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).
Overload test report on various chassis ammeters to determine their performance under heavy current.
| Identifier | ExFiles\Box 168\5\ img287 | |
| Date | 17th May 1934 | |
| He/Wat.T/EA.17.5.34 OVERLOAD TEST ON CHASSIS AMMETERS. It has been observed that on some R.R. Chassis the coachbuilders have wired certain heavy current accessories such as cigar lighters, so that the current passes through the ammeter. If the ordinary current discharges such as all lamps, windscreen wipers, ignition etc., are in operation the ammeter will become overloaded when these accessories are operated particularly if two or three cigar lighters are operated simultaneously as might easily be the case. We have therefore carried out tests to determine the effect on the ammeter. Five different ammeters were tested e.g. Ferranti moving coil type, C.A.V. moving coil type, Elliot moving coil type, Lucas moving iron type having special damped movement, and a standard Weston moving iron instrument. The tests consisted of an endurance test in which the ammeters were subjected to an intermittent current of 50 amperes every two or three seconds. Each ammeter was carefully calibrated against a master instrument before and after the test to determine what effect the excessive current had on the magnetic characteristics of the instrument. During the test the Elliot ammeter appeared to be the most dead beat, the Ferranti being a close second. The Weston instrument needle repeatedly failed to return to zero but eventually it freed itself and at the conclusion of the test was functioning correctly. The zero errors were negligible except in the case of the Weston which at the conclusion of the test had a zero error of 1.5 amperes. | ||