low cost temp sensor

[Jim Patchell]

    A long time ago, I designed a thermometer that needed to go down to about
70 degrees kelvin.  It also had to be cheap.  I just used a regular 1n914.
If you keep the current constant, they are fairly linear.  If I recal, it was
good to better than a degree over the range of 70 - 280 degrees kelvin.

    -Jim


Martin Czech wrote:

> For obvious reasons (my last mail) I need a very good thermometer.
> Should have 0.1 K resolution and fast settling time.
>
> You can use a bipolar transistor for a cheap temperature sensor (-2mV/K).
> These come in plastic packages.
>
> Now, I would like something smaller and with lower temperature resistance
> to get a faster setling time.
>
> A 1N4148 Diode could be used.
>
> Do you think that the diode will show much error due to parasitic
> resistance in a temperature range from 0C to 90C ?
>
> May be a metal can package transistor would do.
>
> Or should I better consider a LMxxx temperature sensor (not that
> expensive).
>
> What about long time drift? I guess the LMxx parts have a spec for this,
> whereas my homebrew are unknown ....
>
> Any ideas?
>
> m.c.