Digital multimeter diode check

MarkB_MI

Well-known Member
Location
Motown USA
While we're discussing meters, I thought I'd throw out a tip regarding the "diode check" range on your DMM.

Most folks think the diode check range is just another resistance check with an added beep. NOT SO! The measurement you see on the diode range is not in ohms but rather in VOLTS. A good diode has a voltage drop of around .6 to .7 volts. If you use the diode check to measure continuity, don't think the "0.00" reading means you have zero ohms resistance. You need to switch to the ohms range to measure resistance.

Also, when checking a diode, most meters will emit a single "chirp" when the diode is forward-biased, but a continuous tone when the diode is shorted.
 
Geeeeeeee and I have to take my old Simpson 260 and check resistance at both polarities to do that lol. Guess I need to move into this new century huh? Sure, I have a couple digital meters laying around somewhere, maybe I need to dust them off, and get a smart phone as I only have an old DUMB flip phone my kids and grandkids make fun of.

John T
 
I use my Simpson 260 for everything. I've had mine since 1956. An excellent meter. Just used it to check out a neighbors 600 Ford
 
I agree, I love mine but looks like my age is showing lol. Im still old school and haven't caught up to the Digital Generation and dont plan to either......

John T
 
Hello John T,

Two meters is better then one?.... Not really!
He who has one meter knows the reading, he who has two never knows for sure HA! HA! Have a good day........

Guido.
a162718.jpg
 
Hello MarkB_MI

I'm like John T LOVE my 260. Got a new to me last year to replace old on. Here they are both...


Guido.
a162719.jpg
 
I must be of the same vintage. I work in commercial radio and we have lots of digital meters which are good for some measurements but always carry a 260 to fall back on. Usually use it for continuity checks and measurements that do not need a high impedance meter or when close enough is good enough which is most of the time.
 
We had some problems in the Air Force years ago, every thing was going digital but us. Biggest problem is we tried a few digital meters with LCD displays and the darn things froze when out on the flight line during the winter. We had a few PSM-6's thy were great but starting to die and supply didn't have anymore analog meters to replace them. It was a hole in the Nuclear umbrella!
 
Keep in mind that the forward voltage drop increases with current due to the resistive nature of the PN junction. The meter is very low current when it gives the .7 volts or so for a silicon diode. A diode with a larger amount of current will have a forward drop that is higher and in proportion to the current.

The meters in use here are a Fluke 179 and HP 400E for field work and a Keithley 179 and HP 400D on the bench. Also an old WWII surplus DC micro and milliamp meter for RX and TX alignments. I even use it when aiming microwave dishes.

We have a group here with a wide array of knowledge!

Josh
 
Hello MarkB__MI,

I saw the video......WOW! That comes from an Army guy........

Guido.
 
Geeeeeeee and I have to take my old Simpson 260 and check resistance at both polarities to do that lol. Guess I need to move into this new century huh? Sure, I have a couple digital meters laying around somewhere, maybe I need to dust them off, and get a smart phone as I only have an old DUMB flip phone my kids and grandkids make fun of.
John T

me too JohnT just upgraded to a Iphone5... got tired of waiting for the tubes to warm up in mmy old cell phone... Still use my 260 all the time..

and my 'smart' phone will always be smarter than me...

later
John
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top