An electrical moisture meter

After giving an outline of the purpose which moisture meters are intended to serve, and of the various types which have already been described, the paper describes the development and construction of a new type of meter that has already been put to good use in several industries. A constant alternating voltage is applied to a sample of the material contained in a small vessel, which may be regarded as a fixed air condenser, or in some instances as a conductivity cell. The current passing through the material is measured by means of a sensitive thermionic ammeter of special construction, which can be adjusted to read the capacitance current, proportional to the dielectric constant of the material; the conductance current, proportional to its a.c. conductivity; or some function of both these currents. The current selected is that which shows the most favourable variation with moisture content. The use of the meter for testing seeds and grain, dried foods and flax straw is discussed, and typical results are given. Other applications are briefly outlined.