Methods of Measurements
The two categories into which the methods of measurements are segregated into are direct and indirect methods.
What are the direct methods of measurements?
In the direct methods of measurement, the quantity that needs to be measured is compared directly with a standard. The quantity that needs to be measured is often referred to as the ‘measurand’. After the measurement is made, the result is usually expressed as a numerical value followed by a unit. The ‘standard’ can be considered as the ‘unit’ in its physical form.
When physical quantities like time, length, and mass needs to be measured, direct methods are employed. Thus, when the length of an object has to be made, we figure out how many units of the length standard makes up the object.
Meter is the unit for length. Thus, if the object measured is considered to be x meters, then it can be understood that x many meters of the standard make up the length of the object.
It has been arrived at through trials that humans can make direct measurements of length to a precision of 0.25 mm. Thus, human factors, as they are known do not allow accurate measurements to be made. Even though length measurements can be made with some level of accuracy, using the direct methods, volume measurements are almost an impossible. It is impossible for humans to also distinguish between a wide range of masses.
What are the indirect methods of measurements?
Because of the inaccuracy of direct methods of measurements, made impossible due to human factors, it is not considered to be accurate, feasible, or practical. Hence the direct methods of measurements are rarely used. Indirect methods are rather used by ‘measurement systems’ which are what all engineering applications utilize.
What are measurement systems?
Measurements are made using instruments, and instruments serves as a physical means for the determination of unknown quantities. Instruments help man measure unknown quantities by acting as an aid or an extension to his natural faculties; there is a limit to the precision to which man can measure an unknown quantity using his natural faculties and without the use of any external aid.
The instrument in turn gives man the ability to get to know the value of an unknown quantity directly from the instrument’s read-out. An instrument in its most simplest form of construction will have a single unit and it would give a reading on its output based on the amount of unknown quantity that is applied to it.
In more complex systems of measurement the measuring instrument may in turn be made of many separate modules. The modules in turn may be made of elements like transducers which converts energy in one form to another. The transducers may convert energy in form to electrical energy which is then fed to other modules which then processes the information held within the electrical signal, and converts it to a form that can be displayed on to an output display screen.
The various modules that make up the measurement system may be enclosed within a single box, or may be kept separately in different boxes. Due to this segregation of the various modules, the instrument that is constructed by bringing together of the various modules is referred to as the measuring system.