Performance testing of a Lucas Ammeter.
| Identifier | ExFiles\Box 168\5\ img344 | |
| Date | 11th December 1937 | |
| Lucas Ammeter. -2- RM {William Robotham - Chief Engineer} /RC. {R. Childs} 3/JH.11.12.37 (3) The amount of oscillation of the pointer, before settling down to a position on the scale, does not seem to be worse with the Lucas instrument, than with the standard. For a given impulse, the amplitude of the oscillation is greater with a lower frequency and apparently a greater degree of damping as the pointer settles down just as quickly. (4) As regards reliability, the operation of the instrument should not be effected by the shocks and vibration met with in ordinary handling. Neither should there be any great hysteresis effect, i.e. an indication on one side of the zero, should not be effected by a previous indication on the other side. As a test the instruments were overloaded in each direction, to the extent of 90 amperes, for a period of three seconds, and expected to withstand the resulting shock and heating. While the Lucas instruments were satisfactory in respect of vibration etc. they appeared to be more affected by the overload, the error in the indications increasing by from 10% to 16%. A further test was applied in which the instruments were put into an oven and the temperature raised to 35°C. At the end of an hour they were again checked and found to be no worse. (5) The importance of the pointer lying correctly in the zero position, lies not only in the fact that a zero error is additional to any defleotional error but also in the atmosphere of cheapness that is created by a pointer that is bent, or "off" the zero mark. Two of the instruments were not correct in this respect, the pointers lying close to one edge of a wide zero mark. The provision of a wide zero line does not dispel with maimed appearance. On the other hand it appears that it would be a simple matter to adjust the pointers during the assembling of the instruments. (6) The degree of accuracy of these instruments was undoubtedly low. The maximum error was about 20 minus, and occured in the lower part of the scale. although this was no greater than that of the standard, it was more inclined to vary with the position of rest of the instrument, and with shock. On one instrument the error increased after the over-load test, to about 33%. As already suggested however the majority of drivers probably do not see in the indications of their ammeters a numerical value, but a position of a pointer in relation to markings, which tells him whether the dynamo is delivering current, or whether the battery is being charged, or discharged in the usual way etc. | ||
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).