mesoiam

Activate contactor from intrinsically safe digital output

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Hello, I have a remote io cabinet with a rack of Siemens ET200isp. This was chosen because the almost all of the equipment connected to it comes from the hazardous area and is Ex ia.

This presents me with a problem because I have two pumps that I need to turn on and off with this rack, and I cannot drive a contactor with intrinsically safe io for 2 reasons:

1. The power output is too low to pull in a contactor

2. There would be no barrier to separate the intrinsically safe wiring from the 'safe area' wiring containing the 3 phase for the motors.

Output card is a 4 F-DO Ex 17.4V/40mA (6ES7138-7FD00-0AB0)

My original plan was to use a Pepper and Fuchs KFD2-SR2_Ex2.W on the output of the Siemens DO card to provide a safe area dry contact that I can use to power my contactor. This did not work however as the KFD2-SR2 is not designed to be connected to an active current source, so both the IO card and the barrier were trying to power eachother and switching was not possible.

I can get it to work if i power a standard 24v relay from the DO card, however this does not solve the problem of properly isolating the hazardous area wiring from the safe area wiring as a relay is not an intrinsically safe barrier. I can put a zener barrier in line with the coil of the relay however this cuts the power down too much and the relay contacts do not reliably pull in.

I'm asking if anyone has any ideas, we are beyond the point where installing a new IO rack that is non-ia is an option, it would require a whole new cable run for the profibus.

Is there such a thing as a relay that can be powered by the intrinsically safe output?

I hope that is enough detail, please feel free to ask if more info is required.

Thanks in advance for any suggestions.

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