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).
The bench and accuracy testing of Smith's motor-type electric clocks.
| Identifier | ExFiles\Box 164\1\ img225 | |
| Date | 29th March 1940 | |
| 6026 file elec Rm.{William Robotham - Chief Engineer}9/ML.29.3.40. SMITH MOTOR-TYPE ELECTRIC CLOCKS. The motor-type electric clock was submitted by Messrs Smith's in 1938, as a cheaper instrument than the existing standard. Bench tests carried out revealed the following characteristics: (1) Merely connecting the clock to the battery did not start it. It was necessary to move the hands. (2) It stopped immediately it was disconnected from the battery. (3) The current required to operate it was very small. Tests for accuracy, covering a period of three weeks, were next carried out. These tests showed that the clocks varied between themselves, in the extent to which they gained or lost time, and also that they varied according to the battery voltage. For the same supply of 12.0 volts, one instrument gained 2.0 minutes in a week, and another lost 4.0 minutes Raising the voltage to 14.0 volts had no effect, but lowering it to 10.0 volts caused the clock, which normally gained, to lose 3.0 minutes in a week, and the other to lose still more. i.e. 9 minutes in a week. Since the error is accumulative, it will be seen, that even a good instrument will indicate very incorrect time, if allowed to run on without being set to correct time periodically. In view of the reduction in price for this type of clock (15/- as compared with 28/- for the standard instrument) it was considered that no objection would be raised to adjusting the hands once a week, if necessary. At the same time, it was agreed, that a variation of not more than plus or minus 5 minutes a week, be permitted. Details of the foregoing were reported on 6.4.38. Subsequently, 9 of these clocks were fitted on cars, and later it was reported in Rm{William Robotham - Chief Engineer}/RC.{R. Childs}10/JH.28.10.38 that up to that date, only one clock had given trouble, and | ||