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).
Failure of a Cambridge thermometer with an electrical contact, attributing blame to the manufacturer.
| Identifier | ExFiles\Box 175\4\ img082 | |
| Date | 13th September 1927 | |
| To ROY.{Sir Henry Royce} from EFC. X3875 EFC2/T13.9.27. CAMBRIDGE THERMOMETER WITH ELECTRICAL CONTACT. Herewith we hand to you a Cambridge thermometer with electrical contact for indicating lamp. This thermometer has failed and the failure is due to a contact being made between the main Bourdon tube and the bottom end of one of the insulated terminal screws. This allowed a current at 12 volts to pass through the hair spring of the mechanism and get to earth via this faulty contact, thus damaging the spring. This would appear to be entirely a fault of the makers in not providing sufficient clearances, and we suggest that they should carefully look over the various clearances. We have already sent one back because the base of the mechanism (which is normally insulated) was touching the block from which the main Bourdon tube starts. In addition to this, there is on the present instrument a very small clearance between the teeth of the sector and this same block, and it might happen for an unwanted contact to be made at this point. We consider they should correct this instrument free of charge and that we should respectfully suggest that the instruments could be improved in the directions indicated. To make it clear to them that we are not ascribing all the failures we have had on these instruments to them, we are prepared to tell them that we have had failures which we cannot reasonably ascribe to any fault on their part, but I can only put down to the terminals (which are exposed) having been accidentally earthed while the thermometer has been on contact. To show them that we are also doing something to eliminate failures, it might be of interest to them to know that we intend to provide insulating covers for the terminals of both the thermometer and the bare terminal of the lamp which is lighted thereby. Also that we have made in our electrical laboratory a very careful test of one of these instruments and we are prepared to confirm their previous contention that the ordinary current of the lamp cannot under any circumstances fuse the contact. All the failures that have occurred have been due to some short circuit which we agree have been in some cases our own fault, but in each of the two cases referred to above we must put the failure down as their responsibility. Will you kindly arrange for this thermometer to be returned to this Dept. as soon as received back from the makers. | ||