GB1396253A - Worn brake lining sensing circuit - Google Patents

Abstract

1396253 Brake-lining wear alarms SUMITOMO ELECTRIC INDUSTRIES Ltd 20 July 1973 [24 July 1972] 34811/73 Heading F2E A brake-lining-wear sensing circuit of the type having a detector circuit comprising an electrical conductor 22, 24, 26, Fig. 1, arranged to be broken when the lining 18 or 20 wears down to a predetermined limit, includes the following: voltage-divider means 28, 36 connected to a D.C. power source 34, a negativeresistance diode 32, which is normally non- conducting, connected to a tapping of the voltage divider means, and means (e.g. part of conductor 22) connecting the conductor in series with the voltage divider means and within a detector circuit shunting the diode; the component values of the sensing circuit are so related to the supply voltage 34 that when the detector circuit is (as normally) uninterrupted, the divided voltage applied to the diode 32 is less than its threshold switching voltage but greater than its holding voltage; when the detector circuit 22, 24, 26 is interrupted, even only momentarily, the threshold switching voltage across the diode 32 is exceeded, so rendering it conducting, and it remains conducting; the diode itself may in its conducting state act as an alarm indicator, (see below), but, as shown in Fig. 1, a separate indicator 30 such as a lamp, buzzer or luminous diode is incorporated. In Fig. 2 (not shown), resistance 28 is replaced by the alarm indicator 30 whose internal resistances therefore acts as part of the voltage divider, the other resistance 36 then being chosen to produce the appropriate voltage across the diode 32. Fig. 3 (not shown) resembles Fig. 1, except that diode 32 and alarm indicator 30 are combined in the form of a light-emitting diode having negative resistance (40). Since any breakage in the detector circuit activates the alarm, the arrangement is failsafe.