Measuring principle
The measuring principle is the physical basis of a measurement . This term is in the standard DIN 1319 which defines the essential terms in the measurement sets.
The length is one of the few physical quantities that can be accessed at least in the millimeter to meter range by applying a scale to a measurement . The respective measured value can be read off using a caliper , ruler or measuring tape . For other variables, humans have developed a limited quantitative perception, for example for time ("about five seconds"), temperature ("lukewarm") and mass ("more than two kilograms"). Most physical quantities cannot be recognized with his senses. For this reason, measuring devices are being developed that convert a measured variable into the easily readable size of a length or an angle or into the easily processable size of an electrical voltage, etc.
“The measuring principle makes it possible to measure another variable instead of the measured variable in order to clearly determine that of the measured variable from its value. It is based on a physical appearance (phenomenon, effect) that can be reproduced again and again with a known regularity between the measured variable and the other ”.
The practical application of the measuring principle leads to a measuring method and, in its concrete implementation, to a measuring device. The measured variable is converted into a detectable measurement signal . For example, temperature, pressure or force measurements are transferred to simple length measurements; the length is read off directly on a scale . Other physical quantities are mapped to an electrical resistance, a time, a number of voltage pulses, etc. Depending on the requirements, several measuring principles are applied one after the other.
When choosing the measuring principle, linearity between the variable to be measured (input variable) and the actually measurable variable (output variable) is usually aimed for. Then the relationship can be indicated by a constant sensitivity .
- example 1
- When measuring temperature , a liquid glass thermometer takes advantage of the different thermal expansion of the liquid and the glass vessel. As the temperature rises, the liquid pushes into the glass capillary connected to the vessel, and the liquid thread becomes longer; Change in temperature → change in volume → change in length. Then the current length of the liquid column is measured. The scale connected to the capillary tube is labeled with values for a temperature unit so that the temperature measured value is not read off directly, but directly.
- Example 2
- Even more measuring principles are used in a measuring chain for measuring pressure with a silicon pressure sensor:
- pressure
- → Elastic deformation of the silicon membrane with expansion / compression of the diffused resistors
- → positive / negative changes in resistance
- → Detuning of a Wheatstone bridge with generation of a bridge transverse voltage
- → Further processing into standardized signal transmission (remote measurement, automation) - or
- → Pointer deflection (angle) on a voltage measuring device which, in connection with suitable signal processing, can be labeled with values for a pressure unit on the scale so that the pressure can be read immediately.
- → Detuning of a Wheatstone bridge with generation of a bridge transverse voltage
- → positive / negative changes in resistance