I am trying to generate a perfect square wave on my DO Card, so that it can control opening and closing of an Electronic Valve (EV) installed in the field. My need is that the Valve should remain Open for 350ms and vice versa. But it never happens. It remains open for 350ms (as the high/peak of square wave arrives) and close for approximately 280ms (as the low/ditch of square wave arrives).

I've applied many programming techniques but in vain. Please help me in this regard.

 

Your DO card is probably generating a perfect square wave, but remember that you are driving an imperfect electro-mechanical device, a solenoid valve. The coil of the solenoid stores energy because it is an inductor. The charge from the DO card must dissipate to a certain level before it can change position after the trailing edge of the square wave. You also have reluctance effects from the wiring used between the DO card and the solenoid valve. To compensate, you will need to change the timing of the square wave to allow sufficient time for the valve to react. It's called "tuning the circuit."

Dick Caro
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Richard H. Caro, CEO, CMC Associates
Certified Automation Professional (ISA)
Buy my books at the ISA Bookstore:
Wireless Networks for Industrial Automation
Automation Network Selection
Consumers Guide to Fieldbus Network Equipment for Process Control
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