Two meters show different amperage

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Joey94

Member
Location
Illinois
Occupation
Apprentice
Why is my klein tools CL390 shows different measurements than my CL800 when measuring at the same time the amperage of my kitchen aid ?
7599be05c68b1011adf6a37e05854a3d.jpg

CL 390 & CL900 shows almost the same. But when I try CL700 or CL800 it tells me something different always.
I’m also not a 100% sure what’s the difference between max or inrush current measurements?


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hillbilly1

Senior Member
Location
Atlanta,Ga
Occupation
Field coordinator/ technical support
That’s because you are running it through a doubler. One box multiplies it X amount, the other box multiplies by a different amount. Swap the meters, and I think you will see them read the same as the other in that box. Look for the multiplier imprinted on the box.
 

Joey94

Member
Location
Illinois
Occupation
Apprentice
This is the actual load. I tried swapping them and same thing. The CL800 shows about double the amperage in both cases


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Joey94

Member
Location
Illinois
Occupation
Apprentice
In both clamps I set it on max reading. It’s just not the best picture


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synchro

Senior Member
Location
Chicago, IL
Occupation
EE
I would try measuring the current of something that has a reasonably known current draw like a 1300W heater, which should be around 10.4 amps. Your CL800 is showing about 1.9 times higher current than the CL390, and so you should be able to tell which of the two is way off.
Also, I'd put both meters in normal mode instead of MAX and see if the readings get a lot closer. If the normal readings are close, then perhaps there is a very short burst of current and the CL390 has more filtering that reduces the peak value that it is measuring in the MAX mode of operation.
 

Joey94

Member
Location
Illinois
Occupation
Apprentice
These pictures show 3 meters.
The CL 900 shows 10x the value 26.4A which actually is 2.64 A because I was only able to clamp it to a 10x hole.
The CL 800 shows 4.37 A
CL 390 2.6 just like the CL900
9f05a4aab9031be8de0e5c8e40a91dec.png

dade1f59f25caf18637f76a60eedce3d.png

fbbe86e2e88bdab013c28e51110089a4.png



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hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Also, I'd put both meters in normal mode instead of MAX and see if the readings get a lot closer. If the normal readings are close, then perhaps there is a very short burst of current and the CL390 has more filtering that reduces the peak value that it is measuring in the MAX mode of operation.
Ahh, I didn't realize that you had them in max mode. I agree with @synchro, and further I don't know what the stated accuracy is of the maximum current capture. Do they even give it? It could be +/- 20% for all we know.

-Hal
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
perhaps there is a very short burst of current and the CL390 has more filtering that reduces the peak value that it is measuring in the MAX mode of operation.
This. Or perhaps one of the models samples more frequently. More frequent sampling will come closer to capturing the instantaneous peak of a transient (the motor startup of your mixer).

Cheers, Wayne
 

EmagSamurai

Member
Location
Alabama
Are you trying to measure the inrush? If so, I don't think either of those meters has that function, and their sample rates are going to be too slow to accurately capture the peak inrush current. My guess is the difference is going to be based on the sample timing between the devices.
 

gar

Senior Member
2110118-1354 EDT

You guys need to study, play with, experiment, and get an understand of how instruments work that you use.

Most general purpose analog and digital meters and not very useful peak measuring devices.

Let us start with an ordinary moving coil type meter. This is a mechanical device with an electrical driving element. Being mechanical it has inertia and this is an averaging type mechanism. The electrical part is a force generator with its own time constant, averaging characteristic. Then most of these meters have a linear spring that the electrical force works against to produce a reading by a moving needle over a scale. If you watch the meter for a while you can get a reasonable estimate of its average reading for a steady input signal. Such meters usually have a fixed magnetic field that a moving coil works in.

To make AC measurements two broad classes of meters are used. One type uses two coils that work against each other, called an electrodynamometer meter. This is a true RMS meter. The other major type uses a diode rectifier, and an ordinary AC or DC meter. This second type falls in two categories, average reading calibrated in RMS on a sine wave, and a true RMS type. The mechanical meter movement is the primary averaging unit.

With electronic meters the circuitry provides the same types of measurements that the mechanical meters provide. However, electrodynamometer meters read the RMS value of the combined input AC and DC input signal. Most electronic meters strip out the DC component of an input.

With electronic meters lots of different characteristics can be generated.

.
 

Joey94

Member
Location
Illinois
Occupation
Apprentice
Are you trying to measure the inrush? If so, I don't think either of those meters has that function, and their sample rates are going to be too slow to accurately capture the peak inrush current. My guess is the difference is going to be based on the sample timing between the devices.

Only the CL900 should measure inrush current. As per the manual the inrush measurment period is 100 miliseconds, with a 20 milisecond sampling rate.
The other two are not measuring inrush, only the max value which are 3 samples per second.
So I was trying to compare the three clamp meters to see if they give the same max amperage value and I was surprised that the CL 900 has almost the same amperage like the CL 390.
But the CL700 & CL800 shows higher amperage. Almost double. That’s what I didn’t understand. I thought if I measure at the same time the same start of the kitchen aid they all should show the same amount. But maybe it really is because of the inaccuracy of the meters, one showing +2% the other -2%.


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