Control.com - Nerds in Control

I would like some advice of how to implement remote control for chemical injection skid flow control valve from DCS.

This flow control valve has a DC motor that can turn backward and forward.

It's a little hard with the information you have supplied.

If the valve has it's own motor control and a 4-20 mA signal input use a 4-20 mA signal from the DCS.
If all you have is a DC motor you can control the valve position with short Forward/Reverse pulses using 2 discrete outputs from the DCS to pick up 2 pole relays.

I presume the valve has end of travel limit switches which you would connect into the coil circuit.

You will need some sort of feedback to the DCS, either valve position or flow.

Give us the Make and Model of the valve actuator and the DCS then we can be more helpful.

Regards,
Roy

Make and model of actuator valve is Amflo and AM7B. DCS is Honeywell.

Yes, I am thinking of control with short Forward/Reverse pulses using 2 discrete outputs from the DCS to pick up 2 pole relays. Feedback to the DCS is via flow meter.

Let me know if you have experience with AM7B as I am a little confused with the wirings.

Thanks for your help.

The Amflow AM7B seems to be a pretty fancy mechanical valve, I couldn't find the actuator wiring on the Web.

I haven't used a Honeywell DCS but it must have the capability of generating a time duration pulse based on the magnitude and direction of error. If it doesn't have a controller with pulse outputs you can easily create some logic that uses a regular PID output, e.g.
if output > 50% pulse forward
If output < 50% pulse reverse

You can experiment with the maximum pulse length (error x factor) and cycle time.

You might want to try using a lower voltage supply to slow the motor down (smaller steps). Set a minimum dead-band so the motor doesn't get pulses that are too short to act on.

Good Luck,
Roy

Most DCS systems have some sort of INCREASE / DECREASE controller.

In some cases, the DCS does this with a modified version of the PID controller. In other cases it is a completely separate function.

Check your DCS documentation. If you tell us the type of control system you have then maybe someone can give you more detailed instructions on what to do.

Rob

www[.]lymac.co.nz