mA reading polarity

[Electromatic]

I recently noticed that one of my multimeters (a rather inexpensive Klein MM400) gives a reading of about 1/2 what it should be if I take a mA reading with the test probes connected opposite of what the polarity should be. Has anyone experienced this? It may have done it out of the box; I've only had it a few months. I might contact Klein and see if it's an issue.

 

[Jraef]

How does one get "polarity" for a device that is supposed to be connected in series? In other words if you are connecting to + and - when trying to read a mA signal, you are not doing it right.

Using a Multimeter Series - Current Measuring Basics - kele.com

If you are involved in installing or troubleshooting HVAC systems, sooner or later you will be taking electrical current measurements. This tutorial will discuss the basics of how to take those current measurements. Current is measured in units of amperes, usually abbreviated to simply “amps.”...

www.kele.com

 

[Flicker Index]

How does one get "polarity" for a device that is supposed to be connected in series? In other words if you are connecting to + and - when trying to read a mA signal, you are not doing it right.

Using a Multimeter Series - Current Measuring Basics - kele.com

If you are involved in installing or troubleshooting HVAC systems, sooner or later you will be taking electrical current measurements. This tutorial will discuss the basics of how to take those current measurements. Current is measured in units of amperes, usually abbreviated to simply “amps.”...

www.kele.com

Well, in theory, if you jump across the L in the L across an I source from the text book, it will stay magnetic indefinitely like an MRI magnet.
It was a current source and an inductance, not a current source, a resistor and a reactance in series, right?

In reality, strange asymmetric behaviors are not uncommon in test equipment.

Electromatic, how many mA are you talking about and what's the full scale mA rating? (i.e. 500mA)

 

[hbiss]

I recently noticed that one of my multimeters (a rather inexpensive Klein MM400) gives a reading of about 1/2 what it should be if I take a mA reading with the test probes connected opposite of what the polarity should be.

If you are connecting the meter IN SERIES with a DC circuit there is actually a polarity but it really doesn't matter. One way you will get a (-) in front of the reading, flip the leads and you will now get a (+) in front of the reading. It's only the reading that counts and both ways should be the same numerical value. Most people don't even bother to pay attention to polarity when measuring DC current.

So, I suggest that to get the readings you say you are, you don't have the meter connected properly. I don't know what you are doing, but you NEVER apply voltage to the current jacks. They ALWAYS go in series with a load.

...Or there is some problem with the meter.



-Hal

 

[Electromatic]

The meter is capable of 10A via COM and 10A jacks or 500mA via COM and multi-setting jacks. When I connect in series with the red probe toward DC+ and the black probe (COM) toward DC-, the readings are correct. If I swap the orientation of the probes, the readings end up being slightly less than 1/2 of the true current. I do get the appropriate negative (-) symbol when reversed. (see attached)
I think I'll contact Klein about the issue. I got the meter off Amazon--I'm curious if that will complicate their warranty.

 

[Flicker Index]

What sort of current are we talking about? Briefly skimming the manual for that meter, it can do auto or manual range.
If the spec is 1% + 5 count, that means if you're in 500.0mA range that reads to the smallest 0.1mA and you're trying to measure 0.2mA, it's allowed an error of 0.5mA + 1%. If it reads anything from -0.5mA to +0.5mA with NOTHIGN connected, it's still technically within specs.

 

[hbiss]

When I connect in series with the red probe toward DC+ and the black probe (COM) toward DC-, the readings are correct. If I swap the orientation of the probes, the readings end up being slightly less than 1/2 of the true current. I do get the appropriate negative (-) symbol when reversed. (see attached)
I think I'll contact Klein about the issue. I got the meter off Amazon--I'm curious if that will complicate their warranty.

Fair enough. Looks like a bad meter to me.

-Hal

 

[GoldDigger]

Fair enough. Looks like a bad meter to me.

-Hal

Depending on the exact design of the AC ma function, you could get asymmetric readings on the AC ma range if the current being measured has a DC component.