Absolute instruments in the context of measurement and instrumentation refer to instruments that measure a quantity directly in terms of a fundamental physical unit without relying on any reference or comparison. These instruments provide measurements in absolute terms, which means that the measurements are not dependent on external conditions or standards. They are typically used for measuring quantities such as length, time, mass, temperature, and electric current.
Here are a few examples of absolute instruments for different quantities:
Length: An example of an absolute instrument for measuring length is a Michelson interferometer, which uses the properties of light to directly measure the length of an object or the wavelength of light.
Time: Atomic clocks are considered absolute instruments for measuring time. They use the oscillations of atoms as a reference and are highly accurate and stable.
Mass: A balance that measures mass using gravitational force is an absolute instrument. It compares the force exerted by an unknown mass with the force exerted by standard masses under the influence of gravity.
Temperature: Absolute instruments for temperature measurement include gas thermometers and resistance temperature detectors (RTDs). Gas thermometers rely on the behavior of gases at different temperatures, while RTDs use the change in electrical resistance of a material with temperature.
Electric Current: The Hall effect can be used to measure electric current in an absolute manner. By placing a conductor in a magnetic field and measuring the induced voltage, the current can be directly determined.
Absolute instruments are important in scientific research, industrial applications, and metrology, as they provide accurate and reliable measurements that are not influenced by external factors or changes in environmental conditions. They play a crucial role in establishing standards and ensuring the accuracy of various measurement systems.