PLC Technology Reduces Observing Overheads

New control systems are being implemented for all the instruments on the 4.2-m William Herschel Telescope. The new systems are based on PLC (programmable logic controllers) and Ethernet technology, and are faster, and much easier to maintain, than the old 4MS/RS232 systems originally implemented at the telescope over 20 years ago. The re-engineering is all being carried out in-house at ING.

From the observer's point of view, the changes are transparent, but several slow-moving mechanisms now move much faster than they used to. For example, observers using the ISIS instrument will no longer have to wait a full minute to switch between slit-view and arc-calibration modes. This switch now takes just 15 seconds.

ING engineer Carlos Martín testing PLC control of the WHT's Cassegrain acquisition and guiding unit. [ JPEG | TIFF ].

The Cassegrain acquisition and guiding unit (autoguider, calibration lamps, etc.), PFIP and ACAM instruments, and the GLAS dichroic changer all now run under PLC control and the conversion of ISIS will take place shortly.

Conversion to PLC control is just one of several intiatives aimed at maximising both the efficiency of observing at night, and the reliability of the instrument-control systems. Other initiatives include automatic target-acquisition tools for ACAM and ISIS, and the conversion of UltraDAS camera servers and WHT ICS computers from Solaris to Linux PCs.

Example PLC engineering-level user interface, providing straightforward control and status display for all mechanisms. [ JPEG ].