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).
Service bulletin describing the wiring, operation, and features of an AC petrol gauge with a geared type tank unit.
| Identifier | ExFiles\Box 61\3\ scan0277 | |
| Date | 18th September 1931 | |
| AC SPHINX SPARKING PLUG CO., LTD. BIRMINGHAM BULLETIN GAUGE-106 AC SPHINX SERVICE BULLETIN Date: 18-9-31 Sheet 2 No. of Sheets 3 SUBJECT--AC PETROL GAUGE (With GEARED TYPE TANK UNIT) Cont'd.{John DeLooze - Company Secretary} WIRING The outer terminal of the Dash Unit marked "BATTERY +" is connected by a wire to the ignition switch so that the petrol gauge is operated only when the ignition is turned "ON." The centre terminal marked "TANK" is connected by a single wire to the terminal on the Tank Unit. The return circuit is accomplished through a "ground" as both the Dash Unit and Tank Unit are "grounded" in their respective locations. HOW IT WORKS When the petrol tank is empty, the float is at its lowest position and the rheostat in the tank unit is completely grounded. All of the current through the dash unit then flows through the coil at the "Empty" side of the indicator and the pointer is then moved to the "Empty" position. As the tank is filled with fuel, the float rises. This moves the brush in the rheostat, and resistance is introduced into the circuit which grounds the "Full" coil in the dash unit, so that part of the current flows through this coil and the pointer is attracted away from the "Empty" to a position of balance between the two coils, its point of rest depending on the level of the fuel. The movement of the pointer is reversed, of course, as the fuel level goes down. CURRENT CONSUMPTION Owing to the design of the AC Petrol Gauge, current consumption is very low, between 1-6th to 1-10th ampere. As far as car operation is concerned, this amount of current is negligible and can be entirely disregarded. NO VOLTAGE ERROR The operation of this Gauge does not depend upon the strength of the magnetic field, therefore fluctuations in the battery voltage will not cause any error in the gauge reading. STEADY INDICATION The indicator or pointer remains steady at all times, due to a carefully calibrated friction damper incorporated in the tank unit to prevent moderate surging affecting the reading of the dash instrument. Also the dash unit has an inertia damper to prevent vibration of the pointer on rough roads. | ||