Difference between current and previous data of same channel

[nelson.albarran]

Hi,
I want to calculate the diference between the previous data and current data.

best regards

[Mikhail]

Hi,

You need to create extra input channels:
1st to save the previous value. Use SetData function in the formulas of the source channel for this purpose.
2nd to calculate the difference.

[nelson.albarran]

Hi, I followed your advice, but I have not achieved to obtain the result that i wish.

Channel 1: The data of sensor. // SetVal(2,Cnl)
Channel 2:
Channel 3: Val(1)-Val(2)

Wich is my error?

[Mikhail]

Hi,
I need more info. Could you provide the screenshots of the settings and the steps how you test and what you actually get?

[Mikhail]

Try SetVal(2, Val()) instead of SetVal(2, Cnl)

[nelson.albarran]

My setting is

I have obtained always zero as result.

• This reply was modified 5 years ago by nelson.albarran.

[Mikhail]

Well…

Add this to the Formulas table

double MySetVal(int n)
{
  SetVal(n, Val());
  return Cnl;
}

and use in the channel 1: MySetVal(2)
Channel 2 must be of Calculated real type

[nelson.albarran]

I have set the channels like you said me. But I havent obtain the correct result. Always obtain zero.

For checking the formulas, I generate data to the channel as “source”. But in the channel as “result” always I obtain zero.

[Mikhail]

Untick “Formula used” checkbox for the destination channel.

[nelson.albarran]

The problem is kept. I have set the channels like you say me but in the channel “RESULT” I have obtained zero again. I checked the channel values “SOURCE” and “AUX”, current and previous respectively and both are the same value, then, the AUX channel dont save the previous value.

[Mikhail]

Please try updating the formula

double MySetVal(int n)
{
  SetData(n, Val(), 1);
  return Cnl;
}

Also we can quickly solve the issue by connecting to your machine. This service is commercial.

[Mikhail]

Link to the tested formulas to work with previous values.

[myscada]

Pls. try to change input channel 4051 (SOURCE) from “Calculated Real” to “Real”, and 4052 (AUX) from “Real” to “Calculated Real” (like what Mikhail said). It should be OK.

• This reply was modified 9 months ago by myscada.

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