Fluke 8020a DMM has three diode test functions???? Any Ideas????

[ratiodetector2]

Hi All,
Picked up a Fluke 8020A at a yard sale for next to nothin.........
Its a great meter, fully working on all ranges and the display is
perfect.
However, I have a question, I should really know the answer as we had
these meters at college; but that was 20 years ago!
The 20M, 200k and 2k resistance ranges are marked with the diode test
symbol??
The meter has three diode test functions or what? (I guess "or what is
right")
Can someone check out their own 8020a and let me know please.
Thanks a lot!
Hugh.

 

[Jeff Wiseman]

The meter has three diode test functions or what? (I guess "or what is
right")
Can someone check out their own 8020a and let me know please.
Thanks a lot!

I have a Fluke 27 which if I remember correctly was the next model down from the 8020s around 1984 when I got it. Here's what is says from my Fluke 27 owner's manual:

"Diode Test and Continuity

"In diode test, there is oly one range: 0 to +2.08 volts. Voltage is developed across the component(s) under test by a test current output from the Fluke 25/27. Voltages greater than 2.08V or open test leads produce an overload (OL) condition. Negative inputs produce a negative indication (they are not suppressed). In the diode test function the beeper produces a continuous tone if the input is less than 0.1V, and the beeper beeps once when the input descends through a 0.7V threshold.

"Audible continuity testing is also performed with the function selector switch in the diode test/continuity position. A continuous tone sounds for test resistances below approximately 150 ohms. An intermittent connection produces erratic beeps, and can be a valuable troubleshooting aid. Erratic beeps can also occur, due to environmental noise, if a test value is very close to the threshold (150 ohms). Test resistances from approximately 150 ohms to 1000 ohms produce a short tone similar to a forward biased diode. Test resistances less than approximately 20 kilohms will produce an on-scale reading."

I think that the main issue was that the meter puts out enough current/voltage to forward bias a diode without damaging it. On mine the resistance selection and the diode/continuity-beeper selection are different. On yours, it could simply be that the Ohms ranges all can be used across a p/n junction such as in an IC safely. My spec'ed open circuit test voltage for the Ohms range is 2.8 volts and not 2.08 volts as when on the continuity/diode range. Perhaps yours uses a 2.08 V open circuit voltage for the Ohms ranges as well. Should be easy to check if you have another multimeter laying around.

Hope this helps.

- Jeff

 

[Hugh Prescott]

Have the orig manual and meter circa 1976???

IRRC the ones\ marked with the diode symbol apply enough voltage to the
circut that diodes will conduct.

The ones without the diode symbol apply a much lower voltage and SI diodes
will not conductl

Will see if I can find the manual tomorrow at work.

Hugh