Moisture tester

摘要

A measurement apparatus is provided for use with a moisture tester of the type wherein the moisture content of a sample is determined as a function of the change in capacitance of a sample-receiving test cell when a sample is present therein from the capacitance of said test cell when empty. The tester also includes a reference oscillator and a test cell oscillator in circuit with the test cell, and a variable capacitor coupled in circuit with the test cell and the oscillators for bringing respective outputs of the two oscillators into a balanced condition both with the test cell empty and with a sample present in the test cell. The variable capacitor comprises a fixed member and a movable member which is rotatable through 360 degrees relative to the fixed member. The measurement apparatus comprises a stepping drive coupled with the rotatable member for incrementally rotating the movable member a predetermined number of steps of equal angular extent per revolution; a control circuit is provided for incrementally energizing the stepping drive in a predetermined fashion to achieve incremental rotation thereof. The control circuit also defines a predetermined and repeatable base position of the movable member with respect to the fixed member. A counting circuit counts the number of steps of the stepping drive during rotation of the movable member between the base position and any other position with respect to said fixed member; whereby the capacitance value between any two given settings of the variable capacitor may be determined as a function of the number of steps counted by the counting circuit during rotation between the base position and each of the given settings, respectively.