Hello, I want to know the specific criteria for determining the the Output Faulted Error.
I am currently using a CA4 to connect to a Moog G761 servo valve. The Output Type of The CA4 is set to +/- 20mA. The servo valves are connected in series(B and C are shorted, while A and D are connected to the CA4’s CtrlOut and Cmn, respectively). The drive circuit operates at -20mA to +20mA with a resistance of 160 Ohms. Each channel is connected to a G761 servo valve in the same manner. Some channels trigger the Output Faulted Error, while others do not. I would like to understand why this happens. Sometimes, the Output Faulted Error does not seem to affect the control of the servo valve(the Autostop for Output Faulted is set Status Only), but the alarm bit is shown as set. Therefore, I would like to know the specific criteria for determining the the Output Faulted Error and how to avoid this alarm
Hello Sun,
Output Faulted indicates an Overcurrent or Overvoltage occurred on the respective axis. In the case of the CA4, the output current exceeded 20mA or -20mA. That is the only criteria that triggers the Output Faulted bit. Having the error bit set to Status Only would mean that the Output Faulted error will not stop motion. If motion does stop then my guess is some other error bit is also triggering, you would need to check the Event Log to see. You can find the exact specs of the CA4 module in our RMCTools help, along with details on all of the Error Bits.
The coils in the valves are not perfect. A note from the Moog data sheet states:
The resistance and inductance of standard coils are given below. The 2 coils in each Servo Valve are wound with equal turns giving a normal production tolerance on coil resistance of ±10 %. Copper magnet wire is used, so the coil resistance will vary significantly with temperature. The effects of coil resistance changes can be essentially eliminated through use of a current feedback servo amplifier having high output impedance.
I think it’s reasonable to say that with the +/-20mA output on a “nominal” +/-20mA coil there may be conditions where the overall coil resistance (2 in parallel) exceeds the maximum 500 ohm load for hte CA4 outputs.
They don’t give the thermal coefficient of the coil wire but searching around shows a common value of 0.00393 Ohms/DegC Delta.
Given the datasheet mention of 160 Ohm @ 25C and the coefficient of 0.003393 the coil will reach the 500 Ohms limit of the card at around 78 DegC. This is within the specs of the valve.
Sun, you can set the Output Limit axis parameter to some value less than 100%, which will reduce the maximum Control Output, which in turn should prevent the output current from becoming too large and keep the error bit from turning on.
-Jacob