I heard the Platinum RTD temperature sensor are very accurate and I want to use it for my temperature measurement project (-40 degree to 80 degree range). I don't want to use other type sensors.

Platinum RTD sensor have 2 categories: 1000 ohm and 100 ohm.

Which one should I use?

What are the differences? Is it because 1000ohm will give you higher voltage than 100ohm so you can easily do ADC (0-5V, 10 bit, Arduino)?

  • \$\begingroup\$ 1. There is no such thing as a "PTD". what you're referring to is a platinum Resistance Temperature Detector, or "RTD". 2. Platinum RTDs come in many various resistances, the most common being 100 ohm and 1000 ohm; deciding on which to use depends on what you want to do. A 1000 ohm RTD will give you ten times the resistance change over the same temperature span as a 100 ohm unit, so that's an advantage if that's what you're looking for. Here's a link to get you started: omega.com/toc_asp/… \$\endgroup\$ – EM Fields Oct 14 '14 at 14:06
  • \$\begingroup\$ A 1000 Ohm RTD doesn't necessarily have 10 times the sensitivity of a 100 Ohm RTD. thermometricscorp.com/PDFs/Platinum-1000-Ohm-385.pdf for example, shows 0.00385 sensitivity, nearly the same as 100 Ohm Standard. \$\endgroup\$ – Scott Seidman Oct 14 '14 at 14:39
  • \$\begingroup\$ My bad, it should be Platinum RTD \$\endgroup\$ – Xianlin Oct 14 '14 at 15:54
  • \$\begingroup\$ @Scott: Part 1: That number isn't the sensitivity of the RTD, it's called "alpha" and it's the temperature coefficient, or "tempco", of the material from which the RTD is made. Consequently, an RTD with a tempco of 0.0038 which exhibits a 100 ohm resistance at 0C will exhibit a resistance of 138 ohms at 100C. Similarly, a 1000 ohm RTD made of the same material will look like 1000 ohms at 0C and 1380 ohms at 100C. \$\endgroup\$ – EM Fields Oct 14 '14 at 16:55
  • \$\begingroup\$ @Scott: Part 2: The 100 ohm RTD, then, with a change in resistance of 38 ohms for a 100C change in temperature will have a sensitivity of 0.38 ohms per degree C, while the 1000 ohm unit with a change of 380 ohms for the same 100C temperature change will have a sensitivity of 3.8 ohms per degree C, ten times higher than that of the 100 ohm RTD. \$\endgroup\$ – EM Fields Oct 14 '14 at 17:02

Scatter gunning a few thoughts: -

Given that PTDs can be used in very fast thermally changing applications, using a PTD with a 1000 ohm resistance over a long (ish) length of cable may lead to the cable capacitance ruining the high frequency thermal perturbations that would have been seen more accurately with a lower resistance PTD.

Lower resistance PTDs exhibit lower thermal noise too.

On the other hand, for a given voltage change (for a given temperature change), a smaller excitation current is required for higher resistance PTDs. This can lead to less-self-heating and higher accuracy.

Higher resistance PTDs are less prone to errors due to cable resistance changing with temperature.

  • \$\begingroup\$ I've never heard of a "PTD", but platinum RTDs aren't very fast, "sporting" time constants well into the seconds, so cable capacitance is generally unimportant unless they're being driven by AC, which is rare. And then it's not about RTD speed, it's about crosstalk. \$\endgroup\$ – EM Fields Oct 14 '14 at 14:18
  • \$\begingroup\$ @EMFields not so, we're doing an experiment with very lightweight ones on turbine blades and we're seeing (and expecting) temperature fluctuations up to 50kHz. The whole experiment takes about 10 seconds to ramp up the turbine to ridiculous speed and back down. Yes, they still have thermal lag but the time constant in the very low milliseconds. \$\endgroup\$ – Andy aka Oct 14 '14 at 14:26
  • \$\begingroup\$ Interesting. How much does the temp vary during that 20µs? \$\endgroup\$ – EM Fields Oct 14 '14 at 15:45
  • \$\begingroup\$ @emfields the peak temperature the rtd will see is 100 degC, probably a delta of about 50. \$\endgroup\$ – Andy aka Oct 14 '14 at 15:58

I assume you are asking about platinum RTD's. I used one once. I think they all have about the same bias current (typically 1 mA.) So there is a trade off of sensitivity vs. self heating. (And then what Andy said.)


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