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Philips PM2424 Digital Multimeter

This professional autoranging instrument is one of the last multimeters that used nixies.
The PM2424 is a portable mains powered or battery powered unit. It has five ranges: DC V, AC V, DC mA, AC mA and kOhm, and it is autoranging on all ranges.

The PM2424 has a full 4-digit nixie display. These are multiplexed, as can be seen by the occurrence of ghosting. The logic circuitry uses L-TTL and LS-TTL (Low-power and Low-power Schottky Transistor-Transistor Logic) ICs. Judging by the production dates on the ICs, it has been built in 1973 or 1974.

Two circuit boards contain all the electronics. This instrument looks a lot like the PM2423 so I presume it has been built in Japan, too.

PM2424, top view

PM2424, top view, lid removed.

On the upper board, several low-profile relays and reed relays can be seen. When the unit is switched on, a high pitched note can be heard. I presume this is caused by a switch mode power supply, because the unit can also be used on a 12V DC power supply instead of 220V AC mains.

I bought one of these in 2012. That one was in good condition. It had a tendency though to give erratic measurements every now and then. I suspect the range switching relays. In January 2013, I stumbled upon a second one, which was working just fine. Maybe it needs callibration, it seems to be reading slightly too high. But for now, I don't have the need to take this meter apart. When I'll do that, I can take some more pictures and do some more reverse engineering. In the meantime, these are nice assets for my lab.

Copyright © 2013 by Onno's E-page         published 2013-03-16, last updated 2013-03-17