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HP compatible 5kohm thermistor temperature probe - home made
garrettm:
--- Quote from: bob91343 on June 16, 2020, 12:12:31 am ---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.
--- End quote ---
Little Fuse makes glass DO35 parts in beta value 3892 (0/50) but these and other thermistors with this beta value aren't ideal for temperature measurements with the HP 3456A and 3457A DMMs. The firmware on these DMMs (and possibly the 3458A) assumes that the beta value is 3891 (0/50). The only direct replacement available is the 44007RC or 44034RC made by TE Connectivity (formerly Measurement Specialties). All other parts might be close in value and even usable, but they are not going to meet the accuracy specifications as set out in the user manual. The error in beta from 0-70C for the 44007 is +- 0.8% and +- 0.4% for the 44034, corresponding to +-0.2 and +-0.1 C error in the 0 to 70 C range. Most parts are 1-10% error in beta that I've seen when searching. So expect a much larger error in temperature measurements than the TE parts.
@voltsandjolts, mikerj, and wizard69
Of course one can take any thermistor and log the values to a computer and transform the resistance to an accurate temperature reading with some very simple code. But that is unnecessary work, the HP 3456A and 3457A will do all that for you with the correct thermistor. The OP's primary question was to find either a direct replacement or a good enough replacement that the DMM's displayed value could be used without complicating the measurement. As pointed out earlier, a direct replacement exists and costs about $10, so why burn time getting a substitute working when you don't have to? I'd pay a few dollars more for the replacement part that would save me hours of time getting something else working satisfactory. Now that said, everything each of you have pointed out is great information if one were to go homebrew on say a Arduino project. Something I am actually planning on doing, so the Steinhart model and the conversion applet are good to know about.
Kosmic:
I'm using the PS502J2 from LittelFuse on my HP 974A. Seem to work fine. Beta is 3892.
https://www.digikey.com/products/en?keywords=PS502J2
RT chart is here: https://www.littelfuse.com/~/media/electronics/rt_tables/leaded_thermistors/littelfuse_leaded_thermistors_interchangeable_thermistors_ps502j2_rt_table.xlsx.xlsx
enut11:
@garrettm, I could not find the 44034 thermistor that you mentioned.
@Kosmic, yes the PS502J2 XL chart matches my 'reverse temp' checks using a pot on my 3456A.
Thanks
enut11
garrettm:
--- Quote from: enut11 on June 16, 2020, 06:33:58 am ---@garrettm, I could not find the 44034 thermistor that you mentioned.
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It's not generally avaliable anymore, however, Mouser can backorder it.
https://www.te.com/usa-en/product-11032577-00.html
https://www.mouser.com/ProductDetail/Measurement-Specialties/11030849-00?qs=%2Fha2pyFadujHIHhPedoiU7owJ7wgfoFT2W8XrPQTf%252BW1%2Fv%2FUirZSuA%3D%3D&tetid=yx2MwZBkJq
I would instead buy the very much avaliable 44007RC for $10 on Newark.
https://www.te.com/usa-en/product-11026588-00.html
https://www.newark.com/sensor-solutions-te-connectivity/11026588-00/ntc-thermistor/dp/70K8741?CMP=AFC-OP&TEdistID=005434634PURWEB
Or the much cheaper and arguably closest non-exact part 5K3A1 Series 1 for $3.45.
https://www.mouser.com/ProductDetail/Measurement-Specialties/GA5K3A1A?qs=%2Fha2pyFaduiof4ehfH1JJzkhLcvB74E4rAmTfW8nSY6VNMfwPygatw%3D%3D
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