Experimenting with an proximity sensor based on the ST TDE0160. It is showing a huge temperature dependancy, if ambient temperature changes more than a little then the "range adjustment" is lost. Adjusting Rh brings it back in tune... can I just put a PTC thermistor in series with Rh? or what? thx
I assume this is the device in question:
Page 4 shows the temperature sensitivity of the oscillator negative resistance but it isn't extremely large (maybe 9% over more than 160 degrees C range).
The operation is also affected by the temperature sensitivity of the resonator coil resistance, the resonator capacitance and losses and probably most important, the core permeability and losses.
What kind of capacitor are you using in the resonator?
What kind of core material are you shaping the coil field with?
Yes, that's the part. newer spec sheet:
The resonator cap is a .001uf multilayer ceramic, currently only an X7R. The core is "P" ferrite, 2500 permeability:
That should be pretty good. I was afraid you might be using a Y5V or Z5u, which are terrible.
Since this is a gapped structure, it makes little difference in the shape of the magnetic field if the permeability is
500 or 2500. However, the higher permeability material has a higher core loss sensitivity to temperature, which I think is more important in this application than permeability stability, since this circuit essentially measures resonator energy loss.What frequency is your resonator running at?
What temperature range are you hoping for?
The core is a pot core design. I'm running at around 100K Hz right now. Higher freqs were giving lower sensing distances. I'll need to cover a wide outdoor temperature range: -20F to 120F (-28C to 50C)
I guess I would try to total up all the temperature sensitive losses in the resonator structure and compare that to to the temperature sensitivities of the chip, to determine where the main sensitivity lies.
But if you have a choice of ferrites, you might pick the one with the most temperature independent losses and try substituting a much better capacitor, as an experiment to see how much the ceramic one is involved. At the very least, use an X7R with a voltage rating 10 to 20 times the peak voltage applied.
By the way, what value capacitor are you using?
.001uf
Well, that is small enough to be replaced with a C0G type, to eliminate the capacitor from the problem, pretty conclusively.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.