GB1071577A - Improvements relating to extensometers - Google Patents

Abstract

1,071,577. Measuring length electrically. PHYSICAL SCIENCES CORPORATION. June 23, 1964, No.25963/64. Heading G1N. Variations in the length of a rod due to creep when subjected to a tensile stress are measured by a differential inductance having a core which is made to follow the free end of the test rod, and is connected into an automatically balanced bridge circuit whose servomotor is connected to a counter also indicating the length of the test rod. As shown (Fig. 1), a rod 18 is fixed between the wall of a fluid-tight capsule 10 and the casing of a bellows 16. The interior of the bellows is supplied with atmospheric pressure via conduit 17 and the interior of the capsule 10 is supplied with high pressure gas, e.g. helium, via conduit 56, thus placing the rod under tension. The fixing 24 between the rod and the bellows is mounted on a carriage 25 carrying a centre-tapped winding 26 whose associated core 30 is assembled on a rod 34 with a probe member 35 at one end, co-operating with a stop member 32. Winding 26 is connected in a bridge circuit with a similar winding 40, any unbalance being amplified at 44 to cause servomotor 45 to rebalance the bridge by displacing core 42 by a measured amount. The rod 34 carrying core 30 is displaceable by motor 52 controlled by an automatic reversing switch 70, so that probe 35 is reciprocated over a short distance to and from stop member 32. If the duration of the forward movement is excessive a timing mechanism 96 cuts off the power supply to motor 52 and energizes alarms 98, 100. The initial position of coil 26 is measured by motor 52 and counter 64, and the increase in length of rod 18 under the applied tension is measured by motor 45 and counter 46. Motor 52 may be manually controlled by switch 68 to move the core 30 by unit steps, indicated on counter 64. Mechanical details are shown, including thermocouples 120 Fig. 2 (not shown) for sending the temperature of the test rod 18, associated with means for automatically controlling the temperature at a desired value.