MetraHit Coil Motor Testing Multimeter

RE: MetraHit Coil Motor Testing Multimeter

three-phase — Wed, 04 Dec 2019 20:30:36 GMT

Having still not heard anything back from the manufacturer, I took the decision to take a peak inside the coil adapter in the search for more information. This wasn't as easy as expected as the case is held together by two of the most horrid style of security screws known to mankind. To make matters worse they were both in recessed holes in the bottom of the case behind labels.

[View:/resized-image/__size/620x413/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-eb160185-af45-4ceb-8416-0cbe0db1a1e8/5001.contentimage_5F00_205215.jpg:620:413]

Where there is a will, there is a way, and eventually the screws saw my way of thinking and ar enow lounging around on the workbench.

Inside there is one PCB, containing a capacitor, gas discharge tube and two resistors.

[View:/resized-image/__size/288x192/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-eb160185-af45-4ceb-8416-0cbe0db1a1e8/6562.contentimage_5F00_205216.jpg:288:192][View:/resized-image/__size/288x192/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-eb160185-af45-4ceb-8416-0cbe0db1a1e8/7142.contentimage_5F00_205217.jpg:288:192]

The other side of the PCB has no components. The capacitor has turned out to be a 560nF polypropylene film rated at 1.6kV DC. Alternatives do not seem to be that popular in the UK. I have found a 330nF capacitor, that I could consider getting and dropping it in place to see what effects it has. What I do not know of course is wether or not either of the resistors would also be changed.

[View:/resized-image/__size/620x168/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-eb160185-af45-4ceb-8416-0cbe0db1a1e8/5008.contentimage_5F00_205218.png:620:168]

Kind regards.

RE: MetraHit Coil Motor Testing Multimeter

alsterr — Tue, 26 Nov 2019 21:25:50 GMT

Great review. I have had a metraHit iso for about a year now and when I first started using it I really liked it but once the newness had worn off i have liked it less and less. I find the auto ranging on insulation testing is quite slow and on capacitance its very slow, on ohms it seems inconsistent- i have to re- zero every couple of minutes and the 2 aa batteries seem to die on insulation testing without warning! I like the fluke 1587fc but find having to swap the leads over a pain. At the moment I’ve gone back to my 10 year old Megger MIT400 as my main tester and keep the fluke in the van the more in depth testing when needed. I repair domestic appliances so don’t need the same capabilities as you but I do like to use good quality equipment and although the MetraHit is a nice piece of kit it doesn’t quite live up to it’s high price tag. Alan

RE: MetraHit Coil Motor Testing Multimeter

kmikemoo — Sun, 17 Nov 2019 21:13:22 GMT

Awesome review. Very thorough. I've used a couple of insulation testers, mostly for DAR and PI calculations. This review is right in my wheelhouse of the stuff I use for work. Thanks for sharing.

RE: MetraHit Coil Motor Testing Multimeter

shabaz — Sun, 17 Nov 2019 15:40:14 GMT

Hi Donald,

Interesting (and as usual, very comprehensive and useful) review! Looking at your table of inductance, it is clear the 'coil test' is measuring the time period of a tank circuit with a fixed capacitance. You mentioned a discrepancy between windings, does that discrepancy change if the rotor position is first altered slightly? (in case the volume of material on the rotor in proximity is having an effect).

I wonder if the LDC1000 eval board could be used for a 'coil test' feature too.

It can handle the inductance range mentioned in your blog post. Basically, a capacitor is used to make the tank circuit, 1nF or 10nF should put it into the measurable range.

There's a brief explanation of the LDC1000 here, really just basic experimentation:

Getting Started with the LDC1000 - Small Metal Detection!

[mention:f80b53cee57c44bc9d7c577d07d7c791:e9ed411860ed4f2ba0265705b8793d05] investigated it much further here: Ti LDC1000EVM A Question on Inductance

That latter discussion covers some interesting things brought up by what John noticed, where the presence of metal (I'm thinking rotor in your case) can have effects that we didn't expect, and it turns out that depending on the measurement frequency, the inductance can go down or it can go up, dependant on the measurement frequency. Old books discussed one thing (they referred to using a lower frequency) and we were seeing another (since the LDC1000 was using a higher frequency).

(I'm not knowledgeable in motor measurements so I could have misunderstood the detail, so the comments above could be wrong. I just thought I'd throw it out there, in case it is relevant or gives some ideas).

RE: MetraHit Coil Motor Testing Multimeter

Gough Lui — Sat, 16 Nov 2019 23:10:03 GMT

Some interesting findings - the Coil Test function is quite unique but perhaps unpolished, which is a little disappointing.

The thing that got me most excited was seeing your "lock" feature being implemented ... Time to make sure my bags are stocked with G-clamps [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-eb160185-af45-4ceb-8416-0cbe0db1a1e8/contentimage_5F00_3.png:16:16].

- Gough

RE: MetraHit Coil Motor Testing Multimeter

jw0752 — Sat, 16 Nov 2019 22:07:56 GMT

Great in depth analysis of your target instrument as usual. I am always fascinated learning about this power equipment testing instruments even though I would never have an application in my corner of the electronics world.

John