Low coefficient NTC resistors?...

[whit3rd]

On Friday, December 10, 2021 at 6:14:23 PM UTC-8, palli...@gmail.com wrote:

PT1000/PT100 is ~0.4%/C

Oh, that\'s just about true for all classical metals; getting a non-PTAT (proportional
to absolute temperature) resistor is a notable materials-science achievement.

At 20 C, proportional to absolute temperature means about 0.0034 per kelvin; for
copper, resistance goes 0.00386, for tungsten 0.0045, for aluminum 0.00429,
for platinum 0.0039 ...

The impure (alloyed) metals used for low tempco have very non-ideal metallic nature.

** \" very non- ideal metallic nature\" ???????

Could you please be bit more ambiguous ??

The simple ideal metal doesn\'t expand or contract with temperature changes, hasn\'t
any crystal defects, no bandgap changes, no magnetism, Einstein model phonon
spectrum, and all resistance is the consequence of electron-phonon scattering.
Then, if you know the thermal phonon population, THAT determines the resistivity.
Alloys for low tempco have various deviations from these behaviors, so the thermal phonon
population statistic is not dominant.

 

[Phil Allison]

The biggest Fuckwit on Usenet posts as whit3rd
=======================================

The impure (alloyed) metals used for low tempco have very non-ideal metallic nature.

** \" very non- ideal metallic nature\" ???????

Could you please be bit more ambiguous ??
Cos some fuckheads here will imagine it makes sense.


The simple ideal metal doesn\'t expand or contract with temperature changes, hasn\'t
any crystal defects, no bandgap changes, no magnetism, Einstein model phonon
spectrum, and all resistance is the consequence of electron-phonon scattering.
Then, if you know the thermal phonon population, THAT determines the resistivity.
Alloys for low tempco have various deviations from these behaviors, so the thermal phonon
population statistic is not dominant.

** Jesus FUCKING CHRIST ALMIGHTY !!!

The whitless fucktard troll does not not just live on another planet -
it posts direct from another universe !!!!!



...... Phil

 

[Anthony William Sloman]

On Saturday, December 11, 2021 at 2:22:11 PM UTC+11, palli...@gmail.com wrote:

IEEE Bill ....@ieee.org wrote:

==========================> > > The biggest Fuckwit on Usenet posts as whit3rd
====================================

PT1000/PT100 is ~0.4%/C

Oh, that\'s just about true for all classical metals; getting a non-PTAT (proportional
to absolute temperature) resistor is a notable materials-science achievement.

At 20 C, proportional to absolute temperature means about 0.0034 per kelvin; for
copper, resistance goes 0.00386, for tungsten 0.0045, for aluminum 0.00429,
for platinum 0.0039 ...

The impure (alloyed) metals used for low tempco have very non-ideal metallic nature.

** \" very non- ideal metallic nature\" ???????

Could you please be bit more ambiguous ??

Cos some fuckheads here will imagine it makes sense.

Back when I was in paid work we got a marketing talk from Vishay on their very low temperature coefficient resistors which could get below +/-5ppm per degree > Celcius, if you were willing to buy their most expensive parts (which we were, if not all that often).

They not only mucked about with the composition of the materials they laid down in their thin films,
but they also figured in temperature generated strain by laying down material with one cofficient
of thermal expansion on a substrate with a a different one.
This is a longer way of saying that they got non-ideal behaviour.

** The witless moron posted about PURE METALS & low tempco metal alloys.

Phil doesn\'t understand what is being talked about, and feels hurt about it . He\'\'s the witless moron in this context.

<snipped his characteristic statement of his bewilderment>

--
Bill Sloman, Sydney

 

[Anthony William Sloman]

On Saturday, December 11, 2021 at 3:03:19 PM UTC+11, palli...@gmail.com wrote:

The biggest Fuckwit on Usenet posts as whit3rd
=======================================

The impure (alloyed) metals used for low tempco have very non-ideal metallic nature.

** \" very non- ideal metallic nature\" ???????

Could you please be bit more ambiguous ??
Cos some fuckheads here will imagine it makes sense.


The simple ideal metal doesn\'t expand or contract with temperature changes, hasn\'t
any crystal defects, no bandgap changes, no magnetism, Einstein model phonon
spectrum, and all resistance is the consequence of electron-phonon scattering.
Then, if you know the thermal phonon population, THAT determines the resistivity.
Alloys for low tempco have various deviations from these behaviors, so the thermal phonon
population statistic is not dominant.

** Jesus FUCKING CHRIST ALMIGHTY !!!

The whitless fucktard troll does not not just live on another planet - it posts direct from another universe !!!!!

Or so witless Phil likes to think. If he doesn\'t know about it, it\'s something he imagines happens on another planet. He does seem to post from Planet Under-informed.

--
Bill Sloman, Sydney

 

[Spehro Pefhany]

On Fri, 10 Dec 2021 07:33:18 -0800, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 10 Dec 2021 10:16:46 -0500, Spehro Pefhany
speffSNIP@interlogDOTyou.knowwhat> wrote:

On Fri, 10 Dec 2021 05:43:39 -0800 (PST), Anthony William Sloman
bill.sloman@ieee.org> wrote:

On Friday, December 10, 2021 at 11:43:16 PM UTC+11, Spehro Pefhany wrote:
On Fri, 10 Dec 2021 22:50:31 +1100, Sylvia Else <syl...@email.invalid
wrote:
Anyone aware of such a thing?

Clearly, one can achieve that just by putting a thermistor in series
with an ordinary resistor, but my UPS seems to contain a single
component that behaves that way - perhaps less than 1% at 20 Celcius -
it\'s in the circuit that controls the battery charging float voltage.

Did they perhaps exist 20 years ago (when my UPS was made), for some reason?

Yes, I have purchased custom positive temperature coefficient
resistors in relatively small lots (10K, if memory serves).

They\'re usually in around the tempco of metals and alloys. (a few
thousand ppm per degree C, positive and fairly linear.

You can find a few values of nickel thin film resistors on Digikey
that have a similar tempco.

Putting a resistor in series with a conventional NTC does not work so
well over a wide temperature range because of the nonlinearity of the
thermistor.

My impression was that nickel thin film resistors were the poor man\'s platinum resistance sensor. They had around the same temperature coefficient - the resistance was more or less proportional to absolute temperature around room temperature. They weren\'t as good as platinum resistance sensors - for one thing they oxidise if they get too hot. Wikipedia says that they go non-linear about about 300 Celcius.

https://www.prelectronics.com/the-fundamentals-of-rtd-temperature-sensors/

https://en.wikipedia.org/wiki/Resistance_thermometer

Propietary nickel alloy base metal sensors are used in HVAC
applications by folks like Honeywell.

Ni120 sensors (wound and now thin film) are traditionally used in some
applications like bearing and motor stator winding temperature
(sometimes they use Cu RTDs for the latter).

The SMT 0603 etc. Vishay ones I was mentioning are pretty awful for
sensors, almost a 10% tolerance on Tempco and a max temperature of
150°C minus self-heating so their applications would be limited. The
ones I sourced from a Japanese factory had much tighter tolerance on
tempco.

The ZNI1000 nickel RTD is a cool part. It can be linearized with one
resistor.

Of course, ic temp sensors are cheap and can be had analog or SPI.

--
Best regards,
Spehro Pefhany

 

[Spehro Pefhany]

On Fri, 10 Dec 2021 07:33:18 -0800, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 10 Dec 2021 10:16:46 -0500, Spehro Pefhany
speffSNIP@interlogDOTyou.knowwhat> wrote:

On Fri, 10 Dec 2021 05:43:39 -0800 (PST), Anthony William Sloman
bill.sloman@ieee.org> wrote:

On Friday, December 10, 2021 at 11:43:16 PM UTC+11, Spehro Pefhany wrote:
On Fri, 10 Dec 2021 22:50:31 +1100, Sylvia Else <syl...@email.invalid
wrote:
Anyone aware of such a thing?

Clearly, one can achieve that just by putting a thermistor in series
with an ordinary resistor, but my UPS seems to contain a single
component that behaves that way - perhaps less than 1% at 20 Celcius -
it\'s in the circuit that controls the battery charging float voltage.

Did they perhaps exist 20 years ago (when my UPS was made), for some reason?

Yes, I have purchased custom positive temperature coefficient
resistors in relatively small lots (10K, if memory serves).

They\'re usually in around the tempco of metals and alloys. (a few
thousand ppm per degree C, positive and fairly linear.

You can find a few values of nickel thin film resistors on Digikey
that have a similar tempco.

Putting a resistor in series with a conventional NTC does not work so
well over a wide temperature range because of the nonlinearity of the
thermistor.

My impression was that nickel thin film resistors were the poor man\'s platinum resistance sensor. They had around the same temperature coefficient - the resistance was more or less proportional to absolute temperature around room temperature. They weren\'t as good as platinum resistance sensors - for one thing they oxidise if they get too hot. Wikipedia says that they go non-linear about about 300 Celcius.

https://www.prelectronics.com/the-fundamentals-of-rtd-temperature-sensors/

https://en.wikipedia.org/wiki/Resistance_thermometer

Propietary nickel alloy base metal sensors are used in HVAC
applications by folks like Honeywell.

Ni120 sensors (wound and now thin film) are traditionally used in some
applications like bearing and motor stator winding temperature
(sometimes they use Cu RTDs for the latter).

The SMT 0603 etc. Vishay ones I was mentioning are pretty awful for
sensors, almost a 10% tolerance on Tempco and a max temperature of
150°C minus self-heating so their applications would be limited. The
ones I sourced from a Japanese factory had much tighter tolerance on
tempco.

The ZNI1000 nickel RTD is a cool part. It can be linearized with one
resistor.

Interesting part, thanks. The accuracy is pretty good.

These Pt guys are a bit more expensive but nice:

https://www.vishay.com/docs/28762/ptsserie.pdf

You can do the one resistor linearization trick with them too.


>Of course, ic temp sensors are cheap and can be had analog or SPI.
--
Best regards,
Spehro Pefhany

 

[server]

On Mon, 13 Dec 2021 23:44:11 -0500, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

On Fri, 10 Dec 2021 07:33:18 -0800, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 10 Dec 2021 10:16:46 -0500, Spehro Pefhany
speffSNIP@interlogDOTyou.knowwhat> wrote:

On Fri, 10 Dec 2021 05:43:39 -0800 (PST), Anthony William Sloman
bill.sloman@ieee.org> wrote:

On Friday, December 10, 2021 at 11:43:16 PM UTC+11, Spehro Pefhany wrote:
On Fri, 10 Dec 2021 22:50:31 +1100, Sylvia Else <syl...@email.invalid
wrote:
Anyone aware of such a thing?

Clearly, one can achieve that just by putting a thermistor in series
with an ordinary resistor, but my UPS seems to contain a single
component that behaves that way - perhaps less than 1% at 20 Celcius -
it\'s in the circuit that controls the battery charging float voltage.

Did they perhaps exist 20 years ago (when my UPS was made), for some reason?

Yes, I have purchased custom positive temperature coefficient
resistors in relatively small lots (10K, if memory serves).

They\'re usually in around the tempco of metals and alloys. (a few
thousand ppm per degree C, positive and fairly linear.

You can find a few values of nickel thin film resistors on Digikey
that have a similar tempco.

Putting a resistor in series with a conventional NTC does not work so
well over a wide temperature range because of the nonlinearity of the
thermistor.

My impression was that nickel thin film resistors were the poor man\'s platinum resistance sensor. They had around the same temperature coefficient - the resistance was more or less proportional to absolute temperature around room temperature. They weren\'t as good as platinum resistance sensors - for one thing they oxidise if they get too hot. Wikipedia says that they go non-linear about about 300 Celcius.

https://www.prelectronics.com/the-fundamentals-of-rtd-temperature-sensors/

https://en.wikipedia.org/wiki/Resistance_thermometer

Propietary nickel alloy base metal sensors are used in HVAC
applications by folks like Honeywell.

Ni120 sensors (wound and now thin film) are traditionally used in some
applications like bearing and motor stator winding temperature
(sometimes they use Cu RTDs for the latter).

The SMT 0603 etc. Vishay ones I was mentioning are pretty awful for
sensors, almost a 10% tolerance on Tempco and a max temperature of
150°C minus self-heating so their applications would be limited. The
ones I sourced from a Japanese factory had much tighter tolerance on
tempco.

The ZNI1000 nickel RTD is a cool part. It can be linearized with one
resistor.

Interesting part, thanks. The accuracy is pretty good.

These Pt guys are a bit more expensive but nice:

https://www.vishay.com/docs/28762/ptsserie.pdf

You can do the one resistor linearization trick with them too.


Of course, ic temp sensors are cheap and can be had analog or SPI.

1206 and 0805 thinfilm platinum RTDs are nice and have the virtue of
being multi-sourced.

There\'s a cute one-opamp conditioning and linearizing circuit for
platinum RTDs, assuming you don\'t want to do it in software.



--

I yam what I yam - Popeye

 

[Anthony William Sloman]

On Tuesday, December 14, 2021 at 4:24:19 PM UTC+11, jla...@highlandsniptechnology.com wrote:

On Mon, 13 Dec 2021 23:44:11 -0500, Spehro Pefhany
spef...@interlogDOTyou.knowwhat> wrote:

On Fri, 10 Dec 2021 07:33:18 -0800, jla...@highlandsniptechnology.com
wrote:

On Fri, 10 Dec 2021 10:16:46 -0500, Spehro Pefhany
spef...@interlogDOTyou.knowwhat> wrote:

On Fri, 10 Dec 2021 05:43:39 -0800 (PST), Anthony William Sloman
bill....@ieee.org> wrote:

On Friday, December 10, 2021 at 11:43:16 PM UTC+11, Spehro Pefhany wrote:
On Fri, 10 Dec 2021 22:50:31 +1100, Sylvia Else <syl...@email.invalid
wrote:
Anyone aware of such a thing?

Clearly, one can achieve that just by putting a thermistor in series
with an ordinary resistor, but my UPS seems to contain a single
component that behaves that way - perhaps less than 1% at 20 Celcius -
it\'s in the circuit that controls the battery charging float voltage.

Did they perhaps exist 20 years ago (when my UPS was made), for some reason?

Yes, I have purchased custom positive temperature coefficient
resistors in relatively small lots (10K, if memory serves).

They\'re usually in around the tempco of metals and alloys. (a few
thousand ppm per degree C, positive and fairly linear.

You can find a few values of nickel thin film resistors on Digikey
that have a similar tempco.

Putting a resistor in series with a conventional NTC does not work so
well over a wide temperature range because of the nonlinearity of the
thermistor.

My impression was that nickel thin film resistors were the poor man\'s platinum resistance sensor. They had around the same temperature coefficient - the resistance was more or less proportional to absolute temperature around room temperature. They weren\'t as good as platinum resistance sensors - for one thing they oxidise if they get too hot. Wikipedia says that they go non-linear about about 300 Celcius.

https://www.prelectronics.com/the-fundamentals-of-rtd-temperature-sensors/

https://en.wikipedia.org/wiki/Resistance_thermometer

Propietary nickel alloy base metal sensors are used in HVAC
applications by folks like Honeywell.

Ni120 sensors (wound and now thin film) are traditionally used in some
applications like bearing and motor stator winding temperature
(sometimes they use Cu RTDs for the latter).

The SMT 0603 etc. Vishay ones I was mentioning are pretty awful for
sensors, almost a 10% tolerance on Tempco and a max temperature of
150°C minus self-heating so their applications would be limited. The
ones I sourced from a Japanese factory had much tighter tolerance on
tempco.

The ZNI1000 nickel RTD is a cool part. It can be linearized with one
resistor.

Interesting part, thanks. The accuracy is pretty good.

These Pt guys are a bit more expensive but nice:

https://www.vishay.com/docs/28762/ptsserie.pdf

You can do the one resistor linearization trick with them too.


Of course, ic temp sensors are cheap and can be had analog or SPI.
1206 and 0805 thinfilm platinum RTDs are nice and have the virtue of
being multi-sourced.

There\'s a cute one-opamp conditioning and linearizing circuit for
platinum RTDs, assuming you don\'t want to do it in software.

Back when I did one, back in 1979, you needed a lot of gain in that one op amp. I ended up going with four - it made the low pass filtering a lot easier. My bosses got tetchy, so I had to draw the one, two and three op amp options. Electrotherm had a bulk deal on the uA715, so the one amplifier option wasn\'t all that expensive, but nothing else around at the time had that much gain. The linearising involved a smidgen of positive feedback which frightened the guy who took over the project, and nobody could make him see sense.

--
Bill Sloman, Sydney

 

[Edward Hernandez]

The John Doe troll stated the following in message-id
<sdhn7c$pkp$4@dont-email.me>:

> The troll doesn\'t even know how to format a USENET post...

And the John Doe troll stated the following in message-id
<sg3kr7$qt5$1@dont-email.me>:

The reason Bozo cannot figure out how to get Google to keep from
breaking its lines in inappropriate places is because Bozo is
CLUELESS...

And yet, the clueless John Doe troll has itself posted yet another
incorrectly formatted USENET posting on Tue, 14 Dec 2021 06:40:44 -0000
(UTC) in message-id <sp9e9b$q3d$1@dont-email.me>.

This posting is a public service announcement for any google groups
readers who happen by to point out that the John Doe troll does not even
follow it\'s own rules that it uses to troll other posters.

mFpwbmxNA8bW

 

[Anthony William Sloman]

On Tuesday, December 14, 2021 at 5:40:50 PM UTC+11, John Doe wrote:

Anthony William Sloman <bill....@ieee.org> wrote:
On Saturday, December 11, 2021 at 1:14:23 PM UTC+11, palli...@gmail.com wrote:
whit3rd
========================
===========
PT1000/PT100 is ~0.4%/C

Oh, that\'s just about true for all classical metals; getting a non-PTAT (proportional to absolute temperature) resistor is a notable materials-science achievement.

At 20 C, proportional to absolute temperature means about 0.0034 per kelvin; for copper, resistance goes 0.00386, for tungsten 0.0045, for aluminum 0.00429, for platinum 0.0039 ...

The impure (alloyed) metals used for low tempco have very non-ideal meta llic nature.

** \" very non- ideal metallic nature\" ???????

Could you please be bit more ambiguous ??

Cos some fuckheads here will imagine it makes sense.

Back when I was in paid work we got a marketing talk from Vishay on their very low temperature coefficient resistors which could get below +/-5ppm per degree Celcius, if you were willing to buy their most expensive parts (which we were, if not all that often).

They not only mucked about with the composition of the materials they laid down in their thin films, but they also figured in temperature generated strain by laying down material with one cofficient of thermal expansion on a substrate with a a different one. This is a longer way of saying that they got non-ideal behaviour. I can see whit3rd might have wanted to avoid testing your attention span (which isn\'t all that long).

John Doe posted his usual drivel (which I\'ve snipped)- he seems to be even more ignorant about low TC resistors than Phil Allison, and even more dedicated to being obnoxious.

--
Bill Sloman, Sydney

 

[Jan Panteltje]

On a sunny day (Fri, 10 Dec 2021 22:50:31 +1100) it happened Sylvia Else
<sylvia@email.invalid> wrote in <j1gt8aF63iuU1@mid.individual.net>:

Anyone aware of such a thing?

Clearly, one can achieve that just by putting a thermistor in series
with an ordinary resistor, but my UPS seems to contain a single
component that behaves that way - perhaps less than 1% at 20 Celcius -
it\'s in the circuit that controls the battery charging float voltage.

Did they perhaps exist 20 years ago (when my UPS was made), for some reason?

Sylvia

Used a simple Si diode as temp sensor in some equipment.
-2 mV / degree C or there about, linear at that.

 

[Rick C]

On Friday, December 10, 2021 at 8:51:53 PM UTC-4, bill....@ieee.org wrote:

On Saturday, December 11, 2021 at 11:30:50 AM UTC+11, David Eather wrote:
On 10/12/2021 9:50 pm, Sylvia Else wrote:
Anyone aware of such a thing?

Clearly, one can achieve that just by putting a thermistor in series
with an ordinary resistor, but my UPS seems to contain a single
component that behaves that way - perhaps less than 1% at 20 Celcius -
it\'s in the circuit that controls the battery charging float voltage.

Did they perhaps exist 20 years ago (when my UPS was made), for some
reason?

lead acid batteries are temperature sensitive when recharging
All batteries - as electrochemical devices - are temperature sensitive

https://en.wikipedia.org/wiki/Gibbs_free_energy

If you scroll down to \"In electrochemical thermodynamics\" you will get to the Nernst Equation

https://en.wikipedia.org/wiki/Nernst_equation

which can be seen as the Gibbs Free energy equation for electrochemical systems - curiously, Nernst formulated it in 1888 some twelves years after Gibbs had published the more general formulation. Thermodynamics isn\'t easy to get your head around - even if you are as clever as Nernst, who eventually got a Nobel prize in 1920 for his work on the third law of thermodynamics. Once instilled, it does tend to stick - as an undergraduate in 1961 it took me a while to get my head around that particular bit of the chemistry course.

I remember seeing bumper stickers that read, \"Honk if you passed P-Chem\".

Thermo was the ball buster section of the ball buster P-Chem I course with Castellan who wrote a book and of course used it in his class. The book sucked! The part of the class that covered quantum mechanics was easier and better covered.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

 

[Rick C]

On Friday, December 10, 2021 at 9:02:59 PM UTC-4, Sylvia Else wrote:

On 11-Dec-21 11:30 am, David Eather wrote:
On 10/12/2021 9:50 pm, Sylvia Else wrote:
Anyone aware of such a thing?

Clearly, one can achieve that just by putting a thermistor in series
with an ordinary resistor, but my UPS seems to contain a single
component that behaves that way - perhaps less than 1% at 20 Celcius -
it\'s in the circuit that controls the battery charging float voltage.

Did they perhaps exist 20 years ago (when my UPS was made), for some
reason?

Sylvia

lead acid batteries are temperature sensitive when recharging
Yes, this is presumably the reason for the NTC resistor in the charging
circuit. But if it has a typical thermistor characteristic, then in this
particular implementation, the compensation will be out by a factor of
ten, which is probably worse than no compensation at all.

I may have to remove it from the circuit to better characterise it.

I worked on a design last year where the charging circuit had a thermistor to adjust the batter voltage. I pointed out the resistor was on a board near a motor and other power circuits that would certainly make the PWB hotter than the battery at the other end of the cabinet. The designer didn\'t care. He would often wax on about the various nits he had picked up over the years and yet could not understand something so simple as a temperature sensing thermistor needed to be thermally coupled to the battery rather than the motor the battery would be driving.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

 

[Edward Hernandez]

The John Doe troll stated the following in message-id
<sdhn7c$pkp$4@dont-email.me>:

> The troll doesn\'t even know how to format a USENET post...

And the John Doe troll stated the following in message-id
<sg3kr7$qt5$1@dont-email.me>:

The reason Bozo cannot figure out how to get Google to keep from
breaking its lines in inappropriate places is because Bozo is
CLUELESS...

And yet, the clueless John Doe troll has itself posted yet another
incorrectly formatted USENET posting on Wed, 15 Dec 2021 18:12:56 -0000
(UTC) in message-id <spdb78$p47$3@dont-email.me>.

This posting is a public service announcement for any google groups
readers who happen by to point out that the John Doe troll does not even
follow it\'s own rules that it uses to troll other posters.

1jqv3YkW8CYw

 

[Spehro Pefhany]

On Mon, 13 Dec 2021 22:40:09 -0800 (PST), Anthony William Sloman
<bill.sloman@ieee.org> wrote:

Back when I did one, back in 1979, you needed a lot of gain in that one op =
amp. I ended up going with four - it made the low pass filtering a lot easi=
er. My bosses got tetchy, so I had to draw the one, two and three op amp op=
tions. Electrotherm had a bulk deal on the uA715, so the one amplifier opti=
on wasn\'t all that expensive, but nothing else around at the time had that =
much gain.

Odd, RTDs have such high output even a single LM358 should be about
good enough for *most* purposes unless you\'re running them at much
lower than normal current or looking for off-label uK performance
(which I remember you were doing with thermistors).

At 0.5mA you get ~200uV/°C with a Pt100 ohm DIN RTD. Interchangability
is maybe 1/3°C for inexpensive ones (at room temperature) and a degree
or two at extremes, so for normal purposes- any modern op-amp assuming
you don\'t mind trimming the offset.

Coincidentally, about the same output as you get measuring temperature
with silicon BJT(s) operated at 10:1 current ratio.

The linearising involved a smidgen of positive feedback which fr=
ightened the guy who took over the project, and nobody could make him see s=
ense.

Shouldn\'t be too hard to show mathematically that the net feedback is
strongly negative for all sensible RTD values. And that break
protection is in the safe direction.

He probably would be terrified (with some justification) by an
enhanced Howland current source.

The cool thing is that the same resistor that linearizes the RTD can
be used to avoid having an active current source for excitation. Just
a resistor from a reference voltage will do for excitation- there is
no advantage to using a current source.

--=20
Bill Sloman, Sydney

--
Best regards,
Spehro Pefhany

 

[Sylvia Else]

On 14-Dec-21 8:04 pm, Jan Panteltje wrote:

On a sunny day (Fri, 10 Dec 2021 22:50:31 +1100) it happened Sylvia Else
sylvia@email.invalid> wrote in <j1gt8aF63iuU1@mid.individual.net>:

Anyone aware of such a thing?

Clearly, one can achieve that just by putting a thermistor in series
with an ordinary resistor, but my UPS seems to contain a single
component that behaves that way - perhaps less than 1% at 20 Celcius -
it\'s in the circuit that controls the battery charging float voltage.

Did they perhaps exist 20 years ago (when my UPS was made), for some reason?

Sylvia

Used a simple Si diode as temp sensor in some equipment.
-2 mV / degree C or there about, linear at that.

In the end, it became apparent that this thermistor is in parallel with
an ordinary resistor far away on the board.

Also, that the temperature compensation it provides is much too low.
That will be fixed, along with putting the thermistor on the batteries.

Sylvia.

 

[Sylvia Else]

On 15-Dec-21 3:06 am, Rick C wrote:

On Friday, December 10, 2021 at 9:02:59 PM UTC-4, Sylvia Else wrote:
On 11-Dec-21 11:30 am, David Eather wrote:
On 10/12/2021 9:50 pm, Sylvia Else wrote:
Anyone aware of such a thing?

Clearly, one can achieve that just by putting a thermistor in series
with an ordinary resistor, but my UPS seems to contain a single
component that behaves that way - perhaps less than 1% at 20 Celcius -
it\'s in the circuit that controls the battery charging float voltage.

Did they perhaps exist 20 years ago (when my UPS was made), for some
reason?

Sylvia

lead acid batteries are temperature sensitive when recharging
Yes, this is presumably the reason for the NTC resistor in the charging
circuit. But if it has a typical thermistor characteristic, then in this
particular implementation, the compensation will be out by a factor of
ten, which is probably worse than no compensation at all.

I may have to remove it from the circuit to better characterise it.

I worked on a design last year where the charging circuit had a thermistor to adjust the batter voltage. I pointed out the resistor was on a board near a motor and other power circuits that would certainly make the PWB hotter than the battery at the other end of the cabinet. The designer didn\'t care. He would often wax on about the various nits he had picked up over the years and yet could not understand something so simple as a temperature sensing thermistor needed to be thermally coupled to the battery rather than the motor the battery would be driving.

As I\'ve indicated in my reply to Jan, I believe that the circuit in my
UPS is not providing anything like the required compensation. Perhaps
the designer\'s remit was to provide some temperature compensation, so he
did, without caring whether it was the correct amount.

Sylvia.

 

[Anthony William Sloman]

On Thursday, December 16, 2021 at 5:20:17 PM UTC+11, Spehro Pefhany wrote:

On Mon, 13 Dec 2021 22:40:09 -0800 (PST), Anthony William Sloman <bill.....@ieee.org> wrote:

Back when I did one, back in 1979, you needed a lot of gain in that one op amp. I ended up going with four - it made the low pass filtering a lot easier. My bosses got tetchy, so I had to draw the one, two and three op amp options.

Electrotherm

Actually Eurotherm. I was working for Chessel Recorders at the time (which was part of the Eurotherm group.

had a bulk deal on the uA715, so the one amplifier option wasn\'t all that expensive, but nothing else around at the time had that much gain.

Odd, RTDs have such high output even a single LM358 should be about
good enough for *most* purposes unless you\'re running them at much
lower than normal current or looking for off-label uK performance
(which I remember you were doing with thermistors).

It certainly wasn\'t for micro-Kelvin applications. Chessel Recorders were manufactured in high volume for low end applications like bakeries and breweries.

At 0.5mA you get ~200uV/°C with a Pt100 ohm DIN RTD. Interchangability
is maybe 1/3°C for inexpensive ones (at room temperature) and a degree
or two at extremes, so for normal purposes- any modern op-amp assuming
you don\'t mind trimming the offset.

If you wanted 10 degrees to fill the 0 to 10V span of the chart recorder that\'s a gain of 5000, which is quite high. It\'s forty years ago, so the details are hazy.

Coincidentally, about the same output as you get measuring temperature with silicon BJT(s) operated at 10:1 current ratio.

The linearising involved a smidgen of positive feedback which frightened the guy who took over the project, and nobody could make him see sense.

Shouldn\'t be too hard to show mathematically that the net feedback is strongly negative for all sensible RTD values. And that break protection is in the safe direction.

He seemed to think that any positive feedback was risky

https://en.wikipedia.org/wiki/Geometric_series

makes the point that the sum with any r less than one is finite, which isn\'t exactly higher mathematics, and r was about +0.003

He probably would be terrified (with some justification) by an enhanced Howland current source.

The cool thing is that the same resistor that linearizes the RTD can be used to avoid having an active current source for excitation.

That wasn\'t the approach I was using, We just pushed the current through the sense resistor up a bit as it got hotter to compensate for the slow decline in sensitivity with rising temperature. Very crude.

> Just a resistor from a reference voltage will do for excitation- there is no advantage to using a current source.

There is a bit. A Wheatstone bridge throws away a bit of the sensitivity - in a symmetrical bridge, half of it. It certainly isn\'t worth the trouble of going to current source excitation.

--
Bill Sloman, Sydney

 

[Phil Allison]

Sylvia Else wrote:
=================

As I\'ve indicated in my reply to Jan, I believe that the circuit in my
UPS is not providing anything like the required compensation.

**As if a lying, autistic tenth wit like you would know .

the designer\'s remit was to provide some temperature compensation, so he
did, without caring whether it was the correct amount.

** Maybe he, she, it had brain tumor - big as yours.



....... love, Phil

 

[server]

On Thu, 16 Dec 2021 01:20:00 -0500, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

On Mon, 13 Dec 2021 22:40:09 -0800 (PST), Anthony William Sloman
bill.sloman@ieee.org> wrote:

Back when I did one, back in 1979, you needed a lot of gain in that one op =
amp. I ended up going with four - it made the low pass filtering a lot easi=
er. My bosses got tetchy, so I had to draw the one, two and three op amp op=
tions. Electrotherm had a bulk deal on the uA715, so the one amplifier opti=
on wasn\'t all that expensive, but nothing else around at the time had that =
much gain.

Odd, RTDs have such high output even a single LM358 should be about
good enough for *most* purposes unless you\'re running them at much
lower than normal current or looking for off-label uK performance
(which I remember you were doing with thermistors).

At 0.5mA you get ~200uV/°C with a Pt100 ohm DIN RTD. Interchangability
is maybe 1/3°C for inexpensive ones (at room temperature) and a degree
or two at extremes, so for normal purposes- any modern op-amp assuming
you don\'t mind trimming the offset.

Coincidentally, about the same output as you get measuring temperature
with silicon BJT(s) operated at 10:1 current ratio.

The linearising involved a smidgen of positive feedback which fr=
ightened the guy who took over the project, and nobody could make him see s=
ense.

Shouldn\'t be too hard to show mathematically that the net feedback is
strongly negative for all sensible RTD values. And that break
protection is in the safe direction.

He probably would be terrified (with some justification) by an
enhanced Howland current source.

The cool thing is that the same resistor that linearizes the RTD can
be used to avoid having an active current source for excitation. Just
a resistor from a reference voltage will do for excitation- there is
no advantage to using a current source.

I thought I invented that! One resistor to the + supply and one more
for positive feedback from the opamp output, RTD to ground.

I did invent a 3-wire version too. Can\'t remember that circuit now.
Nowadays we just use a mux\'d differential-input delta-sigma ADC and
measure the RTD ratiometrically against a good resistor; don\'t need a
very good reference.


--

I yam what I yam - Popeye