Lever Type Electronic dial gauge 


Circuit diagram.jpg     schematic
Synchro Sensor.jpg      end view of measuring head
Clocking Workpiece.jpg  set up in mill clocking workpiece centre.

        
          General info

The 7805 regulates a 9v PP9 battery down to 5v
Power consumption is 15mA

12/13/14 opamp splits it into +2.5v & -2.5v

555 timer generates a 1Khz squarewave

555 doesn't like a purely inductive load so
1K damping resistor needed.

Feeds 26v primary of size 08 Control Transmitter 
Should work with pretty well any synchro type or
inductive load but may need different damping resistor.

One 11.8v secondary feeds 1/2/3 gain stage

5/6/7 is analog exclusive OR phase detector

2N3819 switches 5/6/7 gain between +1 & -1
Not critical - pretty well any similar small JFET should be OK

8/9/10 is meter driver - 100 ohm sets the sensitivity - 25mv full scale

2.2k limits maximum current to safe level - inside the feedback
loop so hardly affects gain.

250-0-250 ua meter - just because I had one - probably easier to
use 100uA meter, left zero or centre zero, and adjust sensitivity and 
Zero set R values.

A 1.25" lever arm on the synchro rotor gives +-0.0025" and +-0.025" FSD 

The meter is a stiction free taut band suspension type and easily 
indicates fractions of a tenth movement with none of the jittery jumps
common with mechanical tenths clocks.

An AC coupled additional gain stage is possible (I tried it just for fun)
and pushes the sensitivity into the microinch region.

The electronics should also be directly usable with most types of linear 
inductive transducers