Dear all,

We have some Drager 3 wire gas detectors (Polytron Pulsar 2) to wire up to Foxboro FBM01 cards. This detector has 3 cable terminals for (i) 24Vdc power; (ii) analog current loop; and (iv) power and signal common. Its power supply specification is as follows:
Power Supply: Voltage: 18 - 32VDC (24VDC nominal)/Current: ¡Ü 0.95 A typical @ 24 volts DC.

In order to connect this detector to FBM01, we thought of using an external power supply unit to source the 24VDC, but I'm wondering if we can source this power from the FBM01 card itself through its +P connector. One more thing, my understanding is that there is no issue to share the common between the power and signal. Is that correct?

Regards,

 

I have the experience of connecting the +24Vdc wire and + signal wire together with MSA 3 wires gas detector.

 

This type of 3 wire device is quite common, yes it's OK to share the common. You could power it from the I/O card but personally I would use a separate supply, at 950 mA each you may overload the Foxboro power supply. Each detector is the equivalent of 47 regular 2 wire transmitters.

Roy