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Do-more directly connected to servo valve question

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  • Do-more directly connected to servo valve question

    Hi, I am new to servo valves. I have for years cycled hydraulic cylinders back and forth for life cycle testing on certain fixtures. We use a vickers on/off 12VDC valve and a couple of pressure transducers. We used an AutomationDirect Koyo 405 series PLC to control the process. We cycle the cylinder back and forth based on pressure/force. Extend cylinder till 500PSI/1500LBS, then retract cylinder till 690PSI/1500LBS. Repeat. Now we are upgrading to the Do-more PLC and would like to get faster cycle times and less overshoot. The cylinders are normal generic hydraulic cyclinders, not actuators.

    I have a Moog 760C264A servo valve. It has 80 Ohm Coils and uses +/-20mA. I ordered a F2-02DA-1 2 Channel Analog Current Output Module for the Do-more. It outputs 4-20mA. The conversion settling time is 100uS full scale. The Do-more scan times are usually sub millisecond. I also have an 8 channel analog input card F2-08AD-2 which has a 4mS step response time.

    Can I control generic hydraulic cylinders with the Moog 760 directly connected to the F2-02DA-1? I would be using the analog input card to read a pressure transducer or a load cell. Do I need to have a separate routine from my main ladder program applying a dither signal to the valve? If so, do I apply with the same outputs or parallel outputs from another Current Output Module to the Moog?

    Am I way off and need a completly different system with amplifiers and such?

    Sorry for the blather...not the best at explaining things.


  • #2
    I have a similar application using Parker servo valves and the DO-06 processor. Your problem may be in the servo valve as it is looking for a -20 to +20 signal for full stroke. You may need an analog converter for this. I used the Dataforth unit.

    I programmed a fast and slow "dither" if you will. On the fast side, the accumulator would change the analog output number by a factor of 100 so to speak and in the slow mode the factor would be 1. While a pressure input from the cylinder gets you close, it has been our experience and the client that the ultimate test is the load cell.

    In the system I designed the cylinder must supply a specific amount of force, then when the controls are released, the system locks the hydraulics and the force is measured over time and a camera is set up at the force point. The idea is to test the resilience of the test subject to see if it is yielding to the force applied.

    This method has been in operation for the last 7 years and has been reliable.

    Guy

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