meter with continuity test and diode test on same setting

[bone]

I have this unbranded meter that has a setting to test continuity (w/
a beep) and I noticed a diode symbol next to it as well.
Putting the leads across a diode I think is good I get "1" (infinity)
one way and a cryptic "566" the other way, what do these readings
indicate? I figured infinite was ok but I should be seeing something
relating to .7 voltage drop the other way ... maybe this is .566v
drop? Looking for answers from the pros

thank you.

 

[ehsjr]

I have this unbranded meter that has a setting to test continuity (w/
a beep) and I noticed a diode symbol next to it as well.
Putting the leads across a diode I think is good I get "1" (infinity)
one way and a cryptic "566" the other way, what do these readings
indicate? I figured infinite was ok but I should be seeing something
relating to .7 voltage drop the other way ... maybe this is .566v
drop? Looking for answers from the pros

thank you.

The diode is good with those indications.
That .566 is the drop the meter measures
at whatever current it's producing.

Ed

 

[David L. Jones]

I have this unbranded meter that has a setting to test continuity (w/
a beep) and I noticed a diode symbol next to it as well.
Putting the leads across a diode I think is good I get "1" (infinity)
one way and a cryptic "566" the other way, what do these readings
indicate? I figured infinite was ok but I should be seeing something
relating to .7 voltage drop the other way ... maybe this is .566v
drop? Looking for answers from the pros

thank you.

In the diode test mode the meter puts a fixed current through the
diode (usually 1mA) and the meter displays the voltage drop of the
diode.
The display should show 0.566 and not just "566". If it shows "566"
then you are probably still in continuity mode instead of diode mode,
in which case it's trying to show some meaningless resistance value.
You usually have to push a button (usually a different colour unmarked
button) to switch between continuity and diode mode.
Many meters will show either a diode symbol on the screen when in
diode mode, and an "audio" type symbol when in continuity mode.

Dave.

 

[Michael Black]

I have this unbranded meter that has a setting to test continuity (w/
a beep) and I noticed a diode symbol next to it as well.
Putting the leads across a diode I think is good I get "1" (infinity)
one way and a cryptic "566" the other way, what do these readings
indicate? I figured infinite was ok but I should be seeing something
relating to .7 voltage drop the other way ... maybe this is .566v
drop? Looking for answers from the pros

thank you.

I don't know.

But my DMM has a diode position, and the ".7v" is typical or theoretical
and is bound to not be exact. I do know on my meter that it does what
is needed, show whether a diode is good, and will show a different reading
for diodes with a different voltage drop. So germanium and schottky
diodes will show quite different readings when measured, enough so it's
clear which are which.

A good diode will show infinite in one direction, since it can't conduct
that way, and some finite reading the other way.

Try some known diodes, and get used to what your meter shows with
them, so you can get an idea of what to expect for unknown diodes.

Michael

 

[Jamie]

I have this unbranded meter that has a setting to test continuity (w/
a beep) and I noticed a diode symbol next to it as well.
Putting the leads across a diode I think is good I get "1" (infinity)
one way and a cryptic "566" the other way, what do these readings
indicate? I figured infinite was ok but I should be seeing something
relating to .7 voltage drop the other way ... maybe this is .566v
drop? Looking for answers from the pros

thank you.

Internally a DMM uses one of it's scales as a direct voltage
reading to represent ohms. In cases like you're seeing, it's
the net results of that scale reading the average .6 volts you
get with diodes which most likely in your meter is translating
to 566 Ohms. that does not mean it's actually 566 ohms..
you just got to be aware of the component you're testing and
not assume ohms.


--
"I'd rather have a bottle in front of me than a frontal lobotomy"

"Daily Thought:

SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR ANYTHING BUT
THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.
http://webpages.charter.net/jamie_5"

 

[bone]

In the diode test mode the meter puts a fixed current through the
diode (usually 1mA) and the meter displays the voltage drop of the
diode.
The display should show 0.566 and not just "566". If it shows "566"
then you are probably still in continuity mode instead of diode mode,
in which case it's trying to show some meaningless resistance value.
You usually have to push a button (usually a different colour unmarked
button) to switch between continuity and diode mode.
Many meters will show either a diode symbol on the screen when in
diode mode, and an "audio" type symbol when in continuity mode.

Dave.

no such button to switch from continuity to diode test ... I read some
smallish diodes that are known to be good getting smaller readings on
those than bigger ones so logically it's not measuring voltage
drop ... hm. wish I had the manual ...

 

[John Popelish]

no such button to switch from continuity to diode test ... I read some
smallish diodes that are known to be good getting smaller readings on
those than bigger ones so logically it's not measuring voltage
drop ... hm. wish I had the manual ...

I am willing to bet you a dollar that it is displaying
millivolts of diode drop (usually up to about 2000, before
it switches to the open circuit, off scale display). The
smaller diodes may be Schottkys or germanium, which have
lower forward drop. If you can borrow a second meter, you
can measure the test current, and the millivolts across the
diode under test, for a comparison.

 

[Alice]

Internally a DMM uses one of it's scales as a direct voltage
reading to represent ohms. In cases like you're seeing, it's
the net results of that scale reading the average .6 volts you
get with diodes which most likely in your meter is translating
to 566 Ohms. that does not mean it's actually 566 ohms..
you just got to be aware of the component you're testing and
not assume ohms.

--
"I'd rather have a bottle in front of me than a frontal lobotomy"

"Daily Thought:

SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR ANYTHING BUT
THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.http://webpages.charter.net/jamie_5"

website:
http://www.longtimetrade.com
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[John Fields]

no such button to switch from continuity to diode test ... I read some
smallish diodes that are known to be good getting smaller readings on
those than bigger ones so logically it's not measuring voltage
drop ... hm. wish I had the manual ...

 

[bone]

I am willing to bet you a dollar that it is displaying
millivolts of diode drop (usually up to about 2000, before
it switches to the open circuit, off scale display). The
smaller diodes may be Schottkys or germanium, which have
lower forward drop. If you can borrow a second meter, you
can measure the test current, and the millivolts across the
diode under test, for a comparison.

man so much to learn, I had discounted germanium diodes because the
number on the meter was "160" which apparently could be a schottky
(part I was unaware of) ... I'll have to do more testing.

thank you

 

[David L. Jones]

no such button to switch from continuity to diode test ... I read some
smallish diodes that are known to be good getting smaller readings on
those than bigger ones so logically it's not measuring voltage
drop ... hm. wish I had the manual ...

Which brand and model of meter are you using?
If it really is a combined diode/continuity mode then the display is
probably in millivolts. But this is quite indeed, most meters do not
work like this.

Dave.

 

[John Fields]

..
..
..

Which brand and model of meter are you using?
If it really is a combined diode/continuity mode then the display is
probably in millivolts. But this is quite indeed, most meters do not
work like this.

 

[John]

We can supply many name brand product in different popular designs,
LOL Jamie, how the heck did you end up having your post as being
worthy of Alice's reply?

John

 

[bone]

Which brand and model of meter are you using?

it really is unbranded, I got it years ago from web-tronics.com as a
freebee when I bought a bunch of parts for some (probably failed)
project. (long time electronics geek wanna be, fairly common for CS
guys I think)
the only marking on it at all is "CCL " followed by a 9 digit number.
not helpful.

I still have to do some tests but I probably don't have time tonight.

 

[Jamie]

LOL Jamie, how the heck did you end up having your post as being
worthy of Alice's reply?

John

I have no idea, strange things happen here.


--
"I'd rather have a bottle in front of me than a frontal lobotomy"

"Daily Thought:

SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR ANYTHING BUT
THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.
http://webpages.charter.net/jamie_5"

 

[ehsjr]

Internally a DMM uses one of it's scales as a direct voltage
reading to represent ohms. In cases like you're seeing, it's
the net results of that scale reading the average .6 volts you
get with diodes which most likely in your meter is translating
to 566 Ohms. that does not mean it's actually 566 ohms..

Well, no, not 566 and not translating to ohms. The reading
is .566, and it is displaying volts, not translating into
ohms. It is displaying the voltage drop across the diode at
whatever current the meter is producing.

Ed

 

[redbelly]

I am willing to bet you a dollar that it is displaying
millivolts of diode drop (usually up to about 2000, before
it switches to the open circuit, off scale display). The
smaller diodes may be Schottkys or germanium, which have
lower forward drop. If you can borrow a second meter, you
can measure the test current, and the millivolts across the
diode under test, for a comparison.

And if you can't get a second meter, just use a resistor with the
meter you have. Divide voltage (displayed on meter) by the resistance
to see what the test current is.

Tried the following on my own meter (Extech model 380282), which also
has a "diode + continuity" combined setting:

With a 1k resistor, got 0.669 volts. It's really 0.985 k-ohms, so the
test current seems to be 0.68 mA (that's 0.669/0.985, and I'm not sure
how accurate the 3rd digit is)

Next I tried it with 100 ohms (actually measures 100.3). Now the meter
beeps, and the reading is 0.085 V. So for this lower resistance the
test current is 0.85 mA, somewhat larger than before.

So we can conclude that:
1. The "test current" is not a rigid fixed value, but is somewhat less
than 1 mA, and works good enough for diode/continuity tests.
2. My meter beeps to indicate "good continuity" somewhere between 100
and 1000 ohms.

The OP might try this on his meter and let us know the result. (taking
his meter readings in mV)

Mark

 

[Jamie]

Well, no, not 566 and not translating to ohms. The reading
is .566, and it is displaying volts, not translating into
ohms. It is displaying the voltage drop across the diode at
whatever current the meter is producing.

Ed

Do we have an english problem here ? or are you just one those that
must insist on starting something.
Most Auto range meters will display that as .566 in the K scale
range designated for DIODE test. Why do you think I texted it that way?
..566 would be 566 ohms on these scales.

I won't get into it any deeper on the technical end of it as why ,
because it's obvious the major audience does not care about a
trivial matter in this case and understandably so.

If it wasn't your intention to instigate, then I
apologize.

--
"I'd rather have a bottle in front of me than a frontal lobotomy"

"Daily Thought:

SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR ANYTHING BUT
THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.
http://webpages.charter.net/jamie_5"

 

[John Popelish]

Do we have an english problem here ? or are you just one those that
must insist on starting something.
Most Auto range meters will display that as .566 in the K scale
range designated for DIODE test. Why do you think I texted it that way?
.566 would be 566 ohms on these scales.

I won't get into it any deeper on the technical end of it as why ,
because it's obvious the major audience does not care about a
trivial matter in this case and understandably so.

If it wasn't your intention to instigate, then I
apologize.

You have gotten me to doubt my experience and assumptions on
this. I have two cheap digital multi-meters, a GE2524 and a
DT-830B.

I used each one to measure the open circuit voltage and
short circuit current from the other on its diode test
range. I then calculated a possible internal current
limiting resistance.

GE2524 2.64 V 1.31 mA 2.02 kohms
DT-830B 2.92 V 1.18 mA 2.47 kohms

Then I measured a diode junction with each meter while
measuring the test current and voltage drop with the other
meter. Here is the meter reading (with no decimal point
showing), junction voltage and junction current and
calculated diode resistance at that operating point.

GE2524 487 .518 V 1.06 mA 488 ohms
DT-830B 526 .514 V 0.97 mA 529 ohms

So it looks like both these meters read out whole ohms, not
millivolts, as I have been assuming, on the diode test scale.

The main difference between the diode test scale and the
2000 ohm range is that that scale supplies a much lower open
circuit voltage:

GE2524 295 mV
DT-830B 141.5 mV

Either of those ranges will allow pretty good resistance
measurements without forward biasing silicon PN junctions
very much.

Thank you for inspiring me to get to know some of my test
equipment better.

 

[ehsjr]

Do we have an english problem here ?

I don't think so. We simply disagree. I think
what you posted is wrong, and apparently you
think what I posted is wrong.

or are you just one those that

must insist on starting something.

Nope. I dislike the posts where the issue
is lost and ad hominum junk takes its place.

Most Auto range meters will display that as .566 in the K scale
range designated for DIODE test.

Probably not relevant whether it is auto ranging or not,
but the op did not say he has an Auto range meter.
He said he had an unbranded meter he got from Webtronics
and the only marking on it at all is "CCL " followed by
a 9 digit number. What he said makes the next paragraph
relevant.

I have what is probably the same meter, which I got
from them the same way he did - as a freebie when he
ordered a bunch of parts. The one in my hand right
now has CCL031017886 on it, which I assume is the serial
number. I have at least one more from them, also
received for free when I ordered a bunch of stuff.

Why do you think I texted it that way?

What I think of your reason for texting that
way is not relevant.

.566 would be 566 ohms on these scales.

On the Webtronics meter, assuming it is the same as
his, the reading has no decimal point. It shows
up as 566. When you use a second meter in parallel
with the diode testing meter and set the second
meter to read voltage, it reads .566, or very close
to it. My readings were 570 on the Webtronics, and
..575 volts on the second meter set to volts. Incidentally,
the second meter in diode test reads .572 with the
decimal point, and puts a V on the screen to indicate
it is displaying voltage.

I won't get into it any deeper on the technical end of it as why ,
because it's obvious the major audience does not care about a
trivial matter in this case and understandably so.

Probably true. Considering the information value of the
reading, however, is not something that should be so
easily dismissed. On the one hand, we have information
that says, if you treat it as resistance, this diode has
566 ohms resistance. On the other hand, we have information
that says, if you treat it as voltage, this diode drops .566
volts. In both cases, the value is dependent on the current
in the circuit - an unknown. But .566 volt drop is much
closer to the actual drop that will appear when the diode is
in most circuits, than 566 ohms. For example, look at a 12
volt circuit where you need 100 mA through a diode. The math
says the damn thing would drop 56.6 volts if you use the 566
ohm figure, which is clearly impossible. A drop of .566 is a
lot closer to the truth.

Your disclaimer "you just got to be aware of the component
you're testing and not assume ohms" is right on target.

If it wasn't your intention to instigate, then I
apologize.

That wasn't my intention, but I don't see any reason or
need for you to apologize.

Ed