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:

The user is present in the dome and holds down the Slew Enable button on the console.
The dome floor is fully down and the Floor Down Enable switch in the dataroom is in the On position.

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]

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 X_c and Y_c 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:

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.

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	Research School of Astronomy and Astrophysics Mount Stromlo and Siding Spring Observatories ANU College of Science