HP compatible 5kohm thermistor temperature probe - home made - Page 1
Forum section: electronics / projects

author: enut11
author_rank: Super Contributor
timestamp: April 21, 2020, 09:46:27 pm
content: I have a number of 5Kohm bead thermistors and I want to measure temperature with a HP DMM.Does anyone have access to a temp vs resistance table for the HP thermistor temperature standard?My specific requirement is to accurately monitor the 40C temperature in a voltage reference oven so if I knew the thermistor resistance that the HP DMM expects at that temp I may be able to select some from my batch of 5K units.enut11

author: enut11
author_rank: Super Contributor
timestamp: April 22, 2020, 12:33:58 am
content: Most of my 5Kohm thermistors measure around 5100-5200 ohms at 25C, ie too high for an accurate temperature indication on a HP DMM.For the Ref oven, I will be using them over a very narrow temperature range of about 39-41C.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?

author: helius
author_rank: Super Contributor
timestamp: April 22, 2020, 12:48:48 am
content: The HP E2308A thermistor probe is still available, and not even that expensive.The datasheet specifies "5000 ohm at 25°C, with a 25°C/125°C ratio of 29.26" which should let you calculate a response curve.

author: Vgkid
author_rank: Super Contributor
timestamp: April 22, 2020, 01:41:39 am
content: The thermistor hp used was a 5kohm@25c with a beta of 3891. They were sold by YSI initially, Now sold by Omega.If you want to go with a very close Beta Value of 3892, then your options greatly increase. With Thermistors sold by ametherm, littlefuse, measurement specialties/Betatherm/TE Connecivity.YSIhttps://www.google.com/url?sa=t&source=web&rct=j&url=http://www.farnell.com/datasheets/169207.pdf&ved=2ahUKEwjKgIeb8froAhWbl3IEHTISD40QFjAAegQICBAB&usg=AOvVaw2mRj7qTnQ4YiPiIiguA8f9

author: enut11
author_rank: Super Contributor
timestamp: April 22, 2020, 02:40:05 am
content: Quote from: helius on April 22, 2020, 12:48:48 amThanks. In this application I will have to build my own probe due to space restriction in the oven. I will look for a suitable bead thermistor.

author: bob91343
author_rank: Super Contributor
timestamp: April 22, 2020, 03:00:50 am
content: My HP 3456A has a temperature measurement function using a 5k thermistor. I bought a batch of thermistors for very little money on ebay.I forget the parameters but if you read the 3456A operator manual it should give the information.

author: enut11
author_rank: Super Contributor
timestamp: April 22, 2020, 07:51:52 am
content: Thermistors available on eBay AU are similar to what I already have. Not suited for HP DMMs.Also, no luck in finding resistance/temperature tables for 5K thermistors from YSI, Omega or Fenwal mentioned in the 3456A operator's manual.May have to do it the hard way and reverse test resistance vs temp on the DMM and try and find a close matching thermistor.

author: voltsandjolts
author_rank: Unknown
timestamp: April 22, 2020, 08:13:37 am
content: You can make a resistance table.[Graphic source Wikipedia]

author: enut11
author_rank: Super Contributor
timestamp: April 22, 2020, 09:56:43 am
content: I have found, by using a pot, that the attached pdf temperature/resistance table matches the thermistor characteristics that HP used to program their DMMs.Unfortunately MAMAC Systems do not sell individual thermistors.The HP3456A operator's manual mentions 3 thermistors that are suitable:YSI 44007Omega UUA35J3FENWAL UUA35J1None of which I can source easily. Unless a Forum member knows where to buy them.

author: voltsandjolts
author_rank: Unknown
timestamp: April 22, 2020, 10:37:05 am
content: This seems to match those values quite well in 0-70C rangeDigi-Key 570-1196-ND

author: garrettm
author_rank: Frequent Contributor
timestamp: June 15, 2020, 01:10:25 pm
content: 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.

author: mikerj
author_rank: Super Contributor
timestamp: June 15, 2020, 02:49:21 pm
content: Quote from: voltsandjolts on April 22, 2020, 08:13:37 amWith 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 calculatorwill derive Steinhart and Beta coefficients and let you compare the difference.

author: wizard69
author_rank: Super Contributor
timestamp: June 15, 2020, 06:43:27 pm
content: 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 amDoesn't that meter have the ability to apply a slope function to the read value?QuoteExactly! You should be able to get linearity out of just about any temperature transducer over that narrow range.QuoteIf 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.

author: bob91343
author_rank: Super Contributor
timestamp: June 16, 2020, 12:12:31 am
content: 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.

author: garrettm
author_rank: Frequent Contributor
timestamp: June 16, 2020, 04:03:15 am
content: Quote from: bob91343 on June 16, 2020, 12:12:31 amLittle 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 wizard69Of 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.

author: Kosmic
author_rank: Super Contributor
timestamp: June 16, 2020, 04:18:38 am
content: 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=PS502J2RT chart is here:https://www.littelfuse.com/~/media/electronics/rt_tables/leaded_thermistors/littelfuse_leaded_thermistors_interchangeable_thermistors_ps502j2_rt_table.xlsx.xlsx

author: enut11
author_rank: Super Contributor
timestamp: June 16, 2020, 06:33:58 am
content: @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.Thanksenut11

author: garrettm
author_rank: Frequent Contributor
timestamp: June 16, 2020, 08:56:34 am
content: Quote from: enut11 on June 16, 2020, 06:33:58 amIt's not generally avaliable anymore, however, Mouser can backorder it.https://www.te.com/usa-en/product-11032577-00.htmlhttps://www.mouser.com/ProductDetail/Measurement-Specialties/11030849-00?qs=%2Fha2pyFadujHIHhPedoiU7owJ7wgfoFT2W8XrPQTf%252BW1%2Fv%2FUirZSuA%3D%3D&tetid=yx2MwZBkJqI would instead buy the very much avaliable 44007RC for $10 on Newark.https://www.te.com/usa-en/product-11026588-00.htmlhttps://www.newark.com/sensor-solutions-te-connectivity/11026588-00/ntc-thermistor/dp/70K8741?CMP=AFC-OP&TEdistID=005434634PURWEBOr 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