DCS/ESD

not sure but can't you use the DCS to trigger the ESD system ?? if not i guess the marshilling rack would be a nicer place to join the cables as it is in a safe clean location rather then joins in the field ?? unless the ESD system is not located near the marshalilng rack....... thats just my opion but :) hope it helps

Dear DALLAS

As for as i know it is very bad practice to use DCS signal to trigger a ESD system.

No need for any splitter. Connect the 4-20 mA signal directly to the ESD and establish a soft link between ESD & DCS via RS485 or OPC to read the data on the DCS.

If DCS is down for any reason ESD won't see this signal and take limited logical action.

I would strongly suggest you locate your splitter in a safe and clean environment.

Hard wire connection should be to the ESD system, minimizing the paths of failure for the signal. If you are using the 4-20 in the DCS for control, you should run an analog out out of the ESD to the DCS via hard wire (isolator probably needed) as well, in my opinion. If it is for indication only, utilizing an OPC highway or existing MODBUS highway would be fine. Would you typically use a splitter on signals? In my past, it was usually frowned upon.

Dear

You are right i need it for controlling. but if we send it to ESD then take an out from it and send it to DCS will waste one out of ESD. So i think splitter is the good option. I jst want to know its location whether it would be located in Mashilling cabinet or in the JB? i think it would be in Marshilling cabinet of ESD and then we take a wire to DCS marshilling cabinet. what do you think?

Hi there,

As stated above you should take it to the ESD first - then back to DCS. Usually when you have gone to the expense of having an ESD and a DCS - you would be able to afford to install a second transmitter measuring at the same point as the first. This would give you one signal to DCS for control and one signal to ESD for shutdown. Even then this is not good practice so it would be better to have three transmitters measuring the same point and use a two out of three trip validation.

In my experience ESD signals are digital. i.e. the actual trip points are triggered. So if we had 4-20mA signal we would have to use AD cards that we can set the trip points on. The digital signal then goes to ESD.

If you have to use a splitter - keep it in the ESD marshalling cabinet. I am presuming that you are in an IS area so you would not want this splitter in the field JB as it could be potentially hazardous

Regards

Craig