Patent GB-1508345-A (GB)
Title: Accelerometers
IPC: G01P15/135
Filed: 1975-04-18
Abstract: 1508345 Accelerometers M J SNYMAN 18 April 1975 [19 April 1974] 16018/75 Heading G1J An accelerometer 10 for mounting in a vehicle includes means 12 to provide a first output signal in response to acceleration above a predetermined level, and a signal presence detector 14 to provide a second output signal after the continuous presence of the first output signal for a predetermined time, the second output signal controlling switching means 16 to energize a recorder 20 and a warning device 22 and thereafter to block the recording of any further second output signals for a period substantially greater than the predetermined time. The object is to count and/or warn the driver each time the vehicle is subject to excessive acceleration or deceleration, or lateral acceleration due to cornering, without the apparatus being affected by bumps in the road. The sensing means 12 may be electrical, mechanical, magnetic, or hydraulic, but as described is a pendulum 36 making an electrical contact 36.1 when the acceleration reaches a predetermined magnitude. When contact 36.1 is made, it completes a charging circuit for a capacitor 44 of the signal presence detector 14. After the predetermined time (10- 200 milliseconds) the capacitor is charged sufficiently to render a transistor 46 conductive. This activates a timer 18 to record the total time in excess of said predetermined time that the pendulum contact 36.1 is made, and also causes transistors 56, 58, 68 of the switching unit 16 to become conductive, allowing a charged capacitor 62 to discharge via a resistance 60 and the transistors 56, 58, 68 until the bias on transistor 56 is reversed to render it, and subsequently also 58 and 68, non- conducting. They cannot become conducting again until capacitor 62 is sufficiently charged through a resistance 64, typically in about 2 seconds. The momentary switching on of transistor 68 allows a pulse to advance a counter 20 by 1, and allows a capacitor 82 of the warning device 22 to discharge, rendering transistors 78.1 and 78.2 conductive. These act with a capacitor 80 and a speaker 76 as an oscillator, so that the speaker 76 emits a warning tone and a LED 74 glows. The capacitor 82 is recharged via resistances 84.1 and 84.2 until, after about 1 second, transistor 78.1 is switched off, the warning device then being inactive until a further pulse is passed by the switching device 16. For testing, a switch 38 is moved to isolate the accelerometer 12, and switches 54, 72 opened to isolate the timer 18 and counter 20. A test switch 40 then passes a.signal to the signal presence detector 14. A unit 28 inter-connected with the vehicle controls shortens the predetermined time of the detector 14 when the vehicle headlights and/or windscreen wipers are switched on. In modifications, the accelerometer may enable different signal circuits for different levels of acceleration, or several accelerometers set to emit signals at different levels of acceleration may be used, or accelerometers sensitive to acceleration in different directions, separate presence detectors and recording/warning means being provided for each channel.