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Maker Pro

Checking a BC548B NPN Transistor?

R

Rich Grise

Jan 1, 1970
0
Ok dammit :) Now I have to go dig up a transistor because this is not how
I remember it.

The difference is in the meter. Digital meters put the plus on the red
lead for ohms - analog meters put the plus on the black lead, so that
the resulting current flows the same way through the meter movement.
Digital meters don't need to do that - they do the polarity conversion
in software. :)

Hope this helps!
Rich
 
M

Meat Plow

Jan 1, 1970
0
The difference is in the meter. Digital meters put the plus on the red
lead for ohms - analog meters put the plus on the black lead, so that
the resulting current flows the same way through the meter movement.
Digital meters don't need to do that - they do the polarity conversion
in software. :)

Hope this helps!
Rich

Fluke 77 here. Ok that answers it. I really didn't want to mix the OP up
especially after it took 5 posts to explain which click of the knob was
the diode test function. I've used my Fluke for maybe 24 years so that's
all I know. Before it was tubes and a Simpson 260.
 
R

Ross Herbert

Jan 1, 1970
0
Yes John, but that condition only applies when the polarity reversal
switch is in the AC- position.

Under normal operation, say when measuring DC voltage, you would
connect the RED lead to the more +ve end of a component. That is the
reason why ALL analog (moving coil) meters have a RED lead socket and
a BLACK lead socket - so that when you first connect to a DC voltage
source you would always place the RED lead (RED socket) on the more
positive point in a circuit so the meter pointer doesn't swing
backwards against the end stop and get damaged.

Now if the polarity reversal switch was left in the AC- position from
a previous use, then you may forget to set it to the normal AC+
position before connnecting the RED lead to a +ve source, and the
pointer would bounce hard against the end stop.

My good old AVO model 8 MkIII doesn't have a polarity reversal switch
and neither has any other analog meter I have used, or owned, had one.
The Brits figured that having another switch to check before
connecting the leads was more trouble than it was worth.

When measuring diode junctions with the Triplett you would normally
start off with the polarity switch in the AC+ position and this would
mean that the RED lead was -ve wrt to the BLACK lead and vice versa.
 
R

Ross Herbert

Jan 1, 1970
0
Yes John, but that condition only applies when the polarity reversal
switch is in the AC- position.

Under normal operation, say when measuring DC voltage, you would
connect the RED lead to the more +ve end of a component. That is the
reason why ALL analog (moving coil) meters have a RED lead socket and
a BLACK lead socket - so that when you first connect to a DC voltage
source you would always place the RED lead (RED socket) on the more
positive point in a circuit so the meter pointer doesn't swing
backwards against the end stop and get damaged.

Now if the polarity reversal switch was left in the AC- position from
a previous use, then you may forget to set it to the normal AC+
position before connnecting the RED lead to a +ve source, and the
pointer would bounce hard against the end stop.

My good old AVO model 8 MkIII doesn't have a polarity reversal switch
and neither has any other analog meter I have used, or owned, had one.
The Brits figured that having another switch to check before
connecting the leads was more trouble than it was worth.

When measuring diode junctions with the Triplett you would normally
start off with the polarity switch in the AC+ position and this would
mean that the RED lead was -ve wrt to the BLACK lead and vice versa.

That is, when set to the resistance scales...
 
T

The Phantom

Jan 1, 1970
0
Yes John, but that condition only applies when the polarity reversal
switch is in the AC- position.

Under normal operation, say when measuring DC voltage, you would
connect the RED lead to the more +ve end of a component. That is the
reason why ALL analog (moving coil) meters have a RED lead socket and
a BLACK lead socket - so that when you first connect to a DC voltage
source you would always place the RED lead (RED socket) on the more
positive point in a circuit so the meter pointer doesn't swing
backwards against the end stop and get damaged.

Now if the polarity reversal switch was left in the AC- position from
a previous use, then you may forget to set it to the normal AC+
position before connnecting the RED lead to a +ve source, and the
pointer would bounce hard against the end stop.

My good old AVO model 8 MkIII doesn't have a polarity reversal switch
and neither has any other analog meter I have used, or owned, had one.
The Brits figured that having another switch to check before
connecting the leads was more trouble than it was worth.

When measuring diode junctions with the Triplett you would normally
start off with the polarity switch in the AC+ position and this would
mean that the RED lead was -ve wrt to the BLACK lead and vice versa.

Apparently you didn't carefully read page 21, paragraph 2, of the pdf that
John referenced. It says, and I quote:

"When the polarity switch is in the +AC position, the VOM + jack is
positive with respect to the COM - jack."

Assuming the RED lead is plugged into the VOM + jack in the usual manner,
this means that the RED lead will need to be connected to the base of an
NPN transistor to bias the transistor on, when the polarity switch is in
the +AC position. This is exactly the reverse of what you claimed would be
the proper connection for an analog meter.

You and Rich Grise apparently believe that ALL analog meters put out -V on
the RED lead, but this hasn't been my experience (nor John's, it would
seem) over several decades of using analog meters.

As John said, it depends on the meter, and he has provided a counterexample
to your claim.
 
T

The Phantom

Jan 1, 1970
0
Fluke 77 here. Ok that answers it. I really didn't want to mix the OP up
especially after it took 5 posts to explain which click of the knob was
the diode test function. I've used my Fluke for maybe 24 years so that's
all I know. Before it was tubes and a Simpson 260.

Does this mean that you agree with Ross that:

"...it will bias each diode ON when the RED lead is on
either of the other 2 terminals (assuming the transistor is ok)."
^^^^^^

and NOT:

"The only diode check type conduction in a bipolar transistor should be
between the base and emitter."

as you said in two other posts?
 
M

Meat Plow

Jan 1, 1970
0
Does this mean that you agree with Ross that:

"...it will bias each diode ON when the RED lead is on
either of the other 2 terminals (assuming the transistor is ok)."
^^^^^^

and NOT:

"The only diode check type conduction in a bipolar transistor should be
between the base and emitter."

as you said in two other posts?

Go **** yourself, how's that?



--
#1 Offishul Ruiner of Usenet, March 2007
#1 Usenet Asshole, March 2007
#1 Bartlo Pset, March 13-24 2007
#10 Most hated Usenetizen of all time
#8 AUK Hate Machine Cog
Pierre Salinger Memorial Hook, Line & Sinker, June 2004
COOSN-266-06-25794
 
J

John Fields

Jan 1, 1970
0
Yes John, but that condition only applies when the polarity reversal
switch is in the AC- position.

---
The switch is labeled AC+ -, where the AC+ position is used for AC
measurements and measurements where that lead is connected to the
most positive of two voltages. The '-' position is used for DC
measurements with the meter polarity reversed.

Your:

"Not if he is using his analogue (moving coil) meter. In this case
the BLACK lead will be putting out +ve and when placed on the base
of the NPN transistor it will bias each diode ON when the RED lead
is on either of the other 2 terminals (assuming the transistor is
ok)."

seems to indicate (since you didn't state otherwise) that that was
true for _all_ multimeters all the time, and such is not the case.
---
Under normal operation, say when measuring DC voltage, you would
connect the RED lead to the more +ve end of a component. That is the
reason why ALL analog (moving coil) meters have a RED lead socket and
a BLACK lead socket - so that when you first connect to a DC voltage
source you would always place the RED lead (RED socket) on the more
positive point in a circuit so the meter pointer doesn't swing
backwards against the end stop and get damaged.

---
With the range switch set properly and the leads connected to a DC
source there is _no_ way that the meter will be damaged if the leads
are connected backwards. Do you have any evidence to the contrary?
---
Now if the polarity reversal switch was left in the AC- position from
a previous use, then you may forget to set it to the normal AC+
position before connnecting the RED lead to a +ve source, and the
pointer would bounce hard against the end stop.

---
No. The meter needle will be at zero, already very close to the end
stop, and won't have much time to accelerate to a dangerous velocity
before it hits the end stop. Moreover, if the range switch is set
correctly there is no danger of damage even if the leads are
connected backwards.
---
My good old AVO model 8 MkIII doesn't have a polarity reversal switch
and neither has any other analog meter I have used, or owned, had one.

---
Too bad. My good old Simpson 260 does, and so do/did most Triplett
VOMs, including one I used at work in the early 60's. The model
number escapes me.
---
The Brits figured that having another switch to check before
connecting the leads was more trouble than it was worth.

---
Yes, I can understand that. The manufacturers didn't want to
overload you mentally, and if they managed to save a few pennies in
the bargain, so much the better. ;)

Too bad. As a consequence, you never had the convenience of just
being able to use a switch to reverse polarity, you had to reverse
the leads instead.
---
When measuring diode junctions with the Triplett you would normally
start off with the polarity switch in the AC+ position and this would
mean that the RED lead was -ve wrt to the BLACK lead and vice versa.

---
Seems you need a polarity switch yourself since you got it exactly
backwards! ;)

With the polarity switch in the AC+ position and the red lead
connected to the + lack, the voltage on the red lead would be more
positive than the voltage on the lead connected to the - jack. Go
back and read the manual again or check the schematic on pp. 30-31.
 
T

The Phantom

Jan 1, 1970
0
Go **** yourself, how's that?

You've been giving the OP wrong information because of an incorrect
understanding of transistors you've had for what, more than 24 years?

I point out your error, without using foul language, saving you from
embarrassing yourself in public in the future, and this is how you thank
me?

Sheeesh!!
 
M

Marra

Jan 1, 1970
0
Nip down to Maplin and get a meter with a transistor tester.
While a normal meter can test go or no go it cant test HFE problems.

---
Sure it can. (View in Courier):

1.

+V>-+-----+-------+
| | |
[1M]<--+ [AMMETER]
| |
| C
+-----------B
E
|
GND>--------------+

Starting with the pot cranked to maximum resistance, rotate it so
that some convenient current (Ic) is displayed by the ammeter then,
without disturbing the setting of the pot, disconnect the meter from
the collector, place it in series with the base, and connect the
collector to +V:

+V>-+-----+-------+
| | |
[1M]<--+ |
| |
| C
+-[AMMETER]-B
E
|
GND>--------------+

The meter will now be indicating the base current (Ib) and all
that's left to do is to calculate Hfe:

Ic
Hfe = ----
Ib

and, from the transistor's data sheet, to determine whether the
transistor is in spec or not.

Its much easier to plug into meter !
 
J

JimW52

Jan 1, 1970
0
Nip down to Maplin and get a meter with a transistor tester.

While a normal meter can test go or no go it cant test HFE problems.

---
Sure it can. (View in Courier):


1.

+V>-+-----+-------+
| | |
[1M]<--+ [AMMETER]
| |
| C
+-----------B
E
|
GND>--------------+


Starting with the pot cranked to maximum resistance, rotate it so that
some convenient current (Ic) is displayed by the ammeter then, without
disturbing the setting of the pot, disconnect the meter from the
collector, place it in series with the base, and connect the collector to
+V:


+V>-+-----+-------+
| | |
[1M]<--+ |
| |
| C
+-[AMMETER]-B
E
|
GND>--------------+


The meter will now be indicating the base current (Ib) and all that's left
to do is to calculate Hfe:


Ic
Hfe = ----
Ib


and, from the transistor's data sheet, to determine whether the transistor
is in spec or not.

Hmmm... Next time I need to make some smoke I might just build this
circuit.

Jim
 
R

Ross Herbert

Jan 1, 1970
0
---
The switch is labeled AC+ -, where the AC+ position is used for AC
measurements and measurements where that lead is connected to the
most positive of two voltages. The '-' position is used for DC
measurements with the meter polarity reversed.

Your:

"Not if he is using his analogue (moving coil) meter. In this case
the BLACK lead will be putting out +ve and when placed on the base
of the NPN transistor it will bias each diode ON when the RED lead
is on either of the other 2 terminals (assuming the transistor is
ok)."

seems to indicate (since you didn't state otherwise) that that was
true for _all_ multimeters all the time, and such is not the case.
---


---
With the range switch set properly and the leads connected to a DC
source there is _no_ way that the meter will be damaged if the leads
are connected backwards. Do you have any evidence to the contrary?
---


---
No. The meter needle will be at zero, already very close to the end
stop, and won't have much time to accelerate to a dangerous velocity
before it hits the end stop. Moreover, if the range switch is set
correctly there is no danger of damage even if the leads are
connected backwards.
---
one.

---
Too bad. My good old Simpson 260 does, and so do/did most Triplett
VOMs, including one I used at work in the early 60's. The model
number escapes me.
---


---
Yes, I can understand that. The manufacturers didn't want to
overload you mentally, and if they managed to save a few pennies in
the bargain, so much the better. ;)

Too bad. As a consequence, you never had the convenience of just
being able to use a switch to reverse polarity, you had to reverse
the leads instead.
---


---
Seems you need a polarity switch yourself since you got it exactly
backwards! ;)

With the polarity switch in the AC+ position and the red lead
connected to the + lack, the voltage on the red lead would be more
positive than the voltage on the lead connected to the - jack. Go
back and read the manual again or check the schematic on pp. 30-31.


Firstly, let me say that I did not intend to imply that the assertions
made in my original post applied to ALL analog multimeters, only to
those available to the majority of users worldwide - where Triplett
meters are not commonly found.

I concede... I was wrong in my statements regarding the polarity of
the red and black leads when the polarity switch is in the AC+ and AC-
positions on the Triplett - I misinterpreted the manual. I would also
remind that the Triplett example was only raised in order to
contradict my original post, thus attempting to attribute my
statements to mean ALL analog meters.

Regarding the Triplett - it is BECAUSE there is a polarity switch the
polarity of the RED and BLACK sockets can be arranged to output either
+ve OR -ve on OHMS ranges, depending upon the position of the polarity
switch. In my previous reference to my AVO model 8 Mk III I forgot
that there is a momentary press-button to reverse the polarity of the
meter movement when necessary, but it is not a switch which can be
left in any arbitrary position (as it can on the Triplett) - I doubt I
have ever had cause to use it. The press button remains on the latest
AVO Model 8 Mk 7
http://www.megger.com/common/documents/MOD8_MK7_DS_en_V10.pdf

Triplett takes the cheap option of providing a separate switch to
allow reading AC voltages using a common set of voltage range
positions on the main range switch, and the AC switch also performs
the polarity switching function. To my mind this switch adds an
unneccessary step to the operation of the meter. Most manufacturers
avoided such a switch by having the AC ranges included on the main
range switch, and rather than being penny-pinching, it would be more
expensive due to the requirement for a more complex switch.

With regard to overloading my brain...

It is no problem to remember "when on OHMS, BLACK IS +VE", and I don't
think remembering this simple rule has ever overloaded the majority of
the brains of analog meter users in the rest of the world where
Triplett meters are not seen, anymore than it would for Triplett users
to check which position the AC/polarity switch is in before using the
meter. And, I also haven't found it particularly taxing to change the
leads over when necessary (which is rare if you know what you are
doing - but accidents do happen).

Other than that I can concur that the Triplett would be an excellent
analog meter to have on the bench - if only we had been able to get
them in the rest of the world.
 
J

John Fields

Jan 1, 1970
0
Nip down to Maplin and get a meter with a transistor tester.
While a normal meter can test go or no go it cant test HFE problems.

---
Sure it can. (View in Courier):

1.

+V>-+-----+-------+
| | |
[1M]<--+ [AMMETER]
| |
| C
+-----------B
E
|
GND>--------------+

Starting with the pot cranked to maximum resistance, rotate it so
that some convenient current (Ic) is displayed by the ammeter then,
without disturbing the setting of the pot, disconnect the meter from
the collector, place it in series with the base, and connect the
collector to +V:

+V>-+-----+-------+
| | |
[1M]<--+ |
| |
| C
+-[AMMETER]-B
E
|
GND>--------------+

The meter will now be indicating the base current (Ib) and all
that's left to do is to calculate Hfe:

Ic
Hfe = ----
Ib

and, from the transistor's data sheet, to determine whether the
transistor is in spec or not.

Its much easier to plug into meter !

---
Not if you don't have a meter with a built-in transistor tester, but
that's not the point.

The point is that you claimed, and I quote:

"While a normal meter can test go or no go it cant test HFE
problems."

which isn't true, as demonstrated by the example I gave, above.

Also, not immediately obvious is that by using a multimeter's
built-in beta tester, beta can be tested at only one point on the
Ic/Ib curve. Using the method I outlined will allow beta to be
determined for base currents from:

(+V) - (Vbe)
Ib = --------------
1MR

to some high limit determined by the setting of the 1 megohm pot.
 
J

John Fields

Jan 1, 1970
0
Nip down to Maplin and get a meter with a transistor tester.

While a normal meter can test go or no go it cant test HFE problems.

---
Sure it can. (View in Courier):


1.

+V>-+-----+-------+
| | |
[1M]<--+ [AMMETER]
| |
| C
+-----------B
E
|
GND>--------------+


Starting with the pot cranked to maximum resistance, rotate it so that
some convenient current (Ic) is displayed by the ammeter then, without
disturbing the setting of the pot, disconnect the meter from the
collector, place it in series with the base, and connect the collector to
+V:


+V>-+-----+-------+
| | |
[1M]<--+ |
| |
| C
+-[AMMETER]-B
E
|
GND>--------------+


The meter will now be indicating the base current (Ib) and all that's left
to do is to calculate Hfe:


Ic
Hfe = ----
Ib


and, from the transistor's data sheet, to determine whether the transistor
is in spec or not.

Hmmm... Next time I need to make some smoke I might just build this
circuit.
 
T

The Phantom

Jan 1, 1970
0
Firstly, let me say that I did not intend to imply that the assertions
made in my original post applied to ALL analog multimeters, only to
those available to the majority of users worldwide - where Triplett
meters are not commonly found.

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.

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?

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.

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.
I concede... I was wrong in my statements regarding the polarity of
the red and black leads when the polarity switch is in the AC+ and AC-
positions on the Triplett - I misinterpreted the manual. I would also
remind that the Triplett example was only raised in order to
contradict my original post, thus attempting to attribute my
statements to mean ALL analog meters.

Regarding the Triplett - it is BECAUSE there is a polarity switch the
polarity of the RED and BLACK sockets can be arranged to output either
+ve OR -ve on OHMS ranges, depending upon the position of the polarity
switch. In my previous reference to my AVO model 8 Mk III I forgot
that there is a momentary press-button to reverse the polarity of the
meter movement when necessary, but it is not a switch which can be
left in any arbitrary position (as it can on the Triplett) - I doubt I
have ever had cause to use it. The press button remains on the latest
AVO Model 8 Mk 7
http://www.megger.com/common/documents/MOD8_MK7_DS_en_V10.pdf

Triplett takes the cheap option of providing a separate switch to
allow reading AC voltages using a common set of voltage range
positions on the main range switch,

The polarity switch has no effect on AC measurements.
and the AC switch also performs
the polarity switching function. To my mind this switch adds an
unneccessary step to the operation of the meter. Most manufacturers
avoided such a switch by having the AC ranges included on the main
range switch, and rather than being penny-pinching, it would be more
expensive due to the requirement for a more complex switch.

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.

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.
 
J

John Fields

Jan 1, 1970
0
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.

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?

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.

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.


The polarity switch has no effect on AC measurements.


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.

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.

---
<JF> The polarity switch is there precisely so that you don't have
to switch leads over. A typical scenario might be where you need to
measure voltages on, say, an audio amplifier with positive and
negative rails and various positive and negative voltages around the
amp. Normally, one would connect the black lead to 0V, (ground)
then use the other lead to probe for the various voltages, knowing
that an upscale reading would indicate a positive voltage and a
downscale reading, negative. In order to get the negative voltage
to swing upscale, one would use the polarity reversing switch in
order to keep from having to swap the probes back and forth which is
much more convenient, especially if ground is chassis and you're
using an alligator clip to connect to it.

The momentary polarity reversal switch sounds kind of inconvenient
(and dangerous) to me in that to use it you've either got to press
it when you get a downscale reading, which means you've got to go
looking for it and press it while keeping the probe on the point of
interest and getting the reading, or press it first and then go
looking for the point of interest. Either way requires doing three
things at once, which can be kind of confusing.
---

<JF> I don't believe Triplett or Simpson products were unavailable
outside of the US back then, (whenever that was) just not as easily
(or possibly as cheaply) available as your own domestic stuff was.

BTW, on your meter, when you press the polarity reversal switch on
the resistance ranges do the probe polarities reverse?
 
R

Ross Herbert

Jan 1, 1970
0
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...
 
L

Lord Garth

Jan 1, 1970
0
Ross Herbert said:
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...

Not true with Fluke meters...at least not mine!
 
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