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Now, let's do some measurements. We have three channels - one is high voltage and the other two are currents. The best way to observe the waveform is in the scope. When we first start the scope, we can see almost nothing since the scope is running in the Free run mode. We need to "hold" the measurements by using Trigger → Norm trigger and defining the trigger source and trigger level. For now it is ok to leave the trigger as it is - trigger source is the Voltage channel and the trigger level is 0. We can see the difference between the measurements of current from the shunt resistor and the current clamps. The ohmic load from the light bulb should have the current which follows the voltage curve exactly. This can be seen nicely as the red current measured from the shunt, while the blue current is distorted by the phase angle errors from the current clamps.

This will result in wrong measurements of power. The following sections where the power module is described, the user can see how to compensate for this error, by defining a sensor transfer curve.

 

Let's look at the recorder. If the power supply is unplugged and plugged back in, we can see in the recorder (red curve) that the current raises above the normal consumption . This happens because at a lower temperature, the light bulb has a lower resistance than at operation temperature.

 

Let's catch this event in a better way by going back to scope and going back to the trigger setup. We can't really trigger on voltage, because the voltage levels doesn't change from startup to normal operation. Instead, let's trigger on current. The user should define the trigger source as Current and define a level which is normally not exceeded (for example 0.36 A in our case). When the scope is not triggering, the bar on the right side shows the current levels of the signal so we can optimize the trigger level according the normal values. We can also use the Auto trigger mode. When the trigger is lost for several seconds, the data will be shown as non - triggered.

Returning to Norm mode - when we issue another trigger, the scope will show the current event, which will remain, until the new event occurs.

 

But what if we want to trigger on a glitch? This might not be easily noticeable since the signal could drop by only few percent and it is not possible to define a level where we would catch all the glitches.