Instrumentation Control

The NCCS must control the following hardware :

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select calibration noise diode (8 bit expandable to 12 non-multiplexed),

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master computer fail alarm reset (1 bit),

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select input signals to DVM #1 (4:16 multiplexed),

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select input signals to DVM #2 (4:16 multiplexed),

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select input signals to Pulsar Timer (3:8 multiplexed),

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turn 18cm and 13cm noise adding diode off/on, to be generalised to include any noise adding diodes (see below),

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select input signal to General Purpose Radiometer (GPR) (4:16 multiplexed),

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select GPR IF filter bandwidth (3:8 multiplexed),

At presently Serial Digital Input Output (SDIO) is used by the VLBI field system as an instrumentation bus to control some of the above hardware. SDIO is a general purpose interface for doing input and output which can be daisy-chained to make up a bus. It communicates with the main computer via an RS-232 serial link. SDIO cards have been developed for doing digital input/output and for doing analog input. This system has been developed by Justin Jonas of Rhodes University and has been maintained and adapted by Jonathan Quick at HartRAO. It suffers from the limitation that if one of the interface boards goes down then the whole bus goes down.

The NCCS must continue to use the SDIO. The following improvements have to be made however :

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select input signal to general purpose mixers,

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convert the RS-232 link to RS-422 so as to be able to cover long distances and be immune to noise,

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group devices together logically on independant SDIO buses to prevent faults on a single interface from affecting all devices connected to SDIO,

No major additional development should be put into SDIO. Where SDIO is is found to be lacking in functionality Ethernet, HPIB-488, RS-422 or an industrial solution should be used.

In addition to the above mandatory hardware to control it is desirable that the NCCS controls the following hardware (probably via SDIO) :

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configure all receivers i.e.

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select noise-adding noise diode and modulation on/off,

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select dual/single beam,

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select Dicke switch on/off,

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select polarisation mode.

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configure 3.5cm, 6cm, 13cm, 18cm radiometers (e.g. mode is noise adding/Dicke/total power).

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select input signals to present chart recorders (4 x 3:8 multiplexed)

Note the old radiometers have not been designed for computer control and will need to be modified in order to accept computer control.