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).
Failures of Smith electric clocks and a proposed new testing procedure.
| Identifier | ExFiles\Box 164\1\ img138 | |
| Date | 4th December 1936 | |
| 6026 To By.{R.W. Bailey - Chief Engineer} from Rm{William Robotham - Chief Engineer}/Wst. c. to Hs.{Lord Ernest Hives - Chair} Sg.{Arthur F. Sidgreaves - MD} Hx. c. to EF. Roy.{Sir Henry Royce} Hd.{Mr Hayward/Mr Huddy} Rm{William Robotham - Chief Engineer}/Wst.18/AP.4.12.36. FAILURES OF SMITH ELECTRIC CLOCKS. In connection with the trouble that has arisen with electric clocks fitted to Phantom III. and 25/30 HP. chassis, we have now had an opportunity of carrying out certain tests. New clocks, on arrival at the Stores, have been handed to us for trial, fourteen in all having been tested. We first found that clocks would partially wind on very low voltages; from 3.6 volts upwards. But to wind up fully and open the contacts, which is really the point we are concerned with, the majority required a voltage of not less than 6.0 volts. Of the fourteen clocks tried, twelve wound up fully, and automatically broke the circuit, on 6.4 volts or less; one required about 7.8 volts, and one as much as 11.0 volts. The last was rejected as faulty, and will be returned to the makers as a test case. From these observations, we have arrived at a simple test, which can be applied to any electric clock, including new ones, if considered necessary. It is based on the makers' claim that the clocks wind up fully on 8.0 volts. It consists of connecting the negative terminal of a twelve volt battery through an ammeter to the case of the clock, by means of a clip-on cable. A second cable is clipped to the positive terminal of the clock, and is used to "tap" at various points along the battery. The first "tap" is made at 6.0 volts (3 cells) when the clock will probably wind, and the circuit be broken. That the circuit is broken will be indicated by the ammeter, or in the absence of an ammeter, by the fact that no small sparks can be produced, between the tapping cable and the battery terminal. If it fails to break the circuit, a "tap" at 8.0 volts is made. If, in this manner, the clock requires more than 8.0 volts to wind and open the circuit, it is of course rejected. A voltmeter will be necessary to ensure that the tapping points are of the correct voltage. Should a battery be above 12.0 volts, its voltage can be depressed to the required amount by a suitable loading resistance. We recommend that this test be applied on Production to all electric clocks before assembly on the instrument panel. Rm{William Robotham - Chief Engineer}/Wst. | ||