PC-STEER (J.Quick)

PC-STEER is one of the fundamental components of the NCCS. It refers to the hardware and software used to move and track the telescope. In its original form PC-STEER consisted of a digital and analog interface to the telescope encoders and drive, an HPIB interface to the observer's computer and a control program in Turbo-Pascal running under DOS.

For the NCCS the PC-STEER system underwent a number of major changes :

1.

total redesign of hardware interface; the new interface addressed the problems of unstable powersupply, and noise on link between computer and hardware,

2.

the PC interface card was replaced with a single Eagle PC-14B digital input/output interface card,

3.

fast (100 Hz) synchronous data acquisition via V/F counters was added,

4.

time code acquisition from the time standard using the NASA time code format was added. The time thus acquired is used to synchronise the time of PC-STEER and can also (via ntp) synchronise the rest of the control computers,

5.

acquisition of certain weather parameters ( air temperature, relative humidity and barometric pressure ) was added for future atmospheric refractive correction modelling purposes.

6.

acquisition of hyperbola tilt and focus position was added to support future computerised control of the hyperbola mechanism.

7.

the control program (control) was ported from Turbo-Pascal running under DOS to C running under Linux,

8.

the HPIB interface to the observing computer was replaced by an Ethernet connection and a device server talking TCP/IP protocol,

9.

a time-of-day dependant hour angle and declination error correction fudge was implemented.

Tasks completed :

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DESIGN NEW HARDWARE INTERFACE FOR PC-STEER,

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BUILD TWO COMPLETE HARDWARE INTERFACES,

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PORT steer TO LINUX AND C,

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REPLACE HPIB WITH TCP/IP AND DEVICE SERVER,

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LOCK PC-STEER CLOCK TO ACQUIRED NASA TIMECODE.

Tasks still to be done :

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INTEGRATE PC-STEER WITH PROPOSED ALARM/LOG SERVERS.

Outstanding issues :

• Although the new interface has been designed to handle most of the real-time requirements via hardware synchronous data-acquisition, it may be necessary to add real-time scheduling capabilities into the Linux kernel to ensure that critical software components e.g. the main control process, keep pace.
• The telescope error correction model needs a complete overhaul:

  1.

  The error correction needs to be split into static physical & dynamic atmospheric refraction components.

  2.

  The second declination encoder should be integrated to improve accuracy.

  3.

  Support should be added for handling continuous UT1 time instead of UTC with its associated leap second events.