Definition Sensor

A sensor is a device, machine, or subsystem that detects events or changes in its setting and sends them in sequence to other electronics, often a computer processor. A sensor is always a part of electronics.

The term [sensor] refers to a measuring element that detects the magnitude of a physical parameter and changes it to a signal that can be processed by the system. The active component of a [sensor] is commonly known as a transducer. The design of [sensor]s and transducers always involves some physical or chemical law or principle that relates the amount of interest to a measurable event.

Monitoring and control systems require [sensor]s to measure physical quantities, such as:

1. Linear position

2. Angular position

3. Displacement

4. Deformation

5. Acceleration

6. Pressure

7. Flow

8. Force

9. Linear velocity

10. Angular velocity

11. Temperature

12. Light intensity

13. Distance

14. Vibration.

 

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Smart sensors

Some [sensor]s have a particular module for signal conditioning; therefore, it is possible to have the [sensor] and signal conditioning combined with a microprocessor in the same package. A standard for smart [sensors] is the IEEE 1451.

Passive sensors

They generate signals of the magnitude to be measured but require an auxiliary intermediate source.

Active sensors

They are those that generate signals of the magnitude to be measured autonomously; that is, it does not require an auxiliary intermediate source.

Operating Terminology

The parameters to consider in any calibration and some terms used to define the operation and measurement systems as a whole.

Interval

Defines the limits between which the input of a transducer can vary.

Extension

It is the maximum value of the input minus the minimum amount.

Error

It corresponds to the difference between the measurement result and the actual value. Failures are due to different causes, and they can be foreseen, calculated, eliminated through calibrations, and compensations.

Accuracy

Refers to which near the real value is the measured value; therefore, the accuracy is equal to the sum of all possible errors plus the error in the accuracy of the transducer calibration.

Precision

It is the dispersion of the set of values ​​obtained from repeated measurements corresponding to a magnitude.

Sensitivity

The ratio indicates how much output gets obtained per input unit, that is, output/input. This term show sensitivity to other data in addition to the one measured, such as environmental factors. An example to identify is when adding the temperature variable; this means that our [sensor] or transducer will have a variation to the changes in the ambient temperature.

Hysteresis error

Corresponds to different outputs of the same measured quantity, and also this value changes according to either increase or decrease. The hysteresis error corresponds to the maximum difference obtained from increment and decrement values.

Nonlinearity error

This error is the maximum deviation from the straight line.

Repeatability or reproducibility

Describes the ability of the transducer to produce the same output after applying the equal input value several times.

Stability

It is the ability to produce the same output when used to measure constant input over a period.

Band

Corresponds to the intervals of input values ​​for which there is no output.

Resolution

It is the minimum change of the input value capable of producing an observable change in the output.

Output impedance

When the sensor gets included in a circuit, we should consider its impedance, since the behavior of the system to which it is connected could get modified considerably.

Dynamic Characteristics of a Sensor

It refers to the behavior between the moment at which the input value changes and the time at which the value given by the transducer achieves its stable state value.

Response time

It is the time that elapses from when we apply a constant input, a step input until the transducer produces a response accordingly to the output corresponding to a specified percentage, such as 96% of the input value.

The time constant

It is a measure of the inertia of the sensor, and it is considered the time it takes to react to changes in the input. The higher the time constant, the slower will be your reaction to a variable input signal.

Lifting time

The time required for the exit to reach a specified percentage of the output in a stable state.

Settlement time

The time it takes for the exit to reach a percentage of a given value.

Types of Sensor

There are different types of [sensor]s, depending on the type of variable to be measured. Some [sensor]s are for another purpose like distance [sensor]s could be used as a motion [sensor]s corresponding to “presence.”

Temperature sensor

Thermocouple

Thermometer.

RTD

PT100

Thermistor

LM35

Light sensor

Infrared.

Ultrasonic.

Light sensor:

Photodiode

Photoresistor

Phototransistor

Photoelectric cell.

Proximity sensor

Inductive.

Capacitive

Optical.

Photoelectric.

Pressure sensor:

Membranes

Piezoelectric

Manometer.

Position sensor:

Linear Position

Angular Position

Sensor Selection

It is advisable to know the variables that we want to measure, as well as the specifications of our sensors, for specific applications, we have to consider several factors.

Types of output required from the [sensor]:

We make the selection of possible sensors considering interval, accuracy, linearity, response speed, reliability, maintenance feasibility, availability, and cost.

They are some essential considerations for the selection of the sensor to be used, and it is crucial to make a list of the available variables, desired variables, and possible variables.

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