Wanted wirewound precision resistors and ESI DB877
It seem so because the direct resistance measurement seem ok,
and the current once connected to the fluke 343 source
returns perfect value, but now I fear to repeat the process.
...
Can you advice a tecnique to check the other resistors?
I think, you should better measure the resistance by a high resolution
DMM, on its normal OHM range.
Thats much more stable and less power is dissipated. A comparison
between two of them is also much easier.
I opened one broken resistor ( they are open, with only a tape
on the outside) and the wire is oily, there was also somethin like
wax in some points on the outside. I think you are right that the
wire insulation is probably compromised.
I have seen wax inside very old ww resistors from COHU and KINTEL, on
the soldering junction between resistance wire and leads.
Obviously to protect the solder from corrosion.
Some drops of oil may be used to increase high volt isolation as it
ingresses between the windings. I assume, your resistors are tubular
ones, with plastiv caps around, and they are not hermetically tight,
therefore they cant be filled completely for corrosion protection and
thermal conductivity, like in the Vishay metal foil VHP type.
Besides electrical measurement (on OHM range!), I 'd recommen optical
inspection of the case, and if its possible, of the windings for
burnt/overheated areas. Corrosion may be easily identified, also by
slightly stained parts of the wire.
From your description, the resistors seem to be very old, from the
70ties perhaps, therefore the solder junctions may also be defect, if
you find an "open" resistor. Careful resoldering might help.
Frank
Looks like wax, but more probably it is the carrier for
the flux used in soldering. Back in the days of old, everyone
used a petroleum jelly based, zinc chloride flux for soldering
larger wires to terminals.
-Chuck Harris
Frank Stellmach wrote:
...
I have seen wax inside very old ww resistors from COHU and KINTEL, on the soldering
junction between resistance wire and leads.
Obviously to protect the solder from corrosion.
Some drops of oil may be used to increase high volt isolation as it ingresses between
the windings. I assume, your resistors are tubular ones, with plastiv caps around,
and they are not hermetically tight, therefore they cant be filled completely for
corrosion protection and thermal conductivity, like in the Vishay metal foil VHP type.
Besides electrical measurement (on OHM range!), I 'd recommen optical inspection of
the case, and if its possible, of the windings for burnt/overheated areas. Corrosion
may be easily identified, also by slightly stained parts of the wire.
From your description, the resistors seem to be very old, from the 70ties perhaps,
therefore the solder junctions may also be defect, if you find an "open" resistor.
Careful resoldering might help.
Frank
Here I put some photos of the decade:
http://www.eevblog.com/forum/product-reviews-photos-and-discussion/db877-teardown/
Frank Stellmach frank.stellmach@freenet.de ha scritto:
I think, you should better measure the resistance by a high
resolution DMM, on its normal OHM range.
Thats much more stable and less power is dissipated. A comparison
between two of them is also much easier.
Yes I'm using a pair of multimeters: the keithley 2015 and
a solartron 7061, the keithley should be not far from real
values, but has a maximum count of 1200000, the
solartron is "zeroed" against the keithley,
has a maximum count of 21000000, permitting to compare
the 1M and 2M resistors without changing range and resolution.
I used the fluke to try to test for leackage, I
tought that if there was some leackage, the current
would have been higher than V/R ratio and not
proportional to the voltage.
ingresses between the windings. I assume, your resistors are tubular
ones, with plastiv caps around, and they are not hermetically tight,
therefore they cant be filled completely for corrosion protection
and thermal conductivity, like in the Vishay metal foil VHP type.
See the link, there is a pic of the resistor, it's open, no protection
at all.
Besides electrical measurement (on OHM range!), I 'd recommen
optical inspection of the case, and if its possible, of the windings
for burnt/overheated areas. Corrosion may be easily identified, also
by slightly stained parts of the wire.
yes, the low valued resistors (10/20 ohm) seem a little corroded.
The intermediate valued ones seem ok.
Is the wire used (manganin?) prone to corrosion?
Fabio.
This message was sent using IMP, the Internet Messaging Program.
I accidentally replied just to artechmedia with this reply:
I have seen reports of people having problems reproducing the very low TC's that Vishay has been reporting for their z foil resistors. It seems that the low TC may only be for one particular resistance value in the range? So although they will be stable and usable, do not take the TC for granted...MK
Date: Tue, 19 Jun 2012 20:04:40 +0200
From: FabioEb@quipo.it
To: volt-nuts@febo.com
Subject: Re: [volt-nuts] Wanted wirewound precision resistors and ESI DB877
Here I put some photos of the decade:
http://www.eevblog.com/forum/product-reviews-photos-and-discussion/db877-teardown/
Frank Stellmach frank.stellmach@freenet.de ha scritto:
I think, you should better measure the resistance by a high
resolution DMM, on its normal OHM range.
Thats much more stable and less power is dissipated. A comparison
between two of them is also much easier.
Yes I'm using a pair of multimeters: the keithley 2015 and
a solartron 7061, the keithley should be not far from real
values, but has a maximum count of 1200000, the
solartron is "zeroed" against the keithley,
has a maximum count of 21000000, permitting to compare
the 1M and 2M resistors without changing range and resolution.
I used the fluke to try to test for leackage, I
tought that if there was some leackage, the current
would have been higher than V/R ratio and not
proportional to the voltage.
ingresses between the windings. I assume, your resistors are tubular
ones, with plastiv caps around, and they are not hermetically tight,
therefore they cant be filled completely for corrosion protection
and thermal conductivity, like in the Vishay metal foil VHP type.
See the link, there is a pic of the resistor, it's open, no protection
at all.
Besides electrical measurement (on OHM range!), I 'd recommen
optical inspection of the case, and if its possible, of the windings
for burnt/overheated areas. Corrosion may be easily identified, also
by slightly stained parts of the wire.
yes, the low valued resistors (10/20 ohm) seem a little corroded.
The intermediate valued ones seem ok.
Is the wire used (manganin?) prone to corrosion?
Fabio.
This message was sent using IMP, the Internet Messaging Program.
volt-nuts mailing list -- volt-nuts@febo.com
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and follow the instructions there.
Hi Fabio,
I remembered some problems soldering manganin a while ago, so I googled and this one came up:http://listserv.ipc.org/scripts/wa.exe?A2=technet;a5280f30.1203
So it is possible not all the previous flux was removed. I thought it was fairly stable, hence a good bet for standard resistors, but if overheated like you suspect then all bets would be off as they say.
MK
Date: Tue, 19 Jun 2012 20:04:40 +0200
From: FabioEb@quipo.it
To: volt-nuts@febo.com
Subject: Re: [volt-nuts] Wanted wirewound precision resistors and ESI DB877
Here I put some photos of the decade:
http://www.eevblog.com/forum/product-reviews-photos-and-discussion/db877-teardown/
Frank Stellmach frank.stellmach@freenet.de ha scritto:
I think, you should better measure the resistance by a high
resolution DMM, on its normal OHM range.
Thats much more stable and less power is dissipated. A comparison
between two of them is also much easier.
Yes I'm using a pair of multimeters: the keithley 2015 and
a solartron 7061, the keithley should be not far from real
values, but has a maximum count of 1200000, the
solartron is "zeroed" against the keithley,
has a maximum count of 21000000, permitting to compare
the 1M and 2M resistors without changing range and resolution.
I used the fluke to try to test for leackage, I
tought that if there was some leackage, the current
would have been higher than V/R ratio and not
proportional to the voltage.
ingresses between the windings. I assume, your resistors are tubular
ones, with plastiv caps around, and they are not hermetically tight,
therefore they cant be filled completely for corrosion protection
and thermal conductivity, like in the Vishay metal foil VHP type.
See the link, there is a pic of the resistor, it's open, no protection
at all.
Besides electrical measurement (on OHM range!), I 'd recommen
optical inspection of the case, and if its possible, of the windings
for burnt/overheated areas. Corrosion may be easily identified, also
by slightly stained parts of the wire.
yes, the low valued resistors (10/20 ohm) seem a little corroded.
The intermediate valued ones seem ok.
Is the wire used (manganin?) prone to corrosion?
Fabio.
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volt-nuts mailing list -- volt-nuts@febo.com
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and follow the instructions there.
Hi Fabio,
the DB877 is a nice box and is still available from IET Labs. See http://www.ietlabs.com/sitesearch?q=db877 The manual is here http://www.ietlabs.com/sitesearch?q=db877
They will sell you parts but they are not cheap. You won't find a compact 8 decade box with it's accuracy very easily. Even with standard 0.1% resistors subsituted it's a nice unit.
Robert G8RPI
From: Fabio Eboli FabioEb@quipo.it
To: Discussion of precise voltage measurement volt-nuts@febo.com
Sent: Tuesday, 19 June 2012, 19:04
Subject: Re: [volt-nuts] Wanted wirewound precision resistors and ESI DB877
Here I put some photos of the decade:
http://www.eevblog.com/forum/product-reviews-photos-and-discussion/db877-teardown/
Frank Stellmach frank.stellmach@freenet.de ha scritto:
I think, you should better measure the resistance by a high resolution DMM, on its normal OHM range.
Thats much more stable and less power is dissipated. A comparison between two of them is also much easier.
Yes I'm using a pair of multimeters: the keithley 2015 and
a solartron 7061, the keithley should be not far from real
values, but has a maximum count of 1200000, the
solartron is "zeroed" against the keithley,
has a maximum count of 21000000, permitting to compare
the 1M and 2M resistors without changing range and resolution.
I used the fluke to try to test for leackage, I
tought that if there was some leackage, the current
would have been higher than V/R ratio and not
proportional to the voltage.
ingresses between the windings. I assume, your resistors are tubular ones, with plastiv caps around, and they are not hermetically tight, therefore they cant be filled completely for corrosion protection and thermal conductivity, like in the Vishay metal foil VHP type.
See the link, there is a pic of the resistor, it's open, no protection
at all.
Besides electrical measurement (on OHM range!), I 'd recommen optical inspection of the case, and if its possible, of the windings for burnt/overheated areas. Corrosion may be easily identified, also by slightly stained parts of the wire.
yes, the low valued resistors (10/20 ohm) seem a little corroded.
The intermediate valued ones seem ok.
Is the wire used (manganin?) prone to corrosion?
Fabio.
This message was sent using IMP, the Internet Messaging Program.
volt-nuts mailing list -- volt-nuts@febo.com
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and follow the instructions there.
Hello, as for joining manganin I choose the fast dirty method:
http://tinyurl.com/dxvwy8p
In the 20kohm resistor, I tried to reconnect the broken wire,
I unwound a pair of turns and twisted the two wires together
under the scope. Then I simply brazed them using a little piece
of brazing wire (a speck flattened with hammer) with a little
borax, more a plumbing work than an electronic one :)
Probably the thermal stress and the contamination isnt good for
a precision resistor, I will replace it anyway, but I will
keep the brazed one just to check it periodically.
Naturally this method involves heating the parts at 500-600°C :)
Fabio.
m k m1k3k1@hotmail.com ha scritto:
Hi Fabio,
I remembered some problems soldering manganin a while ago, so I
googled and this one came
up:http://listserv.ipc.org/scripts/wa.exe?A2=technet;a5280f30.1203
So it is possible not all the previous flux was removed. I thought
it was fairly stable, hence a good bet for standard resistors, but
if overheated like you suspect then all bets would be off as they say.
MK
Date: Tue, 19 Jun 2012 20:04:40 +0200
From: FabioEb@quipo.it
To: volt-nuts@febo.com
Subject: Re: [volt-nuts] Wanted wirewound precision resistors and ESI DB877
Here I put some photos of the decade:
http://www.eevblog.com/forum/product-reviews-photos-and-discussion/db877-teardown/
Frank Stellmach frank.stellmach@freenet.de ha scritto:
I think, you should better measure the resistance by a high
resolution DMM, on its normal OHM range.
Thats much more stable and less power is dissipated. A comparison
between two of them is also much easier.
Yes I'm using a pair of multimeters: the keithley 2015 and
a solartron 7061, the keithley should be not far from real
values, but has a maximum count of 1200000, the
solartron is "zeroed" against the keithley,
has a maximum count of 21000000, permitting to compare
the 1M and 2M resistors without changing range and resolution.
I used the fluke to try to test for leackage, I
tought that if there was some leackage, the current
would have been higher than V/R ratio and not
proportional to the voltage.
ingresses between the windings. I assume, your resistors are tubular
ones, with plastiv caps around, and they are not hermetically tight,
therefore they cant be filled completely for corrosion protection
and thermal conductivity, like in the Vishay metal foil VHP type.
See the link, there is a pic of the resistor, it's open, no protection
at all.
Besides electrical measurement (on OHM range!), I 'd recommen
optical inspection of the case, and if its possible, of the windings
for burnt/overheated areas. Corrosion may be easily identified, also
by slightly stained parts of the wire.
yes, the low valued resistors (10/20 ohm) seem a little corroded.
The intermediate valued ones seem ok.
Is the wire used (manganin?) prone to corrosion?
Fabio.
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volt-nuts mailing list -- volt-nuts@febo.com
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This message was sent using IMP, the Internet Messaging Program.