valve limit switches recommended wiring in protection systems

Not sure what happens in your part of the world, but our standard wiring practice is to use normally-closed contacts of valve limit switches and wire the signals back to the control system as 'not open' and 'not closed'.

This has the added advantage that you can wire these signals directly to indicators at the switchboard - two lights indicates valve travelling and no lights indicates limit switch fault.

HTH, Cameron:-)

See the material at Walter Driedgers site.

The link, above, points directly at an article entitled "CONNECTING and INTERPRETING LIMIT SWITCHES". As Walter deals in developing process instrumentation you should find the information very helpful.

Most often I am using the limit switches in a complementary switch arrangement (separate Normally Open and Normally Closed contacts) and have the micro check both parts of the switch.Using a regular pulse power supply to the switches improves your ability to check the wiring to the switches also.

Speaking of Walter, where is he these days?? He used to be a regular poster here...

Cameron:-)

He does seem to have taken a slightly more back seat these days. I think his last posting here was 3 Jan 2005 at 04:40 GMT. I'll have to email him and see what is happening. .

Unfortunately, his "dirty pictures" link seems to have disappeared ... Love those water-powered traansmitters.

Bruce.

He is still very active on the ISA Discussion Group

Steve

Steve YATES MTL >> See the material at Walter Driedgers site.

I received a response from him today and he says that, owing to some problems with his new PC gaining access to newsgroups he decided that he would stick to just the ISA group. Seems he is still very busy in his work-life.

It's good to know he's still around.. Thanks.

Cameron:-)