I first came across high voltage differential probes over ten years ago when I was doing some work to understand the noise present on the 630 V DC traction current used on the London Underground. Since then I’ve always wanted to have one in my own toolkit but was put off by the price until I came across the Micsig DP10007.
Unboxing
The probe and all its accessories come in a compact travel case which I like as it keeps everything together – less chance for me to misplace anything.
When you open it there are foam cut-outs to keep everything secure and protected.
The probe comes with alligator clips, test probes and test hooks – enough for most applications.
Next to the BNC flying lead there is a USB-B socket which you connect the supplied cable to power the device from a USB-A port. There are two rubber buttons on the front of the probe to set its attenuation at either x10 or x100. When the device is powered one of the buttons will illuminate green to show the currently set attenuation. There’s a USB-A socket on the side of the probe – this is a pass-through for power only not data.
The maximum differential voltage this probe can measure is 700V with a bandwidth of 100MHz. I don’t have the equipment to test the probe at its limits but to make sure it worked I connected it to my controllable outlet.
Testing
In the UK the mains electricity runs at a nominal 230VRMS and 50Hz. In order to stay within the limits of my oscilloscope’s voltage range I set the attenuation to x100. The scope trace below shows what the mains voltage looks like when the outlet is switched ON. As you can see it’s not a perfect sinewave, but close enough, with an average voltage and frequency of 230VRMS and 49.95Hz respectively.
If you want to learn more about mains electricity in the UK head over to mainsfrequency.uk.
The solid state relay fitted in my controllable outlet uses a TRIAC which means it only switches ON or OFF at a zero-crossing. The trace below shows the output when I toggle the relay at 100Hz. You can see that initially the top half of the cycle is suppressed as expected. Eventually as the actual mains frequency is slightly less than 50Hz this flips and the bottom half is then suppressed.
I’m not able to test the accuracy of this differential probe and this is where paying money for some of the more expensive probes pays off but I’m only planning to use it for my own personal projects so this is more than enough for me.
If you interested in getting one there only seem to be a handful of retailers in the UK and I ended up buying mine from here.
