regulating pressure

I want to know about connections, wirring and all information to control incomming pressure at (16 +/-0.3 psi).I want to use an analog card with a plc(no specific brand set yet).Bottom line, tell me what hardware configurations and programming requirement. answer can be in general and does not have to be geared to specific plc. Thanks

You will need a pressure sensor that generates a variable voltage or current as the pressure changes. Typical voltage ranges are 0 -10 VDC or 4 - 20 mA. This type of device is often called a pressure transmitter. This is the Process Variable, the signal that tells the controller what the actual pressure is. This signal comes into the PLC through an analog input.

You will need a pressure regulator. Most of the pressure regulators you see are manual. They have a knob or handle that you turn to change the pressure. In your case, you will need a regulator capable of responding to an electrical signal from your PLC. These are sometimes called I to P or E to P transducers. Signal levels are typically 0 - 10 VDC or 4 - 20 mA. This signal comes from a PLC analog output. It's called the Controlled Variable.

Inside your PLC, you will need some type of control algorithm that compares the desired pressure level, the Set Point, with the Process Variable and adjusts the Controlled Variable as necessary to minimize the error. This may be a PID function block, but it doesn't have to be.

Is this enough to get you started?

Actually, if you want to hold the incoming pressure to 16 PSI ±0.3 PSI (IOW, only ONE pressure), an manual precision regulator is all that's needed...

I'm pretty sure that's NOT what you want to do though...



-Eric

pressure regulator

thanks steve. I would have to use a digital regulator to allow plc to control and regulate incomming pressure.using a precission regulator is a good idea, but hard to get other poeple from touching changing it or tempreture arround machine changes from very hot at noon time to cool at night.

Mcmaster Carr Electronic Regualtor Voltage
AutomationDirect DL05
AutomationDirect Voltage In/Out Combo Card
Omega Voltage Pressure Transducer

This, an HMI, PID, and a linear regression give me control of a variable pressure that runs a MIB tool. This tool uses a force to create a linear distance in a pull, and needs to be accurate to +-.05. I've got it under +-.025. Works great.

Proportion-air makes a good electronic pressure regulator. You give it a signal proportional to the pressure you want, and it holds the pressure there. No additional pressure sensor needed. Very robust, and reasonably priced. They have diagrams on their website. Here's a link:

http://www.proportionair.com/family_pressure.asp

Last set up i did was a Dwyer pressure sensor (0-20") for the input and a Fairchild I to P transducer for the 0-60PSI output..ran it thru a a PID loop and it works..I am still working on the PID portion but i have it up and running..