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In a series of experiments carried out by David Crecraft and Roger Loxton the various characteristics of strain gauges are demonstrated.
Metadata describing this Open University video programme
Module code and title: T291, Instrumentation
Item code: T291; 02
First transmission date: 14-03-1974
Published: 1974
Rights Statement:
Restrictions on use:
Duration: 00:24:24
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Producer: David Jackson
Contributors: David Crecraft; Roger Loxton
Publisher: BBC Open University
Keyword(s): Bridge circuits; Cheddar Gorge; Electrical pylons; National Tower Testing Station; Out of balance voltage; Resistors; Sensitivity; Strain gauges; Temperature
Footage description: Roger Loxton with experimental apparatus which measures strain on a steel rule as weights are suspended from one end. Loxton explains how the strain gauge is fixed to the rule. He then uses a model to demonstrate how it measures strain in materials. Loxton demonstrates the apparatus. David Crecraft with a bridge circuit which measures strain in terms of an output of balance voltage. He points out the various components and explains how the bridge circuit works. Crecraft shows how the strain gauge is connected to the bridge circuit. Crecraft and Loxton demonstrate the bridge circuit as they measure strain on the steel rule once again. Loxton plots the readings for various weights on a graph. Loxton and Crecraft examine and discuss the resultant curve. The weights are removed from the steel rule. Loxton and Crecraft discuss reasons why voltage reading has not returned to zero. Crecraft begins discussion on the effect of changes in temperature on strain gauge readings. Loxton demonstrates by spraying freezer spray on the strain gauge. There is a significant change of reading on the voltmeter. Crecraft uses the board showing the bridge circuit and strain gauge to explain how one can compensate for temperature variation when measuring strain. Loxton sprays the rule again. It has been wired up to compensate for temperature changes and the voltmeter remains at zero. Crecraft uses the circuit board again to explain how the compensation actually works. Crecraft and Loxton again measure strain imposed on the steel rule by various suspended weights. This time the temperature compensation gauge is wired into the bridge circuit. Loxton plots the readings on a graph. Crecraft and Loxton discuss the resultant curve. They compare this with the original curve. Crecraft with the circuit board explains why the addition of the temperature compensation gauge increased the sensitivity of the strain measurement. Crecraft also uses a model as an aid. Crecraft introduces a sequence on the practical application of strain gauging. Shots of the C.E.G.B. National Tower Testing Station near Cheddar Gorge. Commentary by Loxton explains why this site was chosen and what sort of tests electricity pylons undergo here. Shots of a test in progress. Roger Loxton, with a piece of steel pylon member, explains how the strain gauges are attached to a pylon for the tests. Shots of strain gauges being attached for an actual test. Commentary by Loxton explains what is happening. Shot of the bridge circuit diagram aids his commentary. Crecraft in the studio explains how bridge circuit output is amplified so that readings can be put on a chart recorder. He uses a circuit diagram to aid. Shots of an actual test in progress at the C.E.G.B. Tower Testing Station. Commentary by Loxton explains what is happening. Several diagrams throughout the sequence are used to aid explanations. Loxton explains how the system is calibrated.
Master spool number: 6HT/71066
Production number: 00525_5118
Videofinder number: 1062
Available to public: no