Proportional & servo valves

[Mahmoud]

hi all

i'm new to tri plcs and i want to know how to control proportional & servo valves using tri plc

[support]

Usually proportional valve will open according to the voltage applied to it. The M-series PLC has two PWM outputs which can vary the average voltage applied to the proportional valve by the SETPWM command . You specify the duty cycle and the desired PWM frequency and the valve opening is proportional to the PWM duty cycle.

Of course for a full control loop you will need to measure the quantity of actual control element. Most likely this is by means of some sensors which can be connected to the PLC via analog inputs, frequency inputs or serial inputs (by RS232 or RS485).  You can also apply PID functions to perform the closed control.

[willpower]

I have done quite a bit of proportional and servo control with the Triangle PLC's.  The analog outputs on the plc only output 0-5vdc or 0-20ma, not the full 0 to +/-10vdc or current commands typically used on hydraulic servo and prop valves., I have gotten around this by using signal conditioners.  Some proportional valve amplifier cards aloow you to bias the input voltage to get a full +/-output to the proportional coil(s).