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 _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
