Empathy List Archives

W

WarrenS

Sat, Jan 26, 2013 8:48 PM

Andreas

If you want to make something in volume which is just pretty good, I would
not recommend this method for a new design.
On the other hand, if this is a nuts thing to make the very best, this is
one of only a very few possible solutions.

Here are some general answers, most of my experience with these parts is
pretty dated, (i.e long ago).
As when pushing the performance limit of any reference, there is a lot of
variation between parts and even more so between manufactures.
Solution is, select, Age, select, test, grade, select.

As far as my experience with 1N823, performance depends on the run and what
is left after the manufacture has selected out the others.
With 1N823's, Yield can often go to zero. With 1N825's a typical yield I've
seen is around 25-50% (from the right manufacture and batch)

Yes the main difference is the zero TC current, with some parts there is no
zero TC current.
So yes you are more likely to get a lower current TC such as 5 ma from a
1N823 or 1N825 than a 1N829, but it could of course be > than 7.5 ma.
I don't use anything that does not have a zero TC between ~ 4 and 10 ma
I found TC to be very much a Batch thing, with up to 50% of the majority of
a batch, tending to be similar.

From a given batch, any that are considerable different, I don't use because

they may have something else wrong going on.

Another thing that needs to be selected for in high end references, and will
vary by manufacturer, is 1/F noise. The random jumps in the voltage.

For me, hysteresis has not been a issue over room temperature changes for
the most part, but something that has to be checked.
Some Manufactures are better than others, and hysteresis can and will be
effected by assembly, layout, or anything that puts any stress on the part.
Don't just solder the parts down on a PCB without a stress relieve loop in
the leads.

The zero TC current can be set so that the voltage at most any two
temperatures will be the same. (<< 1PPM)
If the voltage change in-between those two temperatures is too much, lots of
ways to add an additional second order temperature compensation.

For the best TC performance, consider the mini-oven idea with the zener,
heater resistor, and thermistor all heat shrunk together.
With a lot of outer insulation, it could be done low power by adding an
addition 0 to 5 ma to the heater resistor.

Everything has it's trade offs.
The trade off using these zeners is time and complexity.
For these parts, 5ma is about as low as you are going to get.
For low power, there are many things Much better.
The trade off you make to get low power is "Noise" & stability.
The trade off you make for the good TC of LM399 is long term stability, PPM
noise, and the high cost of selection fall outs.

The best solution will depend on many things including the desired
performance, how many you want to make, the cost you place on selection
time,
and if you can still find the 1N825's at a reasonable price like they where
in the 70s & 80s. (& $0.10 in 2000s)

For a xfer standard, the Most important criteria is 1/f random noise. Most
everything else can be compensated out.
For that, it is hard to build anything better than using a 1N825 selected
device. Plot attached.

ws

Date: Sat, 26 Jan 2013 16:30:34 +0100
From: "Andreas Jahn" Andreas_-_Jahn@t-online.de
Subject: [volt-nuts] Some questions to zeners (1N823-1N829)

Hello all,
Hello Warren,

after having experimented a lot with 5V monolithic zener references
and still not found the ideal solution I want to try a 1N82x based
solution.

For me a extended room temperature range of
25 degrees centigrade +/- 7 degrees (64-90 ?F) is of interest.
Since I plan to have battery supplied instruments a lower supply current
would be of interest.

For the zeners a zero TC current is stated.
Over which temperature range the TC is nearly zero.
How large is the voltage deviation in the above mentioned range?

Does it play a role for the absolute temperature deviation if a 1N823 or a
1N829 is used?
Or is the behaviour equally when the individual zero TC current is used?
Is the only difference between the selections that the zero TC current is
more near the 7.5mA value on the 1N829?

So is it more likely to get a low zero TC current of 4 mA on a 1N823
device than on the 1N829?
Or should I go for the 1N829A for the lowest absolute TC?

How large is the hysteresis on the zeners in a temperature range of 10-40
degrees celsius (50-104?F).
On monolithic unheated reference voltages with hermetic case I have up to
around 2 ppm hysteresis difference
on temperature cycling. (see attached picture with 10-45 degrees celsius
on X-Axis for an ADC with a 5V reference
measuring a LM399 heated reference over a 2:1 precision voltage divider.
The ADC with the 5V reference is temperature cycled).

I blame the temperature hysteresis on the die attach to the lead frame
which seems to be usually a silver filled epoxy compound.
I hope that the hysteresis on a discrete zener is much lower.

With best regards

Andreas

Name: AD586_05_Hyst_20130120.PNG
URL:
http://www.febo.com/pipermail/volt-nuts/attachments/20130126/4a3abca5/attachment.png

Andreas If you want to make something in volume which is just pretty good, I would not recommend this method for a new design. On the other hand, if this is a nuts thing to make the very best, this is one of only a very few possible solutions. Here are some general answers, most of my experience with these parts is pretty dated, (i.e long ago). As when pushing the performance limit of any reference, there is a lot of variation between parts and even more so between manufactures. Solution is, select, Age, select, test, grade, select. As far as my experience with 1N823, performance depends on the run and what is left after the manufacture has selected out the others. With 1N823's, Yield can often go to zero. With 1N825's a typical yield I've seen is around 25-50% (from the right manufacture and batch) Yes the main difference is the zero TC current, with some parts there is no zero TC current. So yes you are more likely to get a lower current TC such as 5 ma from a 1N823 or 1N825 than a 1N829, but it could of course be > than 7.5 ma. I don't use anything that does not have a zero TC between ~ 4 and 10 ma I found TC to be very much a Batch thing, with up to 50% of the majority of a batch, tending to be similar. >From a given batch, any that are considerable different, I don't use because they may have something else wrong going on. Another thing that needs to be selected for in high end references, and will vary by manufacturer, is 1/F noise. The random jumps in the voltage. For me, hysteresis has not been a issue over room temperature changes for the most part, but something that has to be checked. Some Manufactures are better than others, and hysteresis can and will be effected by assembly, layout, or anything that puts any stress on the part. Don't just solder the parts down on a PCB without a stress relieve loop in the leads. The zero TC current can be set so that the voltage at most any two temperatures will be the same. (<< 1PPM) If the voltage change in-between those two temperatures is too much, lots of ways to add an additional second order temperature compensation. For the best TC performance, consider the mini-oven idea with the zener, heater resistor, and thermistor all heat shrunk together. With a lot of outer insulation, it could be done low power by adding an addition 0 to 5 ma to the heater resistor. Everything has it's trade offs. The trade off using these zeners is time and complexity. For these parts, 5ma is about as low as you are going to get. For low power, there are many things Much better. The trade off you make to get low power is "Noise" & stability. The trade off you make for the good TC of LM399 is long term stability, PPM noise, and the high cost of selection fall outs. The best solution will depend on many things including the desired performance, how many you want to make, the cost you place on selection time, and if you can still find the 1N825's at a reasonable price like they where in the 70s & 80s. (& $0.10 in 2000s) For a xfer standard, the Most important criteria is 1/f random noise. Most everything else can be compensated out. For that, it is hard to build anything better than using a 1N825 selected device. Plot attached. ws ************************************ > > Date: Sat, 26 Jan 2013 16:30:34 +0100 > From: "Andreas Jahn" <Andreas_-_Jahn@t-online.de> > Subject: [volt-nuts] Some questions to zeners (1N823-1N829) > > Hello all, > Hello Warren, > > after having experimented a lot with 5V monolithic zener references > and still not found the ideal solution I want to try a 1N82x based > solution. > > For me a extended room temperature range of > 25 degrees centigrade +/- 7 degrees (64-90 ?F) is of interest. > Since I plan to have battery supplied instruments a lower supply current > would be of interest. > > For the zeners a zero TC current is stated. > Over which temperature range the TC is nearly zero. > How large is the voltage deviation in the above mentioned range? > > Does it play a role for the absolute temperature deviation if a 1N823 or a > 1N829 is used? > Or is the behaviour equally when the individual zero TC current is used? > Is the only difference between the selections that the zero TC current is > more near the 7.5mA value on the 1N829? > > So is it more likely to get a low zero TC current of 4 mA on a 1N823 > device than on the 1N829? > Or should I go for the 1N829A for the lowest absolute TC? > > How large is the hysteresis on the zeners in a temperature range of 10-40 > degrees celsius (50-104?F). > On monolithic unheated reference voltages with hermetic case I have up to > around 2 ppm hysteresis difference > on temperature cycling. (see attached picture with 10-45 degrees celsius > on X-Axis for an ADC with a 5V reference > measuring a LM399 heated reference over a 2:1 precision voltage divider. > The ADC with the 5V reference is temperature cycled). > > I blame the temperature hysteresis on the die attach to the lead frame > which seems to be usually a silver filled epoxy compound. > I hope that the hysteresis on a discrete zener is much lower. > > With best regards > > Andreas -------------------------------------------------- > Name: AD586_05_Hyst_20130120.PNG > URL: > <http://www.febo.com/pipermail/volt-nuts/attachments/20130126/4a3abca5/attachment.png> > > ------------------------------

AJ

Andreas Jahn

Sun, Jan 27, 2013 4:45 PM

Hello Warren,

many thanks for your valuable response.

If you want to make something in volume

The planned number of devices is more in the range of 2 up to four.

one of only a very few possible solutions.

I guess that the others are a LM399 or a LTZ1000 based solution (both with
heaters).

Don't just solder the parts down on a PCB without a stress relieve loop in
the leads.

Thats a good hint otherwise I will get the humidity changes of the PCB as
stress on the device.

The zero TC current can be set so that the voltage at most any two
temperatures will be the same. (<< 1PPM)

Do you have typical values over a 64-90 °F range. Will it be above 1ppm/K or
below?

From your plot it would be 0.33ppm per 3 degrees in narrow range i.e. 0.1

ppm per degree.
By the way: is it degrees Fahrenheit or degrees Celsius (= 3 Kelvin)?

From a given batch, any that are considerable different, I don't use
because
they may have something else wrong going on.

Thats interesting since I have 5 pieces of the brand new LT1236AILS-5
devices.
4 of them have a tempco of 2-3 ppm/K around room temperature.
1 piece has a very flat tempco of around 0.2ppm/K (picture attached)
If I understand you right then you would not use this device because it does
behave other than the others?
On the other side it seems to be the device with the largest ageing rate of
the 5 pieces.

One experience that I did is that devices out of one batch which have a low
tempco
around room temperature tend to have a larger hysteresis and vice versa.

So I still hope that anyone has experiences with hysteresis of the zeners.

With best regards

Andreas

----- Original Message -----
From: "WarrenS" warrensjmail-one@yahoo.com
To: volt-nuts@febo.com
Sent: Saturday, January 26, 2013 9:48 PM
Subject: Re: [volt-nuts] Some questions to zeners (1N823-1N829)

Andreas

If you want to make something in volume which is just pretty good, I would
not recommend this method for a new design.
On the other hand, if this is a nuts thing to make the very best, this is
one of only a very few possible solutions.

Here are some general answers, most of my experience with these parts is
pretty dated, (i.e long ago).
As when pushing the performance limit of any reference, there is a lot of
variation between parts and even more so between manufactures.
Solution is, select, Age, select, test, grade, select.

As far as my experience with 1N823, performance depends on the run and
what
is left after the manufacture has selected out the others.
With 1N823's, Yield can often go to zero. With 1N825's a typical yield
I've
seen is around 25-50% (from the right manufacture and batch)

Yes the main difference is the zero TC current, with some parts there is
no
zero TC current.
So yes you are more likely to get a lower current TC such as 5 ma from a
1N823 or 1N825 than a 1N829, but it could of course be > than 7.5 ma.
I don't use anything that does not have a zero TC between ~ 4 and 10 ma
I found TC to be very much a Batch thing, with up to 50% of the majority
of
a batch, tending to be similar.
From a given batch, any that are considerable different, I don't use
because
they may have something else wrong going on.

Another thing that needs to be selected for in high end references, and
will
vary by manufacturer, is 1/F noise. The random jumps in the voltage.

For me, hysteresis has not been a issue over room temperature changes for
the most part, but something that has to be checked.
Some Manufactures are better than others, and hysteresis can and will be
effected by assembly, layout, or anything that puts any stress on the
part.
Don't just solder the parts down on a PCB without a stress relieve loop in
the leads.

The zero TC current can be set so that the voltage at most any two
temperatures will be the same. (<< 1PPM)
If the voltage change in-between those two temperatures is too much, lots
of
ways to add an additional second order temperature compensation.

For the best TC performance, consider the mini-oven idea with the zener,
heater resistor, and thermistor all heat shrunk together.
With a lot of outer insulation, it could be done low power by adding an
addition 0 to 5 ma to the heater resistor.

Everything has it's trade offs.
The trade off using these zeners is time and complexity.
For these parts, 5ma is about as low as you are going to get.
For low power, there are many things Much better.
The trade off you make to get low power is "Noise" & stability.
The trade off you make for the good TC of LM399 is long term stability,
PPM
noise, and the high cost of selection fall outs.

The best solution will depend on many things including the desired
performance, how many you want to make, the cost you place on selection
time,
and if you can still find the 1N825's at a reasonable price like they
where
in the 70s & 80s. (& $0.10 in 2000s)

For a xfer standard, the Most important criteria is 1/f random noise. Most
everything else can be compensated out.
For that, it is hard to build anything better than using a 1N825 selected
device. Plot attached.

ws

Date: Sat, 26 Jan 2013 16:30:34 +0100
From: "Andreas Jahn" Andreas_-_Jahn@t-online.de
Subject: [volt-nuts] Some questions to zeners (1N823-1N829)

Hello all,
Hello Warren,

after having experimented a lot with 5V monolithic zener references
and still not found the ideal solution I want to try a 1N82x based
solution.

For me a extended room temperature range of
25 degrees centigrade +/- 7 degrees (64-90 ?F) is of interest.
Since I plan to have battery supplied instruments a lower supply current
would be of interest.

For the zeners a zero TC current is stated.
Over which temperature range the TC is nearly zero.
How large is the voltage deviation in the above mentioned range?

Does it play a role for the absolute temperature deviation if a 1N823 or
a
1N829 is used?
Or is the behaviour equally when the individual zero TC current is used?
Is the only difference between the selections that the zero TC current is
more near the 7.5mA value on the 1N829?

So is it more likely to get a low zero TC current of 4 mA on a 1N823
device than on the 1N829?
Or should I go for the 1N829A for the lowest absolute TC?

How large is the hysteresis on the zeners in a temperature range of 10-40
degrees celsius (50-104?F).
On monolithic unheated reference voltages with hermetic case I have up to
around 2 ppm hysteresis difference
on temperature cycling. (see attached picture with 10-45 degrees celsius
on X-Axis for an ADC with a 5V reference
measuring a LM399 heated reference over a 2:1 precision voltage divider.
The ADC with the 5V reference is temperature cycled).

I blame the temperature hysteresis on the die attach to the lead frame
which seems to be usually a silver filled epoxy compound.
I hope that the hysteresis on a discrete zener is much lower.

With best regards

Andreas

Name: AD586_05_Hyst_20130120.PNG
URL:
http://www.febo.com/pipermail/volt-nuts/attachments/20130126/4a3abca5/attachment.png

volt-nuts mailing list -- volt-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.

Hello Warren, many thanks for your valuable response. > If you want to make something in volume The planned number of devices is more in the range of 2 up to four. > one of only a very few possible solutions. I guess that the others are a LM399 or a LTZ1000 based solution (both with heaters). > Don't just solder the parts down on a PCB without a stress relieve loop in > the leads. Thats a good hint otherwise I will get the humidity changes of the PCB as stress on the device. > The zero TC current can be set so that the voltage at most any two > temperatures will be the same. (<< 1PPM) Do you have typical values over a 64-90 °F range. Will it be above 1ppm/K or below? >From your plot it would be 0.33ppm per 3 degrees in narrow range i.e. 0.1 ppm per degree. By the way: is it degrees Fahrenheit or degrees Celsius (= 3 Kelvin)? > From a given batch, any that are considerable different, I don't use > because > they may have something else wrong going on. Thats interesting since I have 5 pieces of the brand new LT1236AILS-5 devices. 4 of them have a tempco of 2-3 ppm/K around room temperature. 1 piece has a very flat tempco of around 0.2ppm/K (picture attached) If I understand you right then you would not use this device because it does behave other than the others? On the other side it seems to be the device with the largest ageing rate of the 5 pieces. One experience that I did is that devices out of one batch which have a low tempco around room temperature tend to have a larger hysteresis and vice versa. So I still hope that anyone has experiences with hysteresis of the zeners. With best regards Andreas ----- Original Message ----- From: "WarrenS" <warrensjmail-one@yahoo.com> To: <volt-nuts@febo.com> Sent: Saturday, January 26, 2013 9:48 PM Subject: Re: [volt-nuts] Some questions to zeners (1N823-1N829) > Andreas > > If you want to make something in volume which is just pretty good, I would > not recommend this method for a new design. > On the other hand, if this is a nuts thing to make the very best, this is > one of only a very few possible solutions. > > Here are some general answers, most of my experience with these parts is > pretty dated, (i.e long ago). > As when pushing the performance limit of any reference, there is a lot of > variation between parts and even more so between manufactures. > Solution is, select, Age, select, test, grade, select. > > As far as my experience with 1N823, performance depends on the run and > what > is left after the manufacture has selected out the others. > With 1N823's, Yield can often go to zero. With 1N825's a typical yield > I've > seen is around 25-50% (from the right manufacture and batch) > > Yes the main difference is the zero TC current, with some parts there is > no > zero TC current. > So yes you are more likely to get a lower current TC such as 5 ma from a > 1N823 or 1N825 than a 1N829, but it could of course be > than 7.5 ma. > I don't use anything that does not have a zero TC between ~ 4 and 10 ma > I found TC to be very much a Batch thing, with up to 50% of the majority > of > a batch, tending to be similar. > From a given batch, any that are considerable different, I don't use > because > they may have something else wrong going on. > > Another thing that needs to be selected for in high end references, and > will > vary by manufacturer, is 1/F noise. The random jumps in the voltage. > > For me, hysteresis has not been a issue over room temperature changes for > the most part, but something that has to be checked. > Some Manufactures are better than others, and hysteresis can and will be > effected by assembly, layout, or anything that puts any stress on the > part. > Don't just solder the parts down on a PCB without a stress relieve loop in > the leads. > > The zero TC current can be set so that the voltage at most any two > temperatures will be the same. (<< 1PPM) > If the voltage change in-between those two temperatures is too much, lots > of > ways to add an additional second order temperature compensation. > > For the best TC performance, consider the mini-oven idea with the zener, > heater resistor, and thermistor all heat shrunk together. > With a lot of outer insulation, it could be done low power by adding an > addition 0 to 5 ma to the heater resistor. > > Everything has it's trade offs. > The trade off using these zeners is time and complexity. > For these parts, 5ma is about as low as you are going to get. > For low power, there are many things Much better. > The trade off you make to get low power is "Noise" & stability. > The trade off you make for the good TC of LM399 is long term stability, > PPM > noise, and the high cost of selection fall outs. > > The best solution will depend on many things including the desired > performance, how many you want to make, the cost you place on selection > time, > and if you can still find the 1N825's at a reasonable price like they > where > in the 70s & 80s. (& $0.10 in 2000s) > > For a xfer standard, the Most important criteria is 1/f random noise. Most > everything else can be compensated out. > For that, it is hard to build anything better than using a 1N825 selected > device. Plot attached. > > > ws > > ************************************ >> >> Date: Sat, 26 Jan 2013 16:30:34 +0100 >> From: "Andreas Jahn" <Andreas_-_Jahn@t-online.de> >> Subject: [volt-nuts] Some questions to zeners (1N823-1N829) >> >> Hello all, >> Hello Warren, >> >> after having experimented a lot with 5V monolithic zener references >> and still not found the ideal solution I want to try a 1N82x based >> solution. >> >> For me a extended room temperature range of >> 25 degrees centigrade +/- 7 degrees (64-90 ?F) is of interest. >> Since I plan to have battery supplied instruments a lower supply current >> would be of interest. >> >> For the zeners a zero TC current is stated. >> Over which temperature range the TC is nearly zero. >> How large is the voltage deviation in the above mentioned range? >> >> Does it play a role for the absolute temperature deviation if a 1N823 or >> a >> 1N829 is used? >> Or is the behaviour equally when the individual zero TC current is used? >> Is the only difference between the selections that the zero TC current is >> more near the 7.5mA value on the 1N829? >> >> So is it more likely to get a low zero TC current of 4 mA on a 1N823 >> device than on the 1N829? >> Or should I go for the 1N829A for the lowest absolute TC? >> >> How large is the hysteresis on the zeners in a temperature range of 10-40 >> degrees celsius (50-104?F). >> On monolithic unheated reference voltages with hermetic case I have up to >> around 2 ppm hysteresis difference >> on temperature cycling. (see attached picture with 10-45 degrees celsius >> on X-Axis for an ADC with a 5V reference >> measuring a LM399 heated reference over a 2:1 precision voltage divider. >> The ADC with the 5V reference is temperature cycled). >> >> I blame the temperature hysteresis on the die attach to the lead frame >> which seems to be usually a silver filled epoxy compound. >> I hope that the hysteresis on a discrete zener is much lower. >> >> With best regards >> >> Andreas > -------------------------------------------------- >> Name: AD586_05_Hyst_20130120.PNG >> URL: >> <http://www.febo.com/pipermail/volt-nuts/attachments/20130126/4a3abca5/attachment.png> >> >> ------------------------------ > -------------------------------------------------------------------------------- > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there.

EB

Ed Breya

Sun, Jan 27, 2013 5:36 PM

Andreas,

I think your expectations are not realistic - even if you could make
such a reference, you could not transport its voltage to the ADC without
thermoelectric effects causing error that would swamp the performance.
To keep everything below the 1 ppm/deg C range you would have to put the
entire circuit in controlled temperature - the reference, the ADC, and
the signal connection to the outside world. Constant temperature
operation would help with the overall tempco and hysteresis, but the
long term drift and noise will be intrinsic to the devices, and
unpredictable except in a statistical sense.

Ed

Andreas, I think your expectations are not realistic - even if you could make such a reference, you could not transport its voltage to the ADC without thermoelectric effects causing error that would swamp the performance. To keep everything below the 1 ppm/deg C range you would have to put the entire circuit in controlled temperature - the reference, the ADC, and the signal connection to the outside world. Constant temperature operation would help with the overall tempco and hysteresis, but the long term drift and noise will be intrinsic to the devices, and unpredictable except in a statistical sense. Ed

JB

John Beale

Sun, Jan 27, 2013 8:31 PM

On 1/27/2013 9:36 AM, Ed Breya wrote:

I think your expectations are not realistic - even if you could make such a
reference, you could not transport its voltage to the ADC without
thermoelectric effects causing error that would swamp the performance. To
keep everything below the 1 ppm/deg C range you would have to put the
entire circuit in controlled temperature - the reference, the ADC, and the
signal connection to the outside world.

I don't have the practical experience or measurements to back this up, but
I understand Seebeck thermoelectric effects are a function of the
temperature difference between dissimilar-metal junctions, and not absolute
temperature. So if you have perfectly balanced both the thermal mass and
the thermal conductivity to ambient of every bimetallic junction in your
circuit, there should be zero tempco of the system due to thermocouples,
regardless of both absolute ambient temperature and the rate of temperature
change with time.

So in theory, if you use a symmetrical circuit layout with balanced thermal
mass* and then surround your battery-operated device with a large enough
block of metal (to minimize both thermal gradient, and rate of change with
time), you can get d(temperature)/d(time) of the circuit and the associated
internal temperature differentials to be arbitrarily small. How practical
this "large metal block" would be to meet a <1 ppm/C tempco spec, I do not
know. Assuming you have avoided the copper oxide problem (Cu-CuO: 1000
uV/C) the worst thermocouple will be Cu-Kovar at 40 uV/C so layout at and
around the IC packages will be the most critical.

I assume the hardest connections to keep thermally equalized would be the
terminals connecting your reference/ADC to an external device. If your
voltmeter is limited to low voltages, optimizing this suggests the smallest
and most closely-spaced connections possible, embedded in an insulating but
thermally conductive matrix (ceramic?). Standard banana jacks with 3/4 inch
spacing and surrounded by plastic, seem far from "small" or "closely
spaced" or "well thermally coupled".

The "20-bit DAC" app note mentions this technique:
http://cds.linear.com/docs/Application%20Note/an86f.pdf

John Beale
www.bealecorner.com

On 1/27/2013 9:36 AM, Ed Breya wrote: > I think your expectations are not realistic - even if you could make such a > reference, you could not transport its voltage to the ADC without > thermoelectric effects causing error that would swamp the performance. To > keep everything below the 1 ppm/deg C range you would have to put the > entire circuit in controlled temperature - the reference, the ADC, and the > signal connection to the outside world. I don't have the practical experience or measurements to back this up, but I understand Seebeck thermoelectric effects are a function of the temperature difference between dissimilar-metal junctions, and not absolute temperature. So if you have perfectly balanced both the thermal mass and the thermal conductivity to ambient of every bimetallic junction in your circuit, there should be zero tempco of the system due to thermocouples, regardless of both absolute ambient temperature and the rate of temperature change with time. So in theory, if you use a symmetrical circuit layout with balanced thermal mass* and then surround your battery-operated device with a large enough block of metal (to minimize both thermal gradient, and rate of change with time), you can get d(temperature)/d(time) of the circuit and the associated internal temperature differentials to be arbitrarily small. How practical this "large metal block" would be to meet a <1 ppm/C tempco spec, I do not know. Assuming you have avoided the copper oxide problem (Cu-CuO: 1000 uV/C) the worst thermocouple will be Cu-Kovar at 40 uV/C so layout at and around the IC packages will be the most critical. I assume the hardest connections to keep thermally equalized would be the terminals connecting your reference/ADC to an external device. If your voltmeter is limited to low voltages, optimizing this suggests the smallest and most closely-spaced connections possible, embedded in an insulating but thermally conductive matrix (ceramic?). Standard banana jacks with 3/4 inch spacing and surrounded by plastic, seem far from "small" or "closely spaced" or "well thermally coupled". * The "20-bit DAC" app note mentions this technique: http://cds.linear.com/docs/Application%20Note/an86f.pdf John Beale www.bealecorner.com

PK

Poul-Henning Kamp

Sun, Jan 27, 2013 9:28 PM

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In message 51058EAC.9000309@bealecorner.com, John Beale writes:

So if you have perfectly balanced both the thermal mass and
the thermal conductivity to ambient of every bimetallic junction in your
circuit, there should be zero tempco of the system due to thermocouples,
regardless of both absolute ambient temperature and the rate of temperature
change with time.

This used to be very unrealistic for a host of reasons, all ultimately
terminating at the power dissipation of the various components heating
them to different degrees.

However, with todays low-power ADCs, things are starting to look
far more interesting, and given the size of the parts, submerging
the entire thing in a suitable liquid is also no longer out of the
question.

But it's still a major challenge...

But isn't that why we're on this mailing list to begin with ?

--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

Content-Type: text/plain; charset=ISO-8859-1 -------- In message <51058EAC.9000309@bealecorner.com>, John Beale writes: >So if you have perfectly balanced both the thermal mass and >the thermal conductivity to ambient of every bimetallic junction in your >circuit, there should be zero tempco of the system due to thermocouples, >regardless of both absolute ambient temperature and the rate of temperature >change with time. This used to be very unrealistic for a host of reasons, all ultimately terminating at the power dissipation of the various components heating them to different degrees. However, with todays low-power ADCs, things are starting to look far more interesting, and given the size of the parts, submerging the entire thing in a suitable liquid is also no longer out of the question. But it's still a major challenge... But isn't that why we're on this mailing list to begin with ? -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.

TH

Tony Holt

Mon, Jan 28, 2013 1:48 PM

On 27/01/2013 20:31, John Beale wrote:

On 1/27/2013 9:36 AM, Ed Breya wrote:

I think your expectations are not realistic - even if you could make
such a
reference, you could not transport its voltage to the ADC without
thermoelectric effects causing error that would swamp the
performance. To
keep everything below the 1 ppm/deg C range you would have to put the
entire circuit in controlled temperature - the reference, the ADC,
and the
signal connection to the outside world.

Presumably, if the voltage reference uses an amplifier then a four wire
connection can be used to eliminate all the EMFs between the reference
and ADC other than those at the Kelvin connections at the ADC and
reference/amp so that the reference and the ADC don't have to be in
thermal equilibrium with each other. Could the sense wires be welded to
the ADC pins between the solder connection to the PCB and the package to
avoid the thermal EMFs of a solder joint?

I assume the hardest connections to keep thermally equalized would be
the terminals connecting your reference/ADC to an external device. If
your voltmeter is limited to low voltages, optimizing this suggests
the smallest and most closely-spaced connections possible, embedded in
an insulating but thermally conductive matrix (ceramic?). Standard
banana jacks with 3/4 inch spacing and surrounded by plastic, seem far
from "small" or "closely spaced" or "well thermally coupled"

For a couple of data points, here's one manufacturer's approach to
dealing with thermal EMFs:

http://www.hpd-online.com/reversing_switch.php

Their low thermal reversing switch uses plenty of copper and aluminium
to minimise thermal differences, claiming typical thermal offset of only
3nV, 10nV max! Its not clear (to me) though exactly where that 3nV is
being measured and how effective the 1.5mm thick copper lugs connecting
the reference source/DUT's terminals are at minimising temperature
differences between the terminals in the presence of normal air currents
in a typical Lab.

And this scanner: http://www.dataproof.com/scanner.pdf claims thermal
EMFs of less than 15nV typical (30nV max) using lots of aluminium to
keep relay contacts in thermal equilibrium.

Tony H

On 27/01/2013 20:31, John Beale wrote: > On 1/27/2013 9:36 AM, Ed Breya wrote: >> I think your expectations are not realistic - even if you could make >> such a >> reference, you could not transport its voltage to the ADC without >> thermoelectric effects causing error that would swamp the >> performance. To >> keep everything below the 1 ppm/deg C range you would have to put the >> entire circuit in controlled temperature - the reference, the ADC, >> and the >> signal connection to the outside world. Presumably, if the voltage reference uses an amplifier then a four wire connection can be used to eliminate all the EMFs between the reference and ADC other than those at the Kelvin connections at the ADC and reference/amp so that the reference and the ADC don't have to be in thermal equilibrium with each other. Could the sense wires be welded to the ADC pins between the solder connection to the PCB and the package to avoid the thermal EMFs of a solder joint? > I assume the hardest connections to keep thermally equalized would be > the terminals connecting your reference/ADC to an external device. If > your voltmeter is limited to low voltages, optimizing this suggests > the smallest and most closely-spaced connections possible, embedded in > an insulating but thermally conductive matrix (ceramic?). Standard > banana jacks with 3/4 inch spacing and surrounded by plastic, seem far > from "small" or "closely spaced" or "well thermally coupled" For a couple of data points, here's one manufacturer's approach to dealing with thermal EMFs: http://www.hpd-online.com/reversing_switch.php Their low thermal reversing switch uses plenty of copper and aluminium to minimise thermal differences, claiming typical thermal offset of only 3nV, 10nV max! Its not clear (to me) though exactly where that 3nV is being measured and how effective the 1.5mm thick copper lugs connecting the reference source/DUT's terminals are at minimising temperature differences between the terminals in the presence of normal air currents in a typical Lab. And this scanner: http://www.dataproof.com/scanner.pdf claims thermal EMFs of less than 15nV typical (30nV max) using lots of aluminium to keep relay contacts in thermal equilibrium. Tony H

MS

Mike S

Mon, Jan 28, 2013 5:11 PM

On 1/28/2013 8:48 AM, Tony Holt wrote:

Could the sense wires be welded to
the ADC pins between the solder connection to the PCB and the package to
avoid the thermal EMFs of a solder joint?

I don't think welding would make the difference, unless the wire is made
of the same material as the pin.

I'm also not clear to me how low-EMF solder helps in most cases. Solder
joints tend to be small and local, and it's the temperature difference
between the terminals which brings the thermoelectric effect into play.

For example, two copper wires soldered together - you have a Cu-solder
joint, followed by a solder-Cu joint, in very close proximity. As long
as "close" is close, and/or there's good thermal mass/conductivity,
don't the thermocouples simply offset each other?

More realistically, take a device with common tinned brass terminals on
a PC board. You have brass/tin, tin/solder then solder/copper
thermocouples in very close proximity, essentially resulting in a
brass/copper thermocouple. It seems that the temperature difference
between that connection and the similar thermocouples at the far end
device connection would overwhelm the local effects due to solder, which
require a temperature gradient across some small fraction of a mm.

Even with much larger, hand soldered terminals, something similar would
seem to apply. Wouldn't thermally insulating the terminals (which by
nature have pretty good thermal conductivity) to ensure a consistent
temperature across them be as good or better than just low EMF solder?

Mike

On 1/28/2013 8:48 AM, Tony Holt wrote: > Could the sense wires be welded to > the ADC pins between the solder connection to the PCB and the package to > avoid the thermal EMFs of a solder joint? I don't think welding would make the difference, unless the wire is made of the same material as the pin. I'm also not clear to me how low-EMF solder helps in most cases. Solder joints tend to be small and local, and it's the temperature difference between the terminals which brings the thermoelectric effect into play. For example, two copper wires soldered together - you have a Cu-solder joint, followed by a solder-Cu joint, in very close proximity. As long as "close" is close, and/or there's good thermal mass/conductivity, don't the thermocouples simply offset each other? More realistically, take a device with common tinned brass terminals on a PC board. You have brass/tin, tin/solder then solder/copper thermocouples in very close proximity, essentially resulting in a brass/copper thermocouple. It seems that the temperature difference between that connection and the similar thermocouples at the far end device connection would overwhelm the local effects due to solder, which require a temperature gradient across some small fraction of a mm. Even with much larger, hand soldered terminals, something similar would seem to apply. Wouldn't thermally insulating the terminals (which by nature have pretty good thermal conductivity) to ensure a consistent temperature across them be as good or better than just low EMF solder? --- Mike

DC

David C. Partridge

Mon, Jan 28, 2013 7:04 PM

But if you have five solder joints on conenction to the +ve terminal and 7 on the connection to the -ve terminal at different locations on the PCB, then all bets are off ...

Regards,
David Partridge
-----Original Message-----
From: volt-nuts-bounces@febo.com [mailto:volt-nuts-bounces@febo.com] On Behalf Of Mike S
Sent: 28 January 2013 17:11
To: volt-nuts@febo.com
Subject: Re: [volt-nuts] Some questions to zeners (thermoelectric effects)

On 1/28/2013 8:48 AM, Tony Holt wrote:

Could the sense wires be welded to
the ADC pins between the solder connection to the PCB and the package to > avoid the thermal EMFs of a solder joint?

I don't think welding would make the difference, unless the wire is made of the same material as the pin.

I'm also not clear to me how low-EMF solder helps in most cases. Solder joints tend to be small and local, and it's the temperature difference between the terminals which brings the thermoelectric effect into play.

For example, two copper wires soldered together - you have a Cu-solder joint, followed by a solder-Cu joint, in very close proximity. As long as "close" is close, and/or there's good thermal mass/conductivity, don't the thermocouples simply offset each other?

More realistically, take a device with common tinned brass terminals on a PC board. You have brass/tin, tin/solder then solder/copper thermocouples in very close proximity, essentially resulting in a brass/copper thermocouple. It seems that the temperature difference between that connection and the similar thermocouples at the far end device connection would overwhelm the local effects due to solder, which require a temperature gradient across some small fraction of a mm.

Even with much larger, hand soldered terminals, something similar would seem to apply. Wouldn't thermally insulating the terminals (which by nature have pretty good thermal conductivity) to ensure a consistent temperature across them be as good or better than just low EMF solder?

Mike

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But if you have five solder joints on conenction to the +ve terminal and 7 on the connection to the -ve terminal at different locations on the PCB, then all bets are off ... Regards, David Partridge -----Original Message----- From: volt-nuts-bounces@febo.com [mailto:volt-nuts-bounces@febo.com] On Behalf Of Mike S Sent: 28 January 2013 17:11 To: volt-nuts@febo.com Subject: Re: [volt-nuts] Some questions to zeners (thermoelectric effects) On 1/28/2013 8:48 AM, Tony Holt wrote: > Could the sense wires be welded to > the ADC pins between the solder connection to the PCB and the package to > avoid the thermal EMFs of a solder joint? I don't think welding would make the difference, unless the wire is made of the same material as the pin. I'm also not clear to me how low-EMF solder helps in most cases. Solder joints tend to be small and local, and it's the temperature difference between the terminals which brings the thermoelectric effect into play. For example, two copper wires soldered together - you have a Cu-solder joint, followed by a solder-Cu joint, in very close proximity. As long as "close" is close, and/or there's good thermal mass/conductivity, don't the thermocouples simply offset each other? More realistically, take a device with common tinned brass terminals on a PC board. You have brass/tin, tin/solder then solder/copper thermocouples in very close proximity, essentially resulting in a brass/copper thermocouple. It seems that the temperature difference between that connection and the similar thermocouples at the far end device connection would overwhelm the local effects due to solder, which require a temperature gradient across some small fraction of a mm. Even with much larger, hand soldered terminals, something similar would seem to apply. Wouldn't thermally insulating the terminals (which by nature have pretty good thermal conductivity) to ensure a consistent temperature across them be as good or better than just low EMF solder? --- Mike _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.

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Re: [volt-nuts] Some questions to zeners (1N823-1N829)

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