An Electrical Hot-Wire Inclinometer

Abstract

The hot-wire inclinometer consists essentially of two fine platinum wires (diameter about 0.1 mm.) mounted parallel to one another in a closed chamber at a distance apart equal to about 1 mm. A constant current of from 0.4 to 1.5 ampere (according to the sensitivity desired) is maintained in the wires, which constitute two of the arms of a Wheatstone bridge arranged so that the bridge is balanced in the zero position of the inclinometer. If desired, the bridge may be constituted of two pairs of heated wires as above. The inclinometer wires, in the zero position, may be either vertical or horizontal or inclined at any angle to the horizontal. The indications of the instrument are dependent upon the relative heating or cooling effects experienced by the respective wires when the orientation of the wires with regard to a hozontal plane is altered. The galvanoter deflection occurring with alteration in such orientation serves to indicate the inclination of a definitive radius vector to the horizontal, and calibration curves are given for the cases where the axis of rotation is horizontal, and (a) in the plane of the wires and paralel to the wires, and (b) at right angles to the plane of the wires. The characteristics of the calibration curves are discussed and curves are given showing how the resistances of the respective wires depend upon the orientation of the wires with regard to the horizontal plane referred to. Attention is directed to the finite width of the column of heated gas ascending from the wires, and an empirical formula is deduced expressing the maximum deflection as a function of the bridge current employed.