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I want to preface this by I am a hobby electronics guy with some experience from reading The Art of Electronics. I know how to use a multimeter but I am very confused at what I am seeing.

I am using a marginally more expensive Circuit Specialists multimeter and testing the resistance across a set of fuel injectors I am working on. My procedure to test is as follows:

  1. Set multimeter to Ohms (200)
  2. Measure resistance across the male side plugs

I was looking for a reference range of 10-14 ohms and I got 15.3 ohms. Concerning. So out of curiosity I measured again:

  1. Set the mulimeter to Kilohms (2k ohms)
  2. Measure the resistance across the male side plugs.

However this time I got 0.012! So 12 ohms, right in the middle of the range.

It may be as simple as my multimeter just isn't very high quality but I was hoping there was a better explanation. Having one measurement outside spec, and one inside spec really bothers me.

EDIT:

My multimeter model is #MT-5211

https://www.circuitspecialists.com/3-1-2-digital-lcr-multimeter.html

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    \$\begingroup\$ What is the multimeter make and model? Link to datasheets and specifications? What kind of multimeter leads you used? \$\endgroup\$
    – Justme
    Commented Aug 12, 2020 at 19:07
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    \$\begingroup\$ Any measuring instrument suffers a bit from this. THe bigger the range, the less absolute precision you get. It's best to measure with the smallest range that fits your expected values. If you have it on the 1,000,000 ohm range, you might see "0 ohms" as a result. DOes that mean it's actually zero? Nope! Just means on the 1MEG range, the meter can't report things out to such a fine precision. \$\endgroup\$
    – Kyle B
    Commented Aug 12, 2020 at 19:09
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    \$\begingroup\$ If this is a digital multimeter (which I assume it is), you may be seeing the error in the ADC. You'll have more accurate results picking the smallest measurement range that your tested device fits in. If you let us know the make/model, we can look up the accuracy. \$\endgroup\$
    – Ron Beyer
    Commented Aug 12, 2020 at 19:16
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    \$\begingroup\$ I would consider the 15.3 Ohm reading as acceptable. At such low resistance, the resistance o fthe meter leads and your connections to the injector can easily add a couple of ohms to the reading. \$\endgroup\$
    – Peter Bennett
    Commented Aug 12, 2020 at 19:18
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    \$\begingroup\$ BTW I wouldn't call Circuit Specialists multimeters "high end", my Fluke Processmeter costs over $1,000 and comes with a certificate of calibration/accuracy. \$\endgroup\$
    – Ron Beyer
    Commented Aug 12, 2020 at 19:18

1 Answer 1

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Since no one in the comments posted an answer I will post it here.

First:

My multimeter is not the best multimeter. According to the manual I need to short circuit the probes and record the result for the 200 ohm setting. After taking a measurement I subtract this from the observed value to get the answer.

Second:

The specifications had temperature in a little box next to the resistance tolerances I looked over. Since resistance and temperature are related this was important.

By doing the short circuit and then letting the fuel injectors cool down to ~70 degrees I was able to achieve a reading that was within specification.

I appreciate everyone's help!

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