Switches Indicators & Gauges

The Development of Tools

The basic definition of a tool is an object that creates more effective action of one thing upon another. Simple machines are based on what type of action this involves, whether a lever, wheel and axle, pulley, inclined plane, wedge or screw. These basic categories were defined by Renaissance scientists, and are the basis of complex machines. Although multiple species utilise tools, including monkeys, apes and sea otters, what is unique about humans is that we are the only species that uses tools to create other tools. There are called machine tools.

A machine tool is a powered mechanical device, usually used to fabricate metal components, thus removing the human element in the physical production of tools. After the Industrial Revolution and the development of the steam engine, machine tools were able to be powered by steam. Today most are powered by electricity, and can be operated manually or automatically. Examples of machine tools include the drill press, gear shaper, lathe, hobbing machine, shaper, planer, broaching machine and grinder.

Machine Tools and Mass Production

The invention of machine tools led to the development of mass production. David Hounshell states: “The new manufacturing technology spread first to the production of a new consumer durable, the sewing machine, and eventually it diffused into such areas as typewriters, bicycles, and eventually automobiles.” (1984, p4) It took off from the small arms industry such as Colt’s Patent Firearms Manufacturing Co. As manufacturers worked with the makers of machine tools, they overcame problems related to the cutting, planing, boring and shaping of metal parts.

This ” technological convergence” would lead to the Fordist system of manufacturing and labour division. This system, named after Henry Ford, was based on mass production to lower the price of the product, and simultaneously raising workers’ wages to feed massive consumption. The system emphasised synchronisation, precision and specialisation, and would lead to the economic dominance of the United States from the 1940s onwards.

Solid Level Sensors

Level sensors are used to detect the level of substances within a container or some physical boundary. Solid level sensors measure the levels of substances such as slurries, granules or powders. Level sensors that use point-level detection to measure solids include vibrating point level sensors, rotating paddle level sensors, mechanical (diaphragm) level sensors, microwave/radar level sensors, capacitance (RF) level sensors, optical interface level sensors and ultrasonic level sensors. Two of these are explained below:

Vibrating point level sensors are used to detect levels of fine and very fine powders (between 0.02g.cm³ to 0.5g/cm³) and granular solids (density of 0.5g/cm³ or greater). Single-probe vibrating level sensors tend to eliminate build-up of material on the probe, are not affected by dust or static-charge build-up, changes in conductivity or temperature, pressure or humidity.

Rotating paddle level sensors involve a low speed gear motor that rotates a paddle wheel, sensing the level through the amount of resistance it encounters from the material. It cannot be used for very low density materials as its weight is insufficient to resist the paddle. The main drawback is that material may build up on the paddle.

Liquid Level Sensors

Liquid level sensors can measure continuously or at point-level. Common liquid measurement sensors include magnetostrictive level sensors, resistive chain level sensors, hydrostatic pressure level sensors and air bubbler level measurement systems. Magnetostrictive level sensors consists of a magnet sealed inside a float which travels up and down a stem that has a magnetostructive wire. These are usually used for continuous level measurement in storage and shipping containers holding liquids. They provide a high degree of accuracy as long as the the right float is chosen according to the gravity of the liquid.

Air bubbler systems are suitable for all sorts of liquids containing suspended solids as it contains no moving parts, whether sewage, drainage water, etc. It contains a bubble tube with an external sensor, making it appropriate for hazardous liquids as well. One of the main advantages it that it is self-cleaning through high-pressure air.

Level Sensors

Level sensors are used to detect levels of substances that naturally flow to become level in whatever physical boundaries constrain it. This can include substances such as liquids, semi-liquids (e.g. slurries), or solids (e.g. granules or powders). Level sensors can detect continuous levels, measuring within a specified range to determine the specific amount of substance in a certain place. They can also measure at specific points, generally whether the substance is above or below the sensing point (excessively high or low).

Continuous measurement of liquids can use magnetostrictive level sensors, resistive chain level sensors, hydrostatic pressure level sensors and air bubbler level measurement systems. Sensors for point-level measurement of solids include vibrating sensors, rotating paddle sensors, mechanical sensors, microwave sensors, capacitance sensors, optical sensors and ultrasonic sensors. Sensors that can detect both point-level or continuous-level measurements of solids and liquids include capacitance sensors, optical interface level sensors, ultrasonic level sensors and microwave/radar sensors. The type of sensor used depends on the type of substance (i.e. liquid, semi-liquid, or solid), agitation or vibration, density, whether it must detect measurements in a vacuum or under pressure, the temperature, the type of container, the chemical composition of the substance, noise and so on.

Submersible level sensors

Hydrostatic submersible level sensors are used for measuring the level of corrosive liquids in deep tanks, such as the NivoPress NP that Semrad Pty Ltd offers. This level sensor consists of a probe and a breathing cable containting a capillary pipe (i.e. with a ver small diameter) and a stress resistant inlet. The probe is a stainless steel cartridge, suitable for clean or faintly chemically tainted liquids (whether in tanks or water reservoirs). Its main purpose is to monitor submerged pumps, as it is capable of fully functioning while immersed in water. Hydrostatic level sensors basically sense increasing pressure with depth (calibrated to the specific substance).