Patent GB-883831-A (GB)
Title: Improvements in or relating to instruments for measuring mechanical values by the carrier frequency method
IPC: G01L1/22
Filed: 1958-10-21
Abstract: 883,831. Measuring bridges; batteries. HUGGENBERGER, A. U. Oct. 21, 1958 [Oct. 29, 1957], No. 33684/58. Addition to 782,091. Classes 37 and 53. [Also in Group XXXVIII] The invention relates to the measurement of a physical variable, e.g. torque, by producing corresponding variation in the value of a strain-gauge resistor or an inductor, which is measured in an A.C. bridge circuit, and is characterized in the use of miniaturized amplifier components, a portable motor generator set to produce the bridge A.C. supply, and a plug-in test set for checking the amplifier. As shown (Fig. 1), the bridge comprises two balancing strain gauge resistors 1, 2 and two test strain gauge resistors 3, 4 appropriately mounted on a test object, the bridge unbalance current being fed through a transistor amplifier to be rectified at 15 and led via terminals 17/1, 17/2 to a C.R.O. or milliammeter. To enable the bridge to be initially balanced, resistors ,1, 2 are attached to either side of a steel spring 28 (Fig. 4), whose tension is adjustable by a screw 31. The spring 28 carried a second pair of strain gauge resistors 1a, 2a for a different measuring range. The bridge and amplifier are attached via plug sockets 54, 54<SP>1</SP> to a test set (Fig. 7), used for checking the operation of the amplifier, using the output from a motor generator (not shown) via socket 50 to supply the bridge voltage. A two-pole, rotary switch 52<SP>1</SP>, 52<SP>11</SP> enables the voltage of the battery 19 (Fig. 1), to be measured on a meter 53, or the output voltage of the motor generator to be measured, or the meter to be connected across the amplifier output terminals 17/1, 17/2. The test set also carries two resistance strips 3<SP>1</SP>, 4<SP>1</SP> mounted on a spring 57, whose resistance values can be varied by bending the spring with calibration weights applied to a plate 58, to mechanically check the calibration of the amplifier. The resistors 3<SP>1</SP>, 4<SP>1</SP> can also be unbalanced in equal steps by resistors 62/1 to 62/5 selected by switch 59 to be placed in parallel with either 3<SP>1</SP> or 4<SP>1</SP>, to check the linearity of the amplifier. The calibration of the amplifier is also checked electrically by a series of resistors 6, one of which is chosen by switch 5a to be placed in parallel with resistor 1 to produce a predetermined amount of unbalance. The voltage fed to the bridge is simultaneously modified by a series resistor 7 selected by ganged switch 5. The test transducers may be variable inductors 24, 25 (Fig. 2), whose reactances are balanced by capacitor 13 and potentiometer 26. To test the reactive balance, the unbalance signal after amplification is fed to the rectifier bridge 15 which is converted into a phase unbalance measuring device by operating switch 27 (Fig. 3), to the left as shown. A plastic transparent casing 33 (Fig. 5), for the battery comprises two separate chambers in which cell units 34, 35 are located in reversed positions, interconnected by a bow-spring 36 attached to a second bow-spring 37 which is clipped at 38 to the cover 39. The latter is secured to the casing 33 by a pin 40. At the other end of the chambers are contact plates 41, and protruding pins 42.