-208℃ measurement method
Thread Content
I would like to ask the experienced colleagues: what method should be used for measuring -208°C? Can PT100 be used? According to the relevant information, for PT100, the resistance value is 18.52 at -200°C; below that temperature, no corresponding resistance value exists. The measuring medium is a cryogenic liquid.
For K-type thermocouples, the poster can check their calibration table.
T, J, N, and E thermocouples can all be measured. NiCr-AuFe (nickel-chromium-gold-iron) and Cu-AuFe (copper-gold-iron) are used rarely, but they are thermocouples designed specifically for low-temperature measurements. Thermistors are not suitable for measurements below -200°C.
To measure ultra-low temperatures, a pressure-type thermometer can be used ..........
Why can’t we use PT100? I think it’s fine.
Thank you all for your responses. The user requires a measurement range of -213°C to +80°C; the medium is subcooled liquid oxygen, and the accuracy required is ≤±0.2K within the range of -213°C to -178°C. I’m wondering whether a K-type thermocouple or a PT100 resistance thermometer can meet this requirement. After checking Rosemount’s documentation, it turns out that using a 644 sensor together with a 0065 sensor allows for accurate measurements above -200°C, thus meeting the requirements. However, if a K-type thermocouple is used, the error limit cannot be satisfied.
I checked, and there are indeed corresponding mV values; it should be possible to make measurements. One issue is that after looking up the temperature variations for various manufacturers, I found that when used with temperature transmitters, the error level is quite high. The required error limit is no more than ±0.2K
Thank you for your reply. I checked, and it seems that pressure-type thermometers can only reach temperatures down to -80°C, and they do not have the capability to transmit electrical signals over long distances.
Oh~~~ It’s probably this kind of ultra-low temperature thermometer; too little was used, so you couldn’t find it. It can measure temperatures down to -260°C without any problem, and it also provides power output signals as well as communication output signals. .
Some users with only a few seedlings: firstly, they like to ask for bizarre precision requirements, and secondly, they’re too poor to pay the right price. Go and ask that user of yours what price he’s willing to pay; find out for sure. If you still can’t find a supplier, then you can come and tell me the price you have in mind. If it’s a reasonable price that’s good enough for performing shows, I’ll go ahead and arrange for one to be made for him. Dad is always playing with insects; he likes to eat leftovers and glass shards, and he loves to get stuck in complicated issues and delve deep into them........... :lol
Today I found a few PT100 resistors that can achieve such low temperatures. However, they are different from the integrated temperature transmitters we usually use – they aren’t pre-packaged, so one has to package the PT100 separately. Their temperature sensing module is also different; it’s of the card-type design, similar to a graphics card. From what I’ve seen, these resistors meet the IEC751 resistance standards at temperatures above -200°C, but below -200°C their resistance starts to decrease and deviates from the calculated values. Therefore, it seems that the transmitters used with these resistors are designed with compensation mechanisms built in.