Control.com - Nerds in Control

Friends Please clear my doubt,

In the loop powered IS transmitters in the field , 24 VDC comes from DCS I/O card or the barrier?

Friend,

It all depends on the barrier. If it's a simple Zener barrier it probably comes from the control system. If it's an active barrier, e.g. isolating, it could come from the control system (most likely) or it might come from another power source. Some barriers are installed in a chassis with a common power supply.

I didn't help much, did I?

Roy

For loop powered IS transmitters, power supply of 24 V DC comes from 24 V DC power distribution board fixed in the DCS cabinet (panel).

DCS I/O card receives input signal from field and give output signal to field.

If shunt-diode (zener) barriers are used, then the power could come from the I/O card or a separate Power Source. If galvanically isolated barriers are being used, these are normally powered from a separate Power Source (there are a few exceptions).

Steve

The barrier's IS side is connected to the transmitter, thereby powering the 4 to 20mA current loop in the field. The barrier also drives a current loop in the safe area side into the DCS of equal value to the current flowing in the hazardous area loop. Some DCS have a 250 ohm resistor on the connection unit and the 4.20mA loop flowing in the safe area side is converted to 1 to 5 V inside the DCS connection unit for the DCS to convert to a digital value and use inside the controller.

Therefore by powering the barrier in the safe area from 24V DC it powers the two current loops on either side. There are many variations of this, but this is the most common arrangement.

Regards,

Bryce

What will be the connection in case of NON IS transmitters?