[volt-nuts] Quality Multimeters

[Greg Burnett]

IMO the 3457A, 3456A and 34401A are all excellent DVMs. All three DVMs must
be adjusted at many cardinal points for DCV, ACV and Ohms. Of course these
adjustments are via physical pots in the 3456A, whereas most are via
electronic cal constants in the 3457A and 34401A.

I would say that the 3457A is a little bit the predecessor of the thinking
that went into the development of the 3458A.

But the 3458A is still king by a thousand miles. Nothing else comes close.
Its internal "ACAL" routines take advantage of the 0.02ppm linearity of its
DAC, establishing ratios from one range to the next (and from its LTZ1000A
zener reference voltage to full-scale on its 10V range). Consequently its
adjustments to the external world require only a short, a 10Vdc standard and
a 10k ohm resistor. It even adjusts its own AC freq. response (during ACAL
AC) by adjusting for the most pure flat top of an internally generated
square wave. Its most accurate AC mode (AC SYNC) digitizes AC sinewaves and
then calculates and displays their voltage.

After a 3458A has been adjusted at "0", 10Vdc and 10k ohms (and SCAL AC if
needed for AC HF frequency response above 2MHz) - and after internal ACAL -
it will meet all published specs. (Or else it's broke and needs repair
because there's nothing else to adjust.) It's had an amazing long life (21
years) so far.

Cheers,
Greg