Hi.

I need an assistance on this issue I got.

I would like to detect a rapid change of a value in the PLC. E.g. an operator is change the speed too fast or giving a zero setpoint quickly. I have a drive which will ramp down my motor, but I need additionally to detect this rapid movement. 

Anyone with a great idea how to detect this rapid speed change?

Thank you in advance

Regards,

AliMO

Hello,

sometime for similar application I make inside OB35 compare beetwen actual value and old value to see if increase or decrease is more than my threshold. after comparison save value for next compare.

changing OB35 time and compare value you can change threshold control.

Hope  this helps

Thanks for the feedback.

Is it any other ways to do this?

Hello,

To convert steps into ramps, you can try the following application example :

With STEP 7, how can you control servovalves, frequency converters or current converters via a ramp-function generator?

You can search the SIOS for TIA portal similar issue.

I hope this helps,

hdhosseini

Thanks, I have already looked into that example. Unfortunately this doesn't suit my needs.

Basically, a small function which have e.g.

Inputs: Speed (real), rapid changed to value (real), output pulse length in sec (int)

Output: Rapid movement detected (bool, pulse), elapsed time on output pulse in sec (int)

Something like that, but if you have better idea, I would appreciated if you could share it here.

Thanks again.

pman

upon this issue I would like to make a comment/question. Isn't there any possibility to have an appreciable amount of noise at the analog input which could make this value query not very precise? If we do have some noise, then comparing successive values of the analog value could lead to false results, right? Or am I missing something?

 I tried to read the whole post 2 times and I think the main concept would be rapid changes in operator station (from HMI) like limiting the rate of change and keeping in a reasonable range and avoiding range violation.There is no noise level in this scenarion.

But, the problem you are talking about is important when height of process excitation(MV) can be possibly noticeable(compared to existing noise level in process) in process value (CV).