Patent GB-519259-A (GB)
Title: Improvements in or relating to electrical indicating and/or recording and/or controlling apparatus
IPC: G08C19/02
Filed: 1938-10-10
Abstract: 519,259. Potentiometers ; calibrating instruments. ELECTROFLO METERS CO.. Ltd., and COULING, C. W. Oct. 10, 1938, No. 29293. [Class 37] A self-balancing potentiometer is provided with automatic calibrating means to compensate for variations in battery voltage, such means including a switch for transferring the potentiometer to connections with a standard cell, resistance, or other reference standard, and means for adjusting a calibrating resistance. The potentiometer slide wire 2, Fig. 2, is mounted on a drum 3 rotatable by the balancing mechanism past a fixed contact member. A standardising or calibrating resistance 4 is mounted on a second drum secured to, or movable synclironously with, the drum 3. A contact member 5 engaging the resistance 4 is carried by a disc 6 which normally moves with the resistance 4 owing to the friction of the brush 5. For recalibrating the disc 6 is periodically held stationary by a clutch arm 8, Fig. 1, pivoted at 9 and normally held out of contact with the disc 6 by a spring 10. The clutch arm is provided with a contact switching arm 12 carrying a contact 13 movable between fixed contacts 14. 15 connected to the standard cell circuit and the point switch. Contacts 16, 17 may be provided for shunting the galvanometer with a fixed resistance during the standardising operation. The clutch arm 8 is periodically moved into contact with the disc 6 by means of a cam 20 having two humps 21, 22 which' come into operation successively. When the first hump 21 actuates the clutch arm the contacts 16, 17 shunt the galvanometer and the contact 13 opens the point switch contact. When the hump 22 becomes operative the contact 13 engages the contact 14 to close the standardising circuit, the contacts 16, 17 remaining closed. The cam 20 is rotated synchronously with the multi-point switch 24 for connecting the potentiometer to different measuring points in succession. An oscillating arm 25 carries pawls 26, 27 engaging a ratchet-wheel 28, secured to the cam 20, and a ratchet-wheel 29 coupled with the multi-point selector switch 24. The arm 25 is oscillated by a snail cam 32 driven from the motor 35 that operates the balancing mechanism. The ratchetwheel 28 has a fixed shroud 36 masking a portion of its periphery so that normally only one tooth at a time is operated for each movement of the multi-point switch. The ratchet-wheel 28 also has a pair of teeth 38, 39 projecting beyond the shroud whereby larger movements are obtained to bring the humps 21, 22 into position once during each rotation. The two large teeth may alternatively be formed on a separate ratchetwheel. A rod 45, Fig. 1, or a spindle 46, Fig. 2, may be provided for manual operation. Provision may be made for staggering the standardising operation so as to ensure that omission of measurement does not take place more often at one point of the multi-point switch than at any other. Alternatively a shroud may be arranged on the clutch-operating ratchet-wheel or cam preventing operation at the standardising point so as to delay but not omit measurement at the point where standardisation occurs. A cam 50 causes axial displacement of the disc 6 according to the annular movement of the contact 5 and thereby moves a pointer 52 over a scale 54 to indicate the condition of the battery.