Temperature resolution

[Easychair]

I have a project opportunity (with some promise of volume production) that requires temperature regulation within 0.1 deg C. This of course is also the minimum resolution of the T/C and RTD inputs. I'm considering setting the config to read in deg F which would nearly double the resolution, but I'm fairly sure this still won't be enough.

I belive the inputs are 16 bit, right? Is there any way to improve the resolution? Is custom firmware a possibility?

Thanks for your help!

[Joe Tauser]

The Unitronics inputs are signed 14 bit.

To get 0.1 degree regulation, you need 0.01 degree precision. I've used a third party external universal analog 16 bit Modbus slave module with a Unitronics PLC. In temperature mode, the ranges are predefined for each sensor and the span is typically 1000 degrees C, and it is signed. So what you're really dealing with is 15 bit analog. You'll get your best accuracy with an RTD, because there is an additional error introduced by the cold junction compensator in the thermocouple circuit, typically 0.2% of span. In the case of an RTD on this module, the span is -200 to 850, or 1050 degrees C. Divide this by 2^15 (32,768) and you get 0.032 degrees per count. This may be enough to work. The next step up is a 20 or 24 bit module, and now you're talking about some money.

NI 9219 24 bit module

Google "20 bit analog module" or "24 bit analog module" to see what's out there.

As long as your customer understands that this won't be the cheapest thing in the world, you can combine a basic Unitronics controller using Modbus with a high-end I/O module to produce a very cost-effective solution. My opinion is that you won't be able to do it with the onboard inputs.

Joe T.