Connecting diagram of Analog output module to control valve (4-20mA) controls

Can anyone give me diagram when connecting a conrol valve (with two terminals - 4-20mA) to PLC Analog Output module?
Thank you..

The valve is a chunk of metal with elastomer seals, no electronics, unless you mean this kind of valve:



There's nothing on a 'valve' to connect wires to.

A valve positioner or I/P (eye-to-pea) transducer, on the other hand, has (typically) a 4-20mA analog input.

4-20mA is a DC current, so it has polarity, (+) and (-).

Wire the analog output (+) to the positioner's (+).
Wire the analog output (-) to the positioner's (-).

Don't connect to an auxiliary switch or retransmitting analog output, connect to the positioner's analog input.

Positioners need to be configured for function (rotating or linear); action, direct or reverse; zero and span; characterization, linear or equal percentage; and a host of other factors. Smart positioners can self learn.

The plumbing (getting the right port connected where) determines how the valve drives and what happens when the air supply fails. Pay attention to that as well the electrical.

Have fun.

Thanks for the info danw. I just have another question.. Do I need another 24V power supply for the valve? by the way the valve is pneumatically actuated and electrically (4-20mA) controlled.

How can we check the 4-20mA output of the analog output module of a PLC

Do you need a separate 24 volt supply?
What is the make and model of the valve as it may be possible that you need
It and this would be called powering the loop.
The check if you are getting 4 -20 ma you will need a meter that can read ma.
Let us know the make and model and the channel you are using and I could look at the manual

Donnchadh

I assumed a 4-20mA industrial positioner, not an HVAC 0-10V 3 wire positioner that needs a power supply.

An industrial 4-20mA positioner or an I/P is NOT a 2 wire, loop powered transmitter, it is final control element. They operate differnetly.

The positioners that I'm familiar with are designed to be driven by the 4-20mA output directly WITHOUT a 24Vdc power supply.

For that matter the ones I've used specifically state that a power supply is NOT to be connected in the output loop circuit. Doing so can damage the positioner.

Analog outputs from PLCs are generally active outputs, powered from their own internal power supplies, and do not need any additional power supply.

There are HVAC positioners (as opposed to industrial positioners) that use 0-10Vdc. These are 3 wire devices that do need a power supply.

What does the manual say for connections?

danw said:

The positioners that I'm familiar with are designed to be driven by the 4-20mA output directly WITHOUT a 24Vdc power supply.

Click to expand...

I agree with Danw. Another thing that you have to watch out, is the max air pressure. Some modulating valves require low air pressure and the installation of an air regulatting unit is necessary.

In this kind of situation I always recommend contacting the manufacturer's representative for assistance. There are lots of ways this circuit can be implemented. When you see smoke it is too late.

Most current to pneumatic (I/P) transducers convert the 4-20 mA signal from your controller to a 3-15 psig pneumatic signal that either acts directly on the valve stem or in turn controls another higher pressure cylinder. You need clean, dry, pressure regulated instrument air for the positioner to work properly. Most I/P devices are "sinking" devices - that is, the power for the loop is external and they drop the current over an internal resistor. Most controllers require a common 24 VDC power supply for the analog output card, and they power the 4-20 mA circuit.

So, following the manufacturer's diagrams, most of the time you hook 24 VDC to the analog output card, and run the "+" output from the card to the "+" input of the I/P, and the "-" terminal of the I/P is wired to the "-" terminal of the analog output card.

Most of the time.

Usually.

Unless yours is different.

You can check the signal the same way you do any 4-20 mA. Break open the circuit and put a meter in series with the signal. Or, if you know the internal resistance of the I/P you can measure the voltage across its terminals.