Tonghui TH2821A LCR Meter

[John S]

Foreigners are not allowed to own land in the Philippines, let alone
beachfront property, which is probably just as well. Long term leases
(eg. 50 years) are possible.


Best regards,
Spehro Pefhany

I'm 70. I don't need to own anything anywhere. I'm renting life (and
beer) as it is.

 

[John S]

Here's something that may interest some folks here. I just got my new
Tonghui TH2821A LCR Meter, and I'm starting to become quite impressed.

Hey, Mike -

Mine came in yesterday. Since the wall wart is 220V, it is useless to me
so I cut the chord and used a lab power supply to charge it. This got
interesting.

With the meter off, the current was only about 5mA. I turned the meter
on and the current went to about 140mA. After a period of time which I
did not measure, the current dropped back to about 50mA and the battery
symbol indicated full charge.

This makes me wonder if fast charge takes place only when the meter is
on and it just trickle charges with the meter off. Have you noticed a
long charging time with the meter off?

Cheers,
John S

 

[Jon Kirwan]

Mine came in yesterday. Since the wall wart is 220V, it is useless to me
so I cut the chord and used a lab power supply to charge it. This got
interesting.

Ordered mine _after_ you and got mine a week ago, partly
because I asked them to rush it and they responded by saying
they'd heard me and would work quickly. I mentioned that I
was US 60Hz 120V, failing to find anything on the topic on
the web page, and received email saying that they'd look into
it and figure something out.

When it arrived, they had included another wall-wart (about
six times heavier and much larger than the one that comes in
the package) without a cord but instead an interesting power
socket that the "regular" 220V wall wart could plug into. No
charge. Just had to ask.

Manual is in chinese, had to download an English version.

With the meter off, the current was only about 5mA. I turned the meter
on and the current went to about 140mA. After a period of time which I
did not measure, the current dropped back to about 50mA and the battery
symbol indicated full charge.

This makes me wonder if fast charge takes place only when the meter is
on and it just trickle charges with the meter off. Have you noticed a
long charging time with the meter off?

I noticed a long charge time when off, but a significantly
shorter charge time when on. I hadn't measured the current,
though, probably because I didn't need to hack my power
supply into bits before using it.

System came up in 'delta' mode, whihc caused me confusion
despite seeing the symbol there telling me what probably was
going on. I knew what was probably causing the odd readings
but until I got the English version manual, I wasn't entirely
sure what else to correctly do to fix it. While playing with
that before reading the manual, I did uncover how to
auto-calibrate it in 'short' and 'open' mode, though.

So far, it's been very nice and I've been impressed with what
was included at the price -- including the extra, weighty 110
to 220 wall wart. But I've yet to put it to serious use. I
have used it to help quickly figure out the core material
types of some randomly collected toroids I have in a drawer,
using some windings and calcs. Time will tell, but happy for
now.

Jon

 

[John S]

Ordered mine _after_ you and got mine a week ago, partly
because I asked them to rush it and they responded by saying
they'd heard me and would work quickly. I mentioned that I
was US 60Hz 120V, failing to find anything on the topic on
the web page, and received email saying that they'd look into
it and figure something out.

When it arrived, they had included another wall-wart (about
six times heavier and much larger than the one that comes in
the package) without a cord but instead an interesting power
socket that the "regular" 220V wall wart could plug into. No
charge. Just had to ask.

Manual is in chinese, had to download an English version.


I noticed a long charge time when off, but a significantly
shorter charge time when on. I hadn't measured the current,
though, probably because I didn't need to hack my power
supply into bits before using it.

System came up in 'delta' mode, whihc caused me confusion
despite seeing the symbol there telling me what probably was
going on. I knew what was probably causing the odd readings
but until I got the English version manual, I wasn't entirely
sure what else to correctly do to fix it. While playing with
that before reading the manual, I did uncover how to
auto-calibrate it in 'short' and 'open' mode, though.

So far, it's been very nice and I've been impressed with what
was included at the price -- including the extra, weighty 110
to 220 wall wart. But I've yet to put it to serious use. I
have used it to help quickly figure out the core material
types of some randomly collected toroids I have in a drawer,
using some windings and calcs. Time will tell, but happy for
now.

Jon

Thanks for your input, Jon.

I'm pretty sure it will charge faster (based on my amperage readings)
when power is applied.

I've been subjecting it to tests as well as I can muster. I have a
Boonton 71K capacitance meter that I used as a "standard". I have a
..01uF, 1% cap Wima cap that I bought because it was the lowest D I could
find. The Boonton agrees with the 2821A as best as my eyes will make out
considering that the Boonton has an analog meter.

I have a Xicon 18 ohm, 25 watt resistor I measured. In inductance mode,
it showed 2.95uH and a Q of .0105 at 10kHz. That calculates to give a
series R of about 17.65 ohms. So I then measured the resistance with the
2821 (in the resistance mode) to be 17.73 ohms. Well, then I fired up my
HP3456A and measured the resistance at 17.75 ohms.

I am impressed. So far, it has been correct for every test I can give it
considering my limited standards situation. Oh, wait! I have some .1%
resistors I checked with it. I didn't record the readings, but they were
well withing the .1%.

I don't know how they do it.

John S

 

[Mike]

Thanks for your input, Jon.

I'm pretty sure it will charge faster (based on my amperage readings)
when power is applied.

I've been subjecting it to tests as well as I can muster. I have a
Boonton 71K capacitance meter that I used as a "standard". I have a
.01uF, 1% cap Wima cap that I bought because it was the lowest D I
could find. The Boonton agrees with the 2821A as best as my eyes will
make out considering that the Boonton has an analog meter.

I have a Xicon 18 ohm, 25 watt resistor I measured. In inductance
mode, it showed 2.95uH and a Q of .0105 at 10kHz. That calculates to
give a series R of about 17.65 ohms. So I then measured the resistance
with the 2821 (in the resistance mode) to be 17.73 ohms. Well, then I
fired up my HP3456A and measured the resistance at 17.75 ohms.

I am impressed. So far, it has been correct for every test I can give
it considering my limited standards situation. Oh, wait! I have some
.1% resistors I checked with it. I didn't record the readings, but
they were well withing the .1%.

I don't know how they do it.

John S

Jon & John,

Sorry for the delay. Have been quite ill.

It looks like they sent Jon a 110V to 220V step up transformer. That
would explain the weight. After complaining about not being able to run
on 110V, they sent me a small, lightweight 110V switching power supply
that looked similar to the original 220V unit. I'm surprised they did not
send you both the same transformer instead of the 220V version.

I did the initial charging with the instrument turned off. After about 4
hours, it indicated full charge. But I had been playing with it trying to
figure out how it worked until I finally decided there was an internal
battery that needed charging. So it got at least a partial charge while I
was fooling around.

I found the instrument may do strange things until it is fully charged.
This makes sense if you consider the uP may not be getting the correct
voltage during the initial charging cycle. After it was fully charged, it
stopped doing silly things and started giving good results.

Thanks to John for the calibration info. I was also quite impressed with
the performance. It is quite outstanding, especially for the price. I
think we will get many years of useful work from these units. But I have
to caution everyone to make absolutely certain any capacitor is fully
discharged before measuring it. I lost a good LCR meter by accidentally
losing track of which capacitors were discharged and which were still
fully charged. It made a dull thud and stopped working.

So we can't depend on ourself to protect the unit. There has to be
dedicated protection circuity.

I'm thinking of making a small adapter with a discharge resistor and a
power bridge rectifier across the input terminals. I found the instrument
did not respond to having a single diode across the capacitor, so a
bridge should have no effect. I'll add a SPDT switch so the dump resistor
is normally in the circuit, and have the bridge rectifier across the
terminals to the instrument as insurance.

Thanks,

Mike

 

[John S]

Jon& John,

Sorry for the delay. Have been quite ill.

It looks like they sent Jon a 110V to 220V step up transformer. That
would explain the weight. After complaining about not being able to run
on 110V, they sent me a small, lightweight 110V switching power supply
that looked similar to the original 220V unit. I'm surprised they did not
send you both the same transformer instead of the 220V version.

I did the initial charging with the instrument turned off. After about 4
hours, it indicated full charge. But I had been playing with it trying to
figure out how it worked until I finally decided there was an internal
battery that needed charging. So it got at least a partial charge while I
was fooling around.

I found the instrument may do strange things until it is fully charged.
This makes sense if you consider the uP may not be getting the correct
voltage during the initial charging cycle. After it was fully charged, it
stopped doing silly things and started giving good results.

Thanks to John for the calibration info. I was also quite impressed with
the performance. It is quite outstanding, especially for the price. I
think we will get many years of useful work from these units. But I have
to caution everyone to make absolutely certain any capacitor is fully
discharged before measuring it. I lost a good LCR meter by accidentally
losing track of which capacitors were discharged and which were still
fully charged. It made a dull thud and stopped working.

So we can't depend on ourself to protect the unit. There has to be
dedicated protection circuity.

I'm thinking of making a small adapter with a discharge resistor and a
power bridge rectifier across the input terminals. I found the instrument
did not respond to having a single diode across the capacitor, so a
bridge should have no effect. I'll add a SPDT switch so the dump resistor
is normally in the circuit, and have the bridge rectifier across the
terminals to the instrument as insurance.

Thanks,

Mike

Good to hear from you, Mike. I hope you are recovering rapidly from your
illness.

One thing I learned that you may or may not know is, when measuring
capacitors, you can switch to the R mode and read the capacitor's ESR
directly rather than having to calculate it from D. I was truly pleased
to discover that.

When I received my meter, I cut the cord off of the 220V wall wart and
used the cord and a lab power supply to charge the meter while watching
the current. Very interesting. Unless I did something wrong, I found
that the meter will not charge at more than a few mA when in the "off"
condition. So, I turned it on and watched the charging current until it
took a drop and the bars on the display indicated "full".

The vendor did send me a 120V supply. I have not used it yet, and I
think I will charge the meter next time just as I did last time (with a
lab supply) and make more measurements until I am comfortable that I
have a good feel for the meter's charging characteristics.

Cheers,
John S

 

[Mike]

==

Good to hear from you, Mike. I hope you are recovering rapidly
from your illness.

Thanks very much. It will be a continual struggle but I'm starting
to get a handle on things.

One thing I learned that you may or may not know is, when
measuring capacitors, you can switch to the R mode and read the
capacitor's ESR directly rather than having to calculate it from
D. I was truly pleased to discover that.

Yes, I discovered that also. I thought it was just a quirk, but it
did seem to work reliably on capacitors. BTW, I did find the ESR
does decrease rapidly with frequency at low frequencies. It starts
to remain constant around 10KHz and above. So the Q does appear to
remain the same with different test frequencies below 1KHz. You can
see the effect by looking at any electrolytic datasheet.

When I received my meter, I cut the cord off of the 220V wall wart
and used the cord and a lab power supply to charge the meter while
watching the current. Very interesting. Unless I did something
wrong, I found that the meter will not charge at more than a few
mA when in the "off" condition. So, I turned it on and watched the
charging current until it took a drop and the bars on the display
indicated "full".

The charging arrangment seems strange. It looks like they wanted to
simplify things by leaving it in trickle charge when it is turned
off, then they simply put the charger, the battery, and the
instrument in parallel when you turn it on.

I don't even know what kind of battery is inside. I don't think a
NiCd will trickle charge at 5mA, and most of the more exotic
batteries require special charging circuits to prevent destruction.
Maybe I'll take mine apart this weekend and have a look.

The vendor did send me a 120V supply. I have not used it yet, and
I think I will charge the meter next time just as I did last time
(with a lab supply) and make more measurements until I am
comfortable that I have a good feel for the meter's charging
characteristics.

First step is to find out what kind of battery is inside. OK, you
talked me into doing it now.

Pfaff! First thing I do is drop a screw on the floor. Took five
minutes to find it!

The battery is a 200mA/hr 8.4V NiMh. Here's the datasheet:

http://www.rapidonline.com/pdf/18-4168.pdf

It looks like it wants 20mA for 14~16h. I don't think 140mA is going
to do it much good

But I'm surprised that you only measure 5mA with it turned off. What
voltage are you delivering to the unit?

Cheers,
John S

Thanks,

Mike

 

[John S]

==


Thanks very much. It will be a continual struggle but I'm starting
to get a handle on things.


Yes, I discovered that also. I thought it was just a quirk, but it
did seem to work reliably on capacitors. BTW, I did find the ESR
does decrease rapidly with frequency at low frequencies. It starts
to remain constant around 10KHz and above. So the Q does appear to
remain the same with different test frequencies below 1KHz. You can
see the effect by looking at any electrolytic datasheet.


The charging arrangment seems strange. It looks like they wanted to
simplify things by leaving it in trickle charge when it is turned
off, then they simply put the charger, the battery, and the
instrument in parallel when you turn it on.

I don't even know what kind of battery is inside. I don't think a
NiCd will trickle charge at 5mA, and most of the more exotic
batteries require special charging circuits to prevent destruction.
Maybe I'll take mine apart this weekend and have a look.


First step is to find out what kind of battery is inside. OK, you
talked me into doing it now.

Pfaff! First thing I do is drop a screw on the floor. Took five
minutes to find it!

The battery is a 200mA/hr 8.4V NiMh. Here's the datasheet:

http://www.rapidonline.com/pdf/18-4168.pdf

Thanks for the great information!

It looks like it wants 20mA for 14~16h. I don't think 140mA is going
to do it much good

A bit scary, huh.

But I'm surprised that you only measure 5mA with it turned off. What
voltage are you delivering to the unit?

I set the lab supply to 12V.

Here is the data I took:

Time Meter mA Notes

19:21 Off 3.55 Battery indicator at 1 bar
19:32 On 143 Battery indicator at 1 bar
19:40 On 136 Battery alternating between 1 bar and 2 bars
19:44 On 135 Battery at 2 bars
20:27 On 138 Battery alternating between 2 bars and 3 bars
20:19 On 140 Battery at 3 bars
21:02 On 27 Battery at 3 bars
21:06 On 33 Battery at 3 bars
21:10 On 38 Battery at 3 bars
21:15 On 41 Battery at 3 bars
21:20 On 42 Battery at 3 bars

 

[John S]

It looks like it wants 20mA for 14~16h. I don't think 140mA is going
to do it much good

BTW, Mike, one of the recommended batteries in the back of the manual is
a GP20R8H. Take a look at those specs.

John S

 

[Mike]

A bit scary, huh.

I set the lab supply to 12V.

Here is the data I took:

Time Meter mA Notes

19:21 Off 3.55 Battery indicator at 1 bar
19:32 On 143 Battery indicator at 1 bar
19:40 On 136 Battery alternating between 1 bar and 2 bars
19:44 On 135 Battery at 2 bars
20:27 On 138 Battery alternating between 2 bars and 3 bars
20:19 On 140 Battery at 3 bars
21:02 On 27 Battery at 3 bars
21:06 On 33 Battery at 3 bars
21:10 On 38 Battery at 3 bars
21:15 On 41 Battery at 3 bars
21:20 On 42 Battery at 3 bars

Thansk for the excellent data!

Obviously the battery isn't charging very heavily with the unit
turned off. Maybe that is just a trickle charge to keep the battery
topped up.

With the unit turned on, it looks like they are really charging the
battery at 140mA. It is amazing how the current snaps off at 21:02

I wonder if the 40mA drain with the unit turned on is the normal
power drain for the instrument. Actually that's not too bad
considering what's inside.

I guess the other thing is NiMh has a pretty severe self-discharge
curve. It looks like the unit would have to remain plugged in on
standy to keep the battery trickle-charged. Otherwise it would have
to go through the complete 140mA charge cycle every time we turn it
on. And while it is charging, it may be be usable due to the funny
readings.

It turns out some of this information is available in the manual at

"http://www.pinsonne-elektronik.de/media/daten/TH2821A Operation%
20Manual.pdf"

Section 3.3 on page 30 talks about battery recharge. They state it
takes 2~3 hrs to charge, and this gives 5~6 hrs of use. They also
state twice that it may not operate correctly while charging, which
I already found out by trying to fiddle with the unit when it first
arrived.

If the battery has 200mAh, and it lasts 5 hrs, that's about 40mA,
which is what you measured in the table above. So it is beginning to
make some sense.

So, it has a battery, which is nice. But the battery turns out to be
a hassle if we are not using the unit constantly, which is a bit of
a pain.

Since we cannot predict when we are going to need the unit, it looks
like it will have to stay on trickle charge all the time. That's not
much of a problem. It doesn't take much power, but probably the
biggest hassle will be finding a spare plug.

Further update on the Q of electrolytics. I found some curves on
ESR vs Frequency in Fig. 1 - 11 of Impedance, ESR vs. Frequency
Characteristics. This is on page 7 of

http://www.nmr.mgh.harvard.edu/~reese/electrolytics/tec1.pdf

What this says is the ESR curve decreases as the frequency
increases, and doesn't start to flatten until we reach about 10KHz.

Below that, the ESR increases as we lower the frequency. Since the
capacitive reactance is also decreasing, the Dissipation Factor, or
Q, will tend to remain constant. And that's what the Tonghui is
showing.

I never knew that.

Also, did you notice there is a black strip along the top of the
unit? That looks like it might be part of an IR data port. I didn't
take the unit completely apart since there was somethng snagging it.

But next time I go in, I will try to see if there is anything
mounted in that area that might be of interest.

Thanks,

Mike

 

[Mike]

BTW, Mike, one of the recommended batteries in the back of the manual
is a GP20R8H. Take a look at those specs.

John S

OK, I'm looking at http://www.gpina.com/pdf/GP20R8H_DS.pdf

It shows the same 20 mA for 16 hrs as recommended for this battery. It
also shows the fast charge cycle, which requires a charge control
circuit. They give the following parameters:

Fast Charge : 100 mA to 200 mA (0.5 to 1C)
charge termination control recommended
control parameters:
-dV : 0 - 35mV
DT/dt ** : 0.8 o C/min (0.5 to 0.9C)
: 0.8 - 1 o C/min (1C)
TCO ** : 45 - 50 o C

So it looks like they really do intend to do a fast charge. Also, there
was no temperature sensor anywhere near the battery when I took it
apart, so maybe they are relying on the delta V hump at full charge. I'm
not sure how they keep track of things when the user (me) keeps turning
the unit on and off, but they do seem to be able to charge the battery
since the charge indicator appears to work well.

So it seems they do have things under control. That's good. Gives more
confidence that it will continue working as the battery ages.

Thanks for the headsup.

Mike

 

[John S]

Thansk for the excellent data!

My pleasure. I wasn't trying very hard. I'll do better next time.

Obviously the battery isn't charging very heavily with the unit
turned off. Maybe that is just a trickle charge to keep the battery
topped up.

With the unit turned on, it looks like they are really charging the
battery at 140mA. It is amazing how the current snaps off at 21:02

Well, the snap-off occurred somewhere between 20:19 and 21:02. I'll try
to nail it down a bit better next time.

I wonder if the 40mA drain with the unit turned on is the normal
power drain for the instrument. Actually that's not too bad
considering what's inside.

I believe you are correct. It was my suspicion as well.

I guess the other thing is NiMh has a pretty severe self-discharge
curve. It looks like the unit would have to remain plugged in on
standy to keep the battery trickle-charged. Otherwise it would have
to go through the complete 140mA charge cycle every time we turn it
on. And while it is charging, it may be be usable due to the funny
readings.

Actually, I took that data on 11/20/2011. I have not charged it since
then and it still shows two battery bars remaining. I have used it only
occasionally, maybe an hour total, since then. I'm pleased that it is
holding up so well.

It turns out some of this information is available in the manual at

"http://www.pinsonne-elektronik.de/media/daten/TH2821A Operation%
20Manual.pdf"

Yes. I got that manual when you provided the link to me weeks ago.
Thanks again. As I mentioned in another post, take a look at the
recommended GP20R8H specs as mentioned on page 31. It makes me breathe
easier.

Section 3.3 on page 30 talks about battery recharge. They state it
takes 2~3 hrs to charge, and this gives 5~6 hrs of use. They also
state twice that it may not operate correctly while charging, which
I already found out by trying to fiddle with the unit when it first
arrived.

If the battery has 200mAh, and it lasts 5 hrs, that's about 40mA,
which is what you measured in the table above. So it is beginning to
make some sense.

So, it has a battery, which is nice. But the battery turns out to be
a hassle if we are not using the unit constantly, which is a bit of
a pain.

Since we cannot predict when we are going to need the unit, it looks
like it will have to stay on trickle charge all the time. That's not
much of a problem. It doesn't take much power, but probably the
biggest hassle will be finding a spare plug.

I've not had a problem with battery self-discharge, as I mentioned
above. I do not leave mine charging all the time, but it might not be a
bad thing.

Further update on the Q of electrolytics. I found some curves on
ESR vs Frequency in Fig. 1 - 11 of Impedance, ESR vs. Frequency
Characteristics. This is on page 7 of

http://www.nmr.mgh.harvard.edu/~reese/electrolytics/tec1.pdf

What this says is the ESR curve decreases as the frequency
increases, and doesn't start to flatten until we reach about 10KHz.

Yes. I discovered the same thing with the meter and in a CDE paper:

www.cde.com/catalogs/AEappGUIDE.pdf

Thanks for your link. I've saved the file.

Below that, the ESR increases as we lower the frequency. Since the
capacitive reactance is also decreasing, the Dissipation Factor, or
Q, will tend to remain constant. And that's what the Tonghui is
showing.

I never knew that.

Neither did I. It gives me a good feeling that the meter is telling me
the things I want to know.

Also, did you notice there is a black strip along the top of the
unit? That looks like it might be part of an IR data port. I didn't
take the unit completely apart since there was somethng snagging it.

Yes, I did. I'm sure it is a data port. I saw something in the manual
about reserved function concerning that. For example, see the last
bullet on page 5 of the manual.

But next time I go in, I will try to see if there is anything
mounted in that area that might be of interest.

Thanks,

Mike

I'm certain you'll find IR emitter and detector.

It's possible that the contributors on this group don't care about our
detailed discussions. I will give you a temporary email address whereby
you can reach me and we can then privately exchange more permanent
addresses, if you like.

tonghui dot meter dot is_nice at xoxy dot net

Cheers,
John S

 

[John S]

OK, I'm looking at http://www.gpina.com/pdf/GP20R8H_DS.pdf

It shows the same 20 mA for 16 hrs as recommended for this battery. It
also shows the fast charge cycle, which requires a charge control
circuit. They give the following parameters:

Fast Charge : 100 mA to 200 mA (0.5 to 1C)
charge termination control recommended
control parameters:
-dV : 0 - 35mV
DT/dt ** : 0.8 o C/min (0.5 to 0.9C)
: 0.8 - 1 o C/min (1C)
TCO ** : 45 - 50 o C

So it looks like they really do intend to do a fast charge. Also, there
was no temperature sensor anywhere near the battery when I took it
apart, so maybe they are relying on the delta V hump at full charge. I'm
not sure how they keep track of things when the user (me) keeps turning
the unit on and off, but they do seem to be able to charge the battery
since the charge indicator appears to work well.

So it seems they do have things under control. That's good. Gives more
confidence that it will continue working as the battery ages.

Thanks for the headsup.

Mike

I agree. And, you're welcome. Nice to have someone to compare notes with.

John S

 

[Mike]

On 1/10/2012 5:04 PM, Mike wrote:

My pleasure. I wasn't trying very hard. I'll do better next time.

You really did fantastic! That's what opened this whole subject.

[...]

Actually, I took that data on 11/20/2011. I have not charged it
since then and it still shows two battery bars remaining. I have
used it only occasionally, maybe an hour total, since then. I'm
pleased that it is holding up so well.

I think my original problem started when I tried to operate the unit
with a completely dead battery. That may have dropped the voltage to
the uP enough to give the erratic results I was getting.

Now I'm thinking as long as there is some charge remaining in the
battery, it should work fine while it is charging.

So I think it probably can sit on the shelf for long periods when it
is not needed, and still be ready for use when it is required for a
new project.

Apparently NiMh shares some of the same features as regular NiCd,
and it doesn't particularly care what state of charge it is in. The
fast charge cycle that your measurements show probably charges the
cell at 100mA, with the other 40mA going to the electronics.

That amount of charge is well within the recommended limits for the
battery, so I think the designers have done a good job to give a
long life to the battery, and it should not be a concern. New ones
are available for $5.00 if you shop around, and some sales might
even drop that to $1.50. So I'm not worried about the battery life
or replacement cost any more. I think we should just use the unit
when it is needed, and leave it on the shelf the rest of the time.

[...]

It's possible that the contributors on this group don't care about
our detailed discussions. I will give you a temporary email
address whereby you can reach me and we can then privately
exchange more permanent addresses, if you like.

tonghui dot meter dot is_nice at xoxy dot net

Thanks, John. That would be a special privilege. But recall that Jon
Kirwan has a unit, and P E Schoen has the MCP BR2822 which appears
to be identical:

http://www.multimeterwarehouse.com/BR2822f.htm

So there are some who might be interested in the discussions, and
maybe others who might be interested in getting one also. But if we
disappear, no one else will be able to find out more about it.

What I would like to do is find out more about how this thing works
and why it is so accurate. Is it because of good snr, good
circuitry, quality a/d's, software, components, or some other
factor. What can we learn from this instrument that can help in
other projects?

But there are times when the readings fluctuate for no apparent
reason. I'd also like to find out why it does that and what can be
done to overcome the problem. The new model has averaging, so that
would help. But it probably slows down the measurement, and it also
costs much more. Is there any way we can get the same effect without
the added cost?

And I certainly would not mind modifying my instrument if if would
improve the performance. For me, that is a given.

Someone may come across a piece of information or some data that
helps unravel these mysteries, and post it here. But if we go
private, this is unlikely to happen.

We are not taking up much room, and we are not bothering anyone, so
my vote is to stay here and not worry.

Cheers,
John S

Thanks,

Mike

 

[John S]

On 1/10/2012 5:04 PM, Mike wrote:

My pleasure. I wasn't trying very hard. I'll do better next time.

You really did fantastic! That's what opened this whole subject.

[...]

Actually, I took that data on 11/20/2011. I have not charged it
since then and it still shows two battery bars remaining. I have
used it only occasionally, maybe an hour total, since then. I'm
pleased that it is holding up so well.

I think my original problem started when I tried to operate the unit
with a completely dead battery. That may have dropped the voltage to
the uP enough to give the erratic results I was getting.

Now I'm thinking as long as there is some charge remaining in the
battery, it should work fine while it is charging.

So I think it probably can sit on the shelf for long periods when it
is not needed, and still be ready for use when it is required for a
new project.

Apparently NiMh shares some of the same features as regular NiCd,
and it doesn't particularly care what state of charge it is in. The
fast charge cycle that your measurements show probably charges the
cell at 100mA, with the other 40mA going to the electronics.

That amount of charge is well within the recommended limits for the
battery, so I think the designers have done a good job to give a
long life to the battery, and it should not be a concern. New ones
are available for $5.00 if you shop around, and some sales might
even drop that to $1.50. So I'm not worried about the battery life
or replacement cost any more. I think we should just use the unit
when it is needed, and leave it on the shelf the rest of the time.

Sounds good to me.

[...]

It's possible that the contributors on this group don't care about
our detailed discussions. I will give you a temporary email
address whereby you can reach me and we can then privately
exchange more permanent addresses, if you like.

Thanks, John. That would be a special privilege. But recall that Jon
Kirwan has a unit, and P E Schoen has the MCP BR2822 which appears
to be identical:

http://www.multimeterwarehouse.com/BR2822f.htm

So there are some who might be interested in the discussions, and
maybe others who might be interested in getting one also. But if we
disappear, no one else will be able to find out more about it.

What I would like to do is find out more about how this thing works
and why it is so accurate. Is it because of good snr, good
circuitry, quality a/d's, software, components, or some other
factor. What can we learn from this instrument that can help in
other projects?

But there are times when the readings fluctuate for no apparent
reason. I'd also like to find out why it does that and what can be
done to overcome the problem. The new model has averaging, so that
would help. But it probably slows down the measurement, and it also
costs much more. Is there any way we can get the same effect without
the added cost?

It fluctuates around zero quite a bit when I check the resistance of an
8200pF, c0g MLCC capacitor. However, I think it is because the
resistance is so low. The cap showed a D of .0000 to .0001 so it was
pushing the limits. The capacitance reading is steady.

And I certainly would not mind modifying my instrument if if would
improve the performance. For me, that is a given.

Someone may come across a piece of information or some data that
helps unravel these mysteries, and post it here. But if we go
private, this is unlikely to happen.

We are not taking up much room, and we are not bothering anyone, so
my vote is to stay here and not worry.


Thanks,

Mike

You make some good, valid points. I agree.

John S

 

[josephkk]

What I would like to do is find out more about how this thing works
and why it is so accurate. Is it because of good snr, good
circuitry, quality a/d's, software, components, or some other
factor. What can we learn from this instrument that can help in
other projects?

But there are times when the readings fluctuate for no apparent
reason. I'd also like to find out why it does that and what can be
done to overcome the problem. The new model has averaging, so that
would help. But it probably slows down the measurement, and it also
costs much more. Is there any way we can get the same effect without
the added cost?

And I certainly would not mind modifying my instrument if if would
improve the performance. For me, that is a given.

Someone may come across a piece of information or some data that
helps unravel these mysteries, and post it here. But if we go
private, this is unlikely to happen.

We are not taking up much room, and we are not bothering anyone, so
my vote is to stay here and not worry.


Thanks,

Mike

I'll buy some of that. These have just about the properties i am looking
for. So i am real interested.

?-)

 

[Mike]

I tried the link and the resulting pdf has a problem and Adobe won't
render it. I there another English manual for it?

?-)

Hi Joseph,

I just tried the link and it worked fine. Maybe there was a glitch in the
download.

Here are three links that I just checked and they all work fine:

"http://www.pinsonne-elektronik.de/media/daten/TH2821A Operation%
20Manual.pdf" (original link)

"http://www.4shared.com/office/HSPQhiv7/TH2821A_Operation_Manual.html"
(must wait 20 seconds)

"http://www.aidetek.com/New_products_info/Datasheet/tonghui/2821A.pdf"
(secured - cannot copy text)

Mike

 

[Mike]

I'll buy some of that. These have just about the properties i am looking
for. So i am real interested.

?-)

If you want to find bad electrolytics, I don't think you can find a
better bargain. It gives the dissipation of the capacitor, so you don't
have to fool with lookup tables like you do with a conventional ESR meter
to see if the cap is good or bad. Besides giving an easy way to check
electrolytics, it also gives the capacitance value to four digits. No ESR
meter does that. It also measures inductors and resistors, which no ESR
meter can do. It has settable upper and lower limits for bin sorting. And
it's less expensive than most ESR meters that I could find.

I just checked eBay. On Jan 14, 2012, the lowest price was $159.99 with
$25.00 shipping. Another is available at C $187.99 and C $12.00 shipping,
so you have to check both carefully for the best deal.

I'd also get the TH26029 SMD Test Tweezer Probe for $29.99.

The newer model has averaging, but it is closer to $500. I don't think
it's worth considering. Once you start getting into those numbers, might
as well consider going to a more expensive bench model with greater
accuracy and frequency range.

If you order one, make certain to get a 120VAC adapter instead of the
220VAC one that normally comes with it. Get them to confirm that they
received your request and will comply.

Hope this helps.

Mike

 

[Mike]

If you want to find bad electrolytics, I don't think you can find
a better bargain. It gives the dissipation of the capacitor, so
you don't have to fool with lookup tables like you do with a
conventional ESR meter to see if the cap is good or bad. Besides
giving an easy way to check electrolytics, it also gives the
capacitance value to four digits.

Update : it actually displays 4 digits plus a decimal on large
electrolytics. But the two least significant digits dance around a
lot.

I switched to a 10uF 250VAC +/-5% film capacitor, and it read
10.045uF with the last digit fluctuating between 4 and 6. So I
conclude electrolytics are not very stable. But the readings are
quite consistent on a quality part.

I've been monitoring the battery self-discharge. It is terrible. It
loses a significant fraction of the charge in a week. Leaving it
plugged in has no effect. It does not trickle charge while it is
turned off.

One solution might be to simply leave it plugged in a turned on. It
says "Auto Power Off" under the display, so that might not work. But
it seems to stay turned on when it is measuring something, like a
large electrolytic.

I found it really is necessary to turn it off when moving from one
AC plug to another, otherwise it may give strange results. In fact,
it might be a good idea to post the operating notes found on page 5
of the manual:

Notes on Use

1. This meter is only for indoor use.

2. Turn off the TH2821A while switching the power supply between
battery and DC adapter or replacing the battery.

3. Although internal circuit protection is provided, DC voltage or
current may damage TH2821A. Before you measure a capacitor, be sure
the capacitor is fully discharged.

4. Charging may disturb measurement result sometimes.

5. Nickel Metal Hydride rechargeable battery can be used for the
power supply. TH2821A will not work normally when battery voltage is
less than 6V.

6. The 12V AC to DC adaptor is recommended to be used for TH2821A
power supply.

7. Perform Open and Short corrections for accurate measurement
especially when test fixture is changed.

8. The functions locked with password are not accessible by users.

My biggest problems have been from ignoring rules #2 and #4. I used
to freak out when it didn't do what I thought it should be doing,
but after following the notes, it works fine. And I will add
protection against charged caps, as stated in rule #3. I found that
human error can quickly wipe out a good instrument when you are
working with caps charged to high voltage.

Now I'm wondering if a plain 9V NiCd can be used in place of the
NiMH battery. They are supposed to be interchangeable, but the NiCd
may have a capacity of 120mAh, where the NiMh has 200mAh. So it may
last 3 hours on NiCd, and 5 hours on NiMh. The difference is not
significant for me.

But the NiCd has a much lower discharge rate, so you wouldn't be
running into the issue of leaving it on the shelf for a month, then
trying to use it when the battery is completely discharged. I'm
tempted to get a 9V NiCd and see how it works. If it solves the
self-discharge problem, that's the way to go.

So now I'm happy with the stability of the meter readings on a
quality capacitor, and I won't worry about fluctuation on
electrolytics.

But I'm very unhappy with the self-discharge of NiMh. That may be
solved by switching to a plain NiCd, so it is more likely to have
plenty of charge remaining when I want to use it for some quick
measurements. Afterwards, I can just leave it plugged in and turned
on to bring the battery back up.

I think that covers the issues up to now on this instrument. It is
still by far the best bargain for LCR measurements I have found
anywhere.

Mike

 

[John S]

Update : it actually displays 4 digits plus a decimal on large
electrolytics. But the two least significant digits dance around a
lot.

Try different frequency settings if you have not already

I switched to a 10uF 250VAC +/-5% film capacitor, and it read
10.045uF with the last digit fluctuating between 4 and 6. So I
conclude electrolytics are not very stable. But the readings are
quite consistent on a quality part.

Are you kidding? Fluctuations of several millifarads out of 10 uF is a
dream come true for me.

I've been monitoring the battery self-discharge. It is terrible. It
loses a significant fraction of the charge in a week. Leaving it
plugged in has no effect. It does not trickle charge while it is
turned off.

One solution might be to simply leave it plugged in a turned on. It
says "Auto Power Off" under the display, so that might not work. But
it seems to stay turned on when it is measuring something, like a
large electrolytic.

I found it really is necessary to turn it off when moving from one
AC plug to another, otherwise it may give strange results. In fact,
it might be a good idea to post the operating notes found on page 5
of the manual:

Notes on Use

1. This meter is only for indoor use.

2. Turn off the TH2821A while switching the power supply between
battery and DC adapter or replacing the battery.

3. Although internal circuit protection is provided, DC voltage or
current may damage TH2821A. Before you measure a capacitor, be sure
the capacitor is fully discharged.

4. Charging may disturb measurement result sometimes.

5. Nickel Metal Hydride rechargeable battery can be used for the
power supply. TH2821A will not work normally when battery voltage is
less than 6V.

6. The 12V AC to DC adaptor is recommended to be used for TH2821A
power supply.

7. Perform Open and Short corrections for accurate measurement
especially when test fixture is changed.

8. The functions locked with password are not accessible by users.

My biggest problems have been from ignoring rules #2 and #4. I used
to freak out when it didn't do what I thought it should be doing,
but after following the notes, it works fine. And I will add
protection against charged caps, as stated in rule #3. I found that
human error can quickly wipe out a good instrument when you are
working with caps charged to high voltage.

Now I'm wondering if a plain 9V NiCd can be used in place of the
NiMH battery. They are supposed to be interchangeable, but the NiCd
may have a capacity of 120mAh, where the NiMh has 200mAh. So it may
last 3 hours on NiCd, and 5 hours on NiMh. The difference is not
significant for me.

But the NiCd has a much lower discharge rate, so you wouldn't be
running into the issue of leaving it on the shelf for a month, then
trying to use it when the battery is completely discharged. I'm
tempted to get a 9V NiCd and see how it works. If it solves the
self-discharge problem, that's the way to go.

So now I'm happy with the stability of the meter readings on a
quality capacitor, and I won't worry about fluctuation on
electrolytics.

But I'm very unhappy with the self-discharge of NiMh. That may be
solved by switching to a plain NiCd, so it is more likely to have
plenty of charge remaining when I want to use it for some quick
measurements. Afterwards, I can just leave it plugged in and turned
on to bring the battery back up.

I think that covers the issues up to now on this instrument. It is
still by far the best bargain for LCR measurements I have found
anywhere.

Mike

I just charged mine from a lab supply and found it to respond as before,
that is, about 3.7 mA in an OFF condition and about 145 mA in an ON
condition. It was at about 1 bar of the battery indicator on the display
when I started. About an hour later the current dropped to 45 mA as
before and the display indicated 3 bars.

I do not seem to have a problem with self-discharge. I'm wondering
what's going on. Maybe I should open mine to see if the battery is like
yours. Maybe you should contact them with your situation and ask for
assistance.

Also, I've learned not to trust inductance measurements of a 60 Hz
transformer even at 100 Hz. Maybe because it is seeing lots of leakage
inductance or iron loss or something.

I agree that it is a great bargain. We just need to learn about its
limitations. However, your battery problem bugs me. Do you suppose it is
not turning off with the power button?

John