From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Investigation into the suitability of a Smiths single wire electric petrol gauge, focusing on the effects of voltage variation.
| Identifier | ExFiles\Box 167\4\ img171 | |
| Date | 14th July 1937 | |
| To By.{R.W. Bailey - Chief Engineer} from Rm{William Robotham - Chief Engineer}/Wst. c. RHC.{R. H. Coverley - Production Engineer} c. Mx.{John H Maddocks - Chief Proving Officer} SMITHS SINGLE WIRE ELECTRIC PETROL GAUGE. "We have now completed an investigation into the possibility of using an ordinary single wire petrol gauge similar to that used on cheaper cars, the idea being to economise on the price of this unit. We have had one of these single wire petrol gauges fitted to an Experimental 25/30.HP. chassis for some considerable time. The following is the result of our observations:- (1) Effect of Voltage Variation. In order to ascertain the effect of voltage variation and roughness of travelling on the indications of the Single wire petrol gauge, some road tests were carried out on car GAE.20, on which this instrument was fitted. The test was commenced with the tank about half full of petrol, the gauge reading, with the car stationary, being 14.0 gallons. This amount was chosen for the purpose of obtaining the greatest amount of turbulence in the tank. Turning the engine with the starter motor, and thus reducing the volts to approximately 11.0, the gauge reading fell to 13.0 gallons. Running the engine and charging, the voltage of the system rose to about 14.5 volts, and the gauge reading was 14.25 gallons. Although, normally, a battery is unlikely to be down to eleven volts, and the reading at that part of the scale is sufficiently accurate to serve as an indication to a driver getting near the end of his supply or one checking fuel consumption, a similar error might prove serious. This variation is more than that obtained with our standard three wire type of gauge, being practically double, although it might be argued that if the single wire gauge was set to read the contents of the tank correctly with the battery at its lowest figure, i.e. 12 volts, there would be no danger of a customer running out of petrol. continued | ||