Voltage vs Current control loops
Voltage vs Current control loops
(OP)
I would like to get some feedback on what method of control most of you prefer 4-20ma or a voltage loop like -10+10, 0-5v etc. I understand the noise considerations with voltage. I use a mix in my plants but determining a standard seems to be a Coke vs Pepsi argument. (all control loops are relatively short, under 30ft.)





RE: Voltage vs Current control loops
I prefer the live zero that 4-20mA or 1-5V provides versus the zero based low end. An open circuit is really obvious with the expectation of a live zero.
A voltage output has the benefit of paralleling to more than one input, which seems to be more intuitive to the uninitiated than a series loop for current outputs.
Can I have a root beer?
RE: Voltage vs Current control loops
RE: Voltage vs Current control loops
"A voltage output has the benefit of paralleling to more than one input, which seems to be more intuitive to the uninitiated than a series loop for current outputs."
But
You can take as many 1-5 inputs as youu like from a 250ohm resistor that carries the 4-20mA. In fact most times you combine 1-5V inputs with 4-20mA loops and 250ohms.
4-20mA provides power to the transmitters so you only have 2 wires.
Francis
www.controldraw.co.uk
www.s88control.blogspot.com
RE: Voltage vs Current control loops
- it is less vulnerable against noise and voltage drop along the wire, especially for long distance.
- the current signal can be converted easily to 1-5V by simply fitting a 250Ohm resistor.
- you can use smart devices with HART technology which have a lot of advantages, including diagnostic and recalibration.
RE: Voltage vs Current control loops
Inside of control panel (assuming no 480 V or high current), the noise is much less of an issue and voltage signals are much easier to deal with. So we generally use voltage signals inside the panel and convert to 4-20 mA when it leaves the panel.
Beware wary of trying to run a 0-10V voltage signal into a VFD enclosure - a very noisy environment.
David Castor
www.cvoes.com