(Editor’s Note: This is a first in a series of articles. Future articles will apply to specific machines, where this first one is general.)
A Digital Panel Meter (DPM) can measure angles to 0.01 degree if a precision instrument potentiometer is used and a stable reference voltage is used. This later version has much lower power consumption that the prior LED model, and can be run from batteries.
Principal of Operation
A trimpot and a sensing potentiometer form a simple voltage divider. Designing for 200 degrees of rotation, each degree equals one millivolt. In actual use, the critical measuring is done at that rotational quadrant from 0 to 90o, or from the Table to Girdle settings. Thus, if the pot is linear to 0.5% over its range, only one quarter of its range is really used. If batteries are used, rather than regulated power supplies, it only takes a minute to check the calibration once in a while. Lithium batteries seem to last forever in this application. The voltage divider only consumes 0.1 milliamp.
Less than 0.125% from zero to 90 degrees.
Cost to build:
Less than $50.
There is a critical