Calibration of Jensen JTM-30 clamp meters (estimation)

[Reality99]

Hi.

I have tons of Jensen clamp meter and I own a Fluke 5500 with 50 turn current coil accesory to perform checks/calibration on them. The clamp meters don't have big clamp in order to fit in the 50 turn current coil (1.5" against 2"" from the coil), so what I do is to make checks until 10 A and create an estimation in my report for high currents according to these first measurements.
Is this valid? I'm not under worry as all these devices are under Maintenance section use and these instruments has not been audited in 15 years (I mean the Maintenance instruments program)

If not, is there a way to perform these checks with what I have? I heard that placing the wires in some way but I'm not sure and I don't want to make blind tests with the Fluke.

Thanks in advance.

Alfred

 

[Marc]

If anyone can help with this one, my appreciation and Thanks in advance!

 

[BradM]

Hi.

I have tons of Jensen clamp meter and I own a Fluke 5500 with 50 turn current coil accessory to perform checks/calibration on them. The clamp meters don't have big clamp in order to fit in the 50 turn current coil (1.5" against 2"" from the coil), so what I do is to make checks until 10 A and create an estimation in my report for high currents according to these first measurements.
Is this valid? I'm not under worry as all these devices are under Maintenance section use and these instruments has not been audited in 15 years (I mean the Maintenance instruments program)

If not, is there a way to perform these checks with what I have? I heard that placing the wires in some way but I'm not sure and I don't want to make blind tests with the Fluke.

Thanks in advance.

Alfred

Alfred, I don't know much in this area, but I will give it a try.

I have seen these setups before used to verify amp meter accuracy.

I am unclear how you are approaching this. If the U.U.T. (the meters you are testing) is physically too small to fit into your test donut (the 5500 attachment, how are you physically performing checks on the ampmeters?

You stated this is under a maintenance program. Are you stating that the instrument activity (which you are performing) is called maintenance? You are not considered the activity as calibration?

Are these instruments used for product acceptance, critical processes?

 

[Hershal]

You may have an advantage.

The meter calibrators (550A/5520A) have a LIMITED, TRUE current capability. There is some, but primarily it relies on Ohms law...I=E/R.

It is possible to rewind the coils - OR - to wind an additional coil, I have done so for the exact reason you mention. Not the "recommended" practice, and requires a specific measurement of the resistance involved so that the appropriate voltage can be applied to achieve the reading. If you do not have that capability, then since it would be "homemade" I suggest putting it on a 24 month calibration cycle.

Why? Wire, like anything else, changes, especially if moved around during connection or disconnection. You need to know exactly what the resistance is, plus the uncertainty. Otherwise, you do not know exactly what the actual value is.

Hope this helps.

 

[Jerry Eldred]

I've often used a home made multiplier coil. Matter of fact, I think I've only ever been in one lab that had the "Good One" (the nice 50 turn coil by Fluke).

There is a little of an art to making a multiplier coil. Use solid copper wire of maybe 14, 16 or 18 gauge wire. I often use electrical household wire, although some folks prefer transformer wire. The issue in building one of these Toroidal coils is not accuracy, but fold back current. I'm not very good at explaining this - maybe someone else can pitch in on this detail.

If you make the loops too small, the current fields are large enough that opposing current fields will couple back to the opposite part of the loop, and create opposing current fields; which will act as an effective impedance, and therefore develop a voltage across the coil, reducing the meter calibrator's ability to provide the desired current output (worse in AC than in DC, and directly proportional to frequency).

The trick is to make the loops diameter big enough (maybe at least 6 to 8 inches), and fan out the outer side of the loops to the approximate shape of a doughnut. then tie wrap the center together for where you want to clamp your clampmeter.

You can do this with 5, 10, 20, or what ever number of turns. Just remember about fold back current. Definitely do not make it with stranded wire, solid copper only.

For some smaller range clamp meters, I've made 10 turn coils, and not even fanned them out toroidially.

There are, I believe, some GIDEP (military) procedures that even provide some detailed construction instructions for a coil.