GB1297804A - - Google Patents

Abstract

1297804 Electro-physical measurement, thickness HARRIS-INTERTYPE CORP 25 Nov 1969 [3 Dec 1968 (3)] 57611/69 Heading G1N [Also in Divisions B6, B8 and G3] The invention relates to a capacitor probe for sensing the thickness of dielectric material passing over a conductive back-member, especially in printing or sheet feeding machines. To COMPENSATE for small changes in PROBE SPACING from the back-member, e.g. due to vibration, an inductance responsive to the position of the back-member is mounted in the probe and connected to the probe capacitor. PROBE ARRANGEMENTS. As shown Fig.2 the probe P 1 comprises two capacitor plate 21, 22, connected with inductor 23 to form the tank circuit of a Colpitt's oscillator 24, whose frequency varies with the thickness of a film F on back-number 20. Alternatively the probe may act as a variable load on an oscillator/detectorcircuit Fig. 5 (not shown), and the inductor (57) may be mounted coaxially with an annular disc electrode (50) and provided with adjustment for spacing from the back-member Fig.4 (not shown). AUTOMATIC CONTROL. As applied to a lithographic press FIG.1, the probe P 1 controlling oscillator 24 senses the thickness of ink on one of the rollers 20 in the inking chain. Thickness variation sensed by frequency discriminator 26 controls the drive motor for the fountain roller 14. Alternatively (i) the loading effect of the probe on an oscillator may produce a variable amplitude signal for motor control Fig.5 (not shown) (ii) the probe may sense the amount of water carried by the dampening roller and control the drive motor therefor. SHEET FEEDING. The probe may be used to sense the thickness of sheets to discriminate between, no sheets, a single sheet, and two or more superimposed sheets, on the feed-board Fig.7 (not shown).