PLUS+1 Hardware > Controllers

Control Valve Operation


Nick Anderson:
I'm trying to use an MC088 HBridge output pins, C1P37 and 38 to drive a Proportional Control Valve.  The neutral value of the control valve is 12mA, so my thought process was, center the output of a PVE driver function block, to operate between 4 and 20 mA with 12 as the neutral value.  I set the outputs up to be H-Bridge and the actual values going to the outputs ranged from 40 to 200 (it seems that the output is in tenths of a mA).  When doing this, we were seeing strange things from our control valve.  We connected an current meter in line, and saw that the output was definitely not what we expected.   On the data sheet for the control valve it says the the input impedance seen is ~500 ohms, so we put a decade box in place of the control valve, with a current meter in line.  We adjusted the resistance from 500ohms all the way down to 20 ohms, but the current we were reading didn't match what we thought we were putting out.  Using the Service Tool, the output value for the pins showed the desired current output, but the feedback value did not.

Does anybody have any insight into this?


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