electronic splitter

[dksj]

I am wondering if there is a device that takes a 4-20ma input signal and outputs 2 4-20ma signals that are equal to the input signal. (Basically an electronic splitter). What would this device be called and where can I buy one? I have a temperature control module that generates a single 4-20ma signal and I want it to go to two places, one to a flowmeter as a density input and the other to an HMI for indication and tracking. Thanks,

Dan

[Dave Williams]

I believe you have two options here, one I'm not sure of & I'm sure others will correct me if I'm wrong. I know for sure you can obtain the data from your 4-20 directly from the PLC to display on your HMI. The other thought I had, this is where I might be corrected, you should be able to run the 4-20 loop through both devices & have the same measurement. Thus, no need for a splitter.

[Tom Jenkins]

You can find signal conditioners that will do what you want from Action Instruments, M-systems, and many other sources. You can probably use an isolator from these same sources by wiring the loop in series to the signal conditioner and the PLC input and using the isolator output for the other destination.

You can also wire the devices in series as Dave suggests as long as only one of them has the signal - tied to common.

[john paley]

Simply series the same 4-20 mA signal through both devices--works great!

[Peter Nachtwey]

Originally posted by john paley
Simply series the same 4-20 mA signal through both devices--works great!

Maybe. You must remember that there is a voltage drop across each of the loads. A common way to do a 4-20ma sensor is to run the current through a 250 ohm precision resister. At 20 ma this causes a 5 volt difference that the A to D converts to counts. Two loads in series will cause a 10 volt drop. If the transmitter/current source is not capable of supplying 20ma at 10 volts then it won't work and it will get hotter than normal. The voltage drop across the loads can't be greater than the power supply voltage of the source. If the power supply for the current source is +/- 12 volts, supplying two loads in series may be stretching it.

So the question are:

What is the output capabilities of the current source.
What is the voltage drop for each of the loads.