IE33657L - Measuring mechanical displacements - Google Patents

Abstract

1275060 Measuring displacement electrically GEORGE SALTER & CO Ltd 27 Nov 1969 [27 Nov 1968] 56194/68 Heading G1N In an electro-mechanical displacement transducer in which the output frequency of an oscillator is varied in accordance with the displacement of a rectilinearly movable sensing member according to a predetermined functional relationship, means are provided for selectively providing fine adjustment of the relationship over different selected portions of the working range of movement of the sensing member. In the embodiment shown in Fig. 2 the transducer comprises a brass tubular body/10a within which is coaxially mounted in sleeve 22a an inductance coil 11a and a central slidable plunger 12a carrying metal slug 14a, the latter forming a variable capacitor with the body portion 15a. Centre part 35a of the plunger 12a has a middle section 75 composed of compacted iron dust and together with sleeve 22a, also containing iron dust, and coil 23a forms a variable inductance. The inductance and capacitance form a parallel tuned circuit of an oscillator, Fig. 3 (not shown) and when the plunger 12a is axially moved in response to movement of the member whose displacement is to be measured and which is coupled to the plunger at 35a the change in values of the capacitance and inductance result in the oscillator operating at a different frequency. Thus the frequency of oscillation is a measure of the displacement of the member coupled to the transducer. The response characteristic of the transducer is modified by means of adjustable screws 71 which together with metal disc 72 on the end of the plunger alter the capacitance. Alternatively Fig. 1 (not shown) a vane of insulating material carrying a conductive coating can be provided instead of disc 72 and this is positioned to be opposite to an aperture of the outer cylinder which is obscured by moving a ring of wire across it. In the embodiment of Fig. 4 the sensing element comprises a movable plate 93 of a parallel plate 90 capacitor and which is connected in parallel with inductance 94 in an oscillator circuit. The apparatus may form part of a weighing apparatus Fig. 4 and Fig. 6 (not shown). The outputs from the oscillator may be applied to a timer counter which displays the displacement in digital, analogue form or which controls a printing device. Alternatively the output may be applied to a radio receiver or VHF transmitter. A visual display may be obtained on an oscilloscope. [GB1275060A]