di/dt detection using microcontroller

[Ravi_H]

I'm having a full rectified current signal sensing using ADC in µC. A spike appears in that signal at a point.

I have attached an image which shows the behavior of the signal. I want to develop a logic to detect that current is rising before the spike appears in the image, so that I can avoid it.

Please can someone tell me what should be the logic for detection. I'm sampling at 30 µs.

 

[schmitt trigger]

How wide is the spike?
If you are sampling at 30 us, but the spike is only 10 us wide, you won't acquire it.

You most likely will require a voltage comparator to detect it RELIABLY.
That is the keyword here, reliably.
Many microcontrollers have internal comparators for which you can set the detection threshold. The comparator may then assert a flag. You can then set an interrupt upon that flag being asserted.

If the microcontroller doesn't have a comparator, you can always use an external one.
If you do so, use a proper comparator!! Like a LM393. Don't use a slow opamp like a LM358.

 

[andre_luis]

If the peak occurs with undefined amplitude, perhaps an approach based on dV/dt (differentiator) could be suitable for this application.

 

[KlausST]

Hi,

I want to develop a logic to detect that current is rising before the spike appears in the image, so that I can avoid it.

What do you mean by "that I can avoid it"?
Avoide the spike? (How do you ant to achieve this?)
Avoid to show it in the picture?

When yo have an ADC, so you can detect it simply with software... Where is the problem?
Why external circuitry?

Klaus

 

[Ravi_H]

Hello,

I'm having output which is controller by an SCR. If I'm able to detect that output current is rising fast then I can reduce the conduction angle of the SCR.

I wanted to know, what is the di/dt logic, so that it can be implemented digitally.

 

[KlausST]

Hi,

I wanted to know, what is the di/dt logic, so that it can be implemented digitally.

A digital differentiator.

Klaus