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HP compatible 5kohm thermistor temperature probe - home made

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voltsandjolts:
This seems to match those values quite well in 0-70C range
Digi-Key 570-1196-ND

garrettm:
I recently ran into this problem when wanting to do temperature measurements with my HP 3456A.

After doing some research, the correct replacement is made by Measurement Specialties (acquired by TE Connectivity in 2014). The salient parameter is a beta value of 3976 for 25/85 or, as pointed out previously, a beta value of 3891 for 0/50.

From what I can tell, the direct replacement for the YSI 44007 is the TE Connectivity 44007RC, which is about $10 on Newark (70K8741) --cheapest I could find. It matches the 93.7 ohms at 150C given in the HP manual, the -80C resistance isn't shown in the R/T table unfortunately.

Using beta value 3976 and 5 kohm NTC as search parameters we find TE / Measurement Specialties "5K3A1 Series 1" for around $3 on Mouser (824-GA5K3A1A). It matches the 44007RC very well from 0C to 125C, but diverges slightly when going below 0C. And a similar 5K3A373I part on Newark (23M9110) for around the same price. Not a bad choice for low cost measurements above 0C, and moderately more accurate than using beta 3892 (0/50) parts. These parts essentially match the MAMAC Systems datasheet as uploaded earlier.

Digging through my parts bin turned up a NOS YSI 44034 thermistor, same as the 44007 with just slightly better accuracy. I had bought a lot of vintage gear from a cal lab that was closing shop a few years ago and nearly threw that thermistor away, lol. I'll still probably pick up a few 5k3A1 to have on hand and compare against the 44034.

mikerj:

--- Quote from: voltsandjolts on April 22, 2020, 08:13:37 am ---You can make a resistance table.

--- End quote ---

With such widely spaced cal points I would use Steinhart-Hart coefficients rather than Beta.  Beta works ok over smaller temperature ranges, but errors can really stack up over large ranges.

This calculator will derive Steinhart and Beta coefficients and let you compare the difference.

wizard69:
Maybe I'm off my rocker but if your temperature range is that narrow why worry about specifics of the thermistors if they are close enough?   There is an assumption that this is just development work and not for shipping hardware.


--- Quote from: enut11 on April 22, 2020, 12:33:58 am ---Most of my 5Kohm thermistors measure around 5100-5200 ohms at 25C, ie too high for an accurate temperature indication on a HP DMM.

--- End quote ---
Doesn't that meter have the ability to apply a slope function to the read value?

--- Quote ---For the Ref oven, I will be using them over a very narrow temperature range of about 39-41C.

--- End quote ---
Exactly!   You should be able to get linearity out of just about any temperature transducer over that narrow range.

--- Quote ---If I shunt the thermistor with a high value resistor to indicate the correct temperature at 40C, this may work. I have a Hanna Checktemp 1 thermometer to help.

Any other ideas?

--- End quote ---
If you have an accurate thermometer to calibrate against you should be able to hand that narrow range around 40 degrees C with little issue.   
Granted most of my experience is industrial but in that environment you may have many different transducers connected to an A/D input.   A different slope is applied to each transducer.   Usually that is to match a voltage range to the process range, say to scale 1-5 VDC to read 0-100PSI (an air pressure transducer).   However it is often a need to linearize over a shorter range or to scale to odd units.   As long as you can calibrate properly you are OK and maybe more importantly handle values outside of your calibrated range properly.

So over that tiny range you could just measure resistance and apply a function to give you temperature value.    The other approach is to plot a look up table.   Look up  tables are not as odd as they might sound, even a couple of years ago a local calibration lab had a calibrated RTD and a resistance meter with a look up table to convert the readings from the resistance meter to reading degrees C.   

In any event there are multiple ways to skin this cat.    With the meter you have you might be able to use a plan old diode as  transducer.

bob91343:
The thermistors I bought were very inexpensive.  I think I got a package of ten for very little, off ebay from China.  They look exactly like diodes such as 1N4147 and are similar in dimension.

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