3

3. The Working principle of Electronic Weight Scale
Electronic weight scales usually display a number on the LCD and equipped with electronic measuring components. The electronic weighing scales operate based on the following principle that is the force exerted by the load situated on the balance pan is transmitted to the load cell which in turn emits an electric signal whose intensity is proportional with the force. The electrical signal is picked up by the electronic balance block, processed , amplified and transmitted to a digital display system that is digital mass indicator, the result show will representing the weight of the mass located on the load pan. A very common solution is to use strain gauges (strain-sensitive transducers). The strain gauge is a passive transducer that use ` electrical resistance variation ` in wire to sense the strain produced by a force on a wire. These commercial weighing devices with low resolution were generally used. The strain gauges are wired as a Wheatstone-bridge to balance for temperature changes . When the pan is not loaded by any object, all four resistors are the same and the input of the amplifier will be zero. When an object is placed on the pan resistor 1 and resistor 4 are compacted and their resistance will decrease , resistor 2 and resistor 3 are strained and their resistance is increased. This because a voltage difference at the input of the amplifier, proportional to the weight of the object. The strain gauges are wired as a `Wheatstone-bridge` to compensate for temperature changes . The figure below shows the diagram of an electronic weight scale with a strain gauge.

1 : Spring body
2 : Weighing pan
3 : Mounting plate
4 : Placing and wiring of the strain gauges
Some of the advantages of electronic/digital weight scale are the plain fact that digital scales are considerably effortless to read. Besides, the electronic weight scale will give more precision of reading value. Here are some disadvantages to electronic/digital scales, most likely the very regular one being incorrect readings. Several people have criticised that when they stand on the scale at one spot and obtain a reading and when they get back after a few seconds they get a different reading altogether. Commonly , digital scales are good but it will be worn after a regular used. This instrument needs to calibrate after years to get better accuracy.