Actuators requiring 50 mA current

J

Thread Starter

Jimmy Mascrehnas

Hello everyone,

I came across a concept that certain actuators have higher power requirements to work. They work on 50mA given by certain controllers. They are generally used in turbine control applications.

But as the process control works on concept of 4 to 20mA current range, how do these control valve work?

Can someone please help?

Thanks
 
I think you've answered your own question; whatever device is using a 50mA control signal needs more energy to do whatever it does than 20mA provides.
 
J

Jimmy Mascrehnas

> I think you've answered your own question; whatever device is using a
> 50mA control signal needs more energy to do whatever it does than 20mA provides.

Yes. But I have the doubt because what I think is that the automation range is 4 to 20mA. In this range, the control valve moves proportionally to control signal. Above that, it will overshoot.

So how does current more than that control it?

It is used to control fuel control valves in case of turbines.
 
2 wire, loop powered, 4-20mA field transmitters use approximately 3.5-3.6mA to run the device's electronics. Any current above that level is used for output signaling purposes.

Before 4-20mA became the standard, some field instruments used the 10-50mA because their electronics needed more than 4mA and with a 10-50mA control signal almost 10mA as available to run the electronics or to do 'work'.

For devices like positioners that expend energy doing work to move physical components, there's more energy available to perform those tasks with a live zero at 10mA than at 4mA.

I'm not a turbine guy but there are lots of others on the forum who are.

If you post a question about your specific fuel control valve (what brand/model turbine), you can probably get a more specific answer.
 
J

Jimmy Mascrehnas

I am working on turbine specific control module of Siemens that is ADD FEM. It has an added advantage of providing 50mA bipolar analog current for functioning of certain final control elements that require higher power.

So I wondered as to how it will satisfy the industrial standard of process automation i.e 4 to 20mA.
 
Player,

Can you please cite the standard which you are referring to? Is it IEC? ANSI? EU/TUV? Which body's or nation's or Corporate standard are you using to say a bipolar 50 mA device violates or fails to conform to?
 
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