Hi,
Good Day. I have a customer who is working with INA326. Please see below his query for your reference. Thank you very much.
In app note SLOA123 (https://www.ti.com/lit/an/sloa123/sloa123.pdf?, page 1), it shows using an INA326 amplifier to interface to a thermocouple. For the RFI filter, it shows using series resistors. For these resistors, do they need to be matched better than 1%?
Best Regards,
Ray Vincent
Hi Ray,
Not only the two resistors should be as equal as possible, but also the two common mode filtering caps (the ones which are connected to signal ground). Best to chose +/-1% toleranced NP0 (C0G) types for these two caps. For the two resistors +/-1% toleranced thin (!) film resistors with low temperature drift should be taken. Or better take +/-0.1% toleranced resistors. Thick film resistors should not be used here, as their long term drift is miserable.
Why is this of importance?
Because using unmatched components at the input of INA326 will ruin the balance and by this the overall common mode rejection.
Kai
Hi Ray,
I think that Kai has provided you with detailed reply. If you have additional questions, please let us know.
The advantage of K thermocouple is the temperature sensing range up to 1260C range (without oxidation in the K TC materials). In order to measure TC correctly, the cold junction temperature compensation reference is required, see the captured image below.
If your temperature sensing application does not require to measure from -200C to +1260C range, PT100 or PT1000 RTD sensor will work better in a lower temperature application in terms of cost and measurement accuracy (20+ years ago, PT100/PT1000 RTD sensors were very expensive, but this is not the case anymore).
If you need additional questions, please let us know.
Best,
Raymond
