The resistance vs temperature relation is well known. But we are using
one with an industrial controller that sends 100 uA into it and provides
the corresponding voltage.
Are there any cheap converters on the market, to convert this voltage
into a nice linear voltage vs temperature relation ? Then there there
are many voltage-to-display converters.
Bye,
Use a lookup table in software, major points, then interpolate between
them, to required accuracy.
The resistance vs temperature relation is well known. But we are using
one with an industrial controller that sends 100 uA into it and provides
the corresponding voltage.
Are there any cheap converters on the market, to convert this voltage
into a nice linear voltage vs temperature relation ? Then there there
are many voltage-to-display converters.
The resistance vs temperature relation is well known. But we are using
one with an industrial controller that sends 100 uA into it and provides
the corresponding voltage.
Are there any cheap converters on the market, to convert this voltage
into a nice linear voltage vs temperature relation ? Then there there
are many voltage-to-display converters.
Bye,
On 2025-04-08 05:54, Jean-Pierre Coulon wrote:
The resistance vs temperature relation is well known. But we are
using one with an industrial controller that sends 100 uA into it and >>provides the corresponding voltage.
Are there any cheap converters on the market, to convert this
voltage into a nice linear voltage vs temperature relation ? Then
there there are many voltage-to-display converters.
Bye,
The usual method of approximate linearization is to put a carefully
chosen resistor in parallel, which may or may not be good enough
depending on what you're doing. (See e.g. ><https://circuitcellar.com/resources/quickbits/ntc-thermistor-linearizat >ion-2/>.)
It doesn't help resolution on the high temperature end, but it does
prevent the ADC from railing at the low temperature end.
A positive resistance works with an NTC, because its resistanance vs >temperature curve is concave upward. A metal RTD's characteristic is
concave downward, so you need a negative resistance for the job.
Because its nonlinearity is smooth and gentle, you can do an amazingly
good job that way--theoretically under 1K error from -100 to +150C
iirc, and much closer over narrower ranges. (I designed a couple of
those in my misspent youth.)
You wouldn't bother nowadays, since it's going into an ADC anyway, and
code is much cheaper than op amps.
Cheers
Phil Hobbs
In message <879d5bd8-a857-e5f8-e9a5-f3c004fbb937@electrooptical.net>,
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> writes
On 2025-04-08 05:54, Jean-Pierre Coulon wrote:
The resistance vs temperature relation is well known. But we are
using one with an industrial controller that sends 100 uA into it and
provides the corresponding voltage.
Are there any cheap converters on the market, to convert this
voltage into a nice linear voltage vs temperature relation ? Then
there there are many voltage-to-display converters.
Bye,
The usual method of approximate linearization is to put a carefully
chosen resistor in parallel, which may or may not be good enough
depending on what you're doing. (See e.g.
<https://circuitcellar.com/resources/quickbits/ntc-thermistor-linearizat
ion-2/>.)
It doesn't help resolution on the high temperature end, but it does
prevent the ADC from railing at the low temperature end.
A positive resistance works with an NTC, because its resistanance vs
temperature curve is concave upward. A metal RTD's characteristic is
concave downward, so you need a negative resistance for the job.
Because its nonlinearity is smooth and gentle, you can do an amazingly
good job that way--theoretically under 1K error from -100 to +150C
iirc, and much closer over narrower ranges. (I designed a couple of
those in my misspent youth.)
You wouldn't bother nowadays, since it's going into an ADC anyway, and
code is much cheaper than op amps.
Cheers
Phil Hobbs
I tried to do that in the 1970s to control the gain of an APD with temperature. I ended up using a diode as a temperature sensor as I
couldn't get it linear enough.
Later on I wanted a non-linear control for another application.We tried
OP amps with piece-wise shaping circuits. We concluded however the best
way to do it was a PIC with a built in ADC and DAC and a lookup table
as you suggest. That might be the cheapest way for the OP
I've also used AD590s which are pretty good.
Brian
I ended up using a diode as a temperature sensor as I
couldn't get it linear enough.
brian wrote:
<snip>
I ended up using a diode as a temperature sensor as I
couldn't get it linear enough.
Interesting. Thank you for sharing. When operated in Zener mode (as
opposed to avalanche mode) a Zener diode's NTC apparently remains approximately the same, regardless of orientation (forward or reverse biased).
Whether a reverse biased diode breaks down in Zener mode or avalanche
mode depends entirely on the diode you have selected.
if it breaks down at less than 5V reverse voltage it is breaking down by
the Zener mechanism (with a negative temperature coefficient) , and if
it the breaks down at an 8V or a higher reverse voltage the avalanche mechanism is dominant (with a positive temperature coefficient.
Am 11.04.25 um 08:13 schrieb Bill Sloman:
Whether a reverse biased diode breaks down in Zener mode or avalanche
mode depends entirely on the diode you have selected.
if it breaks down at less than 5V reverse voltage it is breaking down
by the Zener mechanism (with a negative temperature coefficient) , and
if it the breaks down at an 8V or a higher reverse voltage the
avalanche mechanism is dominant (with a positive temperature coefficient.
Noisewise, the mode is easy to be seen. The avalanche effect is MUCH
worse. Already small avalanche contributions spoil the pot.
in
< https://www.flickr.com/photos/137684711@N07/24411798996/in/album-72157662535945536/ >,
I have measured the NXP BZX84 family. The 2V7 or 5V6 in the type number
mean exactly that. At 4V7 the low noise property is already gone.
The pics to the left & right show some LEDs and regulators.
BTW: the leftmost pic of the peaceful Blau river valley is where the
Gauss family runs a hotel. Yes, "our" Mr. Gauss. They have an oil
painting of him in the dining room.
??? of him / of his: which one is correct?????
BTW2: For the sake of scientific honesty, Prof. Zener sued the semi
industry that they should not use his name for avalanche diodes.
They settled for calling them Z-diodes and pretended it referred to the
form of the U/I curve.
Don wrote:
brian wrote:
<snip>
I ended up using a diode as a temperature sensor as I
couldn't get it linear enough.
Interesting. Thank you for sharing. When operated in Zener mode (as
opposed to avalanche mode) a Zener diode's NTC apparently remains
approximately the same, regardless of orientation (forward or reverse
biased).
Whether a reverse biased diode breaks down in Zener mode or avalanche
mode depends entirely on the diode you have selected.
if it breaks down at less than 5V reverse voltage it is breaking down by
the Zener mechanism (with a negative temperature coefficient) , and if
it the breaks down at an 8V or a higher reverse voltage the avalanche mechanism is dominant (with a positive temperature coefficient.
https://toshiba.semicon-storage.com/us/semiconductor/knowledge/faq/diode/are-there-any-special-considerations-for-the-temperature-coeffic.html
doesn't exactly conform to your claim.
Bill Sloman wrote:
Don wrote:
brian wrote:
<snip>
I ended up using a diode as a temperature sensor as I
couldn't get it linear enough.
Interesting. Thank you for sharing. When operated in Zener mode (as
opposed to avalanche mode) a Zener diode's NTC apparently remains
approximately the same, regardless of orientation (forward or reverse
biased).
Whether a reverse biased diode breaks down in Zener mode or avalanche
mode depends entirely on the diode you have selected.
if it breaks down at less than 5V reverse voltage it is breaking down by
the Zener mechanism (with a negative temperature coefficient) , and if
it the breaks down at an 8V or a higher reverse voltage the avalanche
mechanism is dominant (with a positive temperature coefficient.
https://toshiba.semicon-storage.com/us/semiconductor/knowledge/faq/diode/are-there-any-special-considerations-for-the-temperature-coeffic.html
doesn't exactly conform to your claim.
My statement
When operated in Zener mode (as opposed to avalanche mode)
pertains Zener diodes in Zener mode. Why do you want to talk about the positive temperature coefficient of Zeners in avalanche mode?
Am 11.04.25 um 08:13 schrieb Bill Sloman:
Whether a reverse biased diode breaks down in Zener mode or avalanche
mode depends entirely on the diode you have selected.
if it breaks down at less than 5V reverse voltage it is breaking down
by the Zener mechanism (with a negative temperature coefficient) , and
if it the breaks down at an 8V or a higher reverse voltage the
avalanche mechanism is dominant (with a positive temperature coefficient.
Noisewise, the mode is easy to be seen. The avalanche effect is MUCH
worse. Already small avalanche contributions spoil the pot.
in
< https://www.flickr.com/photos/137684711@N07/24411798996/in/album-72157662535945536/ >,
I have measured the NXP BZX84 family. The 2V7 or 5V6 in the type number
mean exactly that. At 4V7 the low noise property is already gone.
The pics to the left & right show some LEDs and regulators.
BTW: the leftmost pic of the peaceful Blau river valley is where the
Gauss family runs a hotel. Yes, "our" Mr. Gauss. They have an oil
painting of him in the dining room.
??? of him / of his: which one is correct?????
BTW2: For the sake of scientific honesty, Prof. Zener sued the semi
industry that they should not use his name for avalanche diodes.
They settled to call them Z-diodes and to pretend it was for the
form of the U/I curve.
cheers, Gerhard
The problem is that you choose the mode when you choose the diode. Your formulation suggests that you think somebody could to operate one diode
in one mode or the other. Only a hopeless newbie could think that, but
some of the lurkers aren't all that sophisticated, and a few of our
posters aren't much better.
Gerhard Hoffmann has pointed out that even a 4.7V zener diode has enough avalanche component in it's breakdown mechanism to introduce lots of
noise though the temperature coefficient of the reverse voltage is still marginally negative.
Professor Zener was being optimistic. Language is defined by the words
people use, and if the majority makes a habit of using words incorrectly
that usage becomes part of the language.
On 4/11/25 07:37, Bill Sloman wrote:
Like incorrectly using mantissa for the significand of a floating point number. Note that the word mantissa does not appear anywhere in the IEEE spec.
Professor Zener was being optimistic. Language is defined by the words
people use, and if the majority makes a habit of using words incorrectly
that usage becomes part of the language.
https://www-users.cse.umn.edu/~vinals/tspot_files/phys4041/2020/IEEE%20Standard%20754-2019.pdf
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