I am having trouble getting either of these thermistors to read accurately on a Keysight DAQ970A:
I have them set up as 10K thermistors. Based on the data sheets, these are both 10K thermistors. I have added 5’-10’ leads to each sensor. When comparing the resistance value between the sensor with and without leads, I get a negligible difference in resistance. When measuring a known temperature I am a few degrees off and am curious if there is something I am missing or don’t know.
- Is there something special I need to do with the leads?
- Is there a setting on the DAQ or something I am forgetting to do when hooking this up?
- Is there some reason these thermistors are not compatible with the DAQ I am using?
- Any other thoughts on why I may be having issues getting accurate temperatures?
you have a change with other changes like material , so the parts maybe similar they are NOT a direct cross , they are more a alternative cross.
Thermistors are not all created identically, and therefore will not have identical characteristics at all temperatures. Each vendor creates thermistors with their own materials, and their characteristics will vary. Besides basic tolerances at a specific temperature (commonly 25°C), they have characteristic curves regarding change in resistance vs. change in temperature which are not linear, but which are characterized by “Beta” values. These Beta values have their own tolerances, and they will also vary depending upon where within the temperature range they are characterized (such as between 0 and 50°C or between 25 and 85°C, etc.
Point being, the values read will vary, depending upon which thermistor is used. See note on page 18 of the DAQ970A datasheet:
Looking into the datasheet for the DAQ970A, I see on page 21 (image below) that it was characterized using the “44006” (the 10k version, that is). It looks like that was a Thermometrics part number, and they were acquired by TE Connectivity. The TE part number is now “701006”, which is Digi-Key part number 223-1279-ND. So if you want your temperature readings to more closely follow those calibrated into your DAC, this might be one to consider.
Before I even got to this quote in the thread I was thinking that this was almost certainly designed to use a YSI 44006 thermistor (Yellow Springs Instrument, they stopped manufacturing precision thermistors years ago due to lots of lower priced competition). That specific formulation/characteristic curve has been commercially available in high accuracy thermistors since the 1960s. IIRC correctly it was used in NASA’s manned flight programs. Where I work it has been used for all our remote thermometer designs since 1973, (lower cost YSI equivalents since the 1980s).
There are many precision thermistor manufacturers who make electrical direct equivalents with a wide range of interchangeability tolerances.
ETA: found their history page, YSI History - From the 1940's to today, timeline of products, people, and company development
Looks like ITT Corporation owns their thermistor line now.
Thank you for the answer! This is all very helpful. I am new to this type of measurement so I have a few follow up questions to try and better understand.
I do see that they have recommended thermistors for use with this DAQ. Does this mean these are the only ones I should use in order to get accurate temperatures? Is there a way to adjust the settings on the DAQ to accept the thermistors I have?
Is there any way that I can use the sensors that I have already purchased to measure accurate temperature or are they simply not compatible with the DAQ I have? I’m thinking some way to use an equation and collect just the resistance values and convert in excel to temperature? I could not identify the resistance to temperature values or an equation for the 235-1423-ND sensor data sheet.
If any thermistor I buy could have a different beta value, how do you read accurate temperatures from any thermistor? Is there a standard measurement tool I should be using?
This post contains a fair bit of information on the topic of thermistors for temp measurement, and might be useful. Feel free to skip to the section on NTC devices…
Defining what precisely you have in mind when you say you want “to measure accurate temperature” is important; measuring temp changes to half a degree is one thing, measuring absolute temperature to 0.001°C is very much another.
At day’s end, your meter is not measuring temperature, it’s measuring the resistance of a device that has a predictable temperature/resistance relationship. When you tell the device you want to measure temperature, it’s using some pre-programmed assumptions about the characteristics of your thermistor to translate a resistance reading into a temperature reading. Those pre-programmed assumptions are, to some degree, going to be incorrect and and not representative of your thermistors’ actual characteristics. Whether or not your DAQ device offers a means of adjusting the equations used to translate resistance into temperature or not, I don’t know. The workaround would simply be to record resistance data and translate it into temperature terms yourself, either using the information in your thermistors’ datasheets or derived through calibration of individual devices.
Page 12 of this document, referring to “Type F” material gives information on how to calculate resistance for the 235-1423-ND (SC30F103A) at any temperature between -50°C and +150°C.
Reading through the datasheet for your DAQ device, it does not appear to have any means of adjusting calibration values, so using it to measure resistance and then calculating temperature from that seems to be the best option.