[time-nuts] Fury - Rubidium

Scott Mace smace at intt.net
Tue Jul 27 22:55:06 EDT 2010

Any particular thermistor you would recommend?


On 07/27/2010 09:07 PM, SAIDJACK at aol.com wrote:
> 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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