.92
H1-24.29 24.29
H1-24.65 24.65
H1-25.01 25.01
H1-25.37 25.37
H1-25.72 25.72
H1-26.07 26.07
H1-26.41 26.41
H1-26.75 26.75

graraw ­ GratingRawSteps ­ integer ­ read/write ­ normal
Keyword to set or report the grating position in raw motor steps CW from the home (graraw =0) position.
Keyword values: Valid keyword values lie in the range [0, 599999].

grangle ­ GratingAngle ­ double ­ read/write ­ normal
Keyword to set or report the grating position angle.
Keyword values: Input units: degrees. Internal units: radians. Valid keyword input values lie in the range [0, 360.0).

gratellm ­ GratingTellMotor ­ string ­ write only ­ normal
Keyword used to send an arbitrary ASCII command string to the grating stepper motor.
Keyword values: Arbitrary ASCII command string automatically prefaced with the grating motor number.
Convient strings to remember:
  • ST0 ­ Turn motor controller on; i.e., modify -service lws gratellm=ST0
  • ST1 ­ Turn motor controller off.
Note: Turning motor power off and on will not reset counter, but motor is likely to move to nearest pole.

grahome ­ GratingHome ­ Boolean ­ write only ­ normal
This keyword is used to move to the home position for the grating wheel and to zero graraw, grangle, and grapos. Note that before grahome can be used, the internal home microswitch must be connected to the motor controller. This is done by setting msrelay =closed. After the home position is reached, the microswitch must be disconnected for low noise operation. This is done by setting msrelay =open.
Keyword values: Valid values of this Boolean are ``t'' and ``f''. Note that setting grahome=t causes a slow seek of the home position and resetting of the values of graraw, grapos, and grangle. To move to the home position without resetting the position counter, use graname =home.

gradel ­ GratingDeltaRawSteps ­ integer ­ write only ­ normal
Keyword to move the grating by an incremental number of steps from the current grating position. Positive value move CW. Negative values move CCW.
Keyword values: Valid keyword values lie in the range [0, 599999].

cenlam ­ CenterLambda ­ double ­ read/write ­ normal
This keyword specifies the wavelength to place at the center of the detector array.
Keyword values: Any wavelength in the 5, 10, and 20 micron atmospheric windows are potential values of this keyword.
Note: Calculation of grapos from cenlam is as follows: , where for d the appropriate value of either dhigh or dlow must be selected and for the appropriate value of zposhigh or zposlow must be used depending on whether the high or low resolution gratings are used.

startlam ­ StartLambda ­ double ­ read/write ­ normal
This keyword specifies the wavelength to place at the start (beginning) of the detector array.
Keyword values: Any wavelength in the 5, 10, and 20 micron atmospheric windows are potential values of this keyword.
Note: Calculation of grapos from startlam is as follows: , where for d the appropriate value of either dhigh or dlow must be selected and for the appropriate value of zposhigh or zposlow must be used depending on whether the high or low resolution gratings are used.

endlam ­ EndLambda ­ double ­ read/write ­ normal
This keyword specifies the wavelength to place at the end of the detector array in high resolution mode.
Keyword values: Any wavelength in the 5, 10, and 20 micron atmospheric windows are potential values of this keyword.
Note: Calculation of grapos from endlam is as follows: , where for d the appropriate value of either dhigh or dlow must be selected and for the appropriate value of zposhigh or zposlow must be used depending on whether the high or low resolution gratings are used.

gramode ­ GratingMode ­ string ­ read/write ­ normal
This keyword specifies the grating that is being used.
Keyword values: Valid keyword values are in the set {low, high}.

graorder ­ GratingOrder ­ integer ­ read/write ­ normal
This keyword specifies the order of the grating. Note that only certain orders are useful for the LWS.
Keyword values: Any integer order number in the set {1,2,4,6} are viable order numbers.

gramove ­ GratingMove ­ Boolean ­ write only ­ normal
This keyword is used to cause the grating motor to move. The reason there is a gramove and not equivalent commands for the filter wheel and the aperture wheel is because in order for a valid grating position to be specified, several keywords may need to be specified; i.e., valid values for gramode, graorder, and cenlam, and it is desirable only to start the grating motor motion after all of these keywords are specified.
Keyword values: A value of ``t'' causes the grating motor to move. A value of ``f'' means that the grating motor is not in motion.

cenlamr ­ CenterLambdaReadOnly ­ double ­ read only ­ cached
Because of the order in which wavelength calculations are made, read only versions of cenlam, startlam, and endlam are required. cenlamr is the read only version of cenlam.
Keyword values: Double precision number expressing the value of the wavelength (in microns) at the center of the array.

strtlamr ­ StartLambdaReadOnly ­ double ­ read only ­ cached
Because of the order in which wavelength calculations are made, read only versions of cenlam, startlam, and endlam are required. strtlamr is the read only version of cenlam.
Keyword values: Double precision number expressing the value of the wavelength (in microns) at the start of the array.

endlamr ­ EndLambdaReadOnly ­ double ­ read only ­ cached
Because of the order in which wavelength calculations are made, read only versions of cenlam, startlam, and endlam are required. endlamr is the read only version of cenlam.
Keyword values: Double precision number expressing the value of the wavelength (in microns) at the end of the array.

lamcov ­ LambdaCoverage ­ double ­ read only ­ cached
Keyword which specifies the total wavelength coverage of the detector at the current grating setting.
Keyword values: Double precision number expressing endlam - startlam.

lampix ­ LambdaPerPixel ­ double ­ read only ­ cached
Keyword which specifies the delta lambda per pixel.
Keyword values: Double precision number expressing , where 64 is the total number of good pixels in the array along the dispersion direction.


Low-Level Data Aquisition Configuration Keywords

frmreads ­ FrameReads ­ integer ­ read/write ­ cached
This keyword specifies the number of frame readouts consistent with irefreq in chop-nod and chop modes, and with savefreq in nod and stare modes.
Keyword values: Dimensionless number of frames to readout and co-adding in the DSP before saving data to disk. , see the definitions of frmsettl and frmcoadd below. The value of this keyword is calculated by the collect daemon.

frmsettl.p ­ FrameSettle ­ integer ­ read/write ­ normal
This specifies the number of frames in a frmreads set discarded to allow time for the chopper to settles in chop-nod and chop modes.
Keyword values: Dimensionless number of frames to discard before beginning DSP co-adding.

frmcoadd.p ­ FrameCoadd ­ integer ­ read/write ­ normal
This specifies the number of frmcoadd sets coadded into DSP memory in chop-nod and chop modes for a given chop position.
Keyword values: Dimensionless number of frames.

chpcoadd.p ­ ChopCoadd ­ integer ­ read/write ­ normal
This specifies the number of frmreads sets to coadd into DSP memory in chop-nod and chop modes before transfering data to be saved on disk.
Keyword values: Dimensionless number of frames.

savesets.a ­ SaveSets ­ integer ­ read/write ­ normal
In chop-nod or chop mode, this specifies the number of chpcoadd sets written to media during each nodtime; i.e., the time spent in one nod position. In nod and stare modes, this specifies the number of frmcoadd sets written to media during each nodtime. In the LWS FITS structure, the value of this keywords defines NAXIS4.
Keyword values:
  • chop-nod or chop mode: Dimensionless number of chpcoadd sets.
  • nod or stare mode: Dimensionless number of frmcoadd

saveovhd.a ­ SaveOverhead ­ double ­ read/write ­ cached
Overhead associated with transferring data from coadder buffers to main memory.
Keyword values: The dimensions of this keyword are seconds.

savtmout.a ­ SaveTimeOut ­ double ­ read/write ­ normal
The time to wait before notifying the observer of deliquency of the DSPs.
Keyword values: The dimensions of this keyword are seconds. The value of this keyword should be of order

nodsets.a ­ NodSets ­ integer ­ read/write ­ normal
Number of nod cycles of the telescope in a complete observation. In the LWS FITS structure, the value of this keyword defines NAXI6.
Keyword values: Dimensionless number of nod cycles.


Array Readout Configuration Keywords

Overview

In order to understand the workings of the detector, a schematic of the detector unit cell and all pertinent voltage and control lines is presented in Figure 1. Figure 2 and Figure 3 present the on-chip clock timing logic and timing diagrams for the Aerojet 96×96 array.

Figure 1.

Figure 2a.

Figure 2b.

Figure 3.

The temporal relationship between the assertion of detector reset and the enabling of the output source-followers for each column of pixels is fixed by the gating logic of the "L" cell. The essential points of the L-cell logic are:

  1. Detector reset for the Nth column is asserted as long as QN is held high--the QNs are the reset controls for their respective columns.
  2. The output source-follower for the Nth column cannot be enabled while QN is held high. Consequently, the ``reset-asserted'' level can never be presented at the detector output.
  3. The enabling of the output source-follower for the Nth column requires that either the previous column or following column has reset asserted (i.e., QN-1 or QN+1 is high).

The detector array is reset by propagating a QN pattern through the slow shift-register. This QN pattern is specified via the Slow-in input and clocked through the shift-register (SR) via CKS and CK1S. Note that because the QN logic levels are supplied by the shift-registers, their duration (the duration of reset assert) will be an integral multiple of the SR clock-cycle.

The QN pattern is combined with the PEAK and INIT patterns in the L-cell to determine the detector readout-enable sequence. Note that it is possible to specify a readout pattern for which the array output is meaningless; e.g., it is possible to specify a QN pattern in combination with a PEAK and INIT pattern which enables more than one output source-follower per readout line.

The simplest QN pattern is shown in Figure 3. This pattern consists of a single high pulse with a duration of one SR clock-cycle. When this pattern is propagated through the shift-register, the array is sequentially reset, column by column, with only one column at a time being held at the reset level. The output source-followers are enabled in a ``legal'' fashion by applying the indicated PEAK and INIT clock pattern. This readout pattern will be referred to as the ``NORMAL'' mode.

In the NORMAL mode, the output source-followers for each column are enabled twice during a frame readout. The first enable for a particular column begins one SR clock-cycle prior to reset being asserted for that column. The duration of the readout-enable is half of a SR clock-cycle. The second enable begins half a SR clock-cycle after reset is deasserted and also has a duration of half of a SR clock-cycle. The first readout-enable for a column is referred to as PIXEL-read-enable or just PIXEL. The second readout-enable is referred to as RESET-read-enable or RESET.

From Figure 3, it is clear that the PIXEL and RESET for a given column are interlaced with the PIXEL and RESET of nearby columns. In particular, the PIXEL/RESET pattern for a single frame readout is given by

(P01 xxx) (P02 xxx) (P03 R01) (P04 R02) ... (P96 R94) (xxx R95) (xxx R96)
where P## represent PIXEL for column ##, R## represents RESET for column ##, and the ``xxx'' represent a null state (i.e., no output source-followers are driving the readout lines). The pair groupings indicated by the parentheses show the duration of a SR clock-cycle. RESET for a given column is shifted by two SR clock-cycles with respect to the corresponding PIXEL. Since the last valid column is 96, a complete frame readout requires 98 SR clock-cycles; i.e., 96 SR clock-cycle plus an additional 2 clock-cycles in order to obtain the last two valid RESETs (R95 and R96). As an aside, note that the shift-register contains a 97th cell (Figure 2a) even though there are only 96 columns in the detector array. This 97th shift-register cell is required in order to obtain RESET for the 96 th column. That is, obtaining RESET for the Nth column requires that reset be asserted for the N+1 th column (i.e., QN+1 must be high (L-cell logic)).

To summarize the NORMAL mode:

  1. A complete set of PIXELs and RESETs is obtained every 98 SR clock-cycles. This set is called a ``frame''. The PIXELs and RESETs constituting this frame do not represent true ``correlated double sampling'' (CDS) pairs since the PIXELs are obtained prior to the RESETs. These pairs are more appropriately referred to as ``delta-reset sampling'' (DRS) pairs. The RESETs from the previous frame, combined with the PIXELs from the current frame, however, do represent true CDS pairs.
  2. The duration of Slow-in asserted high (slowinhi ) is fixed at 1 SR clock-cycle. This implies that reset for each column is asserted for 1 SR clock-cycle.
  3. The duration of PIXELs and RESETs is 1/2 a SR clock-cycle.
  4. The relative shift between PIXELs and RESETs is 2 SR clock-cycles.
  5. A MINIMUM of 98 SR cycles must be clocked in order to obtain RESETs corresponding to PIXELs for columns 95 and 96 as described previously. However, clocking more than 98 SR cycles does nothing on-chip.
  6. If the number of SR clock-cycles in a frame is 98, the integration duty cycle (i.e., time between RESET and PIXEL for a column compared to the frame time) is given by (98-1-1.5)/98 = 97.45%. The ``-1'' accounts for the duration of reset assert (slowinhi ) and the ``-1.5'' accounts for the duration of PIXEL itself and the duration of an interlaced PIXEL and RESET.
  7. Readout of a sub-portion of the array, specified as column 1 to column lastcol, where 1 lastcol 96, requires lastcol +2 SR clock-cycles (again with the extra two SR cycles required to obtain obtain the RESETs corresponding to the PIXELs for the last 2 columns, lastcol -1 and lastcol ). Before initiating a new frame acquisition, the Slow-in pattern must be flushed from the shift register by supplying 98-lastcol fast CKS/CK1S clocks. These ``quick'' SR clock-cycles may be done with PEAK and INIT held low to disable the output source-followers while clocking through the columns to be skipped.

Figure 4.

A second mode of operation has been implemented and is referred to as the ``NDF'' mode. In this mode, the on-chip integration duty cycle is reduced by asserting detector reset for a period longer than one SR clock-cycle (as is done in the NORMAL mode). The effective result obtained by reducing the on-chip integration duty-cycle is the same as would be obtained through the use of a Neutral Density Filter (NDF) in the optical path (i.e., throwing photons away).

The implementation of the NDF mode is as follows:

  1. This Slow-in pattern must be initiated every 97 SR clock-cycles EXACTLY. In this mode, 97 SR clock-cycles defines a ``frame''.
  2. The Slow-in pattern consists of a single high pulse having a width 1 slowinhi 95 SR clock-cycles (i.e., reset is asserted for slowinhi SR clock-cycles). The clocks PEAK, INIT, CKS and CK1S have the same relationship with respect to the low-to-high transition of Slow-in (i.e., the initialization of Slow-in), as exists for the NORMAL mode.
  3. The duration of PIXELs and RESETs is 1/2 a SR clock-cycle.
  4. The relative shifts between PIXELs and RESETs is given by slowinhi +1.
  5. The time between the last RESET of one frame and the first PIXEL of the next frame should be exactly the same as the time between RESETs and PIXELs within a frame. (This is satisfied to within a few percent in the current NDF mode implementation.) Corollaries to this:

    No ``quick-clocking'' of columns is permitted; i.e., every PIXEL and RESET must be obtained.

    No frame delays are permitted.

  6. The integration duty cycle (i.e., time between RESET and PIXEL for a column compared to the frame time) is (97-slowinhi -1.5)/97 = 98.45%. The ``-slowinhi '' accounts for the duration of reset assert and the ``-1.5'' accounts for the duration of PIXEL itself and the duration of an interlaced PIXEL and RESET.
  7. In a single frame, PIXELs and RESETs from columns 1 to 96-slowinhi represent DRS pairs and pixels 97-slowinhi to 96 represent CDS pairs. The following shows the PIXEL/RESET pattern for a single frame in the NDF mode with slowinhi=2:
    (P01 R95) (P02 R96) (P03 R97) (P04 R01) (P05 R02) ...
         ... (P94 R91) (P95 R92) (P96 R93) (P97 R94)
Note that P97 and R97 are essentially null states in that detector column 97 does not exist (only the shift register cell is present which provides input to the L-cell of column 96).

Keyword Detail

In the sections below, some of the keywords have ``.''-suffixes. These indicate to which part of the IRE the data is passed: ``.t'' indicates the Timing Generator, ``.c'' indicates the Co-adders, and ``.a'' indicates the RPC-server and the acquire process. The absence of a suffix indicates that only the LWS keyword library knows about the variable.

pxtime ­ PixelTime ­ double ­ read/write ­ cached
This keyword specifies the total amount of time the DSP has to deal with a pixel value before needing to handle a new value. It is equal to the readout pattern length plus the PolyCom preamp/MUX switching time.
Keyword values: The unit is seconds. This time is composed of the adcdelay time, the dspdelay, the dsplatch, and muxswoh (nominally 6)--see Figure 4; i.e., The value of this keyword is calculated by the collect daemon.

muxswoh.t ­ MUXSwitchOverHead ­ integer ­ read only ­ normal
This keyword provides the value of the overhead in number of instructions allowed for switching of the PolyCom MUX.
Keyword values: The unit is a machine instruction. The nominal value 6.

slowinhi.t ­ SlowInHigh ­ integer ­ read/write ­ normal
Used only in NDFMode (ndfmode=t). This keyword indicates how many reptitions of muxptime s and muxrtime s that the SLOWINHI clock is held high. Holding slowin high controls the relative position of the pixel reads and reset reads. The shift between the pixel and reset values for a given column is slowinhi + 1 detector clock cycles. Large values of slowinhi cause the resets to occur just before the pixel read (since timing pattern wrap around is enforced in the on-chip shift register), reducing the effective integration time on the chip and causing photons to be thrown away. A non-unity value of slowinhi would logically require an fstretch value of 0. In fact, in NDFMode, fstretch is ignored.
Keyword values: The valid values of slowinhi are multiples (1 to 95) of a machine instruction time (e.g., Peak, CKS, CK1S--see Figure 3).

pxsettle.t ­ PixelSettlingTime ­ integer ­ read/write ­ normal
This keyword specifies the value of the settling time for pixel reads in the MUX frame time--see Figure 4.
Keyword values: The units are machine instructions. The nominal value of this quantity is 25; i.e., roughly 2.5 .

rssettle.t ­ ResetSettlingTime ­ integer ­ read/write ­ normal
This keyword specifies the value of the settling time for reset reads in the MUX frame time--see Figure 4.
Keyword values: The units are machine instructions. The nominal value of this quantity is 25; i.e., roughly 2.5 .

fstretch.t ­ FrameStretch ­ integer ­ read/write ­ normal
This keyword is only applicable in normal timing generator mode (ndfmode =f). This keyword specifies the idle time for the Timing generator at the end of frame readout clocking. It can be used to extend the detector integration time.
Keyword values: The units are machine instructions. The nominal value for this keyword is 0. The value of this keyword is calculated by the collect daemon.

fsscale.t ­ FrameStretchScale ­ integer ­ read only ­ normal
This keyword specifies the proportionality constant for calculation of the frame stretch time.
Keyword values: Units are machine instructions.

fsoh.t ­ FrameStretchOverhead ­ integer ­ read only ­ normal
This keyword specifies the overhead for the frame stretch in terms of machine instructions.
Keyword values: Units are machine instructions.

mic.a ­ MachineInstructionCycle ­ double ­ read only ­ normal
This keyword specifies the time for a timing generator machine instruction cycle in units of seconds.
Keyword values: Units are seconds per machine instruction.

ndfmode.a ­ NDFMode ­ Boolean ­ read/write ­ normal
This Booleans specifies whether or not NDF mode is active. Changing ndfmode.a requires reconfiguring the DSPs in order to take effect.
Keyword values: Valid values for this Boolean are ``t'' and ``f''. A value of ``t'' indocates the LWS is in NDF mode. A value of ``f'' indicates ``normal'' mode--see detector timing overview above.

frmtime ­ FrameTime ­ double ­ read/write ­ cached
This keyword contains the value of the frame time. If frmtime is written, it should only affect fstretch. If an unviable frmtime is written, an error message to this effect is returned.
Keyword values: The units of this keyword are seconds. The value of this keyword is given by:
  • NORMAL mode:
  • NDF mode:
where The value of this keyword is calculated by the collect daemon.

normfmoh.t ­ NormalFrameOverhead ­ integer ­ read only ­ normal
This keyword specifies the number of machine instructions overhead at the beginning of a normal frame.
Keyword values: Nominal value = 52. It is only used when ndfmode =``f'''.

ndffmoh.t ­ NDFModeFrameOverhead ­ integer ­ read only ­ normal
This keyword specifies the number of machine instructions in overhead at the beginning of a frame in NDF mode.
Keyword values: Nominal value = 40. It is only used when ndfmode =``t''.

frmdc ­ FrameDutyCycle ­ double ­ read only ­ cached
This keyword contains the duty cycle (or data collection efficiency) of a single frame of data.
Keyword values: The value of this keyword is a fraction in the range [0,1]. This keyword is the fraction of time that data is been collected during a frame time. The formula for this keyword is given by where for NORMAL mode, slowinhi =1. See definition of frmtime for definitions of muxp and muxp. The value of this keyword is calculated by the collect daemon.

lastcol.a ­ LastColumn ­ integer ­ read/write ­ normal
This keyword specifies the number of the last detector column for which ADC conversion and DSP data collection will be performed. This keyword is only valid in ndfmode =f. Changing lastcol requires reconfiguring the DSPs in order to talk effect.
Keyword values: The units for this keyword is column number. Typical values lie between 1 and 96; i.e., one column past the last active detector column.

convert.t ­ Convert ­ integer ­ read/write ­ normal
This keyword specifies the total time (in units of instructions) the DSP has for data capture.
Keyword values: The natural unit is a machine instruction.

colswoh.t ­ ColumnSwitchOverhead ­ integer ­ read only ­ normal
This keyword specifies the overhead in units of machine instruction allowed for switching to a new column.
Keyword values: Dimensionless. Nominal value = 8.

fcolswoh.t ­ FastColumnSwitchOverhead ­ integer ­ read only ­ normal
This keyword contains the total time for a PolyCom clock MUX group; i.e., the time required to just clock though a column without reading out the data.
Keyword values: The natural unit of this keyword is seconds. The nominal value for this keyword is corresponds to12 mic.


IRE Configuration Keywords

The timing for the capture of data in the Co-adders is given schematically in Figure 4. This figure indicates the various times required for a pixel (or reset) adc conversion, including the PolyCom preamp/MUX switching overhead time and the DSP convert time, convert. Included in the MUX group time is the time required for the signals to settle (either pxsettle or rssettle ) which is separately controllable for pixel slews and reset slews.

osdac.c ­ OffsetDAC ­ integer ­ read/write ­ normal
This keyword specifies the value of the offset DAC ( DAC ``C'') which should be used to cancel some of the DC operating point of the Aerojet detector.
Keyword values: The units for this keyword is DAC numbers. The IRE DACs are 16-bit DACs, so values between 0 and 65535 are valid.

smainput.c ­ SMAInput ­ string ­ read/write ­ normal
This keyword specifies which of the SMA inputs the Co-Adders are to read the data from.
Keyword values: Units for this keyword are SMA input number. Valid values are "SMA1", "SMA2", "SMA3", and "SMA4".

gain.c ­ CoadderGain ­ string ­ read/write ­ normal
This keyword specifies the LWS electronics gain in units of electrons per ADC unit.
Keyword values: Valid values are and the corresponding saturated ADC are given in the Table below.

Gain
[e-/DN]
Full Well
(4095 ADC units)
38E 1.6 × 105
82E 3.6 × 105
117E 5.1 × 105
120E 5.2 × 105
160E 7.0 × 105
200E 8.7 × 105
240E 1.0 × 106
360E 1.6 × 106
400E 1.7 × 106
440E 1.9 × 106
480E 2.1 × 106
510E 2.2 × 106
560E 2.4 × 106
600E 2.6 × 106

lpassfil.c ­ LowPassFilter ­ string ­ read/write ­ normal
This keyword specifies the computer controllable value of the frequency foot of the input filter.
Keyword values: The units for this keyword are kHz. Valid values are "2KHZ", "20KHZ", "200KHZ", "2MHZ", and "OFF".

tvmode.a ­ TVMode ­ Boolean ­ read/write ­ normal
This keyword specifies whether or not the data coming off the detector is to be recorded or just displayed. TV mode is used for setting up the detector without recording all of the invalid data that occurs during setup.
Keyword values: The values of this Boolean are ``t'' and ``f''. A value of ``t'' indicates that TV mode is on and active. In this case data is not recorded. A value of ``f'' indicated that TV mode is off and data is to be recorded.


Housekeeping Keywords

Dewar Tilt Motor Control Keywords

tiltadel ­ TiltMotorADelta ­ integer ­ write only ­ normal
This keyword specifies how many steps to increment or decrement the ``A'' dewar tilt stepper motor. Note: Positive steps turns the motor CW and increases the gap in the LWS mounting bracket for motor A. (Motor A is a right-handed mechanism.)
Keyword values: Valid values are positive and negative integers.

tiltbdel ­ TiltMotorBDelta ­ integer ­ write only ­ normal
This keyword specifies how many steps to increment or decrement the ``B''dewar tilt stepper motor. Note: Positive steps turns the motor CCW and increases the gap in the LWS mounting bracket for motor B. (Motor B is a left-handed mechanism.)
Keyword values: Valid values are positive and negative integers.

tiltaraw ­ TiltMotorARaw ­ integer ­ read only ­ normal
Reads the raw number of steps the ``A'' dewar tilt stepper motor has moved from zero. Note: Note: Positive steps turns the motor CW and increases the gap in the LWS mounting bracket for motor A. (Motor A is a right-handed mechanism.)
Keyword values: Valid keyword values are any legal signed integer value.

tiltbraw ­ TiltMotorBRaw ­ integer ­ read only ­ normal
Reads the raw number of steps the ``B'' dewar tilt stepper motor has moved from zero. Note: Note: Positive steps turns the motor CCW and increases the gap in the LWS mounting bracket for motor B. (Motor B is a left-handed mechanism.)
Keyword values: Valid keyword values are any legal signed integer value.

tiltrad ­ TiltRadial ­ integer ­ read/write ­ normal
This keyword tilts the dewar in the radial direction by moving both the ``A'' and ``B'' dewar tilt motors the same amount.
Keyword values: Valid keyword values are any legal signed integer value. Positive values tilt the dewar toward the axis.

tilttang ­ TiltTangential ­ integer ­ read/write ­ normal
This keyword tilts the dewar in the tangential direction; i.e., perpendicular to motions toward or away from the telescope axis, by moving both the ``A'' and ``B'' dewar tilt motors opposite amounts.
Keyword values: Valid keyword values are any legal signed integer value. Positive values increment motor ``A'' and decrement ``B'', tilting the beam towards the fliter/grating mechanism side.

tmatellm ­ TiltMotorATellMotor ­ string ­ write only ­ normal
Keyword used to send an arbitrary ASCII string to the ``A'' dewar tilt motor.
Keyword values: Arbitrary ASCII control string automatically prefaced by the ``A'' dewar tilt motor number.
Convient strings to remember:
  • ST0 ­ Turn motor controller on; i.e.,
    modify -service lws tmatellm=ST0
  • ST1 ­ Turn motor controller off.
Note: Turning motor power off and on will not reset counter, but motor is likely to move to nearest pole.

tmbtellm ­ TiltMotorBTellMotor ­ string ­ write only ­ normal
Keyword used to send an arbitrary ASCII string to the ``B'' dewar tilt motor.
Keyword values: Arbitrary ASCII control string automatically prefaced by the ``B'' dewar tilt motor number.
Convient strings to remember:
  • ST0 ­ Turn motor controller on; i.e.,
    modify -service lws tmbtellm=ST0
  • ST1 ­ Turn motor controller off.
Note: Turning motor power off and on will not reset counter, but motor is likely to move to nearest pole.

Xycom Keywords

In order to read temperatures, the breakout box microswitches enabling the temperature feedback circuits must be thrown. This causes additional noise in the detector. Consequently this is done only at appropriate times; e.g., when the detector is not being readout. The keywords basetmpl, lhetmpl, decktmpl, and dettmpl are read only keywords that are written by the acquire program at appropriate times when these temperatures can be read. The appropriate display keywords (for control GUI's) are basetemp, lhetemp, decktemp, and dettemp which report the last valid values of basetmpl, lhetmpl, decktmpl, and dettmpl.

basetemp ­ BaseTemperature ­ double ­ read only ­ normal
Keyword for reading back the temperature of the base of the LHe optics work surface.
Keyword values: Expected value of this keyword is roughly 5 K during operation. Valid values lie in the range of roughly [4.2 K, 300.0 K].

lhetfrt ­ LHeTemperatureFront ­ double ­ read only ­ normal
Keyword for reading back the temperature of the front of the LHe cryogen can.
Keyword values: Expected value of this keyword is roughly 4 K during operation. Valid values lie in the range of roughly [4.2 K, 300.0 K].

lhetbak ­ LHeTemperatureBack ­ double ­ read only ­ normal
Keyword for reading back the temperature of the back of the LHe cryogen can.
Keyword values: Expected value of this keyword is roughly 4 K during operation. Valid values lie in the range of roughly [4.2 K, 300.0 K].

decktemp ­ DeckTemperature ­ double ­ read only ­ normal
Keyword for reading back the temperature of the upper optics deck.
Keyword values: Expected value of this keyword is roughly 7 K during operation. Valid values lie in the range of roughly [4.2 K, 300.0 K].

dettemp ­ DetectorTemperature ­ double ­ read only ­ normal
Keyword for reading back the temperature of the detector.
Keyword values: Expected value of this keyword is roughly 8 K during operation. Valid values lie in the range of roughly [4.2K, 300.0 K].

basetmpl ­ BaseTemperatureLocal ­ double ­ read only ­ normal
The keyword basetmpl reports the appropriate value of the base of the optics plate; e.g., lower deck which is attached directly to the LHe flask.
Keyword values: Expected values of this keyword lie around 5 K.

lhetmpl ­ BaseTemperatureLocal ­ double ­ read only ­ normal
The keyword basetmpl reports the appropriate value of the LHe flask.
Keyword values: Expected values of this keyword lie around 4 K.

decktmpl ­ BaseTemperatureLocal ­ double ­ read only ­ normal
The keyword basetmpl reports the appropriate value of the optics deck; i.e., the platform above the base that holds the pre-spectrograph optics.
Keyword values: Expected values of this keyword lie around 7 K.

dettmpl ­ BaseTemperatureLocal ­ double ­ read only ­ normal
The keyword basetmpl reports the appropriate value of the detector temperature.
Keyword values: Expected values of this keyword lie around 8 K.

stbias ­ SwitchedTempertureBias ­ double ­ read only ­ normal
Keyword for reading back the switched temperature bias voltage; i.e., the voltage supply for the temperture resistor network.
Keyword values: Expected value of this keyword is roughly 5 volts.

detbias ­ DetectorBias ­ double ­ read only ­ normal
This keyword reads back the detector bias volatge value.
Keyword values: Expected value of this voltage is roughly -4.5 volts.

vref ­ VoltageReference ­ double ­ read only ­ normal
This keyword reads back the reference voltage to which the integrating node on the unit cell source follower gate is set to upon issuing a reset command.
Keyword values: Expected value of this voltage is roughly -2.1 volts.

detheatr ­ DetectorHeater ­ integer ­ read/write ­ normal
Keyword used to read back and set the bias voltage connected to the detector heater to maintain a constant and predetermined detector temperature.
Keyword values: The keyword values are in DAC units. Valid values lie in the range [0, 65535]. The value of this keyword is automatically set to an appropriate value given by the value of the frmtime keyword upon filter and/or grating mode changes. Direct setting of this keyword over rides the suggested default settings.

msrelay ­ MicroswitchRelay ­ Boolean ­ read/write ­ normal
This keyword specifies whether or not the internal microswitches of the aperture, grating, and filter wheel are connected to the outside world. These switches need to be closed when setting the home position of these motors and open when not needed to reduce noise introduced into the dewar.
Keyword values:
  • ``t'' = relay closed, microswitches connected to motor controller.
  • ``f'' = relays open, microswitches deactivated. This is the state for low noise operation; i.e., data collection.

lvlon ­ LevelShifterPowerOn ­ Boolean ­ read/write ­ normal
Keyword used to turn on the Level Shifter power.
Keyword values: The keyword values are ``t'' (turn power on) and ``f'' (turn power off).

peckon ­ PeckPowerOn ­ Boolean ­ read/write ­ normal
Keyword used to turn on the Peck cage power.
Keyword values: The keyword values are ``t'' (power on) and ``f'' (power off).


Chopping Secondary Mirror Keywords

The keywords defined below describe the LWS keyword interface to the Keck chopping secondary mirror. Some of the keywords defined below belong to the CARA chopper keyword library. Some of the keywords are LWS specific although some of them may eventually find themselves elected to the more general purpose CARA chopper keyword library if they are found useful for other and future IR instruments.

chpamp ­ ChopperAmplitude ­ double ­ read/write ­ normal
This keyword specifies the amplitude of the chopper throw. This keyword belongs to the CARA chopper keyword library.
Keyword values: Input units: arcsec. Internal units: radians.

chpecorr ­ Chopper ErrorCorrection ­ Boolean ­ read/write ­ normal
This keyword specifies whether or not the chopper uses error correction. This will always be true for the LWS. This keyword belongs to the CARA chopper keyword library.
Keyword values: A value of ``t'' (integer 1) indicates that chopper error correction is on. A value of false (integer zero) indicates that error correction is off.

chpfreq ­ ChopperFrequency ­ double ­ read/write ­ normal
This keyword specifies the frequency at which the chopping secondary mirror should chop. This keyword belongs to the CARA chopper keyword library.
Keyword values: Input units: Hertz. Internal units: Hertz.

chpon ­ ChopperOn ­ Boolean ­ read/write ­ normal
This Boolean keyword determines the state of the chopping secondary mirror. This keyword belongs to the CARA chopper keyword library.
Keyword values: A value of ``t'' (integer 1) indicates that the chopper is ready to accept chopper trigger commands from the IRE and that it will move to the next beam position as soon as the IRE gives the next chopper trigger.

chpang ­ ChopperAngle ­ double ­ read/write ­ normal
This keyword specifies the chopping position angle measured relative to the coordinate system set by the keyword chprel2. Note that there is no equivalent nodpa keyword since these position angles are always assumed to be the same. This keyword belongs to the CARA chopper keyword library. The meaning of chppa depends on chprel2 as follows:
  • chprel2 = sky Keep position angle (from N to E) on sky fixed.
  • chprel2 = el Keep position angle relative to elevation fixed. CW is positive.
  • chprel2 = inst Keep position angle relative to instrument fixed. CW from columns to rows.

Keyword values: Input units: degrees. Internal units: radians.

chppos ­ ChopPosition ­ integer ­ read/write ­ normal
This keyword specifies the beam position and moves the chopper to that position. This keyword belongs to the CARA chopper keyword library. It is expected that this keyword will be extended to support multiple beam position chopping.
Keyword values: Valid values are -1 (home position), 0 (``minus'' beam) or 1 (``plus'' beam).

chppostr ­ chopper-post-trigger-time ­ double ­ read/write ­ normal
This keyword specifies the delay time after the chopper trigger is received before the chopper will begin to move. This keyword belongs to the CARA chopper keyword library.
Keyword values: Units are double precision seconds.

chppretr ­ chopper-pre-trigger-time ­ double ­ read/write ­ normal
This keyword specifies the interval before the chopper trigger is expected. During this period the chopper error correction is disabled. The chopper trigger is permitted to be asserted only during this period. This keyword belongs to the CARA chopper keyword library.
Keyword values: Units are double precision seconds.

chprelto ­ ChopRelativeTo ­ string ­ read/write ­ normal
This keyword determines the nature of the chop (and nod) position angle. This keyword belongs to the CARA chopper keyword library.
Keyword values: Character string. See chppa for their effects.

chptrig ­ chopper-trigger-mode ­ Boolean ­ read/write ­ normal
This keyword allows one to set/read the current chopper trigger mode. When in chop trigger mode the chopper moves in response to a signal from the instrument. This keyword belongs to the CARA chopper keyword library.
Keyword values: Integer zero is false. Integer 1 (non-zero) is true.
Notes:
  1. Chop trigger mode is initially disabled. It should only be enabled when the chopper is inactive (a bug at present allows it to take immediate effect even when chopping).
  2. When chop trigger mode is enabled, CHPPRETR and CHPPOSTR govern how early chop trigger is allowed to be asserted and how long after chop trigger before the chopper starts moving (at which point chop synch is asserted).
  3. Chop trigger mode should work together with error correction and the reason for CHPPOSTR is to allow error correction to be disabled when waiting for chop trigger, and at a time when it is expected not to be doing much. If error correction is off, CHPPOSTR can be set to zero.

iretrig.p ­ IREChopperTrigger ­ Boolean ­ read/write ­ normal
This keyword send the command to the IRE to begin sending chopper triggers to the chopping secondard mirror or sector wheel chopper. This keyword belongs to the IRE chopper keyword library.
Keyword values: Integer zero is false; i.e., do not send triggers to the chopper. Integer 1 (non-zero) is true; i.e., begin sending chop trigger signals.

irepostr.p ­ IREChopperPostTrigger ­ double ­ read/write ­ normal
This keyword specifies (for the IRE) the delay time after the chopper trigger is received before the chopper will begin to move. This keyword belongs to the IRE chopper keyword library.
Keyword values: Units are double precision seconds.


Telescope Motion Keywords

nodamp ­ NodAmplitude ­ double ­ read/write ­ normal
This keyword specifies the amplitude of the nod motion.
Keyword values: Input units: arcsec. Internal units: radians.

nodon ­ NoddingOn ­ Boolean ­ read/write ­ normal
This Boolean keyword indicates the status of telescope nodding.
Keyword values: A value of ``t'' indicate that the telescope is currently in nod mode and that it will move after the LWS collects the specified number of frames in the current nod position. A value of ``f'' indicates that nod mode is disabled.

nodpos ­ NodPosition ­ integer ­ read/write ­ normal
This keyword specifies the nod beam position and moves the telescope to that position.
Keyword values: Valid values are -1 (home position), 0 (``minus'' beam) or 1 (``plus'' beam).


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Last modified: Tue Jun 8 17:14:34 HST 1999