Quite shockingly poor protection, know one would know without this thread. Uni-T can make good meters as its been the OEM for several Amprobe models, I have an older post on eevblog with copies of testing documents showing the OEM.
Joe, do you know the output voltage of your spark igniter? Its really not supposed to kill the meter unless the input protection components didn't work for various reasons: counterfeit, wrong spec used, PCB defect etc.,. The tear down you showed shows it should have worked. It would be great for you to trace it out and zoom into the protection areas.
When you look at how many meters survived this with no problems, they certainly have a few examples they could have copied from.
I posted my homemade targets a page back and had looked for the data I took but looks like I did not save anything.
Keep in mind, I am not sure that a hand held meter is even required to pass any sort of ESD event. What I can tell you is looking at a manual from Fluke and Hioki, they both call out EN61326, which references 61000-4-2. My guess is that the meters would fall under Annex A, criteria B. Looking at the manual for the UNI-T, I do not see a reference to an EMC standard, only for the safety. The basic current wave shape for the -4-2 standard should be on-line.
Let me start with again, I have no idea what the meter are required to pass, if anything for ESD. And again, EN6132601:2013 Annex A calls for an 4KV contact, 8KV air criterion B. Looking at 61000-4-2:2009, 4KV contact is level 2 and 8KV air is level 3.
Taking the grill starter and roughly measuring the air gap when it will arc, assuming 33KV/cm. Of course, we all know this is a swag. I would estimate the peak is about 15KV.
OK, I know, the meters only rated to
and your hitting it with
, why would you ever think it would survive..... Keep in mind, the product is not supposed to be damaged during this test.
Well, while everyone who asked, asked about the peak voltage. Not one person asked me about the current. Level 2, contact is 4KV and requires a first peak of 15A with a rise time of 0.8ns. At 30ns it decays to 8A. At 60ns it decays to 4A.
Measuring this is normally done with a target. This is called out in the standards. Of course, as a hobbyist I built my own. So keep this in mind... The target is 2 ohms and you follow this with a 20dB attenuator then less than 1 meter of good coax. The standard recommends RG400. Then into the DSO. Of course, you need a fast DSO to look at this.
What I have is my homemade target. I think this is 1206's or 0805s placed inside the PCB. All in parallel to reduce the inductance. As you can see from the picture, I use an SMA to couple to target to the attenuators. In my case rather than 20dB (10x) I use 26dB. Why? Because as much fun as I am having destroying meters, I have no desire to damage my best DSO. The is also a very fast clamp in-line with the DSO, just in case. The attenuators are all Mini-Circuits and are rated to 6GHz. I am using roughly 0.5 meters of RG400 cable terminated with SMAs. This mess then connects to the 5GHz LeCroy 8500A, set to 20GS/s.
Next, I hold the grill starter to the target and push the button. That's it.
Looking at the attached screen shot (which I just took so ignore that fact I am too lazy to set the clock) the peak is roughly 100mV. So 0.1 * 19.19 = 2 Volts across our 2 ohm target or 1Amp peak. Even a level 1 requires 7.5A!! We can see at 30ns we are supposed to be at 8A but our signal is fully settled out by then as we only have a width of about 5ns!!
Now sure, we can say the peak, open circuit voltage is about double but the energy is not even in the ballpark. Hope this helps answer anyone who has a question about this test.
I have added a picture of the test setup.
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Topic: Handheld meter robustness testing (Read 1163694 times)
