Re: circuit too temperature sensitive

thomas wrote:
"John Popelish" <jpopelish@xxxxxxxx> wrote in message news:DP2dnbJ4LtV0bnLbnZ2dnUVZ_sOrnZ2d@xxxxxxxxxxxxxx
Thomas wrote:
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?
I assume this is the device in question:
http://www.tranzistoare.ro/datasheets/185/325768_DS.pdf

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 ***: http://www.st.com/stonline/products/literature/ds/1513/tde0160.pdf

The resonator cap is a .001uf multilayer ceramic, currently only an X7R.

That should be pretty good. I was afraid you might be using a Y5V or Z5u, which are terrible.

The core is "P" ferrite, 2500 permeability: http://www.mag-inc.com/pdf/2006_Ferrite_Catalog/2006_Materials.pdf.

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 "sensitivity" pot is 50K, TCR=150ppm/C


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