Your statement was ambiguous. In the study of logic the convention
is that an unqualified statement is assumed to have the universal
qualifier, ALL. Plain English is not formal logic, of course, and in
the absence of a qualifier the context must be used to try to guess
what the speaker intended. If you want to avoid being misunderstood,
use an explicit qualifier, such as SOME, or MOST, or A FEW.
I also, like John, took the absent qualifier to be ALL.
I think John may simply have wanted to point out that my claim did not
apply to ALL meters by pointing to the Triplett, which on a world
scale is rare outside the US. But I also don't think he wanted to make
a big issue of it. Yes, I am guilty of failing to include a qualifier
(the word "most"), but it shouldn't be a hanging offence and any
reasonable person would allow such an oversight unless it was of
extreme importance. I am sure that John did this adequately but I then
compounded the issue by failing to fully inspect and understand the
Triplett manual in my haste to respond.
How would you know what the "majority of users worldwide" use for
analog meters? What do they use in Russia? In China? In India?
And of those that are available to the "majority of users worldwide",
have you examined all of them to determine what polarity of voltage
is on the RED lead? Did you commission a survey?
Of course I didn't do a survey, but then if you want to get specific
then we also need to make some qualifications as to the time period we
are talking about. The era of high quality analog (non-electronic)
multimeters (at least outside the US) extended up to the 1970's or
thereabouts. Outside of the US there are still a few manufacturers of
quality analog multimeters but in the main this sector is left to the
low cost Asian manufacturers for the majority of product found. Good
quality analog multimeters used outside the USA up to the 70's would
have been dominated by AVO (now Megger), Philips, Yokogawa (then
branded YEW), perhaps Weston, and to a lesser degree Kyoritsu (KEW) to
name but a few. Undoubtedly there would have been good Russian, German
or Czech or other brand meters such as UnaOhm, but these would hardly
have been readily available to the west. While Russia has a
longstanding history of electronics manufacture, China hardly is in
the same category. And India would probably have adhered to its old
British ties and used AVO or Philips from Holland. Of course I don't
know that for a fact, I am just surmising based on historical ties.
I'll wager that most analog meters still being used by techs today
were obtained before 1970 or thereabouts - maybe a bit later due to
being readily available as second hand or disposal items. In commonly
found meters today the resistance ranges rely upon a simple series
connection of the internal battery, the meter and the resistance being
measured (plus internal limiting components). Triplett, Simpson, AVO,
Philips etc all used this method but probably due to local demand the
US manufacturers also included a polarity switch. As such, and where
no polarity switch is involved, it is inevitable that the BLACK lead
MUST output +ve on resistance ranges.
Furthermore, you seem to be assuming, although you haven't said it
explicitly, that only Triplett meters put +v on the RED lead. This
isn't so. I've seen other meters that do.
Even you will have to admit that the Triplett, depending upon which
position the AC/polarity switch is left in, can output either +ve OR
-ve on the RED lead when on resistance ranges. Admittedly for most
measurements it won't matter a jot which position it is in. Equally,
where the polarity is fixed - ie. no polarity switch is used, as for
meters made outside the US - there can never be any argument as to the
polarity when on resistance ranges. Again, this hardly matters a jot
either. The main use for the polarity switch is to enable polarity
reversal without changing the leads over when performing semiconductor
tests. On meters without this switch, as long as you remember the
simple rule, you may only have to swap the leads when determining
whether NPN or PNP semiconductors, but this is no big deal for most
people. Where you know the semiconductor polarity and pin-out you
always get it right.
With regard to other meters outputting +ve on the RED lead, Yes they
do, but these would be without exception modern production electronic
multimeters which use a moving coil meter as a display. Gossen
Metrawatt is one manufacturer of this type of instrument but the
majority of analog meters found today are low cost Chinese/Asian
instruments for the hobby market, and it is likely that the audience
here would be more likely to own one of these units rather than a
Triplett or a Simpson with a polarity switch.
My main aim of my original post was to alert users of analog meters
which are most likely to be in use today (even in the US), and which
don't have a polarity switch, that the polarity will not be as per the
lead colour when testing semiconductors. For these meters the rule
'when on OHMS, BLACK is +VE" will apply. For those owners who do have
a polarity switch, simply ignore my posts.
But, since your original statement *seemed* to be claiming that ALL
analog meters put +v on the black lead, one counterexample was all
that was needed to falsify it, and that was the Triplett example John
provided.
Outside of the USA Triplett meters would be extremely rare - and USA
users do not constitute the majority of people who use such
instruments worldwide despite what you might like to think. I
certainly wasn't about to do an extensive world survey to find which
meters employ a polarity reversal switch such as on the Triplett, but
since then I have now done a bit of research I can let you know the
only companies I have been able to find who do so are Triplett and
Simpson (USA).
As I previously mentioned AVO (Megger) still uses a reversal switch,
but this is a momentary action switch only and would only be used on
DC voltage or current measurements, not on resistance measurements or
for semiconductor testing.
The polarity switch has no effect on AC measurements.
I read p.15 first and the inference is that this switch does have an
effect on AC voltage measurements. But as you point out schematic
inspection indicates this is not so.
Once again, you have failed to carefully examine the pdf file John
provided as a reference. Look on page 11. The main range switch has
a set of AC voltage ranges as well as DC ranges.
Yes, I see that now. I was more concerned with reading the
operational instructions which appear to be in error.
I have a Triplett model 630-NS, a very similar meter with the same
polarity reversing switch. When the main range switch is set to an
AC range, the polarity switch has no effect on the direction of the
meter deflection (I just now tested this behavior on the actual
meter, and this is correct).
And, even though on page 15 of the pdf document it says to set the
polarity switch to the +AC position, I can see from the schematic
that it doesn't matter, because the rectifier comes *after* the
polarity switch.
This appears to be correct. The polarity switch simply transposes the
AC rectifier from one socket to the other but it remains in circuit
for AC voltage ranges irrespective of which position it is in. Perhaps
the manual author didn't see that and nobody picked it up or ammended
the manual.
My final word is if you own a multimeter without a polarity switch
then remember that when on OHMS, BLACK is +VE when testing
semiconductors. Otherwise ignore everything I have written. Phew....it
would have been so much simpler if I had said that from the start -
except that I had only heard of Triplett or Simpson, but never seen or
used one...