[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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