Dual channel input, single output isolator

[d0ubleth1nk]

I'm looking for a signal isolator/repeater, that can accept 2 current loop inputs, and based upon a seperate digital input, only repeat 1 of the input signals. Is there such a device, and who makes it? Thanks.

[Ken Moore]

Would a DPDT relay work? A dual channel isolator with the output going through a relay. The loops would be isolated, so no problem there, I've never ran a 4-20 signal through a relay contact, but I don't see why you couldn't.

[DanW]

I have. It works fine for current output signals (like a control output driving a valve), but can be tricky and sometimes not useable with loop powered, 2 wire field transmitters. For field devices, power is the issue. I found that I needed to try a DPDT relay, so that the unselected 4-20mA could be directed to a dummy load resistor to complete the 4-20mA circuit. Otherwise, the source device was unhappy, needing initialization time when to recover from a power down situation. I seem to recall a frantic search for make-before break contacts. But it was some years ago.

[Mike Lamond]

It's been a while, but I recall seeing some signal modules that would do high or low select of two or three inputs. What's your criteria to select between the two signals? Anything I've seen lately has two inputs to the controller and the selection done in the programming. The usual logic is manual selection by the operator or automatic changeover in case of signal failure. Mike

[OkiePC]

If you use a relay, choose one with gold contacts. Sure they cost a lot more, but they will pass low currents at low voltages much better than your standard 10amp silver relay contacts.

[Ken Moore]

Not Knowing the application we are all guessing. If it was me I would bring both signals into a Plc and have logic coded to select the signal, high select, low select or what ever.

[JeffKiper]

Ken you always want to take all the fun out of a project. Use the right tool for the right job where is the fun I'm that?