[time-nuts] Fury - Rubidium

SAIDJACK at aol.com SAIDJACK at aol.com
Wed Jul 28 02:07:20 UTC 2010


Hi Scott,
 
yes the pads are there, you can use the through-hole pad right next to C67  
and a standard ground pad for the Thermistor. There will be 10.5V across  
the thermistor. Connect the thermistor to your Rb case.
 
You should be able to connect two 10K Thermistors in parallel to get a good 
 reading without excessive self-heating of the thermistors, while 
generating  enough current through them that can be measured by the ADC.
 
You can check the thermistor current using the meas? command. If the  
thermistor is not drawing enough current for the ADC, then simply place a 2.2K  
resistor in parallel to it.
 
The software needs to be enabled to support measuring and applying a tempco 
 correction, by default I think the boards were shipped with only aging  
compensation enabled.
 
Us the following command to enable tempco correction:
 
serv:tas 2,288,600,50,0.05
 
Check the settings with:
 
serv:tas?
 
The first number is the mode (0 is all off, 1 is aging only, 2 is aging and 
 tempco correction). The second number is the memory usage, 288 points in 
this  case. The third number is the sensing frequency in seconds, so 10 
minute  intervals in this example. 288 points * 10 minutes is 48 hours of memory. 
The  fourth number is the maximum phase offset allowed for a sense point, 
in this  case +/-50ns. The last item is the required frequency error  
estimate for a sense point, in this case +/-0.05ppb.
 
bye,
Said
 
 
 
 
In a message dated 7/27/2010 17:07:31 Pacific Daylight Time, smace at intt.net 
 writes:

Said,  Did the OEM units (from way back) ship with an open pad for  the 
thermistor?  I thought that wouldn't work unless it was drawing  oven 
current from the Fury.  It would be neat to add some tempco into  the mix 
instead of just trying to shield it from HVAC cycling.  The  particular 
LPRO-101 that I'm using now, doesn't seem to be as sensitive as  others 
to temp.  I was using a different LPRO originally and when I  plotted the 
Fury board temp sensor with GPSCON you could see the impact of  the 
cycling, now with this one you would be hard pressed to pick it out.  
The X72 was very sensitive to temp changes, EFC tracked the temp quite  
well.


Scott



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