Control current using a PLC

PaulKraemer

Member
Join Date
Jan 2005
Posts
24
Hi,

I have a control system with a PLC and a PC based HMI (human machine interface).

I have an application where I have two bare resistance strips through which I want to pass a current. (I will be using these to seal the edges of two pieces of mylar). The current through these strips will typically be about 8 amps at 115 VAC.

I would like to be able to control and monitor the current through these resistance strips using my PLC/HMI. Basically, if an operator enters a setpoint of 8 amps on the HMI, I need a way for this setpoint to be communicated to the current controlling device. I also would like to be able to read the actual current into my PLC/HMI so that I can check to make sure the actual current equals the setpoint current.

Does anyone know of an instrument that would allow me to do this?

Thanks in advance,
Paul
 
For controlling your current check out Control Concepts. Some of Control COncepts SCR power controllers will give you feed back on what the current is.

For current measurement check out Ohio Semitronics.

Chances are you will need to close the loop in your PLC to regulate the actual current if you want to achieve a specific amperage. A PID can do this for you. I use PID power control loops driving Control Concepts SCRs that loop at 20 hz and can achieve very good power control.

If you decided to use a 0 to 100% power setting that the operator adjusts as needed then you can drive the SCR power controller directly by scaling the percentage setpoint to the analog output and the CCI SCR will use its own feedback loop to control power at that percentage, in that case you don't need feedback.
 
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