Deep Dive Into a 1960s Printing Plate Exposure Timer!

The VISOMAT BWS2 is an obscure '60s East German made device which measures the amount of light using a photocell and advances the wind-up mechanism with an adjustable stop. After the operating dial returns to its neutral position, the exposure lamp is switched off.

It's built in a heavyweight die-cast aluminum enclosure (an order of magnitude more than enough to make ‪@EEVblog‬ drool!), industrial strength. Spare no expense, cost no object! And it's so simple - all electromechanical, not too much electronics in it. The only semiconductor here is a single-wave selenium rectifier.

My unit comes from the Book Art Museum in Łódź, where I worked for five years. We had a small dark room in the very heart of the basement, that was used for exposing the photosensitive aluminum plates for offset printing. It had an enormous Klimsch UV light exposure device that was in a state of disrepair ever since, and it originally used arc discharge lamps as a source of light. At some point of the machine's life, these were replaced with quartz glass mercury vapor discharge lamps. One of my big projects through my museum years was discombobulating all the old equipment in the room (plumbing, wiring etc.) because it was to be repurposed as a typefounding matrix archive, with racks full of galleys containing whole typefaces from over a hundred years of Polish typographic legacy.

This exposure timer was installed on the wall and connected to the Klimsch exposure machine, and I decided to preserve it (I couldn't keep the machine for its sheer enormous size). Now that I'm Fresh-Off-The-Boat-In-The-Lab-Again, it ended up on my bench, on my hard drive, up in Youtube's cloud.

0:00 Intro
1:00 Turn It On? Take It Apart? The Story So Far
2:47 User Interface
4:00 Fire To The Wire!
5:00 Taming It
6:00 No Limits
7:00 Goes Like Crazy!
7:40 Getting In
9:00 Inner Life... with Thyratron!
10:12 Taking a Deeper Dive
12:30 Mechanism
15:13 Deeper!
16:55 Escapement Mechanism
19:00 Electrical Parts
21:20 Schematic
25:10 Missing 20nF Time Constant Cap
27:47 Photocell Ionization
28:30 Thyratron Ionization
29:40 Afterword

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