voltage requirements for current output

[DYV1973]

LS,

When connecting analog output signals (4-20 mA) from flow computers or PLC's, we sometimes run into the problem that the voltage is too low for the input of the connected equipment. (We supply max 15 V, and some equipment requires at least 18 V on the input side). This is not due to the resistance in long or thin cables etc.

Is there a standard for 4-20 mA analog signals, about the height of the voltage to avoid these problems?

thanks,
DYV

 

[Skogsgurra]

Why does your input need 18 V?

That's a lot of voltage. Usually, inputs never need more than 10 volts (500 ohms).

The "standard" supply voltage seems to be 24 V - so that would probably solve your problem.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

Sorry but NO! There is no voltage standard. This is often called the "compliance voltage". There are other names for it too, but that's what I commonly hear.

You always have to look at the transmitter's specs and see if you have the necessary compliance voltage.

I would say that 15V will be a little limiting.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[ScottyUK]

Some DCS equipment uses loop power voltages of up to 40V. 15V leaves little headroom for a cable run of any length if using a loop-powered transmitter. I'm not aware of a particular standard.


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Sometimes I only open my mouth to swap feet...

 

[waross]

The supply voltage must exceed the sum of the required voltages of all equipment in the loop, plus any voltage drop.
respectfully

 

[danw2]

Check the documentation for the transmitter for a diagram similar to the one below that shows the required voltage for a loop powered transmitter.

 

[OperaHouse]

This problem can arise because many devices are powered by the loop and there may be 2 or three devices in series such as a loop powered meter. I've seen many pressure sensors that are 18V minimum. Remember that you can always put a small 6-9V power supply in series. Even an unregulated wall wart will work.