Thermistors - Type 2 / Type 3 ?

Log in or register to post comments
Go To Last Post
11 posts / 0 new
Author
Message
schtevo
schtevo's picture
Level: Hangaround
Joined: Mon. Nov 19, 2001
Posts: 493 View posts
Location: Melbourne, Australia
#1
Posted by schtevo: Thu. May 8, 2014 - 02:51 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hello Freaks, (I mean that in a nice way of course)

My google foo has failed me. :(
I have written software to process NTC thermistors using the Beta version of the Steinhart"“Hart equation.
I wish to add some processing to handle some different types of thermistors including some which are classified as 10k type 2 or type 3. Obviously these are 10k@25°C types but I have been unable to find either the Beta value or even A,B,C coefficients corresponding to type 2 or type 3.

Am I correct in assuming type 2|3 refer to a standard R-T curve or am I mistaken?

All I seem to find is a table for R-T. Working backwards, I have used these to calculate the Beta value however it varies considerable across the range and does not instill me with a lot of confidence.

Does anyone know the details are or where I might find them?

Steve

Tags:

Learning and Information, General Electronics
Top
Bronze Markbobgardner
bobgardner's picture
Level: 10k+ Postman
Joined: Wed. Sep 4, 2002
Posts: 26609 View posts
Location: Orlando Florida
Posted by bobgardner: Thu. May 8, 2014 - 02:53 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

US Sensors has a good applet and app notes

Imagecraft compiler user

Top
schtevo
schtevo's picture
Level: Hangaround
Joined: Mon. Nov 19, 2001
Posts: 493 View posts
Location: Melbourne, Australia
Posted by schtevo: Thu. May 8, 2014 - 03:54 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Nice one.
They suggest that Beta is calculated from the R-T data at 0°C and 50°C and provide a formula.
A little different than transposing Steinhart–Hart but at least it equates to 1 Beta value for the whole range.

Thanks Bob.

Top
Bronze Marktheusch
theusch's picture
Level: 10k+ Postman
Joined: Mon. Feb 19, 2001
Posts: 40129 View posts
Location: Wisconsin USA
Posted by theusch: Thu. May 8, 2014 - 03:34 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I also have never heard the "type 2" or "type 3" designation.

I do know that e.g. 10k thermistors can be manufactured with quite different curves.

There has been a lot of discussions in the past on thermistors. Lookup table; bias resistor and linear; beta; Steinhart; ...

Link to recent thread, with links to many other priod discussions:
https://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&p=114025...

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

Top
Bronze Marktheusch
theusch's picture
Level: 10k+ Postman
Joined: Mon. Feb 19, 2001
Posts: 40129 View posts
Location: Wisconsin USA
Posted by theusch: Thu. May 8, 2014 - 03:45 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Quote:

Am I correct in assuming type 2|3 refer to a standard R-T curve or am I mistaken?

From HVAC?
http://hvac-talk.com/vbb/showthr...

osiyo post.

"Precon" tables:
http://www.preconusa.com/oem/tem...

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

Top
billysugger
billysugger's picture
Level: Wannabe
Joined: Thu. Jan 5, 2012
Posts: 50 View posts
Posted by billysugger: Thu. May 8, 2014 - 09:14 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I published the following on using thermistors just a few days ago. Wonder if it helps?
[url]http://www.billysugger.blogspot.co.uk/2014/05/billysugger-simples-how-to...

Electronic components work on the principle of smoke; I know this because when I let the smoke out, they stop working. Also, sanity is over-rated.

Top
schtevo
schtevo's picture
Level: Hangaround
Joined: Mon. Nov 19, 2001
Posts: 493 View posts
Location: Melbourne, Australia
Posted by schtevo: Fri. May 9, 2014 - 01:18 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thanks Lee; I did find the 2 links from HVAC-talk and Precon. Although Precon's table is listed in Fahrenheit gibberish it does indicate that the Type 2 is not just referring to 10k @ 25°C(77°F) types. Though type might.

Thanks for your link too Billy. Looks pretty much the same as how I'm doing it. Nice to have confirming evidence from time to time. I recall going the hard way with full Steinhart–Hart to begin with. Wikipedia has an excellent page on this.

And the results...

Found a couple of similar matched in R-T for Type 2 & 3:

Type 2

Device         R @ 25  R @ 50  Beta           R @ 20

10k3A1         32650   3601    3888           12494

Veris TED00    32770   3599    3895           12500

*Honeywell TB  32190           3975(listed)   12460


Type 3

Device         R @ 25  R @ 50  Beta

10k4A1         29490   3893    3571

TEH00          29588   3894    3576

The Honeywell TB device actually had a Beta value listed which it specified as calculated at 25/85°C. Doesn't quite match but to be expected I suppose. It's R-T table also stopped at 29°C so I just compared values at 20°C. The are also a little ways off the other type2s.

Anyway, looks like I have some reasonable looking Beta values. Just need to apply to the formula an check back against the tables.

Thanks again all.
Steve

Top
billysugger
billysugger's picture
Level: Wannabe
Joined: Thu. Jan 5, 2012
Posts: 50 View posts
Posted by billysugger: Fri. May 9, 2014 - 08:17 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Quote:
I recall going the hard way with full Steinhart–Hart to begin with. Wikipedia has an excellent page on this.

Steinhart-Hart is great for precision sensing in extended temperature ranges, but TBH it's completely over the top for most sensing applications. It's only as good as the coefficients and the accuracy of your sensor, and most thermistor manufacturers do not publish S-H coefficients. You can calculate them from three values derived from the beta curve, but then the result is no more accurate than the Bets method, and takes more processing time to calculate. Keep S-H up your sleave for when you really need it, and can make a sufficiently accurate 3-point calibration.

Electronic components work on the principle of smoke; I know this because when I let the smoke out, they stop working. Also, sanity is over-rated.

Top
Bronze Markbobgardner
bobgardner's picture
Level: 10k+ Postman
Joined: Wed. Sep 4, 2002
Posts: 26609 View posts
Location: Orlando Florida
Posted by bobgardner: Fri. May 9, 2014 - 12:15 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

You can calculate the coefficients from 3 resistance measurements at three temperatures also. Room temp, boiling water, and ice bath are pretty stable temps to measure resistance at.

Imagecraft compiler user

Top
Bronze Marktheusch
theusch's picture
Level: 10k+ Postman
Joined: Mon. Feb 19, 2001
Posts: 40129 View posts
Location: Wisconsin USA
Posted by theusch: Fri. May 9, 2014 - 02:37 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Quote:

It's only as good as the coefficients and the accuracy of your sensor, and most thermistor manufacturers do not publish S-H coefficients.

I did some playing around with my spreadsheet (that I use as an aid for selecting bias resistor), integrated with the spreadsheet from Measurement Specialties that aids in these calculations.

The results so closely match R-T tables from a couple thermistor models, that I suspect the manufacturers are creating the R-T tables using Steinhart-Hart.

Quote:

US Sensors has a good applet ...

That seemed hard to find the last time I looked for it. As I mentioned, I found the Measurement Specialties spreadsheet helpful...follow this link for links:
https://www.avrfreaks.net/index.p...

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

Top
billysugger
billysugger's picture
Level: Wannabe
Joined: Thu. Jan 5, 2012
Posts: 50 View posts
Posted by billysugger: Fri. May 9, 2014 - 10:59 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Quote:
You can calculate the coefficients from 3 resistance measurements at three temperatures also.

I would think that unless you have something very much better than ice and boiling water, (and another accurate third temperature), you'll get about the same level of precision as R25 and Beta. Choice is yours.

Quote:
The results so closely match R-T tables from a couple thermistor models, that I suspect the manufacturers are creating the R-T tables using Steinhart-Hart.

Lol! Very likely.

Electronic components work on the principle of smoke; I know this because when I let the smoke out, they stop working. Also, sanity is over-rated.

Top