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Old 11-05-2014, 07:48 AM   #1
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Default How much accuracy to measure stators?

Ho much accuracy is needed on a meter to measure stators? Can you use a meter good to 0.01 Ω or do you need a true milliohm meter working at 0.001 Ω?
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Old 11-05-2014, 07:56 AM   #2
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Ho much accuracy is needed on a meter to measure stators? Can you use a meter good to 0.01 Ω or do you need a true milliohm meter working at 0.001 Ω?
INSTEK is the ONLY meter worth having to measure stators. Its about 350.00 though but its now become the industry standard and repeats its numbers in a fraction of a second. clip wiggles not needed!

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Old 11-05-2014, 08:04 AM   #3
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Make sure you don't mistake the resolution of the meter (.01, .001) with the accuracy of the meter (usually given in %). The meter might read to .001, but that doesn't mean that it is accurate to that number. Accuracy means you will get the same, or nearly the same, reading from meter to meter on the same stator. Without that, you won't be able to compare your numbers with someone else, though you might still get useful comparative readings for your own stators.

I believe ROAR uses the Instek GOM-802, which is about $500.
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Old 11-05-2014, 08:05 AM   #4
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I'm familiar with precision versus accuracy its a concept we use regularly at my work. I've got access to a range of benchtop multimeters just wondering how much precision is needed to see meaningful differences in stators.
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Old 11-05-2014, 08:47 AM   #5
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I'd recommend better than 1% accuracy of reading. Ten times better would be fantastic, if you have access to a good benchtop meter. I sure miss my old HP3456A!

FYI, the Instek 802 is, on average, about 10 times more accurate than the 801H for our purposes. The 801H has about 1.7% accuracy on a 13.5 motor. The 802 has 0.12% accuracy on the same motor. That's probably overkill, but as there is nothing in between the price of the 801H and the 802, the 802 would get the nod if you were to purchase one. It sounds like you don't need to, which makes me jealous!
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Old 11-05-2014, 09:01 AM   #6
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Make sure you don't mistake the resolution of the meter (.01, .001) with the accuracy of the meter (usually given in %). The meter might read to .001, but that doesn't mean that it is accurate to that number. Accuracy means you will get the same, or nearly the same, reading from meter to meter on the same stator. Without that, you won't be able to compare your numbers with someone else, though you might still get useful comparative readings for your own stators.

I believe ROAR uses the Instek GOM-802, which is about $500.
I also believe the one ROAR uses has built in temperature compensation as well to take into account the air temp right?

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Old 11-05-2014, 09:06 AM   #7
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I also believe the one ROAR uses has built in temperature compensation as well to take into account the air temp right?

EA
Yes, that's a very good point, although it's actually stator temperature, not air temperature. Otherwise one needs to either bring the stator to a known temperature or measure the stator temperature, then apply a correction factor to the meter reading, which is a bit inconvenient.

The rules package I proposed to ROAR included the following:

"...when measured over a range of 20 to 30 degrees C and multiplied by a correction factor of (1-((T_measured-25)*0.00393))."
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Old 11-05-2014, 09:20 AM   #8
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Thats what I meant. The measured component temp.

Even the 801 uses an internal temp sensor to adjust the readings for air temp but does not factor in component being tested temp.

5 degrees stator temp does make a huge difference!!!

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Old 11-05-2014, 01:34 PM   #9
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Are you measuring the resistance or the inductance of the stator?
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Old 11-06-2014, 05:05 AM   #10
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Are you measuring the resistance or the inductance of the stator?
I'm just starting to turn into a motor head and starting to figure out how to test and profile motors, I was told that resistance is a good measure of how good a given stator is. What would measuring the inductance show me? My understanding is that there are a lot more parameters to an inductance test where resistance simply needs a reference temperature and a sufficiently precise ohm meter.
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Old 11-06-2014, 10:52 AM   #11
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I wanted to know if they wanted a measurement of the inductance, the resistance to change in current through a coil, or the resistance off the wire itself.

Typical DMMs can measure resistance, ohms, but typically higher end meters are required to measure inductance correctly.

When the Instek meter was brought up I wanted to know which function was used.
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Old 11-06-2014, 11:47 AM   #12
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Originally Posted by RacinJ View Post
I wanted to know if they wanted a measurement of the inductance, the resistance to change in current through a coil, or the resistance off the wire itself.

Typical DMMs can measure resistance, ohms, but typically higher end meters are required to measure inductance correctly.

When the Instek meter was brought up I wanted to know which function was used.
the Instek is for resistance of each pole.

Measuring inductance is just another way of checking the motors but you cant compare one brand to another because the stator itself and metal affects the inductance. Resistance checks will measure the amount of wire on the motor itself and is quicker and easier to check and compare one brand to another brand.

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