:On Tue, 06 Jan 2009 07:16:28 GMT, Ross Herbert
:
:>
:>:
:>:Sorry Ross, but that's all bullshit. If you connect the
:>
MM set to measure resistance of a circuit with a capacitor
:>:in parallel with a resistor and are mislead by what you see
:>
n the meter, that is *not* the meter's fault. It's yours.
:>:You seem to think that the meter should show you the value
:>
f the resistor, and that, if it doesn't, it's wrong. It's
:>:not wrong, you are, for not understanding what you are
:>:measuring and how it can affect the reading.
:>:
:>:Suppose there is a resistor in the circuit and you connect
:>:your DMM, set to measure resistance, across it, not knowing
:>:that the circuit is applying a voltage across the resistor.
:>
o you expect to get the correct value for the resistor
:>:displayed on the DMM? When it is not, do you blame the
:>
MM for being wrong?
:>:
:>:Ed
:>
:>What you are suggesting is that a resistance reading taken with a digital
meter
:>can not necessarily be relied upon. And where an unexpected reading does occur
:>the user should completely analyse the system undermeasurement in order to
:>determine why the expected resistance measurement is not being returned. That
is
:>just ludicrous.
:
:I do not know where you got this steaming pile from. I can see cases
:that will make almost all digital meters fail with inconsistent
:results, where analog meters of any topology would do fine. Even in
:that case it is the technician's issue to understand that the
:measurement is not valid. Moreover, if they get odd measurements that
:they cannot figure out they must report it to more skilled personnel.
:Lab technique for all domains 001.
:
:>
:>A technician using a digital meter to measure a specific resistance
combination
:>should have no reason to suspect that there should be a significant difference
:>in the result comapred to using an analog meter. The fact that there may be
some
:>parallel capacitance will have no effect on the analog meter reading (once the
:>capacitance is charged) and the analog meter reading will be accurate.
:>
:>A technician has every right to expect that a digital meter will also present
an
:>accurate reading without having to analyse whether or not any particular value
:>of capacitance might be present to upset the reading. The fact is that digital
:>multimeters, being sampling devices, can be upset by a certain combination of
:>resistance and capacitance, but is it wrong to say that where an unexpected
:>result occurs, the fault lies with the user because he has failed to analyse
:>what might be upsetting the meter? Of course not. The digital meter is just a
:>measuring tool the same as the analog meter and the technician should not have
:>to be conversant with the specifics of the design of the two items in order to
:>determine whether a reading is correct or not.
:>
:>The user has every right to expect the same result (within reason) for the
same
:>measurement whether using an analog or digital meter, "particularly for
:>resistance measurements". If the digital meter produces an unexpected result
and
:>the analog meter doesn't then where does the fault lie? The meter producing
the
:>unexpected result is obviously "wrong", despite any excuses, legitimate or
not,
:>which might be made to explain its erroneous measurement.
:
:You seem to know less than nothing about measurement. First, few
:analog ohmmeters are based on CC excitation.
I never said that analog ohm meters used CC.
:Nor are all digital ohmmeters.
True, but many do.
:It is still the technicians job to report anomalous
:readings; this requires sufficient skill to recognize the anomalous
:reading.
Example:
Tech trying to measure resistance across a network he has measured on identical
production units many times before with a particular DVM without error..
"Hey, boss, the resistance reading on this unit should be xyz ohms and the meter
is reading abc ohms. All units I have measured till now were ok. What gives?"
Of course, if you had been the boss you would have immediately analysed the
particular network where the symptom was noted, wouldn't you? And you would have
concluded that so far as you could see, this unit was identical to all previous
units which had already been measured without any symptoms of an erroneous
reading being noted.
"Buggered if I know, try another meter."
"I used my old AVO Model 8 and that gives the right result."
"Great, keep on using it then."
:Hell, i have built computer measurement systems that do this.
Bully for you - you hero...
