GB1211575A - Improvements relating to indicating devices - Google Patents

Abstract

1,211,575. Retractive switches. D. A. PINCHES. 18 Sept., 1968 [26 Jan., 1968], No. 4105/68. Heading H1N. [Also in Division G1] A tyre tread depth gauge comprises a tread probe or plunger 19, Fig. 2, mounted in a part 20 sliding vertically in a guideway 12 of a casing 11, and a metal strip 23 encased by the part 20 and provided with a cross contact bar 25 which electrically connects the probe 19 through a spring 22 to a metal clip 35 contacting the edges of top plate 28 electrically connected to lamps 30a, 30b covered by amber and red coloured domes 34b, 34a. Electric batteries 14a, 14b connect the centre terminals of the lamps with upstanding metal strips 26a, 26b, provided with vertically offset contacts 27a, 27b, so that when the probe 19 enters the tread pattern and the datum or bottom surface 18 of the casing contacts the wearing surface of the tyre, then the cross bar 25 either does not contact 27a or 27b, in which case no lamps light, thus indicating sufficient tread, or the bar 25 will contact 27b or 27a to light lamps 30b, 30a to indicate that the tread is just satisfactory or unsatisfactory in thickness. In Fig. 4 the probe is depressed against the action of a spring 422 until contacts 446, 448 abut to light amber lamp 430b through cable 445b. Further depression of the probe causes contact 446 to abut contact 444a and light red lamp 430a in addition to the amber lamp, to indicate that tyre replacement is necessary. In Figs. 6 (not shown), the movable probe additionally actuates a sliding resistance connected to a meter in the housing to give a thickness reading.