circuit too temperature sensitive

T

thomas

Guest
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
 
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?
Click to expand...
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?
 
"John Popelish" <jpopelish@rica.net> wrote in message
news:DP2dnbJ4LtV0bnLbnZ2dnUVZ_sOrnZ2d@comcast.com...
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?
Click to expand...
Yes, that's the part. newer spec sheet:
http://www.st.com/stonline/products/literature/ds/1513/tde0160.pdf

The resonator cap is a .001uf multilayer ceramic, currently only an X7R.
The core is "P" ferrite, 2500 permeability:
http://www.mag-inc.com/pdf/2006_Ferrite_Catalog/2006_Materials.pdf.
The "sensitivity" pot is 50K, TCR=150ppm/C
 
thomas wrote:
"John Popelish" <jpopelish@rica.net> wrote in message
news:DP2dnbJ4LtV0bnLbnZ2dnUVZ_sOrnZ2d@comcast.com...
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 sheet:
http://www.st.com/stonline/products/literature/ds/1513/tde0160.pdf

The resonator cap is a .001uf multilayer ceramic, currently only an X7R.
Click to expand...
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.
Click to expand...
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
Click to expand...
 
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 sheet:
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
Click to expand...
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)
 
thomas wrote:

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)
Click to expand...
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?
 
"John Popelish" <jpopelish@rica.net> wrote in message
news:dMmdnVbGwO15w23bnZ2dnUVZ_j2dnZ2d@comcast.com...
thomas wrote:

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?
Click to expand...
..001uf
 
thomas wrote:
"John Popelish" <jpopelish@rica.net> wrote in message
news:dMmdnVbGwO15w23bnZ2dnUVZ_j2dnZ2d@comcast.com...
thomas wrote:

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
Click to expand...
Well, that is small enough to be replaced with a C0G type,
to eliminate the capacitor from the problem, pretty
conclusively.
 
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