## Picolog derivative function

Forum for discussing PicoLog
JulianEdgar
Newbie
Posts: 0
Joined: Mon Dec 06, 2021 5:38 am

### Picolog derivative function

Can someone please show me the maths to input so that I can sound an alarm when a rate of temperature rise is too great? I can't get anything to work so I am obviously not using the correct syntax.
Gerry
PICO STAFF
Posts: 1158
Joined: Mon Aug 11, 2014 11:14 am

### Re: Picolog derivative function

Hi Julian,

As the derivative function is computing the rate of change of a waveform, any high changes between high and low frequency data will significantly impact the plotted values. Noise is a type of waveform that is continually switching between different frequency data, so it can create significant noise in the Derivative calculated waveform (even to the extent that it completely masks the rate of change of the waveform, with the rate of change of the noise. For this reason there was an additional function introduced in version 6.2.6 (when the Derivative function was released) for Averaging the data before the Derivative is applied. The usage guidance for this is in the release Notes of version 6.2.6, below:

I have created an example showing what happens when you just use the Derivative function:

versus following the guidance:

You can see in the example that the captured Triangle wave is very large, in amplitude, relative to the Noise in the waveform (the blue waveform in the top plot, below):

The Derivative Math Channel (the red waveform in the middle plot, above) shows the derivative noise completely masking the derivative signal (i.e. the rate of change of noise is very large).

When the waveform is first averaged every second, and the Derivative is then calculated from that (the Green waveform in the bottom plot, above) the rate of change of the noise is significantly reduced, so that you can see the expected 2 constant levels for the 2 rates of change of the triangle wave.

The data file is below:
Derivative Math Channels.picolog

Regards,

Gerry
Gerry
Technical Specialist
JulianEdgar
Newbie
Posts: 0
Joined: Mon Dec 06, 2021 5:38 am

### Re: Picolog derivative function

Thnaks Gerry, but that's all too complicated for me. To return to my question (which isn't really about a waveform), can you give me an example derivative function that operates an alarm if a temp rises at more than, say, 8 degrees C per minute? That's all I am after.