[time-nuts] Temperature sensors and quartz crystals

jimlux jimlux at earthlink.net
Sun Jun 4 21:55:30 EDT 2017

On 6/4/17 4:59 PM, Attila Kinali wrote:

>> Where did you get the idea to use a 1 k load for an AD590?
> Jim was refering to a circuit _he_ used in a satellite. Not to your circuit.

We've also used 3k.  It's more about supply voltage, expected 
temperature range, and the ADC you're using (if any). 1k is handy if 
you're running off 5V and are feeding a 1 volt full scale ADC - room 
temp is 0.3 V.  Note that the *minimum* voltage across an AD590 is 4V, 
so if you've got a 3V supply, you're out of luck.

10k gives you 3V at room temp, and is quite ok into a 5V ADC, as long as 
your supply is at least 7-8 volts.

There is self heating to worry about if you have a high supply voltage 
(12V @ 0.3 mA is 3.6 mW), but realistically, all sensors have that 
problem (unless you are using a PRT in some sort of bridge that nulls 
the current)

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