ECC Forum

BCS series temperature controllers use thermistor based temperature probes. Thermistors work by varying resistance according to temperature in a non-linear fashion. To ensure the highest accuracy, the controller utilizes the Steinhart-Hart thermistor equation to calculate temperature. For more information about this method, visit http://www.betatherm.com/stein.htm or other resources on the web.

In a nutshell, to calibrate a temperature probe we need to have three different measurements of temperature and resistance. These can be gathered experimentally, or taken from a manufacturers datasheet of the probes. These measurements are then programmed into an online calculator (see below), which generates the Steinhart-Hart coefficients. These coefficients can then be programmed into the controller on the System Settings page.

The system defaults use the following values. These were taken from the manufacturer's datasheet, which is attached below.
degF Resistance(ohms)
32 29481
104 5595
158 1991

And from the calculator, the coefficients are calculated as:
A=0.0010281797
B=2.3924024E-4
C=1.5657565E-7

To gather measurements experimentally, use a calibrated thermometer to find the temperature of a sample. Simultaneously use the Thermo Test page in the BCS-460 to find the measured resistance of the probe in the same sample. The probes are sensitive, so its better to take the measurement while its immersed in a liquid, as opposed to a free-air measurement.

Here's one online calculator to generate the coefficients, also linked off the main page of the ECC website.
http://www.thinksrs.com/downloads/progr ... ulator.htm (updated 02/17/2015 with new resource)

A BYO article that gives a good general description of thermometer calibration.
http://www.byo.com/component/resource/a ... techniques

With the excitement of having the BCS on order I may have gotten a little rammy and bought the wrong "thermistors".
While I bought 3 probes from ECC I thought having a dozen loose thermistors laying around for who knows what would be a good idea. I got on Ebay and bought these http://www.taydaelectronics.com/datasheets/A-050.pdf
Are these even compatible? I hooked one up it reads 153 instead of 60... the link above talks about some conversion coefficients but does not seem to be the same as talked about here. Any help is much appreciated.

thanks

Sorry, not compatible. Those aren't thermistors, they have a serial interface.

Is there a particular reason the 3 temperature calibration points are 32, 104 and 158F?

Thanks

0, 40, and 70 celsius...

clearwaterbrewer wrote:0, 40, and 70 celsius...

not trying be a smart a$$, is there something special about 0, 40, and 70C?

Those three points do a really good job approximating the curve of Temp vs. Resistance for what most people use thermistors for.....
2 points would work if it were linear, but 3 points and the Steinhart-Hart equation can map the curve really good with three points...
http://en.wikipedia.org/wiki/Thermistor


here is a graph

Will The BCS work with standard RTD probes or Thermocouples?

Sorry, not compatible. The BCS is designed for use with NTC Thermistor based probes.

been trying to calibrate the probes, and the site you have listed does not work. i cant run the java applet from any browser on any computer.

http://www.capgo.com/Resources/Temperat ... rCalc.html
i keep getting the msg that this particular java applet is unsafe.

i have taken the resistance of the 4 probes i have, and taken at 0, 40, 70. but now i cant do anything..

Help

Thank
ColeR-