Reading measuring testing diodes - Page 1
Forum section: electronics / beginners

author: wertyu
author_rank: Contributor
timestamp: February 24, 2019, 03:31:20 pm
content: My new multimeter seems to measure diodes both ways 0.6 , my fluke does not on same diode .also the fluke measures the diode in ohms but the isotech does not .any ideas on why i like the diode test it simple this has confused me .

author: wertyu
author_rank: Contributor
timestamp: February 24, 2019, 03:36:30 pm
content: i think it might be reading it as a negative 0.6v ?bit confusing i prefer the OL .

author: wertyu
author_rank: Contributor
timestamp: February 24, 2019, 04:58:49 pm
content: is there a way to purposely damaged a diode so i can see the results on this meter ?manual seems to suggest it tests in both directions and tell you if P / N connected and if its faulty it will OL ?

author: Audioguru
author_rank: Super Contributor
timestamp: February 24, 2019, 06:35:56 pm
content: Your new meter has many mistakes in its design.1) It should use a low voltage for measuring ohms so that it does not forward bias a semiconductor diode or transistor. My Fluke uses 200mV.2) When testing diodes it properly shows its forward voltage but the polarity is very confusing. It does not show if a diode or junction is shorted or is leaking. My Fluke shows a forward voltage when forward biased and shows OL when reverse biased and is not leaking.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: February 25, 2019, 04:39:50 am
content: I agree, that diode "measurement" is screwy. The top left illustration presumably shows a correct measurement of the diode's forward voltage drop Vf. The bottom illustration is whacky--- connect diodes in antiparallel like that and if both are good, once again one should only read the Vf of the forward-biased diode. The top right illustration makes no sense whatsoever. If a diode is good it should not conduct in the reverse biased direction, to a first approximation. So how, if the meter just magically flips polarity and reads the forward voltage anyway, how are you supposed to tell if it blocks in the reverse direction properly ... I don't get it.How to damage a diode? That's new-- usually we want to know how to -Not- damage them.They usually fail open, or shorted, in my experience. Easy enough to do by overvolting in reverse or overcurrenting in forward biasing. What this meter will read when it is confronted with an open or shorted diode, or just a leaky one, is an empirical question. Let's do it!

author: wertyu
author_rank: Contributor
timestamp: February 25, 2019, 12:39:58 pm
content: OK glad its not just me confused then , i tried the antiparallel test with both a fluke and this tester and this fails to take a reading the fluke like you say reads one .shame as it could of been a very good tester .I tried to kill a diode not as easy as you would think , i tried it to 30v 5 amp max for PSU on reverse but could not get a current to flow .In forwards i tried same V and Amps made it smoke 5 times gradually for longer , and still it worked fine on the 6 attempt it burned my finger and shot across the room so i gave up .Tough them diodes though i doubt they go often .thanks for input on this !! Ive come to conclusion Fluke are the best and for a reason , look , feel and work great .

author: SG-1
author_rank: Regular Contributor
timestamp: February 25, 2019, 03:21:12 pm
content: I do not think there is anything wrong with your meter. I have a Flir & it can test a diode the same way. It is menu selection between the traditional test & this new style, which does not require swapping the leads around. I can see this way would be some what confusing for someone new.To simulate a shorted diode, just touch the leads together.For an open diode, keep the leads from touching anything or use a one meg resistor.Use smaller resistors & learn how the meter reacts to them in diode mode.

author: magic
author_rank: Super Contributor
timestamp: February 25, 2019, 09:10:41 pm
content: There is everything wrong with it and I hope it doesn't become a fad that every vendor copies.Testing diodes and BJTs is a lot faster when you don't need to pull them out of circuit. Circuit which may easily contain reverse paths that would make this dumb meter show overrange.And then there are ICs where you can't isolate individual junctions for testing even if you wanted to.