Voltage Sensor

[dieseltwitch]

Im looking for a voltage sensor and a input card setup for DC Voltages from 0 to 600VDC. I looked through the AD Catalog and couldn't find what i was looking for. the Analog input cards don't seam to be able to handle the voltage. what options do i have?

[BobO]

Your best bet would be to ask that over at AutomationDirect's forum.

That said, when we need to measure high voltages here at Host, we usually just use a couple of resistors to create a voltage divider to reduce the voltage to what is appropriate to the measurement device.

[fiaranch]

Im looking for a voltage sensor and a input card setup for DC Voltages from 0 to 600VDC. I looked through the AD Catalog and couldn't find what i was looking for. the Analog input cards don't seam to be able to handle the voltage. what options do i have?

Do a google search for DC voltage transducers.  Use a transducer to read the voltage and provide a 4-20ma signal to send to the PLC.

[Controls Guy]

I have to agree with fiaranch.  The thought of dropping 600 using dividing resistors and hooking it to a PLC input makes me a little nervous.  Up to 50-100 volts, sure.  But if the high value resistor above the PLC input shorts (unlikely) or the low value below the input opens (more likely fault), you won't like it.  Those signal conditioners can be had with a couple thousand volts of isolation between the process signal and the PLC input signal, and if something were to fail in there, it would be more likely to simply stop working as opposed to putting 600 VDC on the PLC input terminals.

[BobO]

Well...I began with 'ask the PLC experts'... 

Yes, agreed, that if you under-spec your parts and stuff fails, 600vdc will do exactly what you expect: nothing good. On the other hand, the transducer will probably have some kind of voltage divider too, so the problem still persists, although likely on the other side of optical isolation. Which is really beside the point; a hacked up resister network isn't terribly appropriate to an industrial environment. My point remains though: if we were looking for a quick-n-dirty way to measure 600vdc with a 10vdc input, that's how we'd do it in our lab.

Your mileage will vary.

[Controls Guy]

Exactly.  The fault, if one occurs, is "isolated".  If it's on the PLC input terminals, it's liable to end up running across the backplane to the PLC and/or back out the front end of the analog module to all the other analog transmitters and so on, none of which is cheap stuff or fun to see flames coming out of.

[dieseltwitch]

Thanks guys! I picked one up from CR Magnetics!