In your first post, you said some of the steps you took (lifting drain wires) made the spikes worse. Please elaborate or post a plot. Is the digital filtering on the PLC making EMI noise events look like this? I'd be very interested to see how real noise is plotted.
Hello Keith,
I must admit that this was only my first impression and it is not for sure, since I instruct technicians to remove drain wire connection and then I waited not longer than 10 min. This is not sufficient time to make conclusion.
I also thought that these spikes are caused by opening spray water valves (in the closed loop control), but then I found in the archive how trends look like when the unit is off and all spray water control valves are closed.
I checked some measurments on a twin system and found smoothing time constants set to 5 sec!!! I removed then and observed spikes also.
I suspected EMI but definitely I'm not sure and don't know what to think after inspecting the behavior during the plant downtime.
This picture is given in attachment. EMI from energetics cable would be in miliseconds I agree.
I don't know how to explain this behavior.
Remark: some of the values are different color that on the first pics, because one of operators change the trend, but spikes are easily seen. This light red is smoothed measurement (5 sec time constant).