sensor type and function

Sensor Types and Functions

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Sensor Types and Functions – How do we choose Sensor? You can choose sensors with a variety of available in the market with various functions in everyday life. The various types of sensors that are often used are:
1. Temperature Sensor
2. Strains Sensor
3. Sound Sensor
4. Vibration Sensor
5. Position and Displacement Sensors
6. Pressure Sensors
7. Force Sensors

 

A. Temperature Sensors

1. Thermocouples

Thermocouples are the most popular temperature sensors, effective in applications that require a large temperature range.

sensor type and functionThese sensors are known to be inexpensive, prices range from $1 to $50 USD, and have a split second time response. Due to material properties and other factors, the temperature accuracy is less than 1 °C. Learn more Thermocouple >>>

2.  RTD Sensor (Resistance Thermal Detector)

RTD sensors are almost as popular as thermocouples and can maintain stable temperature reading for years. Unlike thermocouples, RTDs have a smaller temperature range between -200 to 500 °C, require excitation currents, and have a slower response time of around 2.5 to 10 s. The RTD sensor is mainly used for accurate temperature measurement (± 1.9 percent) in applications that do not require critical time. The price of sensor RTDs can be obtained at a cost of between $25 to $1,000 USD.

3. Thermistors

Thermistors have a temperature range smaller than -90 to 130 ° C from the sensors mentioned earlier, namely Thermocouples and RTD. Thermistor sensors have the best accuracy ±0.5 ° C, but are more fragile, easily damaged than thermocouples or RTD. Thermistors require excitation voltages rather than excitation currents. A thermistor is usually sold for around $2 to $10 USD.

Thermistor in general is divided into two types:

4. Fiber Optics

Another alternative is the use of optical fiber to measure temperature. Temperature sensors Fiber optics are effective for hazardous environments or where there may be electromagnetic interference. Fiber optic sensors are nonconductive, electrically passive, immune to electromagnetic interference (EMI) – induction due to noise, and are able to transmit data over a longer distance with little or no loss of signal integrity. Learn More >>>

 

B. Sensor Strains

The resistive strain gage sensor is a sensor used to measure strain. This sensor is one flat resistor usually attached to the measured surface. This sensor can flex or bend according to the surface that is measured or detected.

strain gauge
By Pleriche – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=61871859

In principle, strain sensors are measured in 3 directions, namely axial, bending, and torsional and shear. One use case for resistive strain gages is the structure of aircraft wing testing. Strain gages can measure very small bends and draw on the surface.

Another example is when making bridges, more than one strain of resistive gage cable is installed together. By using strain gage sensors, a more sensitive measurement can be done by providing more strain gages. Practical people can use up to four active strain gages to build the Wheatstone Bridge circuit. this is called full-configurigurasu bridge.

There is also a half-bridge configuration (two active strain gages) and a quarter-bridge configuration (one active strain gage). The use of strain gages sensors is more active, the more accurate the strain reading.

Strain gages require current or excitation stresses and are susceptible to temperature drift, strain, and axial flexural strain, this can provide false readings if without using additional resistive strain gages.

Differences in Axial Strain Sensors, Bending and Torque and Shear are:

  • Axial Bridge is used to measure stretches or separate pulls from material.
  •  Bending Bridge is used to measure stretch on one side of the material and contraction on the opposite side.
  • Torsional and sliding bridges measure material twist.

 

C. Sound Sensor

Microphone is a sensor used to measure sound, but there are many types of microphones sound sensors, as shown below:

1. Condenser Microphone

The most common sound sensor is a condenser microphone. This type of sensor is also called prepolarized which has a microphone or external polarized power source.

2. Piezoelectric Microphones

Piezoelectric microphones are used for shock or extreme applications. This type of microphone sensor including a durable microphone sensor can measure high amplitude (decibels) pressure ranges such as explosions. The disadvantage of this type of sensor is that high noise levels can be measured by this sensor system.

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3. Dynamic / Magnetic Microphones

In addition to piezoelectric microphones, magnetic or dynamic microphones can also be used in extreme environments. They rely on magnetic movements to induce electric charges in a way that makes them resistant to water, but obviously this microphone is not very useful in a highly magnetic environment. This type of sensor application is widely applied to the field of music.

Dynamic microphones (mics) consist of a very thin coil attached to a light diaphragm and hanging on a magnet. When the sound source is close to the diaphragm, the diaphragm will vibrate. Because the windings are attached to the diaphragm, these windings will move in a magnetic field that has an electromagnetic field, which will cause an electric force. consequently a small alternating electrical voltage is produced which is proportional to the sound received.

Mica dynamically requires no external power, this type is strong, and is also used extensively in live sounds for vowels and instruments, they correspond to the sounds of certain instruments such as electric guitars and basses, close mic’ed drums and some brass instruments.

These sensors produce punchy sounds that cut through busy mixtures, but they are less effective at capturing detailed transient frequencies. Most have responses that roll-off at around 16kHz and are not too sensitive, this means that this type of sensor has many advantages
preamplifier when used with a sound source quieter or farther. Most dynamic microphones have a cardioid or hypercardioid fixed pickup pattern, which means that they only take the majority of votes.

4. Electret Microphone Microphone

Electret Microphones Electret is a small microphone and effective in detecting high frequency sounds. They are used in millions of computers and electronic devices throughout the world. They are relatively inexpensive, and their only drawback is the lack of bass they provide. In addition, carbon microphones, which are less common today, can be used in applications where there is no problem with sound quality.

 

D. Vibration Sensors

1. Ceramic Piezoelectric Sensor or Accelerometer

The ceramic piezoelectric vibration sensor is the most commonly used sensor because it is the most versatile type. This vibration sensor can be used in shock measurements (explosion and failed tests), high frequency measurements, and slow. This sensor usually has an output in the millivolt range and requires high-input-impedance, low sound detectors to interpret the voltage of its piezoelectric crystal.

Vibration or acceleration measurements most often use a ceramic piezoelectric sensor or accelerometer. The three main factors that distinguish vibration sensors are:
a. natural frequency
b. redama coefficient
c. scale factor.

The scale factor is related to the acceleration of output to input and is related to sensitivity. Natural frequency parameters and damping coefficients determine the accuracy of the vibration sensor.

In a system consisting of a spring and mass, if the mass is pulled back away from the balance and releases it, the mass will vibrate forward (the balance period) and retreat until it is silent. Friction which carries mass for silence is defined as the damping coefficient and the rate at which the mass vibrates forward and backward is a natural frequency.

2. Proximity Probes and Linear Variable Differential Transformers (LVDTs)

Proximity Probes and LVDTs are two similar sensors. Both are limited to acceleration or low frequency vibration measurements. However, the vibration LVDT sensor has a slightly higher natural frequency, which means that it can handle or detect high vibrations. The Proximity Probe is just a mass spring attached to the wiper of a potentiometer.

3. Variable Reluctance Vibration Sensor

Variable vibration sensor Reluctance is a sensor that uses a permanent magnet and moves through the coil to measure movement and vibration. This is a special vibration sensor because the output output is only when the mass is measuring movement. This makes it very useful in the study of earthquake shaking and oil exploration to extract vibrations reflected in underground rock strata.

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E. Position and Displacement Sensors

There are various types of position sensors that are usually the choice for research. The driving factors in choosing a position sensor are:
1. excitation
2. filtering
3. environment
4. No need to touch the object
5. Direct physical connection is needed to measure distance.

There is no single type of universal sensor for pressure or force. Detecting positions has been done with this sensor for a long time, so both preferences and applications play a role in making this decision.

Some position sensors include Hall Effect, Potentiometer, Optical Encoder, Linear Variable Differential Transformers, Eddy-Current and Reflective Light Proximity sensors.

1. Hall Effect Sensors

With Hall effect sensors, the presence of an object is determined like we are pressing a button. When the object approaches it will be “on” and the object away will “off”. Hall effect sensors have been used in keyboards even in robot boxing battle competitions to determine when a punch is delivered. But the disadvantage of this sensor is that it cannot provide a detailed value for the distance of the approaching object.

2. Potentiometers

Potentiometers are sensors that use a sliding system to produce a voltage divider. This voltage is adjusted by measuring the position of the knob. The potentiometer provides a little system physically connected directly to the microcontroller.

3. Optical Encoders

Another commonly used position sensor is an optical encoder, which can be linear or rotational. This device can determine speed, direction, and position quickly and with high accuracy. As the name suggests, optical encoders use light to determine position. A series of striped bars are divided into distances to be measured based on the number of bar lines. The more / higher bar lines in this sensor indicate high accuracy.

Some rotary optical encoders can have bar lines of up to 30,000 quantities to offer exceptional accuracy. Also, because of their fast response time, this ideal sensor is used for many motion control applications.

Sensors with physical components attached to the system, such as potentiometers, add a small amount of resistance to the movement of errors in the system. However, encoders hardly produce any friction when they are moving and are very light, but they must be closed / sealed to operate in a hard or not dusty environment, so that extra costs are needed. Additional costs also usually occur in high accuracy applications because optical encoders require their own bearings to avoid mis-alignment when inserted into the product.

4. Linear Variable Differential Transformers (LVDTs)

Linear differential variable transformers (LVDTs) and rotary similar sensors (RVDTs) use magnetic induction to determine position. Both of these sensors are effective for industrial and aircraft applications because of their durability. Both require signal conditioning, which can add to costs.

In addition, these sensors must be accurately aligned in weight, in the form of packaging that is quite expensive and contains coils that are expensive to produce. One type of position sensor that does not experience mechanical wear problems is “Linear Variable Differential Transformer” or LVDT. This is a type of inductive position sensor that works on the same principle as an AC transformer used to measure movement. This is a very accurate device for measuring linear displacement and whose output is proportional to the position of the moving core.

5. Eddy-Current Sensors

Eddy-Current sensors use magnetic fields to determine position. This type of sensor is rarely applied to applications that require very detailed position information or where large gaps exist between sensors and targets. This sensor is better used on the assembly line when mounted on a fairly stationary mechanical structure to measure the nearest moving machine. For more precise position information, it usually uses a light distance sensor.

6. Reflective Light Proximity Sensors

The reflective light distance sensor uses the light travel time to and from the reflective target to determine distance. They have fast response times and are very good in applications where large gaps exist between sensors and targets. A clear view is needed when using this sensor, and the accuracy and quality of these sensors is directly related to the prices that are on the market.

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F. Pressure Sensor

Note the following example to measure the pressure in a tire, and note how each main type is relative to a different reference pressure.

  • Absolute pressure measurements include standard pressure from atmospheric weight (101.325 kPa) and additional pressure in the tire. Typical tire pressure is 34 PSI or around 234 kPa. Absolute pressure is 234 kPa plus 101.325 kPa or 331,325 kPa.
  • A measurement of pressure gauge relative to local atmospheric pressure and equals 234 kPa or 34 PSI
  • Vacuum pressure is relatively good at absolute vacuum or local atmospheric pressure. A flat tire can have the same pressure as a local atmosphere or 0 kPa (relative to atmospheric pressure). The measurement of the same vacuum pressure can be equal to 234 kPa (relative to absolute emptiness).
  • Differential pressure is the difference between two levels of pressure. In the example of a tire, this means the pressure difference between two tires. This can also mean the difference between atmospheric pressure and pressure in a single tire.
  • Measurement of insulation pressure (Sealed) Differential pressure measurements taken with known comparison pressure. Usually this pressure is the sea level, but it can be a pressure depending on the application. Each of these types of measurements can change the pressure values, so it needs to know the type of measurement that the sensor is getting. Bridge-based (strain gages), or piezoresistive sensors, are the most commonly used pressure sensors.  This is because of simple construction and durability. These characteristics allow for lower costs and make them ideal for higher channel systems. This general pressure sensor can be either conditioned or nonconditioned. The air conditioning sensor is more expensive because it contains components for signal filtering and amplification, and excitation lead and ordinary circuit for measurement. If working with a nonconditioned pressure bridge based sensor, the hardware requirement is a cooling signal. Check the sensor documentation so that you know whether additional components are needed for amplification or filtering.

G. Force Sensors

For a long time the use of a mechanical lever scale was used to measure force. But now, strain gage load cell sensors are the most common because this type of sensor does not require a number of calibration and scale maintenance. Load cells can be either conditioned or nonconditioned. But for normally conditioned sensors it is usually more expensive because it contains components for filtering, signal amplification, and excitation of leads, and ordinary circuits for measurement. If the state of measurement works with a nonconditioned bridge-based sensor, the hardware needs for the signal. For additional components such as sensor documentation, additional components are needed for amplification or filtering.

Tube load cells can handle loads greater than both S and beam load cell forms. It can also handle load movements easily and is very sensitive; However, the sensor requires horizontal load protection. Pancake or low-profile load cells that are designed in such a way that they require absolutely no movement to achieve accurate readings. If your application has limited time or requires rapid measurement, you can consider using a tube load cell instead. Button and load cell washers are usually used to measure smaller object weights (up to 200 lb). Like pancakes or low-profile cell loads, the object being weighed does not have to move to get accurate measurements. The burden must also be centered on what is usually small scale. The benefits for these load cells are that they are cheap.

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