4-20Ma Signaling

[Mr. Stevo]

I am recieving a 4-20Ma signal from a peice of equipment. This signal however has only 14 volts and I am getting nuthin. I am putting into an Allen Bradly flex I/O module. Would a signal Isolator help? Any insight would help.

 

[Gerry]

I am recieving a 4-20Ma signal from a peice of equipment. This signal however has only 14 volts and I am getting nuthin. I am putting into an Allen Bradly flex I/O module. Would a signal Isolator help? Any insight would help.

Is the module set up for current or voltage?

Typical instrument power supply = 24 VDC
Typical 2-wire transducer needs 10 VDC to operate
24 - 10 = 14 VDC maximum to drive the current signal through the load
Typical maximum load resistance is therefore 14V/0.02A = 700 ohms

Voltage input is high impedance.
Selecting current input typically places a 250 ohm resistor in parallel with the input and the module actually measures 1-5 volts.