Analog device control.

[KUSNUJ]

Hello, I am working with the PLC connected to analog devices such as ball valve or pumps. the PLC is Siemens S7. the analog input module is S7-1200.

the problem is, the ball valve is not being controlled with the minor change. for example, when the ball valve is open as 12.5% and I tried to close it to 10%. however, the ball valve did not react. when I put 5% different as 7.5%. It closed it.

As it is, there are several issues about sending signals. what should I do to improve these kinds.

Please advise, thank you.

 

[ABitInTheWord]

What is the scaling of the analog output? Has the valve worked properly before?

 

[parky]

Yes it could be scaling or even the valve has worn actuator, you have not said if the valve has feedback, however, you did mention analogue input so I assume it has. Things to think about, did this work before ? has someone done any changes ? check the valve physically, the actuator pinion may have worn, so if the valve was sent to say 50%, then back to 45% if the pinion is worn it could move the drive but because of worn parts the valve would not close down to 45% the same may happen in the opposite direction i.e. you move it from 70% down to 50% then up to 55% if there is wear it will move the pinion but not the valve to the correct position.

 

[geode]

You may want to check if there is a deadband setup on the valve's controller. If the deadband is 3% for example, then a command of 10% when it is at 12.5% won't move the valve. Similarly, if you make a big change (like when you set it to 5%), the valve will change because the difference is greater than the deadband. Note: The valve will only get within +/- the deadband.

 

[ndzied1]

If you have access to the wires, I would get out my meter and measure the voltage or current signal that you are sending to the valve.

Is it what you expect?

If the measured signal is always what you expect it to be, your problem is the valve. This could be a mechanical issue or an application issue. It could be wear, sticking. It could even be something like sending more flow through the valve than expected is keeping it in place with flow forces...

If the signal is not what you expect, disconnect the wires from the valve and do some more testing. If the signal is good without the valve connected, then there is likely an electrical issue with the valve. If the signal is still not what is expected, it is likely an issue with the analog output on the PLC.

 

[KUSNUJ]

It was mechanical issue. confirmed.

Thank you.