Voltage Output to Low Impedance E/P Transducer 2

[tgmaxx]

I have many old E/P transducer that requires1-5VDC inputs. My PLC voltage output card can supply 1-5VDC, but requires a load impedance of at least 1kohm. The E/P transducer's input impedance is only 333 Ohms. Does anyone have a recommended solution to this problem? (short of replacing the E/P's?)

 

[itsmoked]

Groan.. I just had this problem in reverse. I ended up building an instrument amplifier into a DIN rail case to solve it. You may be able to find a rail mount amplifier you can interpose between the two.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[roydm]

Tgmaxx,
Does your PLC card also put out 4-20 mA? If so the solution is simple, put a 1K resistor in parallel with your 333 Ohm transducer to make the combined 250 Ohm. Your transducers are now 4-20Ma
Regards
Roy

 

[tgmaxx]

Thanks Roy. That will work, as I do have 4-20mA outputs. The easiest place for the resistors would be at the PLC, but the distance between the PLC and E/P's could be up to 200 or 300 feet. Any thoughts on that?

 

[ScottyUK]

Nice solution Roy, that should work well.

The resistors will have to go at the instrument otherwise the resistance of the cables will have to be taken in to account. You would end up with some odd combination like (e.g.) 341[Ω] combined instrument and cable resistance paralleled with 937[Ω] at the PLC. If you can open the instrument up solder them internally across the terminals so they don't get lost.


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