I have a Fluke 87 V True RMS Multimeter. I did buy it used and believed it to have been working properly. Lately however, while inspecting a PCB, I have become suspect of the resistance readings. I also own a Proster BM4070 LCR Meter.
To test my theory I measured 30 resistors ranging from 10 to 1 M using both meters. I prepared a spreadsheet of the results (below) and was very surprised to find that in the range of 51k to 1M, the Fluke had an average -23% accuracy! The Fluke average for all measurements was -7%. By comparison, the Proster LCR meter was an average of <1% across the range.
I did also note that when place in ohms mode, the Fluke shows a reading of .857 M without probes touching and .3 when touching. The .3 seems normal but I’m not certain about the .857 because I never paid attention to it until my suspicion about accuracy arose.
Value Fluke % Diff Proster % Diff
10 R 10.0 0% 10.0 0%
22 R 22.0 0% 22.0 0%
47 R 47.0 0% 47.0 0%
100 R 99.0 -1% 99.0 -1%
150 R 150.0 0% 150.0 0%
200 R 198.0 -1% 200.0 0%
220 R 220.0 0% 220.0 0%
270 R 268.0 -1% 268.0 -1%
330 R 328.0 -1% 329.0 0%
470 R 469.0 0% 471.0 0%
510 R 505.0 -1% 509.0 0%
680 R 677.0 0% 680.0 0%
1 K 1.0 -1% 1.0 -1%
2 K 1.9 -5% 1.9 -5%
2.2 K 2.2 0% 2.1 -5%
3.3 K 3.3 0% 3.3 0%
4.7 K 4.7 0% 4.7 0%
5.1 K 5.0 -2% 5.0 -2%
6.8 K 6.7 -1% 6.7 -1%
10 K 9.8 -2% 10.0 0%
20 K 19.6 -2% 20.0 0%
47 K 45.0 -4% 47.6 1%
51 K 48.0 -6% 51.6 1%
68 K 62.4 -8% 67.8 0%
100 K 91.0 -9% 101.0 1%
220 K 176.0 -20% 220.0 0%
300 K 225.0 -25% 300.0 0%
470 K 318.0 -32% 470.0 0%
680 K 382.0 -44% 680.0 0%
1 M 0.5 -54% 1.0 0%
AVERAGE -7% 0%
AVG 47k-1M -23% 0%
1. Why the aberrant low readings?
2. Does the Fluke need a recalibration/repair?
Sorry for the table formatting but the spreadsheet did not transfer over too well.
Since I am relatively new to the electronics field and am an old geezer, any help should be pretty basic in presentation.
Thanks to all for any assistance.