PV(t)-PV(t-1)

Vsevolod1

Yes, I need to get the difference in values between the value in this cycle and in the previous cycle.

Hello.

What you ask is demonstrated in the attached picture. The design does not aim to solve your application, it is only to show an idea.

Note the interaction between the analog input and analog flag. The value in the analog flag lags with one scan cycle.

I am sure your requirement goes deeper than that. Best you make your idea known if you are wanting deeper assistance. 

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Thanks. This is exactly what I asked about at the beginning of the topic - does the analog flag give a delay of 1 cycle, as it does the digital flag. Judging by the fact that it works for you, the answer is yes.

I tried to do it the way you do, but in the simulation, the Increase output blinks. Now I thought it was due to too slow signal rise. After all, the cycle period is only 1-2ms. So instead of analog flag I need a delay line for about 100ms.

Vsevolod1

Thanks. This is exactly what I asked about at the beginning of the topic - does the analog flag give a delay of 1 cycle, as it does the digital flag. Judging by the fact that it works for you, the answer is yes.

I tried to do it the way you do, but in the simulation, the Increase output blinks. Now I thought it was due to too slow signal rise. After all, the cycle period is only 1-2ms. So instead of analog flag I need a delay line for about 100ms.

Simulation and reality are going to fight each other -- even worse than what you see in your simulation now. The analog to digital conversion of the LOGO takes some time to supply a result. Using the on-board analog of the 24V base LOGO takes 300ms. The AM2 extension card has an update rate of 50ms.

The demo circuit shared will do the task of knowing when is an analog value stable just because there is a settling time built in. Perhaps all you need is some settling timer for your circuit, keeping in mind the update rate of an analog input.

You could build a circuit that works on a clock pulse, which is more complex. Making a complex design is not appropriate when we do not know what you want to do with the circuit.

Good luck.

I was amazed that the analog-to-digital conversion takes 300 or 50ms. Is this your measurements or data from a datasheet?

I made a block to delay the analog signal, but I did not like that the signal at the output stays too long after decreasing the value at the input. And I made a faster circuit. Results in the attached file. Suddenly someone else will come in handy.

Vsevolod1

I was amazed that the analog-to-digital conversion takes 300 or 50ms. Is this your measurements or data from a datasheet?

 It is from a technical manual.
See attached.
Verify this by searching for the LOGO manual.

Why make it complicated? Just use a TOF timer that is set at a little higher rate as the update rate of the analog input. See the attached animation.

Or do you have a reason for attempting a complicated circuit?