Hello

I have a Radio-Shack (Tandy) 22-175b digital multimeter.

Wen I use it to measure capacitors it do not do it's 0 before measuring,
even without any wires plug to it there is alway a .1 nf reading, there is
only two trimpots on the pc board, how can we reajust to have 0 ?

Any body would have the schematic diagram for that meter ?

Thank

Bye

Gaetan

Wen I use it to measure capacitors it do not do it's 0 before measuring,
even without any wires plug to it there is alway a .1 nf reading, there is
only two trimpots on the pc board, how can we reajust to have 0 ?

On the lower capacitance scales, it _shouldn't_ be zero. The test leads have
a certain amount of capacitance.

If you've removed the leads, a residual reading might be due to internal
capacitance, or the converter's LSB flopping.

In any case, if you're reading microfarads, 0.1nF (100pF) is hardly of any
concern.

Hello

Even without tests leads there is a .1 nf reading, I want to use it for
low value cap testing (5 to 50 pf), so it's kind of problematic.

Thank

Bye

Gaetan


"William Sommerwerck" )
writes:
Wen I use it to measure capacitors it do not do it's 0 before measuring,
even without any wires plug to it there is alway a .1 nf reading, there is
only two trimpots on the pc board, how can we reajust to have 0 ?

On the lower capacitance scales, it _shouldn't_ be zero. The test leads have
a certain amount of capacitance.

If you've removed the leads, a residual reading might be due to internal
capacitance, or the converter's LSB flopping.

In any case, if you're reading microfarads, 0.1nF (100pF) is hardly of any
concern.

Okay. Does it have a capacitance scale _intended_ to read 5 to 50 pF? I
doubt it.

Do you have a basic understanding of the terms "resolution" and "accuracy",
and how they relate to measurements?


"Gaetan Mailloux" wrote in message
...

Even without tests leads there is a .1 nf reading, I want to use it for
low value cap testing (5 to 50 pf), so it's kind of problematic.

Thank

Bye

Gaetan


"William Sommerwerck" )
writes:
Wen I use it to measure capacitors it do not do it's 0 before
measuring,
even without any wires plug to it there is alway a .1 nf reading, there
is
only two trimpots on the pc board, how can we reajust to have 0 ?

On the lower capacitance scales, it _shouldn't_ be zero. The test leads
have
a certain amount of capacitance.

If you've removed the leads, a residual reading might be due to internal
capacitance, or the converter's LSB flopping.

In any case, if you're reading microfarads, 0.1nF (100pF) is hardly of
any
concern.

In article , (Gaetan Mailloux) wrote:

Hello

Even without tests leads there is a .1 nf reading, I want to use it for
low value cap testing (5 to 50 pf), so it's kind of problematic.


My Fluke 189 is .065 without leads. Of course I can zero
it by pushing a button. The leads add 20-30 pf depending on the leads.
You can't use leads for that low of a value. You need to insert the caps
directly into a stable fixture. Make thing to plug into the meter
and have a clip or something.


greg



Thank

Bye

Gaetan


"William Sommerwerck" )
writes:
Wen I use it to measure capacitors it do not do it's 0 before measuring,
even without any wires plug to it there is alway a .1 nf reading, there is
only two trimpots on the pc board, how can we reajust to have 0 ?

On the lower capacitance scales, it _shouldn't_ be zero. The test leads have
a certain amount of capacitance.

If you've removed the leads, a residual reading might be due to internal
capacitance, or the converter's LSB flopping.

In any case, if you're reading microfarads, 0.1nF (100pF) is hardly of any
concern.

On 30 Nov 2007 18:28:02 GMT, (Gaetan
Mailloux) wrote:


Hello

Even without tests leads there is a .1 nf reading, I want to use it for
low value cap testing (5 to 50 pf), so it's kind of problematic.

Thank

Bye


1. Don't top post.

2. You cannot use a Radio Shack meter for any precision measurement.
Get a proper meter and you'll not have this problem.

On Nov 30, 10:28 am, (Gaetan Mailloux)
wrote:
Hello

Even without tests leads there is a .1 nf reading, I want to use it for
low value cap testing (5 to 50 pf), so it's kind of problematic.

Thank

Bye

Gaetan

"William Sommerwerck" )
writes:

Wen I use it to measure capacitors it do not do it's 0 before measuring,
even without any wires plug to it there is alway a .1 nf reading, there is
only two trimpots on the pc board, how can we reajust to have 0 ?

On the lower capacitance scales, it _shouldn't_ be zero. The test leads have
a certain amount of capacitance.

If you've removed the leads, a residual reading might be due to internal
capacitance, or the converter's LSB flopping.

In any case, if you're reading microfarads, 0.1nF (100pF) is hardly of any
concern.


Hi
For such low capacitances, there are is only one method that I've
found
that works well. Find or make a coil that when used with you caps to
be measure, will resonate in the 2 to 10 MHz range some place.
Use a few reference caps of known value and tolerance. These should
be close to the values being checked. Use a grid dip meter to measure
the frequency and back calculate the values of the caps.
Do remember that smaller values can be made by stacking ( or series
wiring ).
If you wind your own coil, try to leave at lease one or two wire
widths
between each turn. This will minimize the effects of internal
capacitance
of the coil. This is easiest done by winding wire two or three wires
and then removing the extras while a fixing glue is setting.
I do have a bridge that I get reasonable measurements for around 50
pf
but anything in the 5pf range is not reliable.

2. You cannot use a Radio Shack meter for any precision measurement.
Get a proper meter and you'll not have this problem.

This is not true. It has nothing to do with "precision".

Using a simple digital meter, you can't make accurate measurements of
capacitors whose values are comparable to the lead capacitance. You need
more-specialized test equipment.

On Fri, 30 Nov 2007 13:38:52 -0800, "William Sommerwerck"
wrote:

2. You cannot use a Radio Shack meter for any precision measurement.
Get a proper meter and you'll not have this problem.

This is not true.

Huh? No RS product is going to be noted for accuracy. Low price,
maybe, low quality probably, but not high accuracy.

It has nothing to do with "precision".

Using a simple digital meter, you can't make accurate measurements of
capacitors whose values are comparable to the lead capacitance. You need
more-specialized test equipment.


I'll agree with that... g The OP is lookng for the impossible.

On Fri, 30 Nov 2007 13:00:04 -0800 (PST), "
wrote:

On Nov 30, 10:28 am, (Gaetan Mailloux)
wrote:
Hello

Even without tests leads there is a .1 nf reading, I want to use it for
low value cap testing (5 to 50 pf), so it's kind of problematic.

Thank

Bye

Gaetan

"William Sommerwerck" )
writes:

Wen I use it to measure capacitors it do not do it's 0 before measuring,
even without any wires plug to it there is alway a .1 nf reading, there is
only two trimpots on the pc board, how can we reajust to have 0 ?

On the lower capacitance scales, it _shouldn't_ be zero. The test leads have
a certain amount of capacitance.

If you've removed the leads, a residual reading might be due to internal
capacitance, or the converter's LSB flopping.

In any case, if you're reading microfarads, 0.1nF (100pF) is hardly of any
concern.


Hi
For such low capacitances, there are is only one method that I've
found
that works well. Find or make a coil that when used with you caps to
be measure, will resonate in the 2 to 10 MHz range some place.
Use a few reference caps of known value and tolerance. These should
be close to the values being checked. Use a grid dip meter to measure
the frequency

A chain is only as strong as its weakest link... That grid dip meter
needs to be accurate, and you need to know the inductor's value
accurately as well.

and back calculate the values of the caps.
Do remember that smaller values can be made by stacking ( or series
wiring ).
If you wind your own coil, try to leave at lease one or two wire
widths
between each turn. This will minimize the effects of internal
capacitance
of the coil. This is easiest done by winding wire two or three wires
and then removing the extras while a fixing glue is setting.
I do have a bridge that I get reasonable measurements for around 50
pf
but anything in the 5pf range is not reliable.

On Nov 30, 3:16 pm, PeterD wrote:
On Fri, 30 Nov 2007 13:00:04 -0800 (PST), "



wrote:
On Nov 30, 10:28 am, (Gaetan Mailloux)
wrote:
Hello

Even without tests leads there is a .1 nf reading, I want to use it for
low value cap testing (5 to 50 pf), so it's kind of problematic.

Thank

Bye

Gaetan

"William Sommerwerck" )
writes:

Wen I use it to measure capacitors it do not do it's 0 before measuring,
even without any wires plug to it there is alway a .1 nf reading, there is
only two trimpots on the pc board, how can we reajust to have 0 ?

On the lower capacitance scales, it _shouldn't_ be zero. The test leads have
a certain amount of capacitance.

If you've removed the leads, a residual reading might be due to internal
capacitance, or the converter's LSB flopping.

In any case, if you're reading microfarads, 0.1nF (100pF) is hardly of any
concern.

Hi
For such low capacitances, there are is only one method that I've
found
that works well. Find or make a coil that when used with you caps to
be measure, will resonate in the 2 to 10 MHz range some place.
Use a few reference caps of known value and tolerance. These should
be close to the values being checked. Use a grid dip meter to measure
the frequency

A chain is only as strong as its weakest link... That grid dip meter
needs to be accurate, and you need to know the inductor's value
accurately as well.

As long as your reference parts are on the same scale of the grid dip
meter,
you should be able to ignore the coils actual value. One should be
able
to interpolate the grid dip scale. If more accuracy is needed, a
frequency
counter can be used. In which case, your readings would most likely be
as good as the reference parts.
Your not depending on the absolute accuracy of the meter or knowing
the
actual value of the coil, that is why you use reference parts.
Dwight



and back calculate the values of the caps.
Do remember that smaller values can be made by stacking ( or series
wiring ).
If you wind your own coil, try to leave at lease one or two wire
widths
between each turn. This will minimize the effects of internal
capacitance
of the coil. This is easiest done by winding wire two or three wires
and then removing the extras while a fixing glue is setting.
I do have a bridge that I get reasonable measurements for around 50
pf
but anything in the 5pf range is not reliable.

"William Sommerwerck" ) writes:
Okay. Does it have a capacitance scale _intended_ to read 5 to 50 pF? I
doubt it.


Hello

No it's an auto ranging.

Do you have a basic understanding of the terms "resolution" and "accuracy",
and how they relate to measurements?


Why ?

Thank

Gaetan


"Gaetan Mailloux" wrote in message
...

Even without tests leads there is a .1 nf reading, I want to use it for
low value cap testing (5 to 50 pf), so it's kind of problematic.

Thank

Bye

Gaetan


"William Sommerwerck" )
writes:
Wen I use it to measure capacitors it do not do it's 0 before
measuring,
even without any wires plug to it there is alway a .1 nf reading, there
is
only two trimpots on the pc board, how can we reajust to have 0 ?

On the lower capacitance scales, it _shouldn't_ be zero. The test leads
have
a certain amount of capacitance.

If you've removed the leads, a residual reading might be due to internal
capacitance, or the converter's LSB flopping.

In any case, if you're reading microfarads, 0.1nF (100pF) is hardly of
any
concern.

"Gaetan Mailloux" wrote in message
...
"William Sommerwerck" ) writes:


Okay. Does it have a capacitance scale _intended_
to read 5 to 50 pF?

No it's an auto ranging.

An auto-ranging meter still has ranges. What is the lowest capacitance
range?


Do you have a basic understanding of the terms "resolution" and
"accuracy",
and how they relate to measurements?

Why?

If you understood these things, you probably wouldn't be asking this
question.

On Fri, 30 Nov 2007 16:43:25 -0800 (PST), "
wrote:

On Nov 30, 3:16 pm, PeterD wrote:
On Fri, 30 Nov 2007 13:00:04 -0800 (PST), "



wrote:
On Nov 30, 10:28 am, (Gaetan Mailloux)
wrote:
Hello

Even without tests leads there is a .1 nf reading, I want to use it for
low value cap testing (5 to 50 pf), so it's kind of problematic.

Thank

Bye

Gaetan

"William Sommerwerck" )
writes:

Wen I use it to measure capacitors it do not do it's 0 before measuring,
even without any wires plug to it there is alway a .1 nf reading, there is
only two trimpots on the pc board, how can we reajust to have 0 ?

On the lower capacitance scales, it _shouldn't_ be zero. The test leads have
a certain amount of capacitance.

If you've removed the leads, a residual reading might be due to internal
capacitance, or the converter's LSB flopping.

In any case, if you're reading microfarads, 0.1nF (100pF) is hardly of any
concern.

Hi
For such low capacitances, there are is only one method that I've
found
that works well. Find or make a coil that when used with you caps to
be measure, will resonate in the 2 to 10 MHz range some place.
Use a few reference caps of known value and tolerance. These should
be close to the values being checked. Use a grid dip meter to measure
the frequency

A chain is only as strong as its weakest link... That grid dip meter
needs to be accurate, and you need to know the inductor's value
accurately as well.

As long as your reference parts are on the same scale of the grid dip
meter,
you should be able to ignore the coils actual value. One should be
able
to interpolate the grid dip scale. If more accuracy is needed, a
frequency
counter can be used. In which case, your readings would most likely be
as good as the reference parts.
Your not depending on the absolute accuracy of the meter or knowing
the
actual value of the coil, that is why you use reference parts.
Dwight


With that I am sure we are well beyond the capabilities of the OP!
bg

In article ,
Gaetan Mailloux wrote:
I have a Radio-Shack (Tandy) 22-175b digital multimeter.

Wen I use it to measure capacitors it do not do it's 0 before measuring,
even without any wires plug to it there is alway a .1 nf reading, there
is only two trimpots on the pc board, how can we reajust to have 0 ?

Any body would have the schematic diagram for that meter ?

What is the spec for measuring capacitance?

With a decent ;-) general purpose meter like say a Fluke 110 the maximum
resolution on capacitance is 1 nF, so a 0.1 nF error is neither here nor
there.

--
*Why is it that most nudists are people you don't want to see naked?*

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman " ) writes:
In article ,
Gaetan Mailloux wrote:
I have a Radio-Shack (Tandy) 22-175b digital multimeter.

Wen I use it to measure capacitors it do not do it's 0 before measuring,
even without any wires plug to it there is alway a .1 nf reading, there
is only two trimpots on the pc board, how can we reajust to have 0 ?

Any body would have the schematic diagram for that meter ?

What is the spec for measuring capacitance?

With a decent ;-) general purpose meter like say a Fluke 110 the maximum
resolution on capacitance is 1 nF, so a 0.1 nF error is neither here nor
there.

--
*Why is it that most nudists are people you don't want to see naked?*

Dave Plowman London SW
To e-mail, change noise into sound.


Hello

They say in the booklet a resulution of 1 pf, well it seem that it's not true.

I will look for another meter for real 1 pf resolution.

Thank everybody.

Bye

Gaetan

On 1 Dec 2007 22:23:44 GMT, (Gaetan
Mailloux) wrote:

In article ,
Gaetan Mailloux wrote:
I have a Radio-Shack (Tandy) 22-175b digital multimeter.

Wen I use it to measure capacitors it do not do it's 0 before measuring,
even without any wires plug to it there is alway a .1 nf reading, there
is only two trimpots on the pc board, how can we reajust to have 0 ?


Hello

They say in the booklet a resulution of 1 pf, well it seem that it's not true.

I will look for another meter for real 1 pf resolution.

Thank everybody.

Bye

Gaetan

That spec means that on the lowest range, the least significant digit
is pF. Even if the meter reads 0.1 nF with no capacitor connected,
you may still be able to measure capacitors down to 10 pF or so. Just
note the "no capacitor" reading, and subtract that from the reading
with a capacitor connected to get the actual value of the capacitor.


--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

This is normal for your meter. There will always be some residue
capacitance.

Take the reading with the leads opened up. Then when taking a reading
subtract the difference. The problem will be that even the physical position
of the leads will change the readings a little.

For capacitors in the value range that you want to read, you really need a
high end cap meter. Check out the higher end of the Fluke DVM's with the
capacitor option. With these meters, you will have a much higher resolving
and stability. But, when reading caps below 200 pF, you have to consider the
wires. It is best to use very short wires something less than 4 inches with
small clips in them.

For example, with a Fluke 89 series, they have excellent capacitance
performance. There are also dedicated capacitor meters which are the best.

You can also set up a cap tester using a signal generator and a scope. If
you want to do the math, you can work out a an RC network where you feed in
a frequency and amplitude calibrated signal. You then use a dual trace scope
and plot out the phase and amplitude differential. With some calculations
you can then have a very precise reading of the cap.

--

JANA
_____


"Gaetan Mailloux" wrote in message
...

Hello

Even without tests leads there is a .1 nf reading, I want to use it for
low value cap testing (5 to 50 pf), so it's kind of problematic.

Thank

Bye

Gaetan


"William Sommerwerck" )
writes:
Wen I use it to measure capacitors it do not do it's 0 before measuring,
even without any wires plug to it there is alway a .1 nf reading, there
is
only two trimpots on the pc board, how can we reajust to have 0 ?

On the lower capacitance scales, it _shouldn't_ be zero. The test leads
have
a certain amount of capacitance.

If you've removed the leads, a residual reading might be due to internal
capacitance, or the converter's LSB flopping.

In any case, if you're reading microfarads, 0.1nF (100pF) is hardly of any
concern.

"Gaetan Mailloux" wrote in message
...

They say in the booklet a resulution of 1 pF, well it seem
that it's not true. I will look for another meter for real 1 pF
resolution. Thank everybody.

What you don't understand is that resolution has nothing to do with
accuracy.

JANA wrote:

snip

You can also set up a cap tester using a signal generator and a scope. If
you want to do the math, you can work out a an RC network where you feed in
a frequency and amplitude calibrated signal. You then use a dual trace scope
and plot out the phase and amplitude differential. With some calculations
you can then have a very precise reading of the cap.


One can also make a capacitance bridge from easily obtained components; as
a kid I made one in a cookie tin that served me well even for values in the
10s of pf for many years. Now I rely on a Sprague Tel-Ohm-Mike for the
single digit pf measurements (a better capacitance bridge).

Regards,

Michael

In article , (Gaetan Mailloux) wrote:
"Dave Plowman " ) writes:
In article ,
Gaetan Mailloux wrote:
I have a Radio-Shack (Tandy) 22-175b digital multimeter.

Wen I use it to measure capacitors it do not do it's 0 before measuring,
even without any wires plug to it there is alway a .1 nf reading, there
is only two trimpots on the pc board, how can we reajust to have 0 ?

Any body would have the schematic diagram for that meter ?

What is the spec for measuring capacitance?

With a decent ;-) general purpose meter like say a Fluke 110 the maximum
resolution on capacitance is 1 nF, so a 0.1 nF error is neither here nor
there.

--
*Why is it that most nudists are people you don't want to see naked?*

Dave Plowman London SW
To e-mail, change noise into sound.


Hello

They say in the booklet a resulution of 1 pf, well it seem that it's not true.

I will look for another meter for real 1 pf resolution.

Thank everybody.

Bye

Gaetan

I guess you didn't get it. If you did like I say using a connector board
combination to get rid of the leads, measuring should be no problem.
As long as the .1 nF is constant. It seems your display goes to .001 nF
like my Fluke 189.


greg

Hello

I just found a Metex DMM with capacimeter foction and a zero buton, so I
can do a zero with any lead I would use or wen I use the socket. It's work
since I did measured a 15 pf capacitor with 5 % precision.

Thank all

Bye Gaetan

GregS )
writes:
In article , (Gaetan Mailloux) wrote:
"Dave Plowman " ) writes:
In article ,
Gaetan Mailloux wrote:
I have a Radio-Shack (Tandy) 22-175b digital multimeter.

Wen I use it to measure capacitors it do not do it's 0 before measuring,
even without any wires plug to it there is alway a .1 nf reading, there
is only two trimpots on the pc board, how can we reajust to have 0 ?

Any body would have the schematic diagram for that meter ?

What is the spec for measuring capacitance?

With a decent ;-) general purpose meter like say a Fluke 110 the maximum
resolution on capacitance is 1 nF, so a 0.1 nF error is neither here nor
there.

--
*Why is it that most nudists are people you don't want to see naked?*

Dave Plowman London SW
To e-mail, change noise into sound.


Hello

They say in the booklet a resulution of 1 pf, well it seem that it's not true.

I will look for another meter for real 1 pf resolution.

Thank everybody.

Bye

Gaetan

I guess you didn't get it. If you did like I say using a connector board
combination to get rid of the leads, measuring should be no problem.
As long as the .1 nF is constant. It seems your display goes to .001 nF
like my Fluke 189.


greg

In article , (Gaetan Mailloux) wrote:
Hello

I just found a Metex DMM with capacimeter foction and a zero buton, so I
can do a zero with any lead I would use or wen I use the socket. It's work
since I did measured a 15 pf capacitor with 5 % precision.


Another cheap meter I guess. I actually bought one from Jameco
over 15 years ago. It claimed very good accuracy. Mine has worked
well, and mine has a analog front panel adjustment screw and
there are no leads for the capacitor input. There is a front panel
socket area for different sized caps. I never had any problem with this
meter.

I just looked at it again since I have mostly been using the Fluke.

greg

On Nov 30, 10:35 am, (Gaetan Mailloux)
wrote:
Hello

I have a Radio-Shack (Tandy) 22-175b digital multimeter.

Wen I use it to measure capacitors it do not do it's 0 before measuring,
even without any wires plug to it there is alway a .1 nf reading, there is
only two trimpots on the pc board, how can we reajust to have 0 ?

Any body would have the schematic diagram for that meter ?

Thank

Bye

Gaetan

Greetings, 22-175b Press and hold untill it beeps the "Hold/Relative"
button. The meter will zero out testleads.

Also the old Dataprecision 938 cap meter has .1% basic accuracy + 1
digit + .5pF .1pF to 1,999uF also has ten turn 0 adj pot . Beats the
specs off the B+k 830!!
Dave