Experimental Physics and
Industrial Control System

<[email protected]> · Fri, 16 Jan 2015 10:48:19 +0000

Hi Rod,

I asked one of our electrical engineers about this kind of thing for a cryo system where we needed to protect staff in case of nitrogen leaks. I hope there are some useful comments for you:

Unfortunately with an active alarm the only way is to test periodically or at significant times, e.g. entry to a confined space.  This is how we deal with it for all the oxygen depletion systems:

Power loss - the alarm sounds.  The battery inside the control box lasts and hour.

Sensor disconnected or damaged - alarm sounds.  It's a 4-20mA loop so disconnection and over range are detectable by the control box.

Loss or damage of sounder/flasher circuit - periodic testing - we have an annual test by the supplier under a maintenance contract.  Warning circuits can be activated from the controller front panel allowing more frequent periodic testing if required.

Sensor aging or malfunction - checked at annual service.   Can be done more often if required.

The Crowcon systems we used have proved very reliable.   The only work needing to be done is changing sensor heads which deteriorate with age.   These are however dedicated processors inside sealed boxes with no configuration access when in service.   Power is fed from UPS feed via local outlets which do not have switches.

Regards,

Austen Rose
(x8495)

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System