Differential capacitance measurement

Description: A bubble vial with external aluminum-foil electrodes serves as the sensing element for a simple indicating tiltmeter. To measure bubble displacement, a bridge circuit detects the difference in capacitance between the two sensing electrodes and the reference electrode. This circuit allows a tiltmeter level vial to achieve a 2 mm deflection for 5 arc-seconds of tilt, effectively resolving down to 0.05 arc-seconds.

The four diodes used in the circuit are CA3039 or equivalent components.

The described tiltmeter utilizes a bubble vial that incorporates external aluminum-foil electrodes to function as its sensing element. This design is predicated on the principle of capacitance change in response to the tilting of the vial. The bubble displacement within the vial alters the capacitance between the sensing electrodes and a reference electrode. A bridge circuit is employed to measure this capacitance difference, providing a highly sensitive means of detecting tilt.

The bridge circuit configuration is critical for achieving the desired sensitivity and accuracy. It consists of the two sensing electrodes connected in a manner that allows for the detection of minute changes in capacitance as the bubble moves in response to tilt. The reference electrode provides a stable point of comparison, ensuring that the measurements obtained are reliable and precise.

The performance of the tiltmeter is quantified by its ability to register a 2 mm displacement of the bubble for every 5 arc-seconds of tilt. This sensitivity is impressive, allowing for a resolution of 0.05 arc-seconds, making the device suitable for applications requiring high precision in tilt measurement.

The inclusion of four CA3039 diodes, or equivalent, in the circuit serves a dual purpose. These diodes can be used for signal conditioning, ensuring that the output from the bridge circuit is appropriately processed for further analysis or display. Their characteristics make them well-suited for this application, providing the necessary rectification and protection for the circuit components.

Overall, the described tiltmeter circuit is a sophisticated yet straightforward application of capacitive sensing principles, effectively combining mechanical and electronic elements to achieve high levels of measurement accuracy.A bubble vial with external aluminum-foil electrodes is the sensing element for a simple indicating tiltmeter. To measure bubble displacement, a bridge circuit detects the difference in capacitance between the two sensing electrodes and the reference electrode.

Using this circuit, a tiltmeter level vial with 2 mm deflection for 5 arc-seconds of tilt easily resolves 0.05 arc-second. The four diodes are CA3039, or equivalent.