redbelly wrote:
> On Dec 21, 3:30 am, ehsjr <eh...@bellatlantic.net> wrote:
>
>>Jamie wrote:
>>
>>>ehsjr wrote:
>>
>>>>Jamie wrote:
>>
>>>>>bone wrote:
>>
>>>>>>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..
>>
>>>>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 ?
>>
>>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
>>
>>
>>
>>
>>>>> you just got to be aware of the component you're testing and
>>>>>not assume ohms.
>
>
> Ed,
>
> A simple test to decide whether the meter is reading resistance or
> voltage would be to run the diode test on a couple of resistors.
> Something in the ballpark of 1k, but use two different values in case
> one resistor gives identical numbers for voltage and resistance at
> your particular test current.
>
> Mark

I just posted much the same to John Popelish,
before reading your post. I tested with a 150 ohm
resistor - it read 220 on diode test and 149.2 on
the ohmmeter (200 ohms) setting. The same meter
reads 570 when testing a diode. Clearly, that
meter is not indicating a valid resistance when in
the diode testing position. Actually, a valid test
would have to include a number of different
resistances, all agreeing with the meter indication,
to warrant thinking that it was indicating resistance.

But aside from that, think how absurd it is to treat
a diode as having a 570 ohm equivalent resistance.
When inserting that diode into a circuit, you are not
inserting a ~570 ohm resistance - you're inserting a
voltage drop of at least ~.570 volts. (Forward
assumed for discussion.)

Ed

ehsjr wrote:

> But aside from that, think how absurd it is to treat
> a diode as having a 570 ohm equivalent resistance.
> When inserting that diode into a circuit, you are not
> inserting a ~570 ohm resistance - you're inserting a
> voltage drop of at least ~.570 volts. (Forward
> assumed for discussion.)

Unfortunately, meter manufacturers are not constrained by
what is absurd.

--
Regards,

John Popelish

John Popelish wrote:
> ehsjr wrote:
>
>> John, the test is flawed. When you add a meter in series to
>> measure current, the added meter changes the current supplied
>> by the diode testing meter, due to the internal resistance of
>> the added meter (relatively large on the low mA scales). That
>> automatically upsets the "calibration" such as it is, of the
>> reading on the diode testing meter.
>
>
> I have no argument with your analysis. My only defense is that adding
> the milliamp meter across the diode check meter leads or in series with
> the diode junction changed only the least significant digit of the diode
> check reading. I was not trying to check the accuracy so much as
> determine whether these two meters were displaying voltage or
> resistance. I think the voltage check proves that they are not
> displaying voltage, and the combination of voltage and current
> measurement confirms, pretty closely that these meters are displaying
> something close to resistance. Am I wrong about these conclusions?

I don't know if you are wrong. But what I have done with
3 meters so far indicates that the reading is displaying
voltage, not resistance. I took a number of resistors -
47, 75, 120, 150, 390, 500 and 1K through each in diode
test, with a second meter measuring voltage across each
resistor. In every case, the reading on the diode testing
meter agreed closely with the reading on the voltage
measuring meter. I regret now that I didn't record the
values, but the greatest difference as I recall was 10
mV. But treating the reading on the diode meter as
resistance, gave a much wider variation. For example,
my 500 ohm resistor read 600 ohms or 600 mV, depending
on what you want to call it, on the diode meter, and
600 mV on the voltage meter.

Ed

>
> My tests say nothing about what other meters display, and I am sure that
> there are many variations. I have to repeat this test for every meter I
> use and put a label on the back that reminds me what that meter displays
> on the diode check scale.
>
>> You may happen to get
>> a reading on the diode testing meter that agrees, but you
>> would need to make multiple readings across a range of
>> resistances that always agreed to make a proper conclusion.
>
>
> That would certainly increase my confidence.
>
>> Also, it sounds like you used only 2 meters. You would need
>> 3 to be sure your setup is measuring what you think it is.
>> From your description: "Then I measured a diode junction with
>> each meter while measuring the test current and voltage drop
>> with the other meter."
>> You can't measure both current and voltage simultaneously
>> with the other meter. When you remove it from a series
>> connection for measuring current, to a parallel connection
>> for measuring voltage, you change the current in the circuit.
>
>
> Agreed, if accuracy were important. Also measuring the resistance of
> each meter on its 20 mA scale would be a good idea, so I knew what
> resistance they added when measuring the current through a test resistor.
>
>> There are two ways you can test that come to mind that do
>> not upset that calibration:
>> 1) Diode test normally and measure the voltage
>> across the diode with a second meter.
>> 2) Diode test, except use a low value resistor,
>> like 150 ohms.
>>
>> I've performed test #1 a number of times in the
>> past, and the reading on the second meter (which
>> is voltage drop) has always been close to the
>> reading on the first.
>>
>> I just performed test #2. My 150 ohm resistor
>> read 220 on the Webtronics meter in diode test.
>> (I believe that is the same meter the op has.)
>> On the ohmmeter setting, it reads 149.2
>>
>> I then tested the same way with an Alfa 2360 meter.
>> It reads 149.8 ohms on the ohmmeter setting, and
>> .154 volts on the diode setting.
>>
>> Surprisingly, when I performed the test on the
>> cheap $3.00 meter from Harbor Freight, it read
>> 149 on both diode test and ohms.
>
>
> The two I posted results for are like your cheap one. It is clear that
> there is no standard for what is displayed on the diode test scale.
>
>> Ed
>
>
>

On Dec 21, 12:32 pm, ehsjr <eh...@bellatlantic.net> wrote:
> redbelly wrote:
> > On Dec 21, 3:30 am, ehsjr <eh...@bellatlantic.net> wrote:
>
> >>Jamie wrote:
>
> >>>ehsjr wrote:
>
> >>>>Jamie wrote:
>
> >>>>>bone wrote:
>
> >>>>>>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..
>
> >>>>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 ?
>
> >>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
>
> >>>>> you just got to be aware of the component you're testing and
> >>>>>not assume ohms.
>
> > Ed,
>
> > A simple test to decide whether the meter is reading resistance or
> > voltage would be to run the diode test on a couple of resistors.
> > Something in the ballpark of 1k, but use two different values in case
> > one resistor gives identical numbers for voltage and resistance at
> > your particular test current.
>
> > Mark
>
> I just posted much the same to John Popelish,
> before reading your post. I tested with a 150 ohm
> resistor - it read 220 on diode test and 149.2 on
> the ohmmeter (200 ohms) setting. The same meter
> reads 570 when testing a diode. Clearly, that
> meter is not indicating a valid resistance when in
> the diode testing position. Actually, a valid test
> would have to include a number of different
> resistances, all agreeing with the meter indication,
> to warrant thinking that it was indicating resistance.
>
> But aside from that, think how absurd it is to treat
> a diode as having a 570 ohm equivalent resistance.
> When inserting that diode into a circuit, you are not
> inserting a ~570 ohm resistance - you're inserting a
> voltage drop of at least ~.570 volts. (Forward
> assumed for discussion.)
>
> Ed


I agree that it is an absurd thing to do, but disagree that nobody
would ever make a meter that does it that way.

Actually, I wouldn't have entertained the possibility of a resistance
display if not for John's measurements. I read your objection to his
measurement, and will see if I can figure out how his meter resistance
of 10-13 ohms might affect his results.

Mark

p.s. for my two meters, the meaning of the diode-test numbers are
clear owing to the "V" that is displayed along with the numbers.

On Dec 20, 8:13 pm, John Popelish <jpopel...@rica.net> wrote:

> 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.
>
> --
> Regards,
>
> John Popelish

On Dec 21, 12:26 pm, John Popelish <jpopel...@rica.net> wrote:
> John Popelish wrote:
> > ...Also measuring the resistance of
> > each meter on its 20 mA scale would be a good idea, so I knew what
> > resistance they added when measuring the current through a test resistor.
>
> Resistance of 20 mA scale on each measured with the 200 ohm
> scale of the other meter is:
>
> GE2524 13.2 ohms
> DT-830B 10.1 ohms
>
> --
> Regards,
>
> John Popelish

John,

I've put your numbers for the GE2524 into a spreadsheet, and factored
in the effect of the DT-830B's resistance when used for current
measurements. Even so, your readings are consistent with a
"resistance" interpretation for the Diode Test mode.

Without going into too much detail:
You're actual "short circuit current" values will differ, since your
measurement was actually of the current at 10 (or 13) ohm load, and
not at zero-ohm (short circuit). But the s.c. current values change by
only 0.006 mA.
Likewise, the current-limiting resistance is a little lower, but just
1 or 2 ohms.

Since your meter resistance is only about 0.5% of the current-limiting
resistance (10 ohms vs. 2k ohms), it has a very small effect on the
measurements.
Still, the reading in diode-test mode, should change slightly when
switching the other meter from current-measurement to voltage-
measurement, reading about 1 or 2 mV higher for the voltage
measurement.

Mark

redbelly wrote:
> On Dec 20, 8:13 pm, John Popelish <jpopel...@rica.net> wrote:
>
>> 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.

> On Dec 21, 12:26 pm, John Popelish <jpopel...@rica.net> wrote:
>> John Popelish wrote:
>>> ...Also measuring the resistance of
>>> each meter on its 20 mA scale would be a good idea, so I knew what
>>> resistance they added when measuring the current through a test resistor.
>> Resistance of 20 mA scale on each measured with the 200 ohm
>> scale of the other meter is:
>>
>> GE2524 13.2 ohms
>> DT-830B 10.1 ohms

> John,
>
> I've put your numbers for the GE2524 into a spreadsheet, and factored
> in the effect of the DT-830B's resistance when used for current
> measurements. Even so, your readings are consistent with a
> "resistance" interpretation for the Diode Test mode.
>
> Without going into too much detail:
> You're actual "short circuit current" values will differ, since your
> measurement was actually of the current at 10 (or 13) ohm load, and
> not at zero-ohm (short circuit). But the s.c. current values change by
> only 0.006 mA.
> Likewise, the current-limiting resistance is a little lower, but just
> 1 or 2 ohms.
>
> Since your meter resistance is only about 0.5% of the current-limiting
> resistance (10 ohms vs. 2k ohms), it has a very small effect on the
> measurements.
> Still, the reading in diode-test mode, should change slightly when
> switching the other meter from current-measurement to voltage-
> measurement, reading about 1 or 2 mV higher for the voltage
> measurement.

Yes, I saw the least significant digit change a few counts
when I inserted the milliamp meter in series with the
junction, and a little larger change when I inserted it into
the short circuit measurement. But a little back of the
envelope math indicated to me that even with this small
perturbation, both my meters are indicating resistance
instead of millivolts. I would have found millivolts more
useful.

But now I see that if any meter does not display units, I
will have to test each to find out what it is displaying on
the diode test range. Knowing that is worth something.

I may also write the resistance of each current meter range
on the dial, also, since this is good information to have
when using those ranges.

--
Regards,

John Popelish

On Dec 23, 9:36 pm, John Popelish <jpopel...@rica.net> wrote:
> redbelly wrote:
> > On Dec 20, 8:13 pm, John Popelish <jpopel...@rica.net> wrote:
>
> >> 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.
> > On Dec 21, 12:26 pm, John Popelish <jpopel...@rica.net> wrote:
> >> John Popelish wrote:
> >>> ...Also measuring the resistance of
> >>> each meter on its 20 mA scale would be a good idea, so I knew what
> >>> resistance they added when measuring the current through a test resistor.
> >> Resistance of 20 mA scale on each measured with the 200 ohm
> >> scale of the other meter is:
>
> >> GE2524 13.2 ohms
> >> DT-830B 10.1 ohms
> > John,
>
> > I've put your numbers for the GE2524 into a spreadsheet, and factored
> > in the effect of the DT-830B's resistance when used for current
> > measurements. Even so, your readings are consistent with a
> > "resistance" interpretation for the Diode Test mode.
>
> > Without going into too much detail:
> > You're actual "short circuit current" values will differ, since your
> > measurement was actually of the current at 10 (or 13) ohm load, and
> > not at zero-ohm (short circuit). But the s.c. current values change by
> > only 0.006 mA.
> > Likewise, the current-limiting resistance is a little lower, but just
> > 1 or 2 ohms.
>
> > Since your meter resistance is only about 0.5% of the current-limiting
> > resistance (10 ohms vs. 2k ohms), it has a very small effect on the
> > measurements.
> > Still, the reading in diode-test mode, should change slightly when
> > switching the other meter from current-measurement to voltage-
> > measurement, reading about 1 or 2 mV higher for the voltage
> > measurement.
>
> Yes, I saw the least significant digit change a few counts
> when I inserted the milliamp meter in series with the
> junction, and a little larger change when I inserted it into
> the short circuit measurement. But a little back of the
> envelope math indicated to me that even with this small
> perturbation, both my meters are indicating resistance
> instead of millivolts. I would have found millivolts more
> useful.
>
> But now I see that if any meter does not display units, I
> will have to test each to find out what it is displaying on
> the diode test range. Knowing that is worth something.
>
> I may also write the resistance of each current meter range
> on the dial, also, since this is good information to have
> when using those ranges.
>
> --
> Regards,
>
> John Popelish

Definitely good to know those meter resistances. You can also measure
resistances for "voltage" mode, directly with the other meter since
you have 2 meters.

And if the resistance (in voltage mode) is out of range of the other
meter's resistance measurement, there's a neat trick for getting it
within 10%. With your second meter set to measure resistance, measure
a 1M resistor. Then measure the parallel combination of 1M and the
1st meter in "voltage" mode. Use some algebra to figure out what
resistance the 1st meter is, in order to change the resistance from
the 1st measurement value to the parallel-combination-value.

Mark