Importance

Loading Importance Indicators...

Abstract

A meter overdrive protection circuit is provided using a variable duty cycle drive pulse. Such meters usually comprise speedometers and tachometers used in highway vehicles such as trucks. A programmable pulse generator is utilized to provide a series of pulses of a selected width depending on the truck model. A sensor input corresponding to the rate of rotation of the drive shaft of the truck is used to trigger the pulse generator to produce each output pulse. Such output pulses are supplied to a meter drive which, based on the time average value of the output pulses received, displays an output value related to the rate of rotation of the truck drive shaft. Upon the triggering inputs exceeding a preselected frequency, a microcomputer will change the pulse generator operation to a fixed duty cycle operation whereupon the meter will be held to a full scale deflection. When the triggering inputs decrease below the preselected frequency, the pulse generator will be returned to a triggering output mode. Such meter drive circuit protects electromagnetic meter needle movement from damage due to full scale pinning against a mechanical stop.

Loading the Abstract Image...

First Claim