What seems to be the problem if the 24VDC from the safety barrier drops down to 0VDC every time I connect my temp transmitter. Is there a short or open circuit in my loop? Is there any factor from this:

Wire Resistance disconnected from transmitter is approximately 2030 ohms. I should get open or maximum resistance from my multimeter right?

Resistance when transmitter is connected is approximately 2070 ohms.

 

A-B... it could depend on the type of barrier.

1) What happens to the input-voltage to the barrier?

2) As a test what happens if the transmitter is moved to another barrier?

3) How about additional info like manufacturer and type?

Regards, Phil Corso

 

The loop's large value for wire resistance, >2000 ohms, caught my eye. And that value apparently does not include the analog input's dropping resistor, typically 250 ohms.

Typically, 2 wire loop powered field instruments can drive a total of about 1400 ohms of loop resistance at 42 volts, the limit that the manufacturers show for their resistance vs voltage curves in their documentation. I suspect that the ~42Vdc limit is due to a desire to stay within a generally accepted 'safe' voltage limit, although I know of one installation with a very long wire run that needs all of its 70Vdc power supply.

I looked at 3 or 4 resistance vs voltage curves from the major pressure transmitter suppliers and they all drive about 625 ohms, give or take, at 24Vdc. Your loop resistance is so high that the transmitter will starve for operating voltage at an output of more than about 10mA.

 

I just noticed, it's a temperature transmitter.

Many temperature transmitters are not isolated input to output. Is your transmitter isolated? Does it have I/S approval? Is there a control drawing in the manual for I/S installation?

If you have a grounded thermocouple with a non-isolated thermocouple you could easily have a ground loop that is avalanching the safety barrier.