We have a project where we will be monitoring 0-10 V analog inputs with a PLC. The devices are approximately 500 feet from the PLC.
Besides following the standard practices for analog wiring (grounding shields, routing analog separate from power cables, etc.), is there
anything else we need to watch out for. Will the 500 feet cause any problems?

 

The distance is too long for accuracy. Better to use 4-20 ma.

 

Given the distance I would recommend that you install a remote IO rack near the field and run a communication line back to the PLC.

 

Consider using an industrial network to collect this data. Low cost and a single cable to the PLC. You can use 0-10V with no problem since your Input modules will be close to the field device. The best bet for this type of application is AS-Interface. Feel free to contact me if I can be of any assistance.
[email protected]-fuchs.com

 

It depends on the wire you use and the accuracy tou need for this application. I agree with the other person it would be better to use 4-20 MA.

 

Just use 4-20mA and use a 500 Ohms resistor in paralel over the input terminals of your PLC IO's. The signal seen by your IO will then be 2 - 10V. For the outputs, put the resistor in series and put a galvanic isolator (4-20mA in/4-20MA out) directly behind the resistor. This way the distances are no problem any more.

 

You may want to change the 3 wires into a 4-20. With 500'using low voltage - you will loose some signal. We have a drawing online to change over - if its not clear -email me and I'll send a larger pic. "http://www.almegcontrols.com/4-20_converter.htm":http://www.almegcontrols.com/4-20_converter.htm

Thanks Bob Hogg http://www.almegcontrols.com

 

Resistive voltage drops may be one problem. Noise conducted by a long run of a high impedance circuit may also be a problem.

I suggest using transmitters that convert your signal to 4-20 ma.

Bill Sturm