[time-nuts] Fury - Rubidium

Don @ True-Cal True-Cal at swbell.net
Wed Jul 28 12:18:44 EDT 2010


Said,

I would like to take advantage of the Fury TempCo capabilities when using an Rb. I have been looking for the thru-hole pad which you say is next to C67 but I can't find a C67. Consider that I am over 60 and eyesight is challenged but I have found C68 with nearby pads. Can you give us some additional components nearby to zero in on this allusive component. Thanks!

Regards...
Don
  ----- Original Message ----- 
  From: SAIDJACK at aol.com 
  To: time-nuts at febo.com 
  Sent: Tuesday, July 27, 2010 9:07 PM
  Subject: Re: [time-nuts] Fury - Rubidium


  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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