Can anybody recomend a Pt100 interface chip?  - Page 1
Forum section: electronics / projects

author: Kaptein QK
author_rank: Regular Contributor
timestamp: October 21, 2022, 09:02:55 am
content: I need a Pt100 interface chip, but google fails meCan be either analog or digital output.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 21, 2022, 09:11:25 am
content: First two search results for PT100 ADC:https://www.ti.com/lit/an/sbaa329a/sbaa329a.pdfhttps://www.ti.com/lit/an/sbaa334b/sbaa334b.pdf

author: AndyC_772
author_rank: Super Contributor
timestamp: October 21, 2022, 09:48:04 am
content: I've successfully used TI ADS1120 - there's very comprehensive applications info in the data sheet for 2, 3 or 4 wire connections to a resistive probe.

author: H.O
author_rank: Frequent Contributor
timestamp: October 21, 2022, 10:22:55 am
content: MAX31865 or, if you need multiple channels, LTC2986 are two more.

author: bidrohini
author_rank: Regular Contributor
timestamp: October 21, 2022, 11:34:41 am
content: You can use 741 general purpose OP-AMP too:https://create.arduino.cc/projecthub/Roboro/measuring-temperature-from-pt100-using-arduino-4aed22

author: AndyC_772
author_rank: Super Contributor
timestamp: October 21, 2022, 12:40:10 pm
content: Good grief, does the 741 even still exist?I remember even when I studied electronics back at school, the 741 was described as the 'Model T Ford' of op-amps... in its day, ubiquitous and revolutionary, but before too long, hopelessly outdated and outclassed in every way.That was over 30 years ago.

author: Kaptein QK
author_rank: Regular Contributor
timestamp: October 24, 2022, 08:16:26 am
content: Thanks, I settled on MAX31865.

author: Nominal Animal
author_rank: Super Contributor
timestamp: October 24, 2022, 10:05:39 am
content: I can definitely recommend theMAX31865for interfacing to three and four-wire Pt100 or Pt1000 sensors. Use a precise stable 400Ω reference resistor for Pt100, or a 4000Ω for Pt1000. It has a 15-bit ADC built-in, so if you use good sensors with known Callendar–Van Dusen parameters, you can use the Callendar–Van Dusen equation or either of the ITS-90 polynomials for really precise temperature measurements over the entire sensor range. (In particular, you can use a full 32768-sample look-up tables in current microcontrollers to convert each ADC value to the corresponding temperature in your preferred units, using 64k (16-bit fixed point) or 128k (32-bit fixed point or float) of ROM or Flash, precalculating the table in a simple C program or say a Python or Awk script.)I definitely recommend using three or four-wire Pt100/Pt1000 sensors, too.(I am a hobbyist, with a physics and programming background, and like to interface all kinds of sensors to microcontrollers and Linux-based Single Board Computers.)

author: amaschas
author_rank: Regular Contributor
timestamp: October 25, 2022, 05:04:25 pm
content: Quote from: Nominal Animal on October 24, 2022, 10:05:39 amOut of curiosity since I am also in the process of designing an application that requires temperature measurement with a high level of accuracy (+/- 0.15C), my sense has always been that it's easier to work with a PT1000 because there is a larger change in resistance per unit of temperature. Is that true? Are there particular reasons to use a PT100 over a PT1000?

author: RoGeorge
author_rank: Super Contributor
timestamp: October 25, 2022, 05:45:05 pm
content: Accuracy and resolution are unrelated. A sensor can have plenty of resolution (sensitive to change) yet with low accuracy (its absolute value is incorrect). For example one can sense a 1 millidegree Celsius increase in temperature, but can not tell for sure if it's 24 or 25*C outside.

author: amaschas
author_rank: Regular Contributor
timestamp: October 25, 2022, 06:44:53 pm
content: Quote from: RoGeorge on October 25, 2022, 05:45:05 pmOh yes, sorry. I'm always mixing up my sensor accuracy/precision/resolution terms. To rephrase, is it easier to measure temperature with a higher resolution with a PT1000 than a PT100?

author: Nominal Animal
author_rank: Super Contributor
timestamp: October 25, 2022, 08:16:54 pm
content: Quote from: amaschas on October 25, 2022, 05:04:25 pmThe main difference is with very low temperatures, since passing current through the resistor creates waste heat. Pt1000 has higher resistance at a given temperature, and thus less waste heat.As far as I understand, Pt1000 is not any easier or harder to measure than Pt100 is, except in very cold conditions (say below -50°C or so).Pt100 sensors (of acceptable hobbyist quality at least) are much easier to obtain.

author: SiliconWizard
author_rank: Super Contributor
timestamp: October 25, 2022, 08:39:13 pm
content: I've used an ADS1118 and a wheatstone bridge arrangement for this. It was for a Pt1000 though.The thing with a Pt100 using the classic wheatstone bridge is that it will have higher power draw and, as mentioned above, this can create errors due to heating.You can of course use a different arrangement with a lower "excitation" current - but it will need more gain and thus is likely to get more noise and more error.

author: amaschas
author_rank: Regular Contributor
timestamp: October 27, 2022, 04:53:58 am
content: Quote from: Nominal Animal on October 25, 2022, 08:16:54 pmAh OK, that does make sense. I guess my understanding was that with a PT100, you'd have to measure changes in resistance, and therefore changes in voltage, that are 10x smaller than on a PT1000 to detect an equivalent change in temperature. Essentially you get 10x the resolution with a PT1000 vs a PT100 at the same level of gain (if I'm using that term correctly in this context).

author: LM21
author_rank: Regular Contributor
timestamp: October 27, 2022, 07:34:07 pm
content: I wote for MAX31865. There are Arduino libraries for it, and Adafruit has a small module for it. Beware of cheap clones in Ebay, they have replaced EMI ferrite with a ceramic capacitor, and the module has no power then.

author: wraper
author_rank: Unknown
timestamp: October 27, 2022, 07:46:25 pm
content: Quote from: LM21 on October 27, 2022, 07:34:07 pmSounds like a bad batch with assembly error.