Fluke A40/A40A

[John Treekiller]

Not sure how well I posted previously but, can one of the A40 experts tell me which values of A40 do you minimally need to have to calibrate a Fluke 5720A AC current?  I have the few shunts and working on bringing the lab online over the next year.  So I've been asked by management to provide them with a list of what smallerr items in the lab I need to fully do the calibrations to the Fluke 5720A.  On a related note, I've seen that there is a Holt shunt set that can alternately be used for the high accuracy AC current cals.  Any thoughts on that?  If I only have 100mA, 1A and 2A A40's, are there enough more shunts needed that a good used (and re-certified) Holt set might be a more cost effective, yet accurate enough solution?

In the AF CTO for the 5720A (When they used the A40A Current Shunts) they used the 2 A, 500 mA and 20 mA shunts, of course if you have a 5725A with your 5720A you would require the 20 A shunt.  The 2.2 mA range of the 5720A is calibrated using a 200 Ohm Metal Film Resistor and the 220 uA range uses a 2 kOhm resistor.  The Holt set is listed as a sub-item, not sure about the accuracies though.  The AF cals the 5720A current ranges at a value of 2 for the 2.2 ranges.

[Bryan]

Fluke says you need 20mA/200mA/2A and 10A if a 5725A is included.  The 2mA and 200uA ranges are tested using 200 and 2 K ohm precision resistors.  I use a 20A on my 5725 and 500mA instead of the 200mA.  What I do not know is the dynamic range of the things, they were offered in 1, 2, 5 values.  So how do they perform at half scale or 10% of scale, I cannot answer that with anything concrete but I have had good results with 20mA/500mA/2A and 20A.  Maybe some can chime in with more authorita.  I think we had a complete set at one time but in a cost containing measure several years ago I cut us back to 20mA, 500mA (would have preferred 200mA but it was smoked), 2A and 20A figuring that would give the best acceptable coverage presuming they can run from about 25 to 100% and perform well. 

[beadwork]

The 200 ohm & 2 kohm are not precision resistors, they are metal film resistors ±1% of value AC/DC difference negligible due to metal film construction.

[Bryan]

The 200 ohm & 2 kohm are not precision resistors, they are metal film resistors ±1% of value AC/DC difference negligible due to metal film construction.

Thanks beadwork

[measure]

Fluke says you need 20mA/200mA/2A and 10A if a 5725A is included.  The 2mA and 200uA ranges are tested using 200 and 2 K ohm precision resistors.  I use a 20A on my 5725 and 500mA instead of the 200mA.  What I do not know is the dynamic range of the things, they were offered in 1, 2, 5 values.  So how do they perform at half scale or 10% of scale, I cannot answer that with anything concrete but I have had good results with 20mA/500mA/2A and 20A.  Maybe some can chime in with more authorita.  I think we had a complete set at one time but in a cost containing measure several years ago I cut us back to 20mA, 500mA (would have preferred 200mA but it was smoked), 2A and 20A figuring that would give the best acceptable coverage presuming they can run from about 25 to 100% and perform well.

Actually, Bryan, A40s were offered in 1, 2, 3, 5 increments, beginning with 10 mA, A40 model and ending with the A40A 20 A unit. Initially, the aforementioned values were required, due to the limited dynamic range of the thermocouple-based Fluke 540B, which was used as the detector. Now, even though better dynamic range is achievable using a Fluke 792A or 5790A, problems with low-level and/or common-mode noise can still be a problem. Best advice: When using the A40(A) series of AC-DC Current Shunts, utilize the value closest to that you are trying to measure. Also remember that the shunts themselves will only tolerate perhaps a 10% overload prior to undesirable things occurring.