@Zoltan Somogyi Thanks for good tips! I will keeper them in mind. Best regards Herleik

Thanks for the reply! Maybe, then it probably gets changed out of range when values are sent to HMI, not sure where historical data is saved, in PLC or in HMI. Some times the spikes disappear and is replaced with normal value and new spikes appear another place. It's a mystery to me.

How have this worked out? A datasheet for the valve is useful, but if this can not be found you could measure the resistance between 24V and 0V feedback conductors. Probably they are connected to switches that are open or closed depending on the state of the solenoid valve. In this case you need to supply 24V on one conductor, the other conductor will change from 0 to 24V when the switch closes (solenoid opens or closes). The conductor with 0 and 24V will be the signal to the PLC.