Maker Pro
Maker Pro

Tonghui TH2821A LCR Meter

M

Mike

Jan 1, 1970
0
John S said:
On 1/14/2012 3:49 PM, Mike wrote:
Try different frequency settings if you have not already

Yes, that seems to have little effect on the electrolytics.
Are you kidding? Fluctuations of several millifarads out of 10 uF
is a dream come true for me.

I think you meant fluctuations of several nF. Yes, it has drifted up
to 10.048uF, and is bouncing around between 10.047uF and 10.049uF.

But it spends most of its time on 10.048uF.

I tried to take a picture to show you,but ironically the LiIon
battery in my camera is dead so I have to wait to charge it back up.

I'll post pictures of the display and the capacitor tomorrow. I
expect the reading will change a little, but that's jut normal
drift. Not to worry.

[...]
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.

I charged mine fully then plugged in but left it turned off for
about a week. When I moved it to a different outlet and turned it
on, the battery indicator showed only one bar.

Either the battery status indicator is not accurate, or the NiMh has
a serious self-discharge. I think it's the NiMh.
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 didn't find any problems on the inductors. I'll check more later.
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?

Could be. The operating notes specifically mention turning the unit
off while moving to a different outlet. I did that. The battery did
not last long.

But all the references I can find say the same thing. NiMh has a
high self-discharge. I'll try a NiCd - that should work a lot
better.

I have a bunch of NiCds that I got on sale at RS some time ago. They
sat in my battery box for years without any care or attention. I
discovered a battery charger at a dollar store. I measured the
batteries and they all had some charge remaining even though I never
charged them when I bought them. I charged them and they all came up
with no problems.

So I'm leaning to switch to a 9V NiCd and stop this hassle with NiMh
self-discharge.

Mike
 
J

josephkk

Jan 1, 1970
0
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

Thanks, the third one did it for me. I guess i will finally have to
reconsider dealing with ePrey.

?-)
 
M

Mike

Jan 1, 1970
0
josephkk said:
Thanks, the third one did it for me. I guess i will finally have to
reconsider dealing with ePrey.

?-)

That's great, Joseph. I had a lot of problems with eBay when I first
started using them, but that was many years ago. Since then, it has
turned into a very smooth operation and I've had zero problems. I've only
lost one shipment, and the vendor quickly sent another unit.

One thing I stronly recommend is to split your operating system into
separate installations. One for normal browsing, and a second
installation that is strictly for financial transactions.

I use Ubuntu 10.04 LTS as the host, and VirtualBox as the VM. I have
separate installations of WinXP that provide the services needed for
browsing, banking, software development, etc. I do pcb layout and routing
in Ubuntu so a windows crash will not interrupt an autoroute in progress.

The XP installations are stripped to the bare minimum that is needed for
the required services. That means all unnecessary functions and services
are stripped or disabled. I turn off Auto Update, Restore, Firewall (not
needed), and I don't bother with antivirus programs. Everything else is
turned off and any unnecessary files are deleted.

This allows making a very small installation that is easy to back up to a
spare hard disk. I use a 10GB dynamic hard disk in VBox. The banking file
is only 830MB, and the other installations may be 2GB or so. These copy
very fast to the backup drive, so it is convenient to keep the backups
current. I can increase the size if needed, and shrink it later when the
requirements change.

Then if a virus strikes, or I get a bad software installation that wrecks
the registry, I don't have to reinstall XP and all my files, then try to
get all the original settings back. That takes a very long time and I
never get tham all.

I just copy the backup over the bad file and I am back on the air in a
matter of seconds. The other advantage is I can copy the installation to
a different computer and get a byte-identical installation on the other
computer. XP doesn't know that it is a completely different motherboard
and hard drive, so it doesn't care.

I use the System File Checker from Win98 to check for missing or
corrupted files, and to see if any new ones have suddenly appeared. This
only works with the Win98 version - the XP version does not allow you to
specify the file extensions and folders you want to monitor. It also
eliminates Win7 since that has folders that will not allow Win98 to
enter.

I use the various rootkit detectors to look for keyloggers and other
malware. But the combination of Win98 SFC and Rootkit Revealer pretty
much covers any trojan or virus that can attack the system, so there is
no need to waste time on Symantec or other resource hogs.

The banking installation is the only place where the passwords and logon
information to Paypal and the banks is kept. This information is stored
in Stickey Password manager and is heavily encrypted. So it is not
available to viruses or trojans that may scan the hard disk looking for
text strings. But there is little chance they could be on the banking
computer since it never goes anywhere else except to the financial sites.

If one of the other installations got infected, there is no way the
malware could detect if there is another installation, and none of the
keystrokes on the banking computer can be detected on the other
installations, so a software keylogger will fail.

The banking computer has no access to email, so a phishing attack on the
another computer will fail.

Most of the well-written malware that is aimed at stealing your banking
logon information will shut down as soon as they detect they are running
in a virtual computer. Virtual installations are used in honeypots to try
to find the command servers and lead back to the authors. To protect
themselves, they simply shut down and no longer present any danger. So
using a virtual installation gives added protection against the most
dangerous malware.

Finally, there are two things you can do to vastly increase your
protection against online theft. First, open another account at your
bank. When you do this, it will have the same profile as your current
accounts, and will have the same access rights on a ATM or online. But
have the bank add a block to the account, so the only way you can
transfer money in or out is by visiting the bank in person and having a
manager override the block.

Now you can put most of your money in the account except for what is
needed for miscellaneous purchases. This will keep the majority of your
funds out of the hands of criminals who would otherwise send it to Russia
with love.

The second trick is to change all the answers to the security questions
that the bank asks when you set up your online account, such as "What is
your favorite color", or "What city were you born in."

Instead of answering these questions with the correct information, give
completely nonsense answers such as "!My.Dog.Hass.3.Flees$"

Note the misspelling and punctuation between words. This prevents any
phrase search from finding the string.

This is simple enough that you do not have to write it down, so it will
not be detected by malware that scans the hard disk looking for text
strings.

Use the same answer for all the questions.

Most banks store the browser string from your computer and ask one of the
security questions if they detect a change.

Now, if a criminal somehow manages to get your logon information, they
will probably be logging on from a different computer and will trigger
the security question. But they will not be able to answer it and the
attack will fail.

There are many other attacks that can get through all these protections,
so you always have to be vigilant and keep monitoring your accounts for
unwanted transactions.

But these methods will give a vastly improved security over what you now
have.

Mike
 
M

Mike

Jan 1, 1970
0
Mike said:
[...]
Are you kidding? Fluctuations of several millifarads out of 10 uF
is a dream come true for me.
I think you meant fluctuations of several nF. Yes, it has drifted
up to 10.048uF, and is bouncing around between 10.047uF and
10.049uF.
But it spends most of its time on 10.048uF.
I tried to take a picture to show you,but ironically the LiIon
battery in my camera is dead so I have to wait to charge it back
up.
I'll post pictures of the display and the capacitor tomorrow. I
expect the reading will change a little, but that's jut normal
drift. Not to worry.

OK, here's the original reading on Saturday, Jan 14 2002 at 19:11.
It went up to 10.049uF when I took the picture:

http://static.panoramio.com/photos/original/65001189.jpg

Two days later, on Jan 16 2002, at 06:13, it measured 10.045uF with
the last digit flickering from 4 to 6. Here it is at 5:

http://static.panoramio.com/photos/original/65001190.jpg

I tried to get a picture showing the reading at 10.046uF, but the
best I could do is showing it switching from 6 back to 5:

http://static.panoramio.com/photos/original/65001194.jpg

Another attempt to get it to show 6, but it doesn't stay long
enough. It switches back to 5 as soon as I press the shutter:

http://static.panoramio.com/photos/original/65001199.jpg

Occasionally, it may hit 10.044uF, but I'd have to take a movie to
show it. That would eat up a huge amount of disk space.

So I'm quite happy with the stability on a quality component. Here's
a picture of the capacitor:

http://static.panoramio.com/photos/original/65001201.jpg

I got very similar results on a 25 ohm, 2,000 watt resistor. The
reading was quite stable, with the last digit flickering +/- 1.

I should note that a dmm that can measure a resistor to 5 decimal
places costs a lot more than the Tonghui.

I think it's a fine instrument and can give an honest 5-digits of
resolution. If you see a lot of variation in the readings, I'd check
for a poor connection or try a better component.

Mike
 
M

Mike

Jan 1, 1970
0
[...]
I got very similar results on a 25 ohm, 2,000 watt resistor. The
reading was quite stable, with the last digit flickering +/- 1.

I now see the value of an internal battery. It was a whole lot easier to
take the Tonghui to the resistor than try to move the resistor to the shelf
where the Tonghui was plugged in to the AC adapter.

I can envision lots of situations where the portability would be very
convenient, such as working on transmitters, troubleshooting a problem at a
customer's site, making measurements on a plane or a boat, and so on. The
Tonghui gives the 5 digits of resolution that you normally see on a bench
instrument, but you can hold it in your hand and take it with you.

I'm beginning to like this instrument better the more I use it.

Mike
 
J

josephkk

Jan 1, 1970
0
That's great, Joseph. I had a lot of problems with eBay when I first
started using them, but that was many years ago. Since then, it has
turned into a very smooth operation and I've had zero problems. I've only
lost one shipment, and the vendor quickly sent another unit.

I hardly ever get phishing email saying it is from ebay or paypal any
more, i used to get several per day. Nowdays they all say they are from
my ISP.
One thing I stronly recommend is to split your operating system into
separate installations. One for normal browsing, and a second
installation that is strictly for financial transactions.

I use Ubuntu 10.04 LTS as the host, and VirtualBox as the VM. I have
separate installations of WinXP that provide the services needed for
browsing, banking, software development, etc. I do pcb layout and routing
in Ubuntu so a windows crash will not interrupt an autoroute in progress.

I like this one, i have been wanting to move my financials to a VM. BTW
what PCB software are you using?
The XP installations are stripped to the bare minimum that is needed for
the required services. That means all unnecessary functions and services
are stripped or disabled. I turn off Auto Update, Restore, Firewall (not
needed), and I don't bother with antivirus programs. Everything else is
turned off and any unnecessary files are deleted.

I turn off auto update on everything that i can, and a VM is way easy to
restore. Have you been able to tell VBox where to put its virtual
machines (like to a specific volume)?
This allows making a very small installation that is easy to back up to a
spare hard disk. I use a 10GB dynamic hard disk in VBox. The banking file
is only 830MB, and the other installations may be 2GB or so. These copy
very fast to the backup drive, so it is convenient to keep the backups
current. I can increase the size if needed, and shrink it later when the
requirements change.

Then if a virus strikes, or I get a bad software installation that wrecks
the registry, I don't have to reinstall XP and all my files, then try to
get all the original settings back. That takes a very long time and I
never get tham all.

I just copy the backup over the bad file and I am back on the air in a
matter of seconds. The other advantage is I can copy the installation to
a different computer and get a byte-identical installation on the other
computer. XP doesn't know that it is a completely different motherboard
and hard drive, so it doesn't care.

I have this one figured out already.
I use the System File Checker from Win98 to check for missing or
corrupted files, and to see if any new ones have suddenly appeared. This
only works with the Win98 version - the XP version does not allow you to
specify the file extensions and folders you want to monitor. It also
eliminates Win7 since that has folders that will not allow Win98 to
enter.

I use the various rootkit detectors to look for keyloggers and other
malware. But the combination of Win98 SFC and Rootkit Revealer pretty
much covers any trojan or virus that can attack the system, so there is
no need to waste time on Symantec or other resource hogs.

The use of W98 SFC on XP is a new twist for me.
The banking installation is the only place where the passwords and logon
information to Paypal and the banks is kept. This information is stored
in Stickey Password manager and is heavily encrypted. So it is not
available to viruses or trojans that may scan the hard disk looking for
text strings. But there is little chance they could be on the banking
computer since it never goes anywhere else except to the financial sites.

Cool. Not quite there yet. Still learning to get VMs to do just what i
want.
If one of the other installations got infected, there is no way the
malware could detect if there is another installation, and none of the
keystrokes on the banking computer can be detected on the other
installations, so a software keylogger will fail.

The banking computer has no access to email, so a phishing attack on the
another computer will fail.
Yep.

Most of the well-written malware that is aimed at stealing your banking
logon information will shut down as soon as they detect they are running
in a virtual computer. Virtual installations are used in honeypots to try
to find the command servers and lead back to the authors. To protect
themselves, they simply shut down and no longer present any danger. So
using a virtual installation gives added protection against the most
dangerous malware.

Finally, there are two things you can do to vastly increase your
protection against online theft. First, open another account at your
bank. When you do this, it will have the same profile as your current
accounts, and will have the same access rights on a ATM or online. But
have the bank add a block to the account, so the only way you can
transfer money in or out is by visiting the bank in person and having a
manager override the block.

Now you can put most of your money in the account except for what is
needed for miscellaneous purchases. This will keep the majority of your
funds out of the hands of criminals who would otherwise send it to Russia
with love.

I understand the technique, now i have to reorganize things to make it
work for me.
The second trick is to change all the answers to the security questions
that the bank asks when you set up your online account, such as "What is
your favorite color", or "What city were you born in."

Instead of answering these questions with the correct information, give
completely nonsense answers such as "!My.Dog.Hass.3.Flees$"

Note the misspelling and punctuation between words. This prevents any
phrase search from finding the string.

This is simple enough that you do not have to write it down, so it will
not be detected by malware that scans the hard disk looking for text
strings.

I do a junior grade of this already.
Use the same answer for all the questions.

Most banks store the browser string from your computer and ask one of the
security questions if they detect a change.

Now, if a criminal somehow manages to get your logon information, they
will probably be logging on from a different computer and will trigger
the security question. But they will not be able to answer it and the
attack will fail.

There are many other attacks that can get through all these protections,
so you always have to be vigilant and keep monitoring your accounts for
unwanted transactions.

But these methods will give a vastly improved security over what you now
have.

Except as noted, i do much of this already.
 
J

John S

Jan 1, 1970
0
I think it's a fine instrument and can give an honest 5-digits of
resolution. If you see a lot of variation in the readings, I'd check
for a poor connection or try a better component.

Mike

Agreed.

I found one cause of flickering. Getting within a couple of inches of my
monitor does it. The display was still readable but flickering in the
last two or three digits. If I move the meter a foot or so away, it
stops flickering.

The manual mentions something about using it in a relatively quiet
environment.

John S
 
M

Mike

Jan 1, 1970
0
josephkk said:
[...]

I hardly ever get phishing email saying it is from ebay or paypal
any more, I used to get several per day. Nowdays they all say they
are from my ISP.

All you need is one that downloads a keylogger. That can come from
anywhere.

One thing is to use Gishpuppy for disposable emails. It works great
in Firefox, and you can have an unlimited number of email addresses.
I like this one, I have been wanting to move my financials to a
VM. BTW what PCB software are you using?

I was using PCAD but it has outlived its usefulness. However, it had
macros, which means you can do wonderful things with your own code.

For example, I could overlay a previous layout on the current pcb
and show exactly where the design had changed. I also made my own
parts selection menu that held my complete inventory, plus automatic
links to datasheets and any other useful information.

I'm looking at Eagle since I understand it also has macros. I'm
hoping to re-use most of the code and simply convert the commands to
the new syntax.
I turn off auto update on everything that I can, and a VM is way
easy to restore. Have you been able to tell VBox where to put its
virtual machines (like to a specific volume)?

Do you mean to run the vm on a flash drive? No, I'm not good enough
to figure out how to do that, but my experience with Ubuntu says it
should be possible to do pretty much anything you want. All you have
to do is find someone who has done it and posted the procedure.

One thing I forgot to mention is to turn off the Windows cache. This
simply wastes disk space and has no benefit.

Another thing I should mention is when you are generating the vm,
don't use the latest release of VirtualBox. It will put the vdi file
in its own folder and separated from the other vms, which makes it
difficult to back up.

Instead, use version 3.2.12 to install the vm. This will put all
your vdi files in a single directory where it is easy to pick which
ones you need to back up and do them all at the same time.

However, version 3.2.12 takes forever to boot the vm, so you want to
go to a later version which fixes the slow bootup.

However, don't use the latest release to run the vm. This has
another annoying bug.

VBox added support for Windows Aero starting in version 4.1. Here's
the release note:

"July 19, 2011. Oracle today released VirtualBox 4.1, a new major
release. Introducing VM clones, increased capability for very large
hosts, and Windows Aero support."

This causes the probe in LTspice to align the tail to the wire
instead of the pointer. The problem is described in the LTspice
forum

http://tech.groups.yahoo.com/group/LTspice/message/53351

I found that all the version 4.1.XX releases do the same thing. But
if you go back to version 4.0.12, it fixes the problem. This is the
last version that does not have Aero support, and was released 4
days before. Here's the release note:

"July 15, 2011. Oracle today released VirtualBox 4.0.12, a
maintenance release of VirtualBox 4.0. It improves stability and
fixes regressions."

https://www.virtualbox.org/wiki/News

Also remember to update the Guest Additions when you run 4.0.12.

[...]
The use of W98 SFC on XP is a new twist for me.

It is available online. If you can't find it, I will dig up the url.

It is a marvellous little program that can detect a single bit
change in any file. So you can see if a virus has changed any of the
Windows system files or downloaded other files that you don't know
about.

The malware can change the operating system to make the changes
transparent. But if it does this, Rootkit Revealer will show the
infection.

So you get them coming and going. If they don't mask themself, Win98
SFC will catch them. If they do mask themself, Rootkit Revealer will
find them.
Cool. Not quite there yet. Still learning to get VMs to do just
what I want.

If you figure out any useful tricks, please post!!!

[...]
Except as noted, I do much of this already.

I think these methods will block most malware attacks. It used to
worry me a great deal that I would lose everything in my bank
account and credit cards, since there is almost no way to avoid
doing financial transactions online.

But now that I have blocked the bank accounts and split the vms, I
can do all my banking and Paypal transactions and I am now free of
the worries that some rootkit or trojan can get to the account.

I also use many other methods, such as Proxomitron to filter
IFRAMES, Drop My Rights to prevent Firefox from installing files in
critical system folders, QuickJava for quick enable and disable of
Java, Javascript, Flash, Silverlight, Images, Stylesheets and Proxy
from the Statusbar, and so on.

I used to use Certificate Patrol to check for changes in the SSL
certificate which would indicate a malware had changed the dns to
point to a copy of the banking site. But it turns out that banks may
change their certificate often enough that it just became a pain to
try to keep track.

Finally, the Win98 SFC method won't work on Win7, so I am committed
to XP for the forseeable future. But I have no interest in Win7. The
basic install requires 6GB since they have included every possible
variation of every DLL they have ever released, and put it all in
the WINSXS folder. So there is no way to get rid of the unwanted
junk that you will probably never use, and the vdi now takes a very
long time to back up. Typical Microsoft crap.

I'm happy with XP. It works fine, and I don't need the fancy
resource hogging features in Win7 and later releases.

Thanks,

Mike
 
M

Mike

Jan 1, 1970
0
John S said:
Agreed.

I found one cause of flickering. Getting within a couple of inches of
my monitor does it. The display was still readable but flickering in
the last two or three digits. If I move the meter a foot or so away,
it stops flickering.

The manual mentions something about using it in a relatively quiet
environment.

John S

That's very interesting! Thanks. That means to be careful of switching
power supplies and SCR dimmers.

Are you using a CRT or LCD monitor?

Mike
 
J

John S

Jan 1, 1970
0
That's very interesting! Thanks. That means to be careful of switching
power supplies and SCR dimmers.

Are you using a CRT or LCD monitor?

Mike

LCD.

Hmm... I just repeated the experiment and I don't see much change. I'll
have to be more careful about my observations in the future.

Sorry!

John S
 
M

Mike

Jan 1, 1970
0
John S said:
On 1/16/2012 12:03 PM, Mike wrote:
[...]
That's very interesting! Thanks. That means to be careful of switching
power supplies and SCR dimmers.

Are you using a CRT or LCD monitor?

Mike

LCD.

Hmm... I just repeated the experiment and I don't see much change. I'll
have to be more careful about my observations in the future.

Sorry!

John S

Don't be sorry. You saw the readings fluctuate. That's exactly the kind
of thing we are looking for. Some erratic performance, or a funny glitch,
or strange behavior. I did the same thing when I first got the unit and
tried to figure out how to get it to work with a dead battery. My
observations and conclusions were way off the mark.

Now I wonder if perhaps the Kelvin clips weren't making good contact, and
moving the unit away from the monitor broke through the oxides and
allowed better contact?

5 digits is 10 to 100 ppm. Things have to be pretty stable to get
reliable readings at that level.

I think maybe we are used to 3 1/2 or 4 digit dmms. So we are not
sensitive to making measurements with a 5 digit resolution, especially on
components that have been sitting in a junkbox for several years.

So far all the quirks have turned out to be violations of the operating
notes, poor quality electrolytics, or perhaps poor contact on the
connections. But we need to find these things and list them so we can get
the best performance from the unit.

So don't be afraid to post any anomalies that occur. I think it was Bob
Pease who made sure his support personnel understood the need to question
any strange behavior in the circuits. Good advice.

Thanks,

Mike
 
J

John S

Jan 1, 1970
0
John S said:
On 1/16/2012 12:03 PM, Mike wrote:
[...]
That's very interesting! Thanks. That means to be careful of switching
power supplies and SCR dimmers.

Are you using a CRT or LCD monitor?

Mike

LCD.

Hmm... I just repeated the experiment and I don't see much change. I'll
have to be more careful about my observations in the future.

Sorry!

John S

Don't be sorry. You saw the readings fluctuate. That's exactly the kind
of thing we are looking for. Some erratic performance, or a funny glitch,
or strange behavior. I did the same thing when I first got the unit and
tried to figure out how to get it to work with a dead battery. My
observations and conclusions were way off the mark.

Now I wonder if perhaps the Kelvin clips weren't making good contact, and
moving the unit away from the monitor broke through the oxides and
allowed better contact?

5 digits is 10 to 100 ppm. Things have to be pretty stable to get
reliable readings at that level.

I think maybe we are used to 3 1/2 or 4 digit dmms. So we are not
sensitive to making measurements with a 5 digit resolution, especially on
components that have been sitting in a junkbox for several years.

So far all the quirks have turned out to be violations of the operating
notes, poor quality electrolytics, or perhaps poor contact on the
connections. But we need to find these things and list them so we can get
the best performance from the unit.

So don't be afraid to post any anomalies that occur. I think it was Bob
Pease who made sure his support personnel understood the need to question
any strange behavior in the circuits. Good advice.

Thanks,

Mike

All excellent points. But, I need to verify my observations before posting.

If you have a 60Hz transformer around and you have some time, please
make some measurements on its primary. I'm finding that a couple I have
are showing in the half-henry range, yet current/voltage measurements on
the line are showing about 10 times higher. I'm wondering how to track
down the discrepancy.

Thanks,
John S
 
M

Mike

Jan 1, 1970
0
John S said:
All excellent points. But, I need to verify my observations before
posting.

I'd still be interested in any quirks you find. These may occur only
rarely, and be so fleeting that it's hard to figure out what is
happening. But if we can collect enough observations, maybe we can pin it
down to something that is easy to prevent.
If you have a 60Hz transformer around and you have some time, please
make some measurements on its primary. I'm finding that a couple I
have are showing in the half-henry range, yet current/voltage
measurements on the line are showing about 10 times higher. I'm
wondering how to track down the discrepancy.

I'm not sure what you mean. Is the unloaded current much higher when you
apply 120VAC than the inductance measurement says it should be?

I wonder if there's an issue with waveform distortion or some other
problem with the current meter. Most handhelds do not measure true rms,
so if the transformer is saturating or there is distortion in the line
waveform, they may not give a correct reading.

But I am interested in following up. I just bought two handheld current
clampmeters on eBay, and I made a simple junction box with a small
resistor in the neutral lead so I can look at the current waveform. So
let me know more about the problem and I'll be happy to take a look.
Thanks,
John S

Mike
 
J

John S

Jan 1, 1970
0
I'd still be interested in any quirks you find. These may occur only
rarely, and be so fleeting that it's hard to figure out what is
happening. But if we can collect enough observations, maybe we can pin it
down to something that is easy to prevent.

Repeating some of my recent tests:

I have a 380pF variable cap. When I measured it this time, I got
fluctuations of 1pF on the 100Hz and 120Hz ranges, .2pF excursions on
the 1kHz range, and no change at all on the 10kHz range.

Then I turned on the fluorescent desk lamp about a foot above the
measurement area. I got at least 4pF excursions at 100Hz, 4pF excursions
at 120Hz, 1pF excursions at 1kHz and .2pF excursions at 10kHz.

It appears that the proper frequency range is called for to begin with.
Not a big surprise, I guess, considering how hard it must be to measure
300pF at 100Hz. Not bad, huh?

I'm not sure what you mean. Is the unloaded current much higher when you
apply 120VAC than the inductance measurement says it should be?

No. If I measure the primary inductance on the Tonghui (at 100Hz), I get
about 535mH and Q of 10. That would calculate out to about 600ma of
unloaded (magnetizing) current at 124VAC, 60 Hz. If I then apply 124AC
at 60Hz to the primary and measure the current, I get .078mA. This
calculates out to about 4H. I'd like to learn why there is so much
discrepancy.
I wonder if there's an issue with waveform distortion or some other
problem with the current meter. Most handhelds do not measure true rms,
so if the transformer is saturating or there is distortion in the line
waveform, they may not give a correct reading.

I just verified the current at .078mA using an HP 3456A which promises
true RMS. Actually, transformers don't saturate on RMS, but do so on
volt-seconds (forgive me for this slight backslide into pedantry).
However, the V-T to RMS ratio would have to be extraordinary to make a
difference.
But I am interested in following up. I just bought two handheld current
clampmeters on eBay, and I made a simple junction box with a small
resistor in the neutral lead so I can look at the current waveform. So
let me know more about the problem and I'll be happy to take a look.


Mike

Any info on this I can get would be very much appreciated. I don't like
measurements on things that don't agree, at least by this much.

No hurry. Your job and personal life come first.

Cheers,
John S
 
M

Mike

Jan 1, 1970
0
[...]
Repeating some of my recent tests:
I have a 380pF variable cap. When I measured it this time, I got
fluctuations of 1pF on the 100Hz and 120Hz ranges, 0.2pF
excursions on the 1kHz range, and no change at all on the 10kHz
range.
Then I turned on the fluorescent desk lamp about a foot above the
measurement area. I got at least 4pF excursions at 100Hz, 4pF
excursions at 120Hz, 1pF excursions at 1kHz and 0.2pF excursions
at 10kHz.
It appears that the proper frequency range is called for to begin
with. Not a big surprise, I guess, considering how hard it must be
to measure 300pF at 100Hz. Not bad, huh?

Actually that's pretty good.

I have an office flourescent with two large tubes mounted in the
ceiling about 3 ft above the shelf the Tonghui is on. It doesn't
seem to have affected the readings on the 10uF cap, but I'll run a
test to make sure.

I'll also try to find a variable cap in your range and see if I can
duplicate your results. I also have a smaller desk flourescent lamp
that I can move much closer.

The leads to the Kelvin clips are shielded, but it would be nice to
know if there's any leakage.

I'm quite interested in this topic - any sensitivity to noise could
have undesired results. Thanks for the headsup.

[...]
No. If I measure the primary inductance on the Tonghui (at 100Hz),
I get about 535mH and Q of 10. That would calculate out to about
600ma of unloaded (magnetizing) current at 124VAC, 60 Hz. If I
then apply 124AC at 60Hz to the primary and measure the current, I
get 0.078mA.
This calculates out to about 4H. I'd like to learn why there is so
much discrepancy.

OK, I was thinking the discrepancy went the other direction. That is
a curious effect. I have lots of loose transformers. I'll check a
couple and see if I get similar results.
I just verified the current at 0.078mA using an HP 3456A which
promises true RMS. Actually, transformers don't saturate on RMS,
but do so on volt-seconds (forgive me for this slight backslide
into pedantry).
However, the V-T to RMS ratio would have to be extraordinary to
make a difference.
Any info on this I can get would be very much appreciated. I don't
like measurements on things that don't agree, at least by this
much.
No hurry. Your job and personal life come first.

Aren't you thoughtful!

It's interesting and well worth pursuing. I'll try some checks when
I'm waiting for some other process to finish.
Cheers,
John S

Thanks, John. Very good info.

Mike
 
J

John S

Jan 1, 1970
0
Actually that's pretty good.


Indeed! No complaints from this end.

[...]
No. If I measure the primary inductance on the Tonghui (at 100Hz),
I get about 535mH and Q of 10. That would calculate out to about
600ma of unloaded (magnetizing) current at 124VAC, 60 Hz. If I
then apply 124AC at 60Hz to the primary and measure the current, I
get 0.078mA.
This calculates out to about 4H. I'd like to learn why there is so
much discrepancy.

I've done a couple of investigations since yesterday to try to get to
the bottom of this.

First, I checked my Tonghui data against an old HP4260A Universal
Bridge, bought on eek-Bay and long out of calibration. I can produce the
data if you wish, but the crux of it is that they agree with each other.

Well, I tell myself, the transformer must be producing unexpected data.

First, I checked the Tonghui for output voltage when the transformer was
attached. The lower frequency settings (exclude the 10kHz setting)
produced 98 to 141mV RMS.

I then connected the transformer to an HP audio oscillator set for 60Hz
and an HP3400A RMS meter. The results were not only surprising to me,
but they were good support for the believability of the data produced by
the Tonghui.

E(source) V(L) XL(calc) L(calc)
5 3 450 1.2H
3 1.5 350 .92H
.1 .038 247 .66H

Wow! The inductance goes down as the excitation voltage decreases?

Remember, the Tonghui measured .52H even on the 1kHz setting. That's
plenty good for me.

What this tells me is that I cannot trust *any* RLC meter to give me the
inductance of a 60Hz piece of magnetics at low excitation voltage.

I have a lot more to learn about magnetics. But, the Tonghui is not at
fault and I need more education.

Cheers,
John S
 
M

Mike

Jan 1, 1970
0
[...]
I've done a couple of investigations since yesterday to try to get
to the bottom of this.
First, I checked my Tonghui data against an old HP4260A Universal
Bridge, bought on eek-Bay and long out of calibration. I can
produce the data if you wish, but the crux of it is that they
agree with each other.

That's very good news. Thanks for the info.
Well, I tell myself, the transformer must be producing unexpected
data.

That was my feeling also. I was concerned there might be a bit of
residual magnetism left after running on 120VAC. I thought that
might bias the transformer partway up the BH curve and give spurious
results.

My plan was to measure with the Tonghui, measure on 120VAC, then
back to the Tonghui again. But too busy at the moment to start it.
First, I checked the Tonghui for output voltage when the
transformer was attached. The lower frequency settings (exclude
the 10kHz setting) produced 98 to 141mV RMS.

Is that measuring the output of the Tonghui across the primary of
the transformer?
I then connected the transformer to an HP audio oscillator set for
60Hz and an HP3400A RMS meter. The results were not only
surprising to me, but they were good support for the believability
of the data produced by the Tonghui.
E(source) V(L) XL(calc) L(calc)
5 3 450 1.2H
3 1.5 350 0.92H
0.1 0.038 247 0.66H
Wow! The inductance goes down as the excitation voltage decreases?

What is V(L) - the voltage across the primary? Is that using the
ouput impedance of the sig gen in series with the primary? What is
the output impedance of the sig gen, and the resistance of the
primary?

In the old days, we used transformers to couple the output of 50B5's
and 6L6's to speakers. These transformers used laminations very
similar to power transformers. In fact, if you were in a pinch, you
could use a power transformer as the output transformer.

We also used transformers at the input to audio amplifiers to break
common-mode hum problems, such as PA systems and intercoms.

So the transformers had to be pretty linear wrt amplitude, else we
would see plenty of articles in Electronics World about reducing
low-level distortions.

OTOH, today's power transformers may use different steel, which may
have nonlinear characteristics or some residual magnetism.

Recall the power transformer in a microwave oven is running pretty
close to saturation to minimize the amount of iron needed to reduce
cost and weight.
Remember, the Tonghui measured 0.52H even on the 1kHz setting.
That's plenty good for me.
What this tells me is that I cannot trust *any* RLC meter to give
me the inductance of a 60Hz piece of magnetics at low excitation
voltage.

This is becoming a very interesting subject. Thanks for bringing it
up and for the good data.
I have a lot more to learn about magnetics. But, the Tonghui is
not at fault and I need more education.

I have studiously avoided learning anything about magnetics for over
60 years. But it looks like my golden days of ignorance are about to
come to an end. I had already come to the conclusion it was time to
start learning about magnetics since I need to do some work on pwm
power supplies for a new product. It looks like you have accelerated
the process:)
Cheers,
John S

Thanks John. Very interesting info.

Mike
 
J

John S

Jan 1, 1970
0
[...]
I've done a couple of investigations since yesterday to try to get
to the bottom of this.
First, I checked my Tonghui data against an old HP4260A Universal
Bridge, bought on eek-Bay and long out of calibration. I can
produce the data if you wish, but the crux of it is that they
agree with each other.

That's very good news. Thanks for the info.
Well, I tell myself, the transformer must be producing unexpected
data.

That was my feeling also. I was concerned there might be a bit of
residual magnetism left after running on 120VAC. I thought that
might bias the transformer partway up the BH curve and give spurious
results.

My plan was to measure with the Tonghui, measure on 120VAC, then
back to the Tonghui again. But too busy at the moment to start it.
First, I checked the Tonghui for output voltage when the
transformer was attached. The lower frequency settings (exclude
the 10kHz setting) produced 98 to 141mV RMS.

Is that measuring the output of the Tonghui across the primary of
the transformer?
Yes.

I then connected the transformer to an HP audio oscillator set for
60Hz and an HP3400A RMS meter. The results were not only
surprising to me, but they were good support for the believability
of the data produced by the Tonghui.
E(source) V(L) XL(calc) L(calc)
5 3 450 1.2H
3 1.5 350 0.92H
0.1 0.038 247 0.66H
Wow! The inductance goes down as the excitation voltage decreases?

What is V(L) - the voltage across the primary? Is that using the
ouput impedance of the sig gen in series with the primary? What is
the output impedance of the sig gen, and the resistance of the
primary?


Yes to your first question. Output resistance: 600 ohms. DC primary
resistance: 11.5 ohms.

In the old days, we used transformers to couple the output of 50B5's
and 6L6's to speakers. These transformers used laminations very
similar to power transformers. In fact, if you were in a pinch, you
could use a power transformer as the output transformer.


Usually, audio used thinner laminations than 60Hz transformers. The lams
could be had much less than .014 inches.

We also used transformers at the input to audio amplifiers to break
common-mode hum problems, such as PA systems and intercoms.

So the transformers had to be pretty linear wrt amplitude, else we
would see plenty of articles in Electronics World about reducing
low-level distortions.

OTOH, today's power transformers may use different steel, which may
have nonlinear characteristics or some residual magnetism.

Recall the power transformer in a microwave oven is running pretty
close to saturation to minimize the amount of iron needed to reduce
cost and weight.

Yes. I think the lams run about .014 thick.
This is becoming a very interesting subject. Thanks for bringing it
up and for the good data.


I have studiously avoided learning anything about magnetics for over
60 years. But it looks like my golden days of ignorance are about to
come to an end. I had already come to the conclusion it was time to
start learning about magnetics since I need to do some work on pwm
power supplies for a new product. It looks like you have accelerated
the process:)


Thanks John. Very interesting info.

Mike

You're welcome. I think this is now outside the Tonghui subject into the
subject of magnetics. The lesson, though, is don't trust LCR meters with
their low excitation to give valid results on large magnetics.

Cheers,
John S
 
M

Mike

Jan 1, 1970
0
John S said:
On 1/17/2012 3:54 PM, Mike wrote:

That's good info. Too low to turn on bipolar junctions.
Yes to your first question. Output resistance: 600 ohms. DC
primary resistance: 11.5 ohms.

Thanks. Primary resistance is not going to have much effect. But
what is the last line showing 247 volts and 0.66H? Is that from the
previous 220VAC measurement? If so where do you live that you have
220VAC in a wall socket?

[...]
You're welcome. I think this is now outside the Tonghui subject
into the subject of magnetics. The lesson, though, is don't trust
LCR meters with their low excitation to give valid results on
large magnetics.

It looks like you have opened a Pandora's box issue. We need to
learn more why a low-level measurement doesn't work on laminated
cores. What is the mechanism that is causing the discrepancies? Are
there any web links that discuss this in greater detail? Does the
same thing happen on toroids?

This is a very important subject for the Tonghui. If you want to gap
a core, you need to know the inductance you should get after gapping
to confirm it is correct. If the Tonghui can't measure it, I think
we're in trouble.
Cheers,
John S

Thanks,

Mike
 
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