I see under "Electronic accuracy" on page 1-5 of the Model 218 Temperature Monitor that the accuracy in mK have been pre-calculated for some temperature points.
±318 mK at 30 K
±152 mK at 77 K
±212 mK at 300 K
±299 mK at 675 K
±328 mK at 800 K
The electronic accuracy is stated as ±0.06 Ohms ±0.02% of reading.
I'm assuming that the 0.02% of reading at 30 K is ±0.006 K, leaving a remainder of ±0.312 K
How is the rest of that calculated? I'm currently trying to come up with an accuracy statement for several data points when using a PT-100 probe and I can't get the math to work out properly when checking it against the given points I've listed above.
Post by Lake Shore Ryan on Dec 5, 2017 10:47:52 GMT -5
Thanks for the question. In this case, accuracy is specified in ohms, so the ±0.02% or reading is referring to the resistance reading of the platinum RTD. At 30 K, a platinum RTD is typically 3.66 ohms, so the total accuracy value should be:
Accuracy(Ω) = ±0.06 ±0.02% of reading
= ±0.06 ±0.02% of 3.66
= ±0.06 ±0.0007
= ±0.0607 Ω
Once you have the total accuracy in ohms, you can convert to an equivalent temperature using the sensitivity value of that sensor. in the case of the Platinum RTD at 30 K, this is 0.191 Ω/K
Accuracy(K) = Accuracy(Ω)/Sensitivity(Ω/K)
= ± 0.0607/0.191
= ± 0.318 K
So you can generate your own temperature-based accuracy and resolution numbers from any sensor, provided you know its resistance (or voltage in the case of diodes) and sensitivity values. If you're just looking for indicative values, our sensor response tables will be useful to you.