micapp Posted June 28, 2014 Report Share Posted June 28, 2014 I have a problem with a valve control. The controlsignal is 4-20mA. The control works very good when PLS is running.4-20mA give decimal values 820-4095 on output. If I switch off the PLS, there is of course no value on output that is recognized as control signal by the valve, and it does not move (error condition on 4-20mA signal say that valve shall be in last position). The problem is when the PLS goes to STOP, the value on the PLS Memory Integer is still 4095 (fully open valve), but the output from V200-18-E18 give an output the the valve control read as GO tO 0% (closed posistion). Any idea what to do to get around this? Quote Link to comment Share on other sites More sharing options...
Eyal Koren Posted June 29, 2014 Report Share Posted June 29, 2014 I have a problem with a valve control. The controlsignal is 4-20mA. The control works very good when PLS is running.4-20mA give decimal values 820-4095 on output. If I switch off the PLS, there is of course no value on output that is recognized as control signal by the valve, and it does not move (error condition on 4-20mA signal say that valve shall be in last position). The problem is when the PLS goes to STOP, the value on the PLS Memory Integer is still 4095 (fully open valve), but the output from V200-18-E18 give an output the the valve control read as GO tO 0% (closed posistion). Any idea what to do to get around this? I think that the most important question in you case is - why does the PLC goes to stop mode? This is not normal and might happen from several reasons. If your PLC is going to stop mode right after the valve operation command, I will assume that your power supply is not powerful enough (this is assuming that the same power supply is powering both the PLC and the valve). If this is not the case, your system could be suffering from EMI, that is affecting the PLC normal function. Please write to support@unitronics.com and explain more thoroughly about your system and when it goes to stop mode. Quote Link to comment Share on other sites More sharing options...
micapp Posted June 29, 2014 Author Report Share Posted June 29, 2014 One instance is when downloading new program. Normally is not a problem, and if it is a system definition, I must live with it. But I had a hope that the output should be able to control as long as the MI-value is correct. Quote Link to comment Share on other sites More sharing options...
Eyal Koren Posted June 29, 2014 Report Share Posted June 29, 2014 One instance is when downloading new program. Normally is not a problem, and if it is a system definition, I must live with it. But I had a hope that the output should be able to control as long as the MI-value is correct. Well, you shouldn't "live with it" no matter what. Please send the application to support@unitronics.com. I suspect there is some programming issue there. Quote Link to comment Share on other sites More sharing options...
lawry Posted June 30, 2014 Report Share Posted June 30, 2014 Dear micapp, How do you know that the value of the MI is 4095 during the stopped stage of the PLC? Lawry Quote Link to comment Share on other sites More sharing options...
MVP 2021 Joe Tauser Posted June 30, 2014 MVP 2021 Report Share Posted June 30, 2014 If the PLC can stop and you can't live with the output being stuck at 4095 then you need to put a bifurcated relay in series with the control signal and have the output always on while the PLC is running. It will go off when the PLC stops and disconnect your loop. Joe T. Quote Link to comment Share on other sites More sharing options...
micapp Posted June 30, 2014 Author Report Share Posted June 30, 2014 Lawry: if I monitor the plc in stop mode, it shows 4095. Joe T: I will try that. Thank you. Quote Link to comment Share on other sites More sharing options...
lawry Posted June 30, 2014 Report Share Posted June 30, 2014 Thanks micapp. Lawry Quote Link to comment Share on other sites More sharing options...
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