Other Parts Discussed in Thread: LDC1312,
Hello there,
I would like to discuss different approaches for temperature compensation for LDC system.
My design is going to work in environment of changing temperature 0-60C. It is required to have high precision and especially repeatability over entire range of temperature.
From TI application notes (SNAA212A, Should I measure L, Rp or both) I learnt that L measurement is generally better with lower dependence on temperature shift. The coil should also have higher Q for thermal stability.
Temperature can be compensated by different methods but there always must be additional information of the temperature.
- One method is to use two channel LDC which uses one coil as distance sensor and second as reference coil which is not influenced by distance but only by temperature. Then there is a look up table which uses change of frequency/inductance in reference coil as temperature change. This is then used to compensate distance coil output.
I can use only LDC1101 for its high sample rate. It can operate only one channel. Unfortunately LDC1312 which would be suitable has too low sample rate. Even if I use LDC1312 in this configuration the measurement would loose its precision due to switching between channels correct?
- Other method is to use two LDC1101. One as reference for temperature measurement and other for displacement measurement.
The system seems unnecessary too complex.
- Another method which uses single LDC1101 in mode Rp + L should work too. Using Rp and L as two different input to calculate distance and temperature. This is still unclear because both measurements depend on temperature and distance. They could be coupled.
It might also decrease overall performance of L measurement which is not desired.
- As a most suitable option seems to me to use LDC1101 in LHR mode with distance sensor coil. Additionally place close to the sensor coil a thermistor (pt100 or similar). In this configuration the exact temperature would be known and it can compensate LHR measurement.
Unfortunately even in case of designing self temperature compensated sensor coil there is an effect of changing resistivity of target and permeability change in case of ferrite core in sensor coil. The reference oscillator is also influenced by temperature and it should be compensated. Correct?
Which of these approaches would you recommend to use in order to compensate temperature variation? Is there a better way I missed?
Thank you for your advice.
Best Regards.
Michael
