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Ricardo Borbon
10-21-2013 12:37 AM

Controlling the speed of a DC motor based on a 4-20 mA...

I've been trying to control a speed of a DC motor based on a 4-20 mA. I said the best way to do this was with a PLC with a PID. Is there any other way to do this. All I've found are PID's that control temperature, but it's been difficult to find a stand alone PID.
10-21-2013 02:53 AM
Top #2
Daniel Sheldon
10-21-2013 02:53 AM
I have used the Powers Process Controller in applications successfully. The 535 can provide a stand alone controller. More and more people are going to PLCs as you indicate, but you can get a good loop controller.

10-21-2013 05:12 AM
Top #3
George Lala
10-21-2013 05:12 AM
I have used many different brands of Controllers to do what you are looking for. One good site is http://www.instrumart.com/default.aspx, If you have to use a Temp controller, you can modify the setpoint and Process variable to be a 4...20mA. Would then depend on what your out put is controlling.
10-21-2013 07:40 AM
Top #4
Joe Edmonds
10-21-2013 07:40 AM
There are many single or multiple loop PID controllers on the market. Dwyer's Love division has small single loop Process controllers as well as temperature controllers. The difference is that the temperature controllers are pretty well designed to accept differenty types of temperature input signals but process controllers are designed to handle 4-20mA input signals (or voltage depending upon the model).
10-21-2013 10:23 AM
Top #5
Tracy Biddle
10-21-2013 10:23 AM
Let's clear some things up with your question.

1. You want to control a speed of a DC motor based on a 4-20 mA

If all you are trying to do is send a 4-20ma signal out and have it set a speed, then you need a DC motor controller that takes a 4-20.

1. If you are trying to control the speed of the motor from a setpoint and and must measure the actual output and compare it to the setpoint then a PID algorithm can be handy. You however need to be able to bring back the output of the motor speed (such as pulse from an encoder, etc) This feedback input is necessary for the output to correct itself using the PID control.

Can you please elaborate a bit more on your current components.

Here is a link for a very non industrial DC motor control.
10-21-2013 12:47 PM
Top #6
Lara Jewinat, MBA
10-21-2013 12:47 PM

If you have a variable speed drive that can take a 4-20mA signal for control and gives a 0-10V or 4-20mA feedback signal, then you can use one of National Instruments Programmable automation Controllers and program your PID controller however you wish using LabVIEW, which is pretty easy to do.
10-21-2013 03:15 PM
Top #7
Dharmesh Rana
10-21-2013 03:15 PM

There is one good solution.

PLC --> DC Drive --> Motor --> Encoder or Tacho Generator ( give feedback to DC Drive)

DC Drive have inbuilt PID -- U can auto tune also..

So PLC will give Reference of 4-20mA to DC Drive and DC Drive will control the speed of Motor in the range of zero to rated speed of DC motor.

DC motor will give feedback to DC Drive, Difference of Actual and Set speed will be taken as correction factor and inbuilt PID will adjust speed of Motor to adjust to Set point..

In this way you will have advantage of
1. Variable Speed
2. Good Control ( less variation )
3. Drive will give feedback to PLC about speed, current, voltage and you can program PLC to calculate Energy and can keep it for data control..

Hope useful to you..

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