If computers are an extension of the human brain, then sensors are an extension of our five senses. Sensor technology is one of the most rapidly developing and noteworthy high technologies in the world today, and a significant indicator of contemporary scientific progress. So, what types of sensors are there?
A sensor is a device or apparatus that senses a measurand and converts it into a usable output signal according to a certain rule. It typically consists of a sensing element and a conversion element. While there are many types of sensors, they can be broadly classified based on the measurement method, the characteristics of the measured object, the sensor's properties, and its application. Sensor measurement methods are divided into "active methods" and "passive methods."
"Active methods" refer to sensors that transmit signals to the measured signal and detect its reflection; these are active sensors. They require external energy to provide signals such as light, electromagnetic waves, radiation, and sound to the object being measured, and receive its reflection, transmission, and absorption, thereby detecting characteristic quantities of the measured object.
The "passive method" only receives signals emitted by the subject.
On the other hand, passive sensors do not require their own power source and detect the measured object by receiving a measurement signal from it. A typical example of this distinction is a safety infrared sensor. The choice depends on the intended use and installation location.
An active sensor is a near-infrared sensor that emits infrared light from itself and detects the object to be measured by reflecting or blocking the light. A far-infrared sensor, which receives infrared light emitted from the human body surface and detects the person, is a passive sensor.
In addition, based on the sampling and monitoring frequency of the process, sensors can be divided into "inline analysis", "online analysis" and "offline analysis".
Inline analysis
Inline analysis is a method in which the sensors or detectors of a process analyzer are in direct contact with the object being measured (e.g., a reaction vessel or flow path to be measured) and continuously perform detection, analysis, recording, transmission, and monitoring. Key characteristics of these sensors used for inline analysis are that they can operate in a continuous feedback loop without time intervals and require essentially real-time or high-speed performance, non-destructive measurement, and high tolerances. This is the most ideal method for analyzing and monitoring manufacturing processes because sensors can be placed within the manufacturing process line without sampling.
Online analysis
Online analysis is a method of automated sampling and analysis that is performed on an ongoing basis. Sampling equipment, sensors, and process analyzers are placed near the object being measured. This method is used for compositions that require rapid changes in composition or continuous monitoring (e.g., chemical composition).
Offline analysis
In offline analysis, samples are analyzed and transported to a laboratory equipped with the relevant sensors and analyzers. These transported samples are then analyzed using these instruments. This method is used for time-consuming, precise analyses or for analyzing multiple components in small samples.
It is important to note that the differences between these sensors do not make one type superior or inferior. These are simply different systems used for specific purposes.
A broader approach to differentiating sensors is through measurements of various properties of the domain (the measurand).
