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Old December 20th, 2017, 09:30 PM   #1
kongshitt
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0-10V signal splitter

Were having some debate here at work about adding some passive monitoring to our primary drive system on our production line. We want to use the 0-10V signal from the frequency drive to monitor the amps the motor is using. The PLC is already using this signal, but the OEM doesn't want to give us access to the PLC to give us that as an output. The debate is whether or not we need a signal splitter, or if we can parallel the 0-10V signal. Im pretty sure we can just parallel the signal, but our other electrician swears we need a splitter.
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Old December 20th, 2017, 09:37 PM   #2
DwSoFt
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You can just parallel the voltage Signal. Current on the otherhand you need a splitter
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Old December 20th, 2017, 10:23 PM   #3
rpoet
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Quote:
Originally Posted by DwSoFt View Post
You can just parallel the voltage Signal. Current on the other hand you need a splitter
You may or may not need an isolator when sharing a current signal. It all depends on if the various devices share a common ground reference, and have isolated inputs. There are MANY threads on this side that have thoroughly explored this.

The same goes for a voltage signal; if every piece of equipment that needs the signal shares a common reference, it will work fine. If the references are not connected, or if there is a potential difference between them, you risk erroneous readings and damaged inputs and outputs.

Safest bet is to use an analog isolator. You may not need it, but it doesn't hurt, and it may save you headaches and damaged equipment.

As an aside: time to start putting language in your Purchase Orders that OEM's must supply schematics and source code without password protection. You presumably paid for the machine - you own it. They owe you the info to do this via the PLC if you want to go that route.


-rpoet
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Old December 20th, 2017, 10:50 PM   #4
danw
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+1 for rpoet. He took the words right out of my mouth.
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Old December 21st, 2017, 12:27 AM   #5
Pete.S.
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Quote:
Originally Posted by kongshitt View Post
Were having some debate here at work about adding some passive monitoring to our primary drive system on our production line. We want to use the 0-10V signal from the frequency drive to monitor the amps the motor is using. The PLC is already using this signal, but the OEM doesn't want to give us access to the PLC to give us that as an output. The debate is whether or not we need a signal splitter, or if we can parallel the 0-10V signal. Im pretty sure we can just parallel the signal, but our other electrician swears we need a splitter.

The answer to your question depends on the impedance of the two voltage inputs.
Basically if the output on the VFD has enough current to supply the two inputs it will work fine. If it doesn't you will get a lower voltage than expected.
But since we are only talking about two inputs it will likely work without any problems.

As mentioned above ground potential of the analog voltage needs to be considered. Many times both VFDs and PLCs have both isolated input and outputs in which case you just want to make sure you have the analog grounds connected.

Voltage signals are not suitable to run any distance so I hope everything is in the same cabinet. If it's not it would be much better to convert the 0-10V that you want to monitor into 4-20mA.

Last edited by Pete.S.; December 21st, 2017 at 12:32 AM.
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Old December 21st, 2017, 03:21 PM   #6
kongshitt
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Thanks for the info folks.

I had read a lot on the 4-20mA and we had already looked at a signal splitter, but on closer inspection the signal from the drive is 0-10V. As far as install location and wiring to ensure we are using the same reference, that poses no problem at all. It will be installed 2-3' from the drive, in the same panel. As far as a slight voltage drop I am pretty sure we can just calibrate the signals to account for that.
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