Electronic Weighing Systems Handbook, 3rd Edition
The BLH Electronic Weighing System Handbook has been a primary reference since its first printing in 1967. This third edition presents vital information on weighing system performance, design and implementation tools.
Since the beginning of trade, some kind of measure of weight had to be established. Not only did this measure have to be uniform, it also had to be honest. The equal arm balance scale or the unequal arm beam scale has been used for thousands of years as the standard for comparison. It is still, by far, the most commonly used technique in the world for determination of weight. However, approximately, sixty five years ago a novel technique was invented to make electronic weight measurements reliable and economically practical. This invention was the resistance wire strain gage. The strain gage consists of a filament of thin foil or wire which will change resistance when stretched or compressed.
Dr. Arthur C. Ruge of M.I.T. and E. E. Simmons of CalTech are credited with the simultaneous, but independent invention of the strain gage in 1937/38. Since each inventor had an assistant working on their project, and, since a total of four people worked on the invention, the trade name for this strain gage became SR-4 (Simmons Ruge - 4 people).
Professor DeForest, an inventor in his own right, encouraged Dr. Ruge in his work. From this relationship between two educators/scientists grew the Ruge-DeForest partnership that manufactured strain gages sold by Baldwin in the 1940's.
When a strain gage is bonded to a piece of metal and the metal is loaded with a weight or force, the resistance change of the strain gage can be related directly to the weight or force placed on this piece of metal. The first industrial load, pressure and torque transducers using the strain gage technique were developed by Ruge in 1942 and 1943. Unlike today's high precision load transducers, the early cells were accurate only to 0.25% of full scale and available in limited weight capacities.