Digital Multimeters

I wonder how many of today's DVMs will still be in regular use 75 years from now!? :)

Sure does, especially for tuning. I have an Avometer 8 Mk IV and an Avometer 16--more modern looking but not in the same class at all.

About 1990 I built myself a beam alignment meter that I still use. It's a germanium quad cell, a dual op amp (LT1012 iirc), some resistors, and two edge-reading, centre-zero microammeters. The meters are arranged in a T and read X and Y position.

The diodes in the quad cell are run almost open-circuit, so subtracting voltages effectively divides the photocurrents. With the cell numbered

| 1 | 2 |

--------- | 3 | 4 |

the two op amps form 1-4 and 2-3, so that

X = (1-4) - (2-3) (driving both ends of the horizontal meter) and

Y = (1-4) + (2-3) (both driving the same end of the vertical meter, via separate resistors).

Works great from 350 nm to 1.8 um, over about a 300:1 beam power range. I might sell them except that you can't get edge-reading centre-zero meters anymore. :(

Cheers

Phil Hobbs

Natch. And the fact that it puts a slight load on the CUT helps eliminate false positives that bedevil DVMs with their very high Zin.

I have an Avometer 8 Mk IV and an

Yep. Figures. I'd hang on to that 8 if I were you. I also have a mirror galvanometer among my rather large array of old test gear. I'm not sure what to do with that, if anything! Mebe donate it to a science museum or such like.

I still use my Fluke 75 that I bought when the series was first introduced in 1987(-ish). I think it's on its fifth or sixth 9V battery. Original fuses.

Allan

I've my own compiler ciforth, and I ignore comma's always. Normal facilities will not print comma's, but it is easy to add H. (print in hex with comma's each 4th place) and DEC. (print in decimal with comma's each 3th place)

An interesting alternative is to allow negative digits. (underlined

Groetjes Albert