Analog signal...mA vs. DC?

[GTodd]

I'm designing a new controller that has several analog inputs...pressure and motor current. I have a choice of 4-20mA or 0-5VDC transducers. Is one type more desirable or beneficial over the other?

 

[ScottyUK]

4-20mA is a common industrial standard. It provides positive identification of a broken wire (current drops to zero) and has better noise immunity than a voltage-sourcing transducer, especially over long distances. If this is copntroller which will be used in an industrial environment I would definitely go with a mA output.



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

 

[itsmoked]

If all the inputs are coming from within the same machine chassis then stick with 0-5V.

0-5V:
Less hassles providing the excitation.
No offset hassles.
More available sensors.
Sensors often less expensive.

4-20mA:
Only two wires (usually)
Less noise sensitive. (As Scotty sez)
Input scaling easier.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[whycliffrussell]

go with 4-20mA...seriously.

 

[LionelHutz]

Yes, use 4-20mA.

 

[nbucska]

well it is time to vote: 4 to 20 mA !!!

Plesae read FAQ240-1032
My WEB: <

http://geocities.com/nbucska/>

 

[Skogsgurra]

I wouldn't be so sure. The good old +/-10 V signal has been serving us well in the drive systems field and we seldom see any 4-20 mA. That is process control territory. I think that you should make sure for yourself what you need. A "beauty contest" or popularity vote will not give you the best answer.

What does your controller do? What is it supposed to communicate with? Motor current very often is a V signal. Pressure very often is mA signal. Find out what you are supposed to communicate with and select your inputs accordingly. Many systems have a basic 0-5 V input and a switchable resistor to accept mA signals. Software is then used to change the 0-20 mA into a 4-20 mA signal.

Outputs need a little more design work if you want to have both signal types. There you should find out what the partners are and how they communicate.

Either you know what the signals are and design for that - or you do not know and design to be flexible. It is your choice. Not ours.

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]

Here! Here!

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[jsummerfield]

Distance is a factor with 0-5 VDC. Unless the distance is greater than a mile it is not a significant factor for 4-20 mA.








John

 

[nbucska]

An important factor is frequency range. A slower signal
can take more filtering or even highfrequency pre-
emphasys.

If there is question about the noise, it would be simpler
to use digital interface.


Plesae read FAQ240-1032
My WEB: <

http://geocities.com/nbucska/>