Electronic Dial Gauge

These are some pretty big files.

It would help if you made the titles of the dropbox files start with the same prefix, something like JimPent_dialgage, etc, so that they all show up in a block.

Cool project. It looks like the heart of the matter is a syncro selsyn trasmitter, right? Is this off-the shelf, or was it surplus?

Recently having gotten deep into my Federal electronic readout I appreciate how interesting this stuff is. In that case they ran the phase senstive detector with a resonant circuit front end - and they missed soldering one of the fine wires inside the inductor to the lead-out pin. It worked just fine for about ten years before the connection went open and the thing quit working.

Jim

Many years ago I started building a brute force digital dial indicator by calculating XY coordinates for a circular pattern with 100 equally spaced holes. Then I drilled them using a small mill, dialing in each coordinate. The material was a disk made of engraving plastic stock. My intent was to make an optical reader using up/down counters and attach it to a normal dial indicator stem in place of the hand.

Never finished it , but I still have the disk in my tool box. Inertia was a bitch ; )

The synchro is a surplus size size 08 control transmitter which is a pretty common item in old aircraft instruments.

Sorry about the messy post.

jim

Jim, Nice job! I love the concept.

Any idea on sources for the synchro transmitter? Where the ones you used 400Hz units? I have several, but they are a much larger and are

120V 400Hz units.

Thanks for posting this stuff!

AL A.

The unit I used is a 2608CX4 rated as a 26v 400Hz control transmitter rescued from old aircraft bits. Pretty well any surplus outfit stocking bits of aircraft or military instruments should have something suitable. Where are you? Perhaps someone with local knowledge can provide a few pointers.

The circuit is not fussy on the type of synchro - the 2608CX4 is about the most demanding type. This 26v 400Hz transmitter loads the

555 more heavily than practically any other type. Synchro receivers, resolvers, control transformers, 60 or 400Hz, 26v or 120v should all be OK. The changes needed should be limited to choice of damping R and overall gain.

One other variable is the operating frequency - 1KHz was chosen as higher than 400Hz to reduce the load on the 555 but still low enough for the secondary waveform to be a pretty clean squarewave.

1KHz should still be OK for 60Hz synchros. It could be increased if the synchro you find loads the 555 too heavily.

Jim

Hmm. Nice phase detector.

What's the 50K pot doing at the last (meter) stage?

Jim

Wide range Zero set (about 3x full scale) - it performs the same function as rotating the outer dial on a mechanical dial gauge. Much more convenient because it does it without mechanically disturbing the measuring head.

It also backs off the zero offset error of the earlier stages.

Jim

Ah, got it. The current throught the 680K is summing in with the real measurement current. The layout on the diagram had me stumped there for a bit - it took me a while to realize you were deriving a driven 'ground' on that middle buss there.

Jim