[time-nuts] VRefs - I'm a bigger Voltnut than a timenut..

[Predrag Dukic]

Obsession for precision is the same whether one is after Hertz, 
Volts, or Degrees of Celsius (Or Fahrenheit).

The methods and technology are similar...

I am now trying to fix two HP2804A quarz thermometers, thet are 
giving some error codes, and do not work.

More or less they are oscillators, and measure of temperature is 
measured by frequency shift  between reference and external oscillator.

Reference frequency is unusual 10.000.000,8 in one of them (marked 
exactly so)  and 10.000.001  in the other.

(Yes, yes, not a typo: it is 10MHz plus 0.8 Hz or plus 1.0 Hz)

So precise temperature and precise frequency cross their ways...


By the way, does anybody have op/serv manual for this thermometer?


Predrag Dukic






At 16:18 30.11.2008, you wrote:
>Hello,
>
>there's currently no easy way to convert a frequency into Volt, i.e.
>other than by cryo Josephson junction array or realizing Ohm by a
>Klitzing quantum hall effect device. Otherwise, FLUKE would have
>implemented that already in their Calibrators/Standards. They still rely
>on Artefact Calibration, i.e. ovenized longterm stable Zener References
>and Reference Resistors.
>
>The 5720A uses a stacked double Zener reference on a proprietary hybrid
>circuitry, giving 1-2 ppm/year stability, the 7001 and 732B use the
>LTZ1000 (Zener above BE junction), as the 3458A, the 732A uses the
>Motorola device (Zener below BE junction), and the elder 332D and 335D
>use similar, but less longterm stable references.
>The LM199, AD587 and I think also the Geller device may only be used as
>transfer standards, having poor longterm stabilities of 20ppm/yr. or more.
>
>Therefore, the LTZ1000 only may serve as a really affordable standard,
>i.e. below 8ppm longterm stability, for private use.
>
>I was lucky to get some LTZ1000 samples, and used the standard circuit
>from the LT datasheet for creating a small PCB. I purchased commercially
>available wire wound resistors (TK 3, 25ppm/yr) for the 5 necessary
>reference resistors and two OP07. Those resistors should give less than
>TK 1 and 1ppm/yr additional drifts.
>
>Compared to my HP34401A, the circuitry showed quite good short term
>stability below 1ppm, but shielding still has to be improved, as the
>LTZ1000 circuit is susceptible to external EMC disturbances. This Volt
>reference then costs less than 100 Euros/Dollars in total.
>
>I designed further circuitry (with TK 0.3 and TK 0.1 precision metal
>foil resistors from Alpha and Vishay, chopper amp, precision switches
>and Teflon insulated wires) to have the possibility for precision
>transfers of the 7,2V reference voltage to 100mV, 1V, 10V, 100V, 1000V
>level.
>Only then, a Volt Standard is complete.
>
>All this stuff will emulate or replace the commonly needed 732A (ref),
>720A (Kelvin Varley), 752A (Reference Divider) and 834B (Null Detector).
>
>Got no time yet to finish and improve the system, and to do the repair
>on an old 332B standard, but would like to share my knowledge, if
>anyone's interested.
>
>Frank Stellmach
>
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