[time-nuts] V refs -- Frank S and Bill E

Richard Moore richiem at hughes.net
Sun Nov 30 22:58:25 UTC 2008


Frank wrote:
> <clip> 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.
> ------------------------------

My Fluke 332D uses the Motorola IC (zener below) in a small Klixon  
oven which seems to be an on-off type with relatively poor temp  
control. Of course none of the divider string resistors or other  
circuits are in a temp-controlled space. I've found it very hard to  
keep that box under 10ppm over even short periods. It mostly sits.  
Did I mention its very big and heavy? It does supply 50mA at 1100V  
though.

Bill wrote:
<clip>
> These use a rather clever way of generating 1V and 1.18 volts without
> significant division error. The 10V reference is sampled by a
> pulse-width modulator whose duty cycle is crystal-controlled and
> programmable. The result is then LP filtered using an active filter  
> and
> tracks the primary reference to better than 1ppm.
>
> Bill Ezell
> ---------

All of the newer Fluke calibrators use the PWM/LP filter method to  
vary output, as does my Valhalla 2701C DC 6-1/2 digit, 100mV-1000V  
reference. The Valhalla has an LM299 for its reference, and given its  
generally good overall performance, would be a good candidate for an  
LTZ1000 transplant. Another project.

Dick Moore



More information about the time-nuts mailing list