PC
based
Telescope
Position Readout System
(ETS)
for
the MSSSO
24,
30 and 40 inch Telescopes
A
Short User's Manual
Revision:
1 Jan
van Harmelen 12 July 2000
-
added motion control details
1.Introduction
A
PC based position readout system was first implemented on the 30 inch
telescope at MSO in mid 1994 to make this telescope useable again.
The condition of the PDP-11 based ETS system at the SSO 40 inch
telescope had been deteriorating steadily, causing severe maintenance
problems. The possibilities of interfacing the existing encoder
hardware to a PC was investigated and was found to be surprisingly
simple. Upgrading the 30 inch system software to provide the
functionality required at the 40 inch was also not a very large task.
In the early 1980s, encoders of the same type as are used on the 40
inch were installed on the 24 inch telescope, but as a result of the
2.3m construction project, electronics hardware to provide a readout
was never completed. Because of the limited effort and cost involved,
it was decided to construct a system for the 24 inch during 1995 as
well.
On
the 24 and 30” telescopes the task of the telescope control system
is limited to providing a coordinate display in any desired equinox.
The design of the user interface has attempted to blend widely used
GUI menu and dialog operations with the features of the existing
2.3m, 74 and 50 inch VAX/VMS based telescope control systems. In this
way users familiar with the control systems of the larger telescopes
should have little difficulty operating the systems for the smaller
telescopes.
On
the 40” telescope motion control has been implemented mid-2000 to
coincide with the arrival of the Wide Field Imager. Control of
telescope motion through the existing serial link from the CICADA CCD
control system was also introduced at the same time.
The
software has been implemented with TurboVision, a character based,
'chunky' pseudo-windowing environment based on TurboPascal.
2.Safety
On
telescopes with motion control (currently only the 40”), it is at
all times the user’s responsibility to avoid collisions between the
telescope and objects in the dome and to avoid damage to telescope
and instrumentation cabling. The user should ascertain that the
telescope can safely operate in the area of sky that will be accessed
and re-check when large slew distances are to be covered.
Safety
features such as the Slew_Enable button on the telescope
console, Emergency Stop button(s), Floor_Down switch,
and software defined telescope limits have been implemented to
minimise the risks.
2.1Telescope Limits (40”)
Software
limits have been implemented which allow the telescope to move
between the East and West horizons with minor obscuration by the
bottom of the dome shutter, or to the hardware limits set by the
horizon and rotation limit switches. With the telescope
“West_of_Pier” going North beyond the equator poses a serious
risk to the cable looms. Use extreme care in this area! Move the
floor up and use the Slew Enable button while checking the
cables and keeping them from tangling. The telescope rotation limit
only allows hour angles to the East of the meridian while using the
telescope “West_of_Pier”
Before
executing a motion command, the telescope control system checks the
destination coordinates against the telescope limits. If the limits
would be exceeded by execution of the command, the command is aborted
and an error message is displayed.
If
a limit is reached while tracking, the control software will execute
a Halt command. Five minutes before reaching the limit, a
warning message will be displayed.
2.2Safe Operation Aids
Operation
of the telescope slew drives under computer control is only enabled
if:
3.Telescope Commands
3.1Login
Operation
of the telescope system should be started by the use of the login
command. It makes various checks on the system and prompts for
observer identification. It then changes directory to the user's own
observing subdirectory, or if it does not exist, creates it if the
user so wishes.
The
login command need only be used at the beginning of a user's
run, or if the user suspects that the operation of the computer has
been disturbed (power interruption, daytime use of the computer for
other purposes...), but it can be used at any time that the telescope
system is to be started to make sure things are in order.
3.2Startup
The
telescope system proper is started by the startup command.
There may be several seconds delay before the screen starts updating
while the system initialises. All user settings: configuration,
pointing calibration, etc. are recovered from a file written when the
previous shutdown command was executed.
Startup
makes further checks on the availability of essential telescope
system files. If a file cannot be found, the system will not start.
Seek assistance from technical personnel to rectify the problem.
3.3Shutdown (File menu)
At
the end of a night's observing, the system should be shut down. The
shutdown command can be activated by choosing Shutdown
from the File menu, bringing the cursor over the word Shutdown
on the statusbar at the bottom of the screen and clicking the left
mouse button, or typing Alt-X on the keyboard. All user settings:
configuration, pointing calibration, etc. are written to a file for
use on the next startup command.
3.4Setting Date and Time (Configuration menu)
Depending
on the level of technical support provided at the paerticular
telescope site, the observer may be required to check the accuracy of
the system clock. Civil date and time are shown on the default
display and can be checked by comparison with the Telecom talking
clock (telephone 1-1194 at MSO, 1-068-1194 at SSO).
If
adjustment is required, choose Set Time... from the
Configuration menu. A dialog box will appear with the time
input field highlighted. Type in the time for the next whole minute
(or other convenient time slightly ahead of current time), if
required press "TAB" to advance the highlight to the date
input field and change the date. Check or uncheck the Daylight
Saving checkbox as appropriate by clicking the left mouse button
with the cursor on the checkbox or on the label text. Listening to
the talking clock, press "Enter", or click the left mouse
button with the cursor on the OK button when the typed in time
is correct. Time is to be entered in 24 hour hh:mm:ss format, date as
dd/mm/yy. If the format of the entered time or date is incorrect, an
error mesage box will appear. Dismiss it by pressing "Enter"
or clicking the left mouse button with the cursor on the OK
button, and then correct the error.
3.5Configure (Configuration menu)
Listed
and explained below are the items which appear in the configuration
dialog which is activated by choosing Configure from the
Configuration menu.
Control File indicates the
last loaded configuration file.
Observer's Name set this
to the user's name, the detector system may interrogate the telescope
system for this information to write it in the FITS output file.
Instrument Ident set this
to the identification of the instrument in use, as above, the
information may end up in the detector output file.
Tracking Equinox determines
the equinox of the display coordinates. Valid values for this field
are standard equinox specifications or the word FILE, indicating that
the tracking equinox will be taken from the equinox specified in the
coordinates supplied to the TRACK command (not yet implemented) or
lacking this information, from Default File Equinox.
Default File Equinox if
the coordinates supplied to the TRACK command do not contain an
equinox specification, the Default File Equinox is used. Valid
values for this field are standard equinox specifications
Default Temperature in the
absence of an operational meteorological system, this value is used
in the calculation of atmospheric refraction.
Default Pressure in the
absence of an operational meteorological system, this value is used
in the calculation of atmospheric refraction.
Dome Control (40”) select
either manual or automatic. If automatic is
selected, the dome will automatically follow the telescope.
If
invalid values are entered in the Tracking Equinox, Default File
Equinox, Default Temperature, or Default Pressure fields,
an error message is displayed when the user tries to move to another
field or clicks on the OK button. Sensible ranges are allowed
for the temperature and pressure variables. Valid equinox
specifications are in the form of: J2000 j1995.5 b1950 B1975.0
1900 2000 Apparent APP. If the FK system is not specified, B will
be assumed for dates before 1984, J thereafter. There are no
separators allowed within the value string. The parsing is case
insensitive. "Apparent" can be abbreviated to a single "A"
if desired.
3.6Calibrate Zenith (Configuration menu, 30"
telescope only)
The
30 inch telescope is equipped with incremental encoders which need to
be calibrated at the zenith with the use of spirit levels.
Calibration is maintained by saving the current telescope position to
file on shutdown and reloading it at startup, if the
telescope is not moved while the system is shut down, or the computer
is powered down. Make sure the tracking is switched off before
shutting down.
If
it is necessary to calibrate at the zenith, move the telescope to the
correct position by observing the spirit levels on the mirror cell.
When the correct position is reached, choose Calibrate Zenith
from the Configuration menu. Click on the Calibrate
button.
Spirit
levels are not very accurate devices, and it will be necessary to
find a bright object near the zenith to calibrate more accurately.
Refer to the next section: Calibrate Pointing.
3.7First Calibration (Configuration Menu)
The
two point calibration procedure is used on telescopes with
incremental encoders (MSO 30") to calibrate both
collimation and encoder offset errors. It can also be used on other
telescopes to improve pointing, especially if there may be a time
error.
Select
two objects with known coordinates near the meridian, with
declinations in the ranges: 0 to -10 and -60 to -75 degrees. It does
not matter which object is used first.
Point
the telescope at the first object, centre the object in the view, in
the desired aperture, or place it on the desired position on the
slit. Choose First Calibration from the configuration menu.
Click on OK to dismiss the dialog with instructions, enter the
known coordinates of the object into the input line of the
calibration dialog box in "standard 2.3m telescope format".
Note that for the current release of the software the supplied
equinox must equal the tracking equinox or an error will be
signalled. The full specification of the format allows for entry of
proper motions, but they are ignored in the current release. After
clicking the Calibrate First Object button, move the telescope
to the second object and centre that. Input its coordinates and click
on Calibrate Second Object. The dialog box should be kept open
during the whole procedure. The new pointing coefficients will be
displayed. The dialog box can be dismissed by clicking the Close
button.
The
procedure can be aborted at any time by clicking the Cancel
button. If the separation in declination between the two objects is
not sufficient to allow a reliable solution for the pointing
coefficients, an error message will appear, the procedure should be
aborted and repeated with different object(s).
Valid
coordinate specifications are of the form: hh mm ss.s sdd mm ss
[equinox]
The
fields are separated by single or multiple spaces or tabs, current
tracking equinox is assumed if an equinox is not supplied, for
further details refer to ???.
3.8Calibrate Pointing (Configuration menu)
Because
of the limited resolution of the telecope encoders and the
performance of the mechanics of the telescope and drive system, only
limited all sky blind pointing accuracy can be expected, even with a
reasonably sophisticated pointing model. The pointing performance
over a 1 or 2 degree field becomes considerably better after local
calibration on an object of known position.
Point
the telescope at an object with known coordinates, centre the object
in the view, in the desired aperture, or place it on the desired
position on the slit. Choose Calibrate Pointing from the
configuration menu. Enter the known coordinates of the object into
the input line of the dialog box in "standard 2.3m telescope
format". Note that for the current release of the software the
supplied equinox must equal the tracking equinox or an error will be
signalled. The full specification of the format allows for entry of
proper motions, but they are ignored in the current release. When the
Calibrate button is clicked, the pointing parameters are
updated to make the current display appear equal to the supplied
coordinates. The dialog box can be dismissed by clicking the Close
button.
By
default the last entered coordinates for the Track command are
displayed in the input line if telescope motion is under computer
control (40”). In this case, coordinates in any equinox and
including proper motions will be processed.
Valid
coordinate specifications are of the form: hh mm ss.s sdd mm ss
[equinox]
The
fields are separated by single or multiple spaces or tabs, current
tracking equinox is assumed if an equinox is not supplied, for
further details refer to ???. If invalid coordinates are entered and
the Track button is clicked, a message box with explanatory text will
appear.
3.9Track (Motion Menu, 40” only)
Choosing
the Track… command from the Motion menu opens a
dialog box with an input field for the desired tracking coordinates
in "standard 2.3m telescope format". Clicking on the Track
button activates the telescope drives if either the rising floor at
the 40” telescope is in its fully lowered position, or the user
holds down the Slew_Enable button on the telescope console.
This a safety feature. At all times the user is responsible for
avoiding collisions between the telescope and objects in the dome. If
the distance to the new position is that small that only the slow
motion drives need to be activated, there is no need to hold down the
Slew_Enable button. A Halt button is available in the
dialog box to stop telescope motion if needed. The “tr/here”
button switches on the tracking drive at the current position of the
telescope, a useful feature for testing purposes. This provides the
same functionality as the TRACK/HERE command on the RSAA VAX/VMS
telescope systems. The dialog box can be closed at any time by
clicking on the Close button.
The
Track dialog box can alternatively be opend by typing ‘Alt-T’
on the keyboard. Previously entered coordinates can be recalled
through the history (down arrow) button to the right of the
coordinate entry field. Double clicking on the desired line will
transfer it to the entry field. Once the dialog box has been opened
and input has been supplied, typing ‘Alt-T’ or ‘Enter’
will activate the Track command. At any time, ‘Alt-H’
will execute a Halt command.
On
activation of a Track command the telescope will slew to close
to the specified position and then the slow motion drives will be
used to move to within a few arcsec of the desired position. The 40”
declination drive does only allow a settling accuracy of 10 acrsec.
Further manual correction of the position is possible after the
message “telescope arrived at desired coordinates” has been
displayed. Any attempt to manually operate the telescope drives
before the “arrived” message is displayed will be negated by the
control system. If the telescope only has to move by less than a
predetermined amount (usually in the order of 0.5 to 1.0 degrees),
only the slow motion drives are used.
Valid
coordinate specifications are of the form: hh mm ss.s sdd mm ss
[equinox] [proper motions]
The
fields are separated by single or multiple spaces or tabs, current
tracking equinox is assumed if an equinox is not supplied, for
further details refer to ???. If invalid coordinates are entered and
the Track button is clicked, a message box with explanatory text will
appear.
3.10Offset (Motion Menu, 40” only)
Choosing
the Offset… command from the Motion menu opens a
dialog box with input fields for desired Right Ascension and
Declination offsets. The offests have to be supplied in arcseconds
‘on the sky’. Radiobuttons allow the selection of either
incremental or base offsets. Clicking on the Offset
button activates the telescope drives. In incremental mode the
supplied offsets are added to the current telescope tracking
coordinates, in base mode, they are added to the originally
supplied tracking coordinates. The telescope can be made to return to
the originally supplied tracking coordinates by specifying offsets of
0, 0 in base mode. The dialog box can be closed at any time by
clicking on the Close button.
The
Offset dialog box can alternatively be opend by typing ‘Alt-O’
on the keyboard. Once the dialog box has been opened and input has
been typed in, typing ‘Alt-O’ or ‘Enter’ will activate
the Offset command. At any time, ‘Alt-H’ will
execute a Halt command.
Offsets
are limited to one degree (3600 arcsec) and will be executed by using
the telescope slow motion drives only. Due the settling inaccuracy of
the telescope (up to 10 arcsec in Declination on the 40”), the
errors in small offsets and in the total offset after successive
commands can be large.
3.11Rate (Motion Menu)
On
telescopes which have a programmable tracking rate generator (form
July 1996: 40”, 30”, 24”), a differential tracking rate can be
specified.
Choosing
the Rate… command from the Motion menu opens a dialog
box which displays the current value of the differential tracking
rate, or the last used value if a differential rate is currently not
in use. The display can be in units of arcseconds or seconds per
second, minute, hour or day. Select the desired units by clicking on
the appropriate labels. The default display is in arcseconds per
second, but during a session the last used units are remembered.
The
user can input a desired rate and activate it by clicking the Apply
button. There are also buttons to re-activate the last used rate and
to de-activate (zero) the current rate.
The
hour angle tracking rate is automatically corrected for the effects
of refraction and flexure. Unfortunately, the declination slow motion
drive is not under computer control.
The
Rate dialog box can alternatively be opend by typing ‘Alt-R’
on the keyboard.
3.12Slew (Motion Menu, 40” only)
Choosing
the Slew… command from the Motion menu opens a dialog
box with input fields for desired Hour Angle and Declination.
Clicking on the Slew button activates the telescope drives if
either the rising floor at the 40” telescope is in its fully
lowered position, or the user holds down the Slew_Enable
button on the telescope console. This a safety feature. At all
times the user is responsible for avoiding collisions between the
telescope and objects in the dome. A Halt button is
available to stop telescope motion if needed. The dialog box can be
closed at any time by clicking on the Close button.
The
Slew command is mainly used for maintenance purposes. The Slew
dialog box can alternatively be opend by typing ‘Alt-S’ on
the keyboard. Once the dialog box has been opened and input has been
supplied, typing ‘Alt-S’ or ‘Enter’ will activate the
Slew command. At any time, ‘Alt-H’ will execute a
Halt command.
Th
inputs required are Hour Angle in decimal hours and Declination in
decimal degrees. The inputs are checked for validity and against the
telescope programmed limits. An error box will be displayed if the
inputs are in error.
3.13Zenith (Motion Menu, 40” only)
The
Zenith command on the Motion menu causes the telescope
to slew to the zenith. It activates the telescope drives if either
the rising floor at the 40” telescope is in its fully lowered
position, or the user holds down the Slew_Enable button on the
telescope console. This a safety feature. At all times the user is
responsible for avoiding collisions between the telescope and objects
in the dome.
The
Zenith command can alternatively be executed by typing ‘Alt-Z’
on the keyboard. At any time, ‘Alt-H’ will execute a Halt
command.
3.14Park (Motion Menu, 40” only)
The
Park command on the Motion menu causes the telescope to
slew to a predetermined parking position. It activates the telescope
drives if either the rising floor at the 40” telescope is in its
fully lowered position, or the user holds down the Slew_Enable
button on the telescope console. This a safety feature. At all
times the user is responsible for avoiding collisions between the
telescope and objects in the dome.
The
Park command can alternatively be executed by typing ‘Alt-P’
on the keyboard. At any time, ‘Alt-H’ will execute a Halt
command.
3.15Halt (Motion Menu, 40” only)
Choosing
the Halt command form the Motion menu halts telescope
motion. The Halt command can alternatively be executed by
typing ‘Alt-H’ on the keyboard.
3.16Help
The
only on-line help information currently available are the hints
displayed on the statusline at the bottom of the screen. They give
(very) short descriptions of the commands available on the various
menus. The Help | About menu selection activates a box showing
current system release and update information.
4.What If The Telescope Does Not Move? (40”)
If,
on issuing a telescope motion command the telescope does not move,
check the following:
Is
the Telescope power switched On on the console?
Are
any Emergency Stop buttons pressed (two E.S. buttons:
on console and in dataroom on panel in equipment rack)? Reset as
necessary (pull out button, press E.S. Reset on console).
Make
sure Tracking and Dome are switched on on the console.
Is
the Telescope Control Switch (top right, on console) switched
to Auto?
Hold
down the Slew Enable button (top right, on console), or
Make
sure the floor is fully down and the Floor Down Enable switch
(in dataroom on panel in equipment rack) is On.
5.Using
Telescope Files (File menu)
5.1Note
Note
is a logging utility which writes date, time and telescope
position to a file.
Select
a file name by activating a file dialog by choosing the File|New
Note File menu item.
Consequent
choosing of File|Note or pressing the Alt-N keys writes one
record to the file. A dialog prompts for comments to be appended to
the record. Write in the input line if so desired and press “Enter”
or click on OK.
The
technical staff may be able to modify the Note file format if that is
required.
5.2Configuration Files (CFiles)
Telescope
control files are provided as a convenient means of controlling many
telescope configuration items at once and of storing frequently used
telescope configurations for subsequent observing runs. They may also
contain pointing correction terms, but observers’ control files in
general will not. The files are text files with default file type
“.CFL”, and they will frequently be referred to as CFILES.
5.2.1File Contents
Each
line in a CFILE controls one item of telescope configuration. Many of
them duplicate directly the functions of CONFIGURE commands. Only
those items which are to be altered need to be included in a CFILE;
all others are left unchanged. Most CFILE entries consist of a
keyword followed by a value. For example, the following are two valid
CFILE entries:
Default_Temperature
5.0
Default_File_Equinox
B1950
Extra
characters, such as "=", ":=", and brackets may
be added for clarity, but they are ignored when the CFILE is read.
For example, the two entries shown above could equally well be
written as:
Default_Temperature
:= 5.0
Default_File_Equinox
:= B1950
An
exclamation point “!” indicates that the remainder of the record
is to be treated as a comment.
5.2.2Default Cfile
The
default CFILE: \TEL\DEFAULT\DEFAULT.CFILE is can be used to reset
the telescope configuration to a predetermined state, by choosing the
File|Load Default Cfile menu item. This file is accessible to
observers for reference or copying if required. It defines the
pointing coefficients and certain other system default values. A
typical default CFILE is listed below; it is included as an example
only and is not necessarily the current one.
!----------------------------------------------------------------------------
!
!
40 I n c h T e l e s c o p e C O N T R O L F I L E
! 13-MAY-1995
!----------------------------------------------------------------------------
!
!
Telescope Configuration variables
Default_File_Equinox
:= J2000
Tracking_Equinox
:= J2000.0
Default_Temperature
:= 10.0
Default_Pressure
:= 930.0
!
!
Telescope Pointing Coefficients
IH
[ Cassegrain, East_of_Pier ] := -47.600
ID
[ Cassegrain, East_of_Pier ] := 14.0
NP
[ Cassegrain, East_of_Pier ] := 73.400
CH
[ Cassegrain, East_of_Pier ] := -99.0
and so on.
An
observer defined CFILE would normally contain configuration
information such as Instrument Identification, but would not normally
contain pointing coefficients.
5.2.3Loading and Saving
Cfiles
can be loaded by choosing the File|Load Cfile menu item, and
then choosing a file from the file selection dialog box. If any load
errors occur, all correct entries are still processed, but entries in
error are displayed in an error window, with error messages. The
current Configuration can be saved by choosing File|SaveCfile,
entering the desired filename in the file selection dialog box, and
checking the items that are to be saved in the next dialog. The
default setting of the configuration items which appear on the
configuration screen plus the calibration information is most useful.
Users should generally not record the full pointing model, because
the re-use of the old file would not take advantage of a possibly
improved model installed after the file was recorded.
5.2.4Pointing Model
The
telescope control software implements a pointing correction model in
the form of a linear combination of terms controlled by a number of
pointing coefficients. The effect of each coefficient is additive,
that is, if all are set to zero, no corrections are applied. It is
not expected that observers will need to alter these coefficients
(except for ID and CH as discussed below), and changes to the
functional relationships of the terms can only be made by the design
team because they involve recompilation. However a brief description
of some of the pointing coefficients is included here.
IH hour
angle encoder index error
ID declination
encoder index error (collimation constant Yc)
NP nonperpendicularity
of axes
CH collimation
error (collimation constant Xc)
ME polar
misalignment - elevation
MA polar
misalignment - azimuth
TF tube
flexure—proportional to sin Z
TFP tube
flexure proportional to tan Z
All
pointing coefficients are specified in arcseconds.
These
coefficients are subject to change, and additional ones may be added
as modelling improves. The coefficients can only be set by entries in
a CFILE; there is no command with which to enter them. The main thing
for observers to note is that if they are concerned about telescope
pointing and they wish to log pointing error data for analysis (using
the TPDATA command), they should either zero all of these
coefficients or use the CFILE/SAVE=POINTING command to record the
values before making the pointing test.
The
two coefficients CH and ID effectively model misalignments in the
frame of the telescope tube. They are used as the collimation
parameters Xc and Yc which are adjusted
automatically when the CALIBRATE POINTING command is used.
5.3Display Definition Files
The
contents and format of the observer display screen is defined using
Display Definition Files. Display Definition Files are text files and
by default they have the file type “.DSP”. The standard
Observer’s display is defined by such a file, namely
\TEL\DEFAULT\DEFAULT.DSP. You may wish to examine this file if you
intend defining your own display.
5.3.1Loading a Display Definition file
Choose
the File|Load Display File menu item to load a display
definition file.
5.3.2File Contents
Data
records have the format: Display_Variable [display_format]
Specify
one data record for each display variable which you wish to include
on the screen. The record must commence with the name of the display
variable. For a list of valid display variable names, see below. You
can specify up to 33 variables. The order in which you specify them
determines their locations on the screen--the 1st, 2nd & 3rd
variables make up the top line, etc. To leave a space unfilled,
specify the special variable Undefined.
If
no variables are specified, none are displayed.
The
optional value “display_format” can only be specified for display
variables Hour_Angle, Right_Ascension and Declination.
It may take the value RADIAN, SEXAGESIMAL, or DECIMAL. A sensible
default setting is used for any data record which does not specify a
display format.
RADIAN: mainly
used for engineering purposes;
SEXAGESIMAL: hh
mm ss.d or sdd mm ss format;
DECIMAL: hh.hhhhh
or sdd.ddddd format;
5.3.3Display Variables
The
following variable names may be specified on the telescopes. Only
those variable names shown in bold text are fully implemented. The
others are not yet available, or not kept updated, or only fully
implemented at the 50” or 74” telescopes.
The
units in which the variables are stored internally are shown in
parentheses. Where variables are stored in radian, they are displayed
in hours, minutes and seconds, or degrees, minutes and seconds as
appropriate. (The notation ' = arcminutes, " = arcseconds)
Name Description
Airmass Airmass calculated
by polynomial approximation
Apparent_Dec Geocentric
apparent Dec (rad)
Apparent_RA Geocentric
apparent RA (rad)
Bar_Pressure Current barometric
pressure (absolute) (mBar)
Barometer_QNH Bar. pressure
referred to mean sea level (mBar)
Base_Dec Current telescope
control coord—base posn (rad)
Base_RA Current telescope control
coord—base posn (rad)
Civil_Date Date for
observatory time zone ‘dd-mmm-yy’
Civil_Time Observatory
zone time (hours)
Cos_Dec For sky position
calculations
Cos_HPD To be output to MTEC
control station to allow ‘slit’ direction control of telescope at
coude focus
Dec0 Declination
axis absolute position (rad), range 0–+2π [50” only]
Dec1 Encoded
(telescope) Dec (rad), range -π–+π
Dec2 Observed (telescope)
Dec (rad), range
-π–+π
Dec_Drive_Cmd Dec drive command:
1=forward, 0=off, -1=reverse
Dec_Error Difference between
Ref_Dec and Tracking_Dec (rad)
Dec_ON_Count No. of times Dec
drive has been turned ON in Quick mode during current SLEW or TRACK
command
Dec_Reverse_Count No. of times
Dec drive has been reversed in Quick mode during current SLEW or
TRACK command
Dec_Velocity Velocity
(deriv.) of Dec (rad/control period)
Delta_Dec Accumulated Dec
offset (")
Delta_RA Accumulated RA
offset (s)
Dew_Point Surface temperature
causing condensation (°C)
Dome_Azimuth Position of
dome (rad), range 0–+2π .[50” only]
Ext_Temperature External air
temperature (top of building) (°C)
File_Dec Input file polar
coordinate Dec (rad)
File_Epoch Epoch specification
for file coordinates
File_Equinox Equinox and equator
spec. for file coords
File_RA Input file polar
coordinate RA (rad)
Focus Position of focuser in
focal plane (mm).[50” only]
Focus_Comp Temperature
compensation value for focus position (mm).[50”]
GAST Greenwich Apparent
Sidereal Time (rad)
Geocentric_Distance True
geocentric distance of object (km)
HA0 Polar
axis absolute position (rad), range 0–+2π [50” only]
HA1 Encoded
(telescope) HA (rad), range 0–+2π
HA2 Observed
(telescope) HA (rad), range 0–+2π
HA_Drive_Cmd HA drive command:
1=forward, 0=off, -1=reverse
HA_Error Difference between
Ref_RA and Tracking_RA (rad)
HA_ON_Count No. of times HA drive
has been turned ON in Quick mode during current SLEW or TRACK command
HA_Reverse_Count No. of times HA
drive has been reversed in Quick mode during current SLEW or TRACK
command
HA_Velocity Velocity
(deriv.) of HA (rad/control period)
Hour_Angle Apparent
hour angle of tracking coordinates (rad), range -π–+π, measured
westwards from meridian
Humidity Current relative
humidity (%)
Int_Temperature Internal air
temperature (°C)
J2000_Dec J2000.0 FK5
standard coordinate (rad)
J2000_RA J2000.0 FK5
standard coordinate (rad)
JD Julian Date, defined by
UTC
JD_TDB Barycentric
Dynamical Time in days of 86400 SI seconds
MJD Modified Julian Date =
JD - 2 400 000.5
Obj_Hour_Angle Apparent
hour angle of object (rad), measured -π–+π westwards from
meridian, valid only at
start of slew
Obj_Zenith_Distance Zenith
distance of object (rad), valid only at start of Slew
Offset_Stepsize Offset stepsize
for jog buttons in offset mode (")
Parallactic_Angle Angle at
the tracking coordinates b/n the hour circle and the vertical circle
measured eastwards from the north as in Lee, J British Astron. Assn.
vol 65 no.3 pp114–117, 1955 (rad)
Primary_Temperature Temperature
of primary mirror (°C)
Rain Precipitation sensor
(“Raining”/“NotRaining”)
Raw_Focus Uncompensated focuser
position (mm).[50” only]
Ref_Dec Reference telescope
tracking coordinates (rad)
Ref_Dome_Posn Dome position
setpoint (rad), range 0–+2π [50” only]
Ref_Focus_Posn Focuser position
setpoint (mm in focal plane).[50” only]
Ref_RA Reference telescope
tracking coordinates (rad)
ST Local Apparent Sidereal
Time (rad)
Sec_Z Secant of zenith
distance
Short_Obj_Name Abbreviated object
name
Shutter_Closed_by_Rain Rain
sensor closed shutter (“True/False”)
Side_of_Pier E/W of pier
(“East”/“West”)
Sin_Dec For sky position
calculations
Sin_HPD To be output to MTEC
control station to allow ‘slit’ direction control of telescope at
coude focus
Slew_Dec_Ref Drive velocity
reference (rad/control period).[50” only]
Slew_Enable Quick/Slow motion
Slew_HA_Ref Drive velocity
reference (rad/control period).[50” only]
Tan_Z Tangent of zenith
distance
Temp_Diff Temp. difference
(internal minus external) (°C)
Time_To_Acq Estimated time to
acquisition (s)
Track_Dec_Ref Drive velocity
reference (rad/control period).[50” only]
Track_Equinox Equinox
specification for base & tracking coords
Track_HA_Ref Drive velocity
reference (rad/control period).[50” only]
Tracking_Dec Current
telescope tracking coordinates (rad)
Tracking_RA Current
telescope tracking coordinates (rad)
Tube_Temperature Temperature of
telescope trusses (°C) [50” only]
UTC Coordinated Universal
Time (hours)
UT_Date Date for Greenwich
meridian (UTC) ‘dd-mmm-yy’
Undefined Always set to
null string, used for undefined display fields
Wind_Direction Azimuth from which
wind is coming—averaged (rad)
Wind_Gusting Max. wind speed in
last sample period (m/s)
Wind_Speed Current averaged wind
speed (m/s)
Wind_to_Building Angle between
building azimuth and wind (rad)
Zenith_Distance Zenith
distance of tracking coordinates (rad)
6.Engineering
Information
6.1System Files
The
following list specifies the directories and files which are required
for the system to work, together with items which are to be specified
in the config.sys and autoexec.bat files.
\ntr1000p.sys this
file must be present if an NTR precise clock board is to be used
\config.sys if
an NTR precise clock board is used, the following line must be
included:
device=c:\ntr1000p.sys
/d:
\autoexec.bat \tel\system
must be included in the path
\tel\system contains
the executable files:
login.exe executes
the login command to set up user directories
tel.exe
the actual telescope software
startup.bat executes
tel.exe on the startup command
\tel\default contains
the default files for the system:
tel_db.dat the
telescope database saved from last use
params.txt the
telescope parameters which are loaded on each startup
disfield.txt display
information for each variable which can be displayed
default.dsp the
default display definition file (variables to be displayed)
default.cfl the
default control file (cfile)
bulletin.txt the
sign-on message
lastuser.txt contains
the identification of the last user
\observer general
user area, for those who don't want to bother with their own
\observer\xxxx individual
user directories for keeping personalised telescope files
6.2Communication Ports
Three
of the four available communications ports are used for the system.
Port
1: Mouse
Port
2: Not Used
Port
3: Remote Telescope Display. 9600 Baud, 8 bits, 1.5 stop bits, no
parity.
Port
4: Connection to Instrument Computer. Protocol is described in a
separate document.
For
Astromed CCD systems, use the 74” communication program.
9600
Baud, 8 bits, 1.5 stop bits, no parity.
6.3Engineering
When
the telescope system is started with the tel eng[ineering]
command, the engineering menu is enabled. This allows engineering
personnel to load and save parameter files, to record data from
pointing tests or to set encoder zeros. When started with the tel
debug command, runtime debug code is activated which can assist
in solving problems. No such code is included in V2-000.
6.4Parameter files
The
parameter file \tel\default\params.txt is loaded at startup. This
file contains the telescope identification information and values for
the encoder zeros, servo control parameters, limits etc, as
appropriate. These parameters may need tuning to improve telescope
performance or to assist in faultfinding. A facility to interactively
change parameters may be included later. Currently an editor is
required to construct a new parameter file or modify an existing one.
Choosing the load parameter file... or save parameter
file... items from the engineering menu activates a standard file
dialog to choose a file name.
A
future update may include the interactive setting of parameter
values.
6.5Pointing Tests
After
aluminising, or at least once a year, pointing tests should be
carried out. This should be done as follows:
• Check and adjust the system
time if required.
• Calibrate pointing on a
bright object.
• Choose Save CFILE...
from the file menu, choose a file name, check Configuration and
Pointing in the dialog box, to record the current poining
model.
• Use New TPDATA File...
from the engineering menu to choose a file name for the pointing data
file.
• Point the telescope at
objects selected from the 2.3m pointing catalogue.
• When an object is centered in
the viewfinder, choose TPDATA from the engineering menu (or press
Alt-T on the keyboard), enter the object name in the dialog box which
appears and press <Enter> or click on OK.
• Repeat this for many objects
spread over the sky.
• Process the pointing data
file with the TPOINT data reduction package (after transfer to MAIA
or MEROPE).
• Adjust the pointing model
parameters in the saved cfile by the amounts indicated by the TPOINT
results.
• Those parts of the values of
IH and ID which are common to West and East of pier operation, should
be separated from the calibration values IH and ID and allocated to
the zero point offsets IHZ and IDZ. That way they are applied before
any trigonometry is calculated in the pointing model, improving its
accuracy.
• Do another pointing test
after loading the new cfile to confirm the results.
• If found correct, modify the
default cfile \tel\default\default.cfl accordingly and load it.
6.6Setting Encoder Zeros
The
encoder zeros only have to be set once, during commissioning, unless
the encoders are removed from the telescope for service. They are
only applicable to the dual encoder systems as found on the 24 and 40
inch telescopes. The Encoder Engineering Display dialog is
activated by choosing Encoders... from the engineering menu.
For
all encoders the sense is determined by observing whether,
with the telescope tube West of the pier,
the
raw encoder readings increase while the telescope moves North,
respectively West. If this is the case, the sense is taken as +1,
otherwise -1. The encoder sense is hardcoded in the software (unit
tel_enc.pas, TTxx_Encoder.Init) and is dependent only on the encoder
gearing.
The
coarse encoder zeros are offsets applied to the raw encoder readings,
so that the corrected readings have their half scale points at a
predetermined telescope position. This postion is -6 hours in hour
angle West of pier and -90 degrees in declination. In other words,
the telescope is pointing at the South Celestial Pole with the tube
above the polar axis, the counterweight pointing down (on the 40").
The setting circles or other mechanical devices are used to get to
this position as accurately as is possible.
From
the relationship: Corrected Reading = Sense * (Raw Reading - Zero),
If
Corrected Reading < 0, add Full Scale,
follows
that
for
Raw Reading > Half Scale Zero = Raw Reading - Half Scale,
for
Raw Reading < Half Scale Zero = Raw Reading + Half Scale,
independent
of Sense.
For
the 24 and 40" 11 bit telescope encoders, Full Scale =2048, Half
Scale = 1024.
Offsets
are also applied to the fine encoder raw readings in exactly the same
way. Here the zeros are not used to set the corrected values to half
scale, but to make them equal to the estimated fine encoder readings
determined from the coarse encoder readings. As the estimated fine
readings only change when the coarse reading changes, the procedure
becomes somewhat more complicated. At any telescope position (usually
close to the position used to determine the coarse encoder zeros),
move the telescope slowly to find two consecutive estimated fine
values which do not straddle the zero point. Make sure that the raw
fine reading does not cross the zero point in this interval either.
Note the two estimated values Est1 and Est2. Note also the two raw
fine encoder readings at which the estimated values change to Est1
and Est2 while the estimated readings are increasing (Fine1 and
Fine2). Now move the telescope to a position where the raw fine
reading Fine = (Fine1 + Fine2)/2. The fine encoder zeros have to be
chosen so that at this position the corrected fine reading equals
Est1.
From
the relationship: Corrected Reading = Sense * (Raw Reading - Zero),
If
Corrected Reading < 0, add Full Scale,
follows
that
for
Sense = +1 Zero = Fine - Est1,
for
Sense = -1 Zero = Fine + Est1,
Zero
to be normalised to the interval [0, Full Scale) by addition or
subtraction of
Full
Scale as necessary.
(Note
that the coarse zero determination above is a special case of this
general relationship.)
After
determining the zeros, they are to be entered in their fields and the
Accept new Zeros button is to be pressed. Do not forget to
permanently record the zeros in the default parameters file by
choosing Save Parameter File from the engineering menu after
closing the Encoder Engineering Display dialog, and selecting
the \tel\default\params.txt file.
Because
the fine encoder zeros have been chosen to give maximum robustness to
the encoder combining algorithm, the halfway point of the combined
pseudo encoder does not accurately align with the calibration
position of the telescope. The IH and ID pointing coefficients found
from a first pointing test should be applied to the special zero
correction terms IHZ and IDZ which are used to correct for encoder
offsets before any other pointing corrections are calculated.
