I thought of that as well.
Dozens (over 70) of measurements with the probes shorted at the same temperature greatly reduces the risk it’s the greatest driving factor.
I all but thought it was a meter specific value till it changed when I took it to the school. I can easily do that test again right now.
At room temperature currently: 70.3F, 25% humidity
mOhm readings with probes shorted on 200m setting, after each reading I break contact between the probes:
(1.1 + 1.0 + 0.9 + 1.0 + 1.2 + 1.2) Ă· 6 = 1.067
Turned off then on again (range selector to off then back to 200m):
(1.1 + 1.1 + 1.1 + 1.0 + 1.1 + 1.1) Ă· 6 = 1.083
Turned off then on again:
(1.1 + 1.2 + 1.1 + 1.1 + 1.1 + 1.0) Ă· 6 = 1.1
Turned off then on again:
(1.1 + 1.2 + 1.1 + 1.1 + 1.1 + 1.0) Ă· 6 = 1.1
Lowest reading: 0.9, Highest reading: 1.2, Average: 1.05, Difference: 0.3 mOhms
That makes > 100 shorted probe measurements.
Then it was put outside in the dark at currently: 31F, 68% humidity, 22F dew point, 29.57inHg pressure for 30 minutes.
mOhm readings with probes shorted on 200m setting, after each reading I break contact between the probes:
(1.3 + 1.4 + 1.3 + 1.4 + 1.4 + 1.4) Ă· 6 = 1.37
Turn off then on again:
(1.5 + 1.5 + 1.4 + 1.4 + 1.4 + 1.2) Ă· 6 = 1.4
Turn off then on again:
(1.3 + 1.4 + 1.2 + 1.4 + 1.5 + 1.5) Ă· 6 = 1.38
Turn off then on again:
(1.5 + 1.5 + 1.5 + 1.5 + 1.5 + 1.5) Ă· 6 = 1.5
Lowest reading: 1.2, Highest reading: 1.5, Average: 1.95, Difference: 0.3 mOhms
EM3610 meter not turned off nor range changed.
Measuring 100 mOhm resistor A:
(102.2 + 102.1 + 102.3 + 102.1 + 102.5 + 102.1) Ă· 6 = 102.22 - 1.5 = 100.72 mOhm on 1% resistor.
My freezer is set to 10F and measures as 9F on the top shelf by independent digital RadioShack thermometer. It’s in autodefrost so humidity reads as 72%. In 20 minutes next to my HungryMan dinners. Wiped off some condensing humidity on the probes first.
(1.3 + 1.4 + 1.4 + 1.5 + 1.5 + 1.5) Ă· 6 = 1.43
Turned off then on again:
(1.5 + 1.5 + 1.5 + 1.6 + 1.6 + 1.5) Ă· 6 = 1.53
Turned off then on again:
(1.5 + 1.5 + 1.5 + 1.5 + 1.5 + 1.5) Ă· 6 = 1.5
Turned off then on again:
(1.4 + 1.5 + 1.6 + 1.5 + 1.5 + 1.5) Ă· 6 = 1.5
EM3610 meter not turned off nor range changed.
Measuring 100 mOhm resistor A:
(102.7 + 102.7 + 102.5 + 102.5 + 102.6 + 102.5) Ă· 6 = 102.58 - 1.5 = 101.08 mOhm on 1% resistor.
Note that the English version of the EM3610 manual says the recommended operating environment is from 0C to 40C or 32F to 104F. So it makes perfect sense the resistance reading is a little off (few tenths of a millOhm) after a short trip to 9F.
The EM3610 manual also says it can be operated in environments of <80% humidity. It was simply stored in the freezer off to cool, the test and resistor were done in my work area at that temperature and humidity.
Now last night I took my RadioShack digital thermometer out of the freezer and put it 1 foot from the EM3610 so they both had more than 10 hours to stabilize at my work area temperature. I know this RadioShack thermometer reads humidity with errors as high as +8%/-4% from experience (I have 3 of these units total). It currently reads 28% humidity versus the AcuRite indoor unit 11 feet from it reading 24%. There is a cool mist wicking humidifier in the room but also a forced air infrared heater directly under than humidifier. My AcuRite indoor units as far as I have seen to date are off on humidity by only 2% maximum (I have 5 indoor units in 5 rooms). The RadioShack thermometer reads 68F and the AcuRite reads 70F and that I accept because the AcuRite is more in the path of the heater exhaust and air from other rooms than the RadioShack unit. My outdoor AcuRite reads as: 36.5F, 27F dew point, 69% humidity, 29.52inHg pressure.
mOhm readings with probes shorted on 200m setting, after each reading I break contact between the probes:
(1.0 + 1.0 + 0.9 + 1.2 + 1.2 + 1.1) Ă· 6 = 1.07
Turned off then on again:
(1.0 + 1.0 + 1.1 + 1.2 + 0.9 + 0.9) Ă· 6 = 1.02
Turned off then on again:
(1.2 + 1.1 + 1.3 + 1.2 + 0.9 + 1.2) Ă· 6 = 1.15
Turned off then on again:
(1.0 + 1.1 + 1.3 + 1.1 + 0.9 + 0.9) Ă· 6 = 1.05
Turned off then on again (forgot on 4th try to test resistor):
(1.1 + 0.9 + 1.0 + 1.0 + 1.3 + 0.9) Ă· 6 = 1.03
EM3610 meter not turned off nor range changed.
Measuring 100 mOhm resistor A:
(102.0 + 101.7 + 102.0 + 102.2 + 101.7 + 102.0) Ă· 6 = 101.93 - 1.03 = 100.93 mOhm on 1% resistor.
I placed the EM3610 in front of an Optimus 800W Quartz infrared fixture. It had both bulbs turned on for the full 800W and I placed the meter vertically against a white box 1 foot from the unit. I put the RadioShack digital thermometer next to it and raised the temperature to 100F and because heat rises it was likely right at the 104F specification towards the top of the meter where the transreflective LCD was slightly darkened. I let it cool for 2 minutes to clear the LCD. Then I repeated the tests as quickly as I could.
mOhm readings with probes shorted on 200m setting, after each reading I break contact between the probes:
(0.9 + 0.7 + 0.6 + 0.8 + 1.0 + 1.0) Ă· 6 = 0.83
Turned off then on again:
(0.9 + 0.8 + 1.1 + 1.1 + 1.4 + 1.0) Ă· 6 = 1.05
Turned off then on again:
(1.2 + 1.2 + 1.1 + 1.1 + 1.1 + 1.0) Ă· 6 = 1.12
Turned off then on again:
(0.9 + 0.8 + 0.9 + 1.0 + 0.8 + 0.8) Ă· 6 = 0.87
Just to be sure about this reading I put the meter back into the infrared heater path this time with the RadioShack digital thermometer on top of it. I raised the temperature till it read 102F, 15% humidity.
mOhm readings with probes shorted on 200m setting, after each reading I break contact between the probes:
(1.0 + 0.9 + 0.9 +1.0 +1.0 +1.0) Ă· 6 = 0.97
EM3610 meter not turned off nor range changed.
Measuring 100 mOhm resistor A:
(100.0 + 100.0 + 99.8 + 100.0 + 100.1 + 100.1) Ă· 6 = 100 - 0.97 = 99.03 mOhm on 1% resistor.
So that’s what happens when you heat the EM3610 up to some reasonable temperature I could see in an FRC competition being in a poorly ventilated gym on a hot summer day and the limits of the specified operating temperature for the meter.
Now the EM3610 meter and RadioShack thermometer were left next to each other where they started their day in my work area for at least 6 hours. When I got the meter next the RadioShack digital thermometer read: 70F and 27% humidity. The meter readings were taken kickly as shown below:
(1.1 + 1.2 + 1.3 + 1.2 + 0.9 + 1.2) Ă· 6 = 1.15
Turned off then on again:
(1.0 + 1.1 + 1.2 + 1.3 + 1.2 + 1.3) Ă· 6 = 1.18
Turned off then on again:
(1.3 + 1.3 + 1.0 + 1.2 + 1.3 + 1.3) Ă· 6 = 1.23
Turned off then on again:
(1.4 + 1.5 + 1.4 + 1.3 + 1.5 + 1.3) Ă· 6 = 1.4
EM3610 meter not turned off nor range changed.
Measuring 100 mOhm resistor A:
(101.7 + 101.7 + 101.7 + 101.7 + 101.7 + 101.8) Ă· 6 = 101.72 - 1.4 = 100.32 mOhm on 1% resistor.
Observations:
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It should be noted that having a good connection whether between the meter probes or the meter probes and the circuits or batteries under test is very important when you are talking about millOhms. The probes on this meter are cylindrical and have 4 points on the end like a human molar tooth. I’ve been touching the sides of the probes together, rotating them slightly between readings and when touching I am applying at least as much pressure as I would expect a good pair of alligator clips would apply. This detail is kind of obvious but it’s worth noting for anyone that may try to test a different meter. Sometimes I touched the probe tips to each other’s sides perpendicular, other times I made an angle.
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The EM3610 tends to start each reading a little low then eventually climb and stabilize on the reading value I have provided and while this is apparent it’s pretty fast (< 2 seconds). Sometimes when I release the pressure as I let go, the last reading climbs but I ignore this because as mentioned in #1 above, this is a symptom of seeing very small resistances and having a weak connection. It’s really no different than not adequately tightening down your FRC robot lugs and crimps.
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I also rotated the 100 mOhm resistor I was measuring each time I measured and I tried to measure that resistor as close to the body of the part as possible because otherwise I’d be measuring the lead resistances extending to the body of the part as well.
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The good part about the inconsistency of my testing location is that it simulates repetition in a real environment with various people over time. The Battery Beaks tested have the slight improvement of having a connector that they can depend on to remove a bit of that uncertainty but those Anderson connectors can still get dirty, damaged or be improperly crimped. The opposite side of the issue is that the Battery Beaks work great with the connectors but now if you need to probe around in the circuit you have to make some sort of leads for it.
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