| 摘要 |
668,453. Telemetering systems. DUTILH, J. R. H. May 2, 1950. [May 10, 1949 ; March 25,1950] No. 10757/50. Class 40 (i). [Also in Group XXXVI] A constant current source 8, Fig. 1, e.g. a pentode, is periodically reversed at 9 to feed over a manually operable switch 37 any one of circuits 2, 21, 2<SP>11</SP> each including a resistance 3 to be measured, the resistance 3 being shortcircuited for one direction of current flow, so that the voltages measured at 14 indicate the value of the resistance. As shown in Fig. 1, a relay 4 operates for one direction of current flow to short circuit the resistance 3 ; alternatively, a rectifier 13, Fig. 3, may be used to by-pass the resistance 3 for one direction of current, a further rectifier being connected to compensate for the contact resistance. For one direction of current flow, the voltage across 11, 12 is IR L + IR R -IIRx where R L , R R , R x is the resistance of the leads, the relay (or rectifier) and the unknown resistance ; for the other direction of current flow, the voltage across 11, 12 is -(IR L , + IR R ); if the periods of reversal are equal, the average voltage is proportional to R x and can be registered by an instrument 14 of suitable time-constant. If the periods of reversal are unequal, the instrument can be adjusted to read zero when the resistance 3 is short-circuited, so that the reading when the resistance is in circuit is related to R x . In another arrangement, the voltage arising when the resistance is shortcircuited, charges a condenser 25, Fig. 5, which, on reversal of the current, is placed in series with the voltmeter 28 which thus registers the difference between the voltages developed when the resistance is in and out of circuit. Specifications 400,289 and 601,541 are referred to. |
