IITRI SOIL STRAIN GAGE AN ELECTRONIC EXTENSION
A Fritz · 1968
SOIL STRAIN GAGE INSTRUMENTATION DEVELOPED BY BISON INSTRUMENT, INC., BASED ON CONCEPTS DEVELOPED BY THE ILLINOIS INSTITUTE OF TECHNOLOGY, RESEARCH INSTITUTE (IITRI) IS DESCRIBED. IT IS BELIEVED TO BE A HIGHLY SENSITIVE, ACCURATE AND DEPENDABLE PIECE OF TEST EQUIPMENT BOTH IN THE LABORATORY AND IN THE FIELD. IT IS COMPLETELY PORTABLE AND SELF-CONTAINED. AS WITH THE IITRI CONCEPT, THE STRAIN CENTER CONSISTS OF TWO FLAT-COIL DISKS WHICH ARE EMBEDDED IN THE SOIL IN NEAR PARALLEL AND COAXIAL ORIENTATION. THE INSTRUMENT PACKAGE CONNECTS TO THE COILS AND PROVIDES BOTH A METER INDICATION AND A DC VOLTAGE OUTPUT PROPORTIONAL TO CHANGES IN SPACING OF THE EMBEDDED COILS. THE CIRCUIT UTILIZES A STANDARD BRIDGE MEASUREMENT TECHNIQUE WHERE THE EMBEDDED COILS ARE BALANCED BY A SET OF REFERENCE COILS AND THE UNBALANCE RESULTING FROM A CHANGE IN SPACING OF THE EMBEDDED COILS IS APPROPRIATELY CONDITIONED TO PROVIDE A MEANINGFUL OUTPUT INDICATION. IT IS CONCLUDED THAT THIS GAGE EXHIBITS ALL OF THE GOOD QUALITIES DELINEATED BY IITRI IN THEIR REPORTS, MAKING IT HIGHLY SUITABLE FOR SOIL STRAIN MEASUREMENT. ALTHOUGH THE BASIC CONCEPT OF THE INSTRUMENT OF IITRI REMAINS UNCHANGED, REFINEMENT OF THE ELECTRONIC CIRCUITRY INVOLVED IS PRODUCED BY THE BISON DEVICE.