Navigation:  Tutorials > Measurement tutorials > Voltage and current > DEWESoft 7.0  data acquisition, processing, analyzing and storage software Glitch triggering

For this purpose, it is very nice to use a derivative as the source of the trigger. The glitches will be seen much better on a derived signal (dU / dt), since the derivative is very sensitive to differences in the sine wave.

With the pure 50 Hz sine wave and 220 V, the basic derivative is 315 · 2 · pi · 50=100 kV/s maximum. This way, the glitches are producing higher levels - from 300 kV/s on up. Thus, it becomes easier to set up the appropriate triggers.

Returning to the setup screen, select the Math tab and define the IIR filter. If the IIR icon is not visible, it's either that the filter last used was a FIR or FFT filter. Select IIR from the drop down menu.

 

Now let's click the Setup button to define the filter. We select Voltage as the input, then selects the d/dt icon for the calculation of the derivative. Then the user defines the units as kV/s and defines in Scale field the scaling factor. Normally, if the input unit is V, the output will be in V/s. Since the values will be simply too high, we set the unit to kV/s and define the scaling factor as 0.001 .

The high frequency filter (Filter high frequencies) is not mandatory, but it helps to smooth out the signal. If this filter is not used, the derivative will be calculated as a simple difference from current to the previous sample. This often adds lots of noise, so we could add an additional low pass filter (Fhigh field) to smooth the signal out at the output.

 

If we now observe the result in the scope, we can see what appeared to be a nice sine wave, but is not really a pure sine wave. The derivate of a pure sine wave is again a sine wave, with a phase shift of 90°. This, however, is far away from it.

 

Let's repeat the same scope practice with filtered data. Was it noticeable in the picture on the first page that there is a big capacitor for electric motors? This is not included by sheer chance. We can use it for making voltage glitches. When the capacitor is charged, it takes lots of power from the grid, so there should be a local voltage drop. In this example, there is just the capacitor, which is connected to the normal line plug, where it is charged by inserting it BRIEFLY into the power supply.

To try this,  please remember the two most important things: first, the user should insert the capacitor only for a short amount of time, else it could blow up. Secondly, ALWAYS DISCHARGE the capacitor on a piece of metal! Since these capacitors can hold substantial amounts of power, it is not very wise (and potentially quite dangerous) to discharge it on yourself.

If you try to do this, please remember two most important things: first, you need to insert the capacitor only for a short interval, otherwise it might blow up. Second, ALWAYS DISCHARGE the capacitor on a piece of metal. Since these capacitors can hold substantial amount of power, it is not very wise to discharge it on yourself.

 

To set up the scope - the trigger parameter is changed to the Voltage/Der channel and the Trig(ger) level is changed to 240 kV/s . Now we create some glitches where we easily see how the scope catches these events.

 

The next logical thing is to be able to zoom in to see a glitch with a better resolution. If we clicks "zoom", we will loose the current event. There is, however, a mode which zooms in the scope without losing an event. On the upper right side of the scope there is a "zoom" button which enables an additional zoom window.

On the top, we can see the bar of the current position in the event and with the zoom in/out buttons; one can now zoom in on the specific region. We can also move left or right in the scope picture to see some part of the trigger shot.

 

Let's learn how to store this data.