I am finding a lag time when doing cold junction compensation resulting in a measured temperature offset.
Is the temperature signal low-passed in any way? If so, what is the approximate time constant? I would like to code in some terms digitally to cancel it.
I suppose I should be more specific -- I am finding this when heating the board with the temperature sensor up rather quickly.
While this is obviously not the common use case, I'd like to make it work properly. The offset suggested to me the ADS1118 temperature may be low-passed.
There is no low pass filter on the internal on board temperature sensor of the ADS1118. In order to accurately perform temperature measurements using thermocouples, the temperature of the cold junction (also called reference junction) has to be known. Therefore, the internal temperature sensor of the ADS1118 must be in thermal equilibrium with the reference junctions in order to reduce cold junction errors. In the case where a sudden and very fast change of temperature has occurred in the reference junction, since the temperature in the the PCB board (and thermocouple connector) is changing quickly, there is a delay for the system to reach thermal equilibrium.
The ADS1118 datasheet and the application note below provides some information regarding board layout and design considerations to minimize/eliminate cold junction errors.
ADS1118 Application Note:
All content and materials on this site are provided "as is". TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with regard to these materials, including but not limited to all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement of any third party intellectual property right. TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with respect to these materials. No license, either express or implied, by estoppel or otherwise, is granted by TI. Use of the information on this site may require a license from a third party, or a license from TI.
TI is a global semiconductor design and manufacturing company. Innovate with 100,000+ analog ICs andembedded processors, along with software, tools and the industry’s largest sales/support staff.