# The Human Condition

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# Military ME-418/PSM-37 Multimeter

Here are the PDF specs.

To: K2CBY@aol.com
Subject: Re: ME-418/PSM-37

——–

  ME-418/PSM-37 Multimeter
  I recently purchased one of these meters on -bay.
  On the whole, I am very impressed with the instrument since it appears to
replace both an ordinary VOM and a high impedance VTVM.

Well, 10meg isn't really equal to a vtvm, but it's better than a passive VOM.

It also has the feature that you can't put on the cover without turning the power off (or at least, not without breaking the knob skirt, which someone did to one of the ones I have.)

The only quirk I've seen is spurious high readings in the presence of RF fields. The meter housing is plastic, so not sheilded.

  The unit I bought came without accessories, which the inside cover
describes with typical D.O.D. eloquence:

No pictures, but I have them. They all connect to a probe tip or other tip plug.

Shunt, Instrument, Multirange MX-9127/PSM-37
dual range 2.5A/10A shunt with thumb-screw input terminals 
Prod, Test, MX-1410/U and
5000VDC multiplier adapter with big pee-wee clip.
Adapter, Test, MX-9128/PSM-37
adapter to 1/4" phono plug

Current measurement is the most inconvenient part, as you often have to switch between using the shunt and not using the shunt, which requires moving the input connections.

The schematic pasted inside the back cover is helpful. There doesn't appear
to be anything “tweakable” inside. Do you have any idea where I can find a
copy of the tech manual? It doesn't seem to be on the Army Support Command
on-line site, and none of the usual manual vendors seem to have it.

Date: Fri, 05 Dec 2003 08:41:38 -0500
From: Rob MacLachlan ram@ri.cmu.edu
To: “Allen, Horace $Sam$ $IndSys, Pwr. Equip., ENG$ horace.allen@ge.com
Subject: Re: ME-418/PSM-37 MULTIMETER
Allen, Horace ( Sam ) (IndSys, Pwr. Equip., ENG) wrote:
Rob,
Thanks for the information. I opened mine last night and inspected
it. It really looks good inside and is functioning 100%. I saw the
schematic glued to the back of the case and also saw the potted
modules. I looked a the schematic and came to the same conclusion
that you came to. I wish I could find an operating manual somewhere,
some of the modes are confusing, but, I will work them out.

Best regards,
Sam Allen

I think I figured out all the functions from reading labels and perhaps general VOM experience. So if you have any questions, you can ask me. Do you have the current shunt and 5kv multiplier accessories? Unfortunately even if you have the shunt, current measurements greater than 1A are a pain because you have to connect and disconnect the shunt all the time.

Overall, the design seems clever. I especially like the feature where the flange on the power switch prevents you from putting on the cover without turning the power off. However, in one of my units a gorilla managed to break the flange and do this anyway.

One note from experience is that (presumably due to the plastic case) you can get spurious high readings in high RF fields. Also, DC measurements of DC+RF signals don't agree well with measurements made by a passive VOM, so don't immediately conclude there is a problem if voltages don't agree with values that are spec'd to be taken with a 20Kohm/volt VOM.

The different volts ranges are supposed to mimic the loading of 20kohm and 1kohm VOMS. I usually use the fixed 10meg input range, though the lower input impedance settings can be useful for things like testing whether an AC power line is dead, since otherwise capacitive cross coupling from other circuits can result in a significant voltage reading.

The low ohms function is useful for in circuit resistance checks because the voltage is low enough not to forward bias semiconductors. Normally I use the low-ohms range, but the standard range is useful for diode/transistor tests and short checking when there are large capacitors. The standard ohms function doesn't work on the x1 range.

A nice feature for diode tests is that the ohms output voltage matches the lead polarity (red +) in DC+ mode, but switches in DC- mode, so if you clip on to the leads you can test the junction both ways by flipping the polarity switch.

The ruggedized meter movement is a bit sticky, and you can get a more precise reading by tapping the meter. Of course this is not a precise instrument anyway. But if you do this you can distinguish between between 100meg and an open circuit, which few DMMs can.

“pulse MA” on the current function refers to the fact that that you can break the circuit momentarily by holding down the overload reset button.

 Rob

Date: Fri, 05 Dec 2003 11:29:17 -0500
From: Rob MacLachlan ram@ri.cmu.edu
MIME-Version: 1.0
To: “Allen, Horace $Sam$ $IndSys, Pwr. Equip., ENG$” horace.allen@ge.com
Subject: Re: ME-418/PSM-37 MULTIMETER

Allen, Horace ( Sam ) (IndSys, Pwr. Equip., ENG) wrote:

Rob,
In my haste I did not answer your questions. I only got
the meter with a set of leads. I need to build the current
shunts and the HV multiplier. Saw an article in QST
about building the current shunts but do not remember
seeing how to build the HV multiplier. I really wish I
had waited until one was offered with all the accessories.
But, on the other hand it will be fun to build the accessories
myself. I really enjoy building electronic projects.

The voltage multiplier is just a tip jack in series with a 90meg resistor and a pee-wee clip. Put the meter on 500V range, 20kohms/volt and jack the probe tip into the adapter and measure with the clip. I think it would also work to use a 100meg resistor and the lowest volt range.

The current shunt is 2 range, the 2.5A range is 16 milli-ohm and the 10A range is 4 milliohm. The adapter says to use the 2.5 or 10 ma ranges. In reality it probably doesn't matter much which low ma range to use, as the internal shunt contributes negligibly.

 Rob

## Discussion

, 2015/12/23 18:36

Hi guys. I just bought one of these. Can anyone confirm/explain why x1 resistance does not work?

Thanks

, 2016/01/04 08:20

Well, it could be broken, but IIRC, the x1 range only works on “Low Ohms”. This is the low open-circuit voltage range, which can be used for in-circuit measurements, but can't be used to test diodes or transistors. I use low ohms by default.