Level measurement systems

LEVEL MEASUREMENT SYSTEMS

• Level measurements is an integral part of process control, and may be used in a variety of industries

• Level measurement may be divided into two categories:

¾ point level measurement

¾ continuous level measurement

• Point level sensors are used to mark a single discrete  liquid height, a preset level condition (as a high alarm or a low alarm condition)

• Continuous level sensors provide an analog output that directly correlates to the level within the containing vessel. 

This analog signal may be directly linked to a visual indicator or to a process control loop, forming a level management system.

The material to be measured

• Liquid

  from pure, clean water to viscous, sticky, and corrosive and abrasive fluids

• Bulk material

 from free-flowing, dry crystals to moist, lumpy solids

The processing environments for level sensors extend from vacuum to high-pressure service, and from subzero to elevated temperatures.

Level sensors

• Mechanical sensors

• Float methods
• Buoyancy method
• Vibrating level systems

• Hydrostatic pressure methods

• Differential pressure level detectors
• Bubbler systems

• Electrical methods

• Conductivity probes
• Capacitance probes
• Optical level switches
• Ultrasonic level detectors
• Microwave level systems
• Nuclear level systems

Floats

• The basic float arm indicator comprises very simply a float connected to a pivoted arm that drives pointer or a switch. 

• The unit can be made for either side- or top- entry.

• Moving parts present a very definite disadvantage, since they are situated in the liquid and are thus prone to corrosion and seizing

• Methods of the providing indication other then by linkage to a pointer include the use of a potentiometer, or of magnetic or inductive coupling

Design of floats 

Buoyancy method

• These devices use Archimede's principle

• The mechanical level indicator consists of the immersion body with calibrated measuring spring which transmits the change of level to the mechanical or electrical indicator.

Vibrating level switches

Principle: A vibrating fork or blade 

• An electronic circuit excites the blade of probe to its resonant frequency, and when material comes into contact with the blade, vibration is damped causing switching of the relay

• This device is suitable for control maximum levels of solids and liquids in many types of applications (e.g. foods, grains, granules, pellets, cement, powder)

Hydrostatic pressure methods

• The hydrostatic pressure at the bottom of a container is directly proportional to the liquid height

Bubbler systems

• Clean air from a compressor is forced through a restriction into a tube that leads to the bottom of the tank

• The air pressure after the restriction is equal to the hydrostatic pressure at the bottom of the tank

Conductivity level probes

•  For electrically conductive liquid

• An insulated electrode is used (e.g. an insulated rod)

• The insulator may be polytetrafluorethylene or polyethylene

• The conductive liquid forms the second electrode 

• With increasing liquid level increases the area of the second electrode as well as capacitance 

• An electronic transducer converted capacitance changes into a voltage or current signal

• For nonconductive liquids

Applications

• Suitable for measuring of liquids and bulk (loose) materials

• Suitable for wide temperature ranges (from -40 to +200) °C and high pressures

• Unsuitable for measuring foaming liquids

Optical level switches

• Light must be transmitted and then received

• Optical level sensors consist of:

– Light source (bulb, LED)

– Photoelectric detector (photodiode, phototransistor, photoresistor)

• Devices works with infrared or visible radiation

Ultrasonic level measurement

The measuring equipment consists:

• A transmitter that periodically sends a sound pulse to the surface of the liquid

• A receiver that amplifies the returning pulse

• A time interval counter that measures the time elapsing between the transmission of a pulse and receipt of the corresponding pulse echo

Ultrasonic level-meter with compensation

• Compensation of the influence of the gas density changes

• Cyclical measurement of the sonar pulse velocity in the environment

• Automatic compensation

Microwave level systems

• They are parallels in the operating principles of ultrasonic systems with microwave radar level systems

• Much higher frequencies (around 10 GHz) are used in radar system

• The radar beam is not affected by density changes

Pulse method:

• Microwave pulses are transmitted in short cycles

• The time is measured (ps)

• Demanding at the time measuring accuracy

c - microwave velocity [m.s-1]

t - time [s]

L - distance [m]

• When the reflected signal f0 returns to the receiver, it is mixed with the outgoing signal f1.

• There will be a difference in frequency between the transmitted and the reflected signals Δ f = f1 − f0

• The difference in frequency is proportional to the time difference Δ t = t1 − t0and also to the distance to the liquid surface.

• The frequency difference can be measured very accurately.

Radar level gauge

Nuclear level systems

• Nuclear radiation from a selected source can be related to liquid or solids levels in a vessel

• Cobalt-60, cesium-137 or radium-226 is used as the gamma radiation source

• The radioactive source is capable of transmitting through the container wall

• As a detector for converting nuclear gamma ray radiation into electrical quantities related to level, some systems use Geiger counters

Some guidelines for selecting instruments
to be used for the indication or control of level

• The material to be measured must be looked at to determine its compatibility with the instrumentation. For instance: Is the liquid hot, cold, under pressure, viscous, corrosive, abrasive, hygienic ?

• Is the area hazardous, requiring intrinsically safe or flameproof products ?

• Can the sensor contact the material being measured?

• Can the sensor be inserted into an existing entry or does it require new "hole" ?

• Does the instrument have to be top-enter or can be mounted in the side ?

• Is point or continuous measurement desirable ? 

• Is remote control or indication desirable ?

• Are there objection to the mechanical moving parts?

• The question must be asked whether or not the equipment need becompatible with data loggers microprocessor or computers.

• What is the required accuracy of the measurement ?

• What are costs ?

Process instrumentation.

In oil and gas industries, instrumentation is used to monitor and control the operating conditions of the facility, which helps to meet safety, environmental regulations, quality and productivity, profitable operation and stable plant operation objectives. It can be categorized under two main functions: 1) Input devices, which are measuring instruments that mainly look at the different process variables. 2) Output devices of the control system, which are called the final control elements. These act relative to the measured parameters to institute the required control action.

The input devices (instrumentation) measure four important operating parameters: pressure, temperature, flow and level. Advanced, online analyzers that measure process composition are also considered an element of process instrumentation.

The instrumentation consists of three main components:

1. A sensor, which is sometimes called a primary measuring element, to measure required physical properties
2. A transducer, which converts the sensor signal into a standard signal form that suits the control system such as a pneumatic signal (3-15 psi), an electric signal (4-20 mA), a digital signal of Foundation Fieldbus, etc.
3. A transmitter, which prepares the transducer signal for transmission without loss and then transmits it. Smart transmitters also send meaningful data about the status of the measuring instrument as a whole.

Process instrumentation includes the most common control element, the control valve, which consists of an actuator that converts the output signal from the control system into a signal that can allow the valve to respond, the positioner for adapting the response and the valve. Smart positioners can currently send and receive useful data to and from the control system for predictive maintenance purposes.

Flow Meter

What is a Flow Meter?

A flow meter is a device used to measure the flow rate or quantity of a gas or liquid moving through a pipe. Flow measurement applications are very diverse and each situation has its own constraints and engineering requirements. Flow meters are referred to by many names, such as flow gauge, flow indicator, liquid meter, etc. depending on the particular industry; however the function, to measure flow, remains the same.

Why do I need a precision flow meter? You might not! Precision flow meters are used to provide accurate monitoring and/or flow control. Some industrial applications require precise calculation of quantity, such as precision servo-valve development for the aerospace industry. On the other hand, an application to measure water flow to a vineyard may only require a measurement accuracy of 5% to 10%.

What are the various types of flow meters?

Positive Displacement (Also known as a Volumetric flow meter or PD flow meter). 
All Max Machinery flow meters are Positive Displacement/Volumetric.
Positive displacement flow meters are unique as they are the only meter to directly measure the actual volume. All other types infer the flow rate by making some other type of measurement and equating it to the flow rate. With PD meters, the output signal is directly related to the volume passing through the meter. Includes bi-rotor types (gear, oval gear, helical gear), nutating disc, reciprocating piston, and oscillating or rotary piston.

Mass
The output signal is directly related to the mass passing through the meter.
Thermal and Coriolis flow meters fall into this category.

Velocity 
The output signal is directly related to the velocity passing through the meter.

• Electromagnetic
• Ultrasonic
• Turbine, Propeller, and Paddle Wheel or Pelton Wheel
• Vortex Shedding and Sonar
• Target and Vane
• Variable Area and Rotameter
• Orifice Plate, Open Channel, Flow Nozzle, Laminar, Venturi, and Pitot Tube

What type of flow meter is best? There are no “universal” flow meters which are suitable for all applications. Selecting the proper technology for your application requires writing a flow specification which covers the use of the meter. There are usually trade-offs with each meter type, so knowing the critical specifications will be important. Things you must know:

• What Gas or Liquid will be measured?
• Minimum and maximum flow rates.
• What are the accuracy requirements?
• The fluid temperature and viscosity.
• Fluid compatibility with the materials of construction (See our materials compatibility guide)
• The maximum pressure at the location.
• What pressure drop is allowable?
• Will the meter be mounted in a hazardous location where explosive gases may be present?
• Is the fluid flow continuous or intermittent?
• What type of output signal or readout do you need?

You will use this list to eliminate the technologies that do not apply (ex. Turbines don’t work for viscous fluids, Coriolis meters don’t respond fast enough for injection flow). Then you will have an apples-to-apples comparison of the remaining technologies. Accurate meters are priced based on their capabilities. It is better to locate the type of meter which fits your application before trading features for cost savings. Closely evaluate your extreme conditions, such as low flow rates, high pressure or temperature or the need to measure over a wide operating range. If these conditions are important, do not be swayed by lower priced alternatives that would be applied outside of their capabilities.

Oil refinery process

Motion sensors

Different Types Of Motion Sensors, Working And Application

Motion Sensor

Motion sensors are commonly used in security systems. They work based on a wide variety of principles and are used in a wide variety of applications. Typical usage could be in the exterior doorways or windows of a building for monitoring the area around the building. Upon detecting motion, they generate an electrical signal based on which some actions are taken. Some operate in much the same way as a military radar scanner, while others work based on vibration, infrared radiation and, even sound. All of these different types of sensors have different strengths and weaknesses, which are important to take into account when making a decision to choose a particle motion detection sensor.

Types of sensors

Motion detectors are classified based on how they detect motion of a body. The two classifications are listed below with a brief explanation of their operation

Active Detectors

Active Detectors are also known as Radar-based motion sensors. The active detector sensors emit the radio waves/ microwaves across a room or other place, which strike on nearby objects and reflect it back to the sensor detector. When an object moves in motion sensor controlled area at this time, the sensor looks for a Doppler (frequency) shift in the wave when it returns to the sensor detector, which would indicate that the wave has hit a moving object. The Motion sensor is able to understand these changes and send an electrical signal to the alarm system, light or other types of device that is connected to the motion sensor.

Active Motion Sensor Operation.

When an object moves in motion sensor controlled area at this time, the sensor looks for a Doppler (frequency) shift in the wave when it returns to the sensor detector, which would indicate that the wave has hit a moving object.

The Motion sensor is able to understand these changes and send an electrical signal to the alarm system, light or other types of device that is connected to the motion sensor.

Active sensors use microwaves for movement detection are mostly used in such applications as automatic doors in shopping malls and similar applications, but can also be found in house security alarm systems and are used for indoor lighting systems.

Active motion sensors are not best suitable for outdoor lighting or similar applications as a movement of random objects such as windblown things, smaller animals and, even larger insects can be detected by the active sensor and lightning will be triggered.

Passive Detectors

Passive Motion Sensors are opposite to active sensors, they do not send out anything, but it simply detects the infrared energy. Infrared (heat) energy levels are sensed by passive detectors. Passive sensors scan the room or area, it is installed for infrared heat that is radiated from living beings.

Passive Motion Sensor Operation

Actually, heat is radiated from any object with a temperature above absolute zero. When an object walks into the detection area of a passive sensor, it detects heat emitted from that object and activates the alarm or turns on the light or any application.

These sensors would not be effective if they could get activated by a small animal or insect that moves in the detection range, however, most passive sensors can be adjusted to pick up the motion of an object with a certain level of emitted heat, for example adjusting the sensor to pick up movement only by humans.

Combined (Hybrid) Sensors

Combined or Hybrid technology motion sensor is a combination of both active and passive sensors. It activates light or alarm only in such a case when motion is detected by both active and passive sensors. Combined sensors are useful for alarm systems to reduce the possibility of false alarm triggers.

However, this technology also has its disadvantages. It cannot provide the same level of safety as separate PIR and microwave sensors because the alarm is triggered only when motion is detected by both sensors.

So for example, if a burglar knows how to escape one of the sensors, his movement is going to be detected just by one sensor, but not by another sensor, at that time no signal will be sent to the alarm system and it won’t be turned on. The most popular type of dual technology sensors combines a PIR and a microwave sensor.

So for example, if a burglar knows how to escape one of the sensors, his movement is going to be detected just by one sensor, but not by another sensor, at that time no signal will be sent to the alarm system and it won’t be turned on. The most popular type of dual technology sensors combines a PIR and a microwave sensor.

However, this technology also has its disadvantages. It cannot provide the same level of safety as separate PIR and microwave sensors because the alarm is triggered only when motion is detected by both sensors.

So for example, if a burglar knows how to escape one of the sensors, his movement is going to be detected just by one sensor, but not by another sensor, at that time no signal will be sent to the alarm system and it won’t be turned on. The most popular type of dual technology sensors combines a PIR and a microwave sensor.

The motion sensors come in different shapes and sizes. Here we are explaining below a couple of examples

Passive Infrared Detectors (PIR)

These are one of the widely used sensors nowadays and can be found in many home security systems. Passive Infrared Detectors are looking the changes of infrared energy level that caused by movement of objects (human, pets… etc.).

Passive Infrared Detectors (PIR)

PIR Motion detector is very easy obstructed by the variability of heat sources and sunlight, so PIR Motion detector is more suitable for the indoor movement detection within the closed environment.

Active Infrared Sensors

Designed to emit an electrical signal that connects to a light detector. As soon as the beam gets interrupted, it may sound the motion sensor alarm.

Active Infrared Sensor

Active infrared Detectors use a dual beam transmission as structure, one side of a transmitter for emitting Infrared Ray, and the other side with a receiver for receiving the IR, it is suitable for the outdoor point to point interruption detection.

Active Infra Red Beam motion sensors are mainly installed outside, due to it adopts transmitter and receiver theory for detection. It is important that the beam must go through the detection area and reach the receiver.

Ultrasonic Detector

These motion sensors are available in both active and passive. In theory, an ultrasonic detector sends out high-frequency sound waves that are reflected back to the sensor. If any interruption occurs in the sound waves, the active ultrasonic sensor may sound the alarm.

Mini Ultrasonic Motion Detector

Applications of Motion Sensors

Some of the key applications of motion detectors include:

• Intruder alarms
• Automatic ticket gates
• Entryway lighting
• Security lighting
• Hand dryers
• Automatic doors
• Ultrasonic sensors are used for triggering the security camera at home and for wildlife photography.
• Active infrared sensors used To indicate the presence of products on conveyor belts

Here some of the practical applications of both the active and passive motion detector sensors are given below.

Liquid Level Controller using Ultrasonic Sensors

The below figure shows how Liquid Level Controller using Ultrasonic Sensor works for controlling the liquid levels in a tank by operating a motor by sensing predefined limits of the liquid.

Liquid Level Controller using Ultrasonic Sensors by EDGEFXKITS.COM

When the liquid in the tank reaches lower and upper limits, then the ultrasonic sensor detects this limits and sends the signals to the Microcontroller. The Microcontroller is programmed in such a way that it operates a relay for driving the motor pump based on the limit condition signals from the ultrasonic sensor.

Automatic Door Opening System Using PIR sensor

Similar to the above system, Automatic Door Opening System Using PIR sensor detects the presence of humans to perform door operations, i.e., opening and closing the door. As we have discussed above, a PIR sensor detects the presence of humans alone and enables the Microcontroller pins when motion is detected. Depending on the signals from the PIR sensor, the Microcontroller operates the door by operating the motor in forward and reverse rotation modes with the help of a driver IC.

Automatic Door Opening System Using PIR sensor by EDGEFXKITS.COM

This is a brief description regarding the motion sensors and their applications with some practical examples of motion detectors. 

Credits : Edgefx.in

Understanding about Industrial Instrumentation in Real Time Applications

Industrial Instrumentation Process

For all real time process related operations in industries, the entire system has to be controlled properly for achieving more economical, efficient, and reliable operations. Hence, some devices are used for measuring the physical quantities such as temperature, pressure and so on , which are called as instruments. Industrial automation and industrial instrumentation are required to control various operations in industries. But, first of all, let us know about what is Instrumentation?

What is Instrumentation?

The process in which assembly of several electrical, measuring and control instruments interconnected for measuring, analyzing and controlling the electrical and non-electrical physical quantities is called as Instrumentation. Basically, there are different types of instruments such as electrical instruments, electronic instruments and mechanical instruments. Instrumentation is further classified into many types such as electrical instrumentation, industrial instrumentation, electronics instrumentation, mechanical instrumentation, and so on.

Industrial Instrumentation

The process of measuring and controlling various quantities in industries by utilizing various industrial instruments is called as industrial instrumentation. For controlling any quantity, primarily that particular quantity has to be measured. The common quantities used in industries and which are considered for measurement include fluid pressure, fluid flow rate, temperature of a device, volume of fluid, motion or position or physical dimensions or acceleration of the machine, electrical current, electrical voltage and electrical resistance.

Thus, after measuring the desired quantity, the measured values are transmitted for indication or computation or controlling purpose either with manual operation or automatic operation. In an automatic- controlling operation the quantity can be controlled using the control signal sent by the computer to the controlling devices.

Industrial Instrumentation

In general, controlling devices are electric motor, control valve and electric heater. These instrumentation and control devices are connected to the measuring devices by using some physical system referred to as “process”.

Most of the industries are automated for ease of operation for this purpose;  the microcontroller and microprocessors are required for programmable switching. For example, in many industries, the industrial power schedule is automated using embedded systems.

Structure of Industrial Instrumentation in Real Time Applications

This can be easily analyzed with its simple structure as shown below. It majorly consists of sensors or transducers or input devices, controllers or processors, transmitters and actuators or output devices.

Structure of Industrial Instrumentation

Input instrumentation is used for measuring, regulating physical quantities such as flow, level, pressure, temperature and so on.

Output instrumentation includes control devices such as valves, regulators, circuit breakers and relays. These are intended for controlling desired output variable, providing control capabilities either remotely or automatically. These are considered as final control devices or elements.

Three major elements in industrial instrumentation are explained in brief below.

1. Sensors

There are many sensors used as input devices in real time electronics instrumentation and control applications, but frequently used sensors include temperature sensor, pressure sensor, optoelectronic sensor, flow sensor, level sensor, speed sensor, inductance coil pulse generator, manometer, optical pyrometer, orifice plate, thermistor, thermocouple, image sensor, position & displacement sensor,  and so on.

Temperature Sensor

Temperature Sensor

The temperature sensor is used to detect the changes in temperature of a particular device or machine or system and such that gives the signal to the controllers in case of change in temperature limits. There are different types such as thermistor, thermostat, thermocouple and so on, specific sensor used based on the application.

Pressure Sensor

Pressure sensor acts as a transducer and it is used to measure pressure of liquids or gases, it converts the pressure into electrical signals.

Pressure Sensor

Thus, specified process which is intended to work in a particular manner is connected to a specific sensor to detect any changes in the operation, to sense the output and transmit it to the controllers for controlling or monitoring or operating the process in a predefined manner.

2. Controllers

Most of the controllers or valves are generally implemented using mechanical systems or solid electronics. But the recent industrial controllers of industrial control systems depends on computers, which makes ease of implementation of complex control algorithms than using a mechanical system.

Frequently used control systems in instrumentation are PLC, DCS, SCADA systems.

Programmable Logic Controller (PLC)

Programmable Logic Controller (PLC)

The Programmable Logic Controller is a digital computer frequently used in several industries and machines for automation of industrial electromechanical processes. It is a real time system used to produce output within limited time as a response to changes in input conditions. The general relay control systems are replaced by PLCs.

The industrial instruments or machines such as electric motors, pneumatic or hydraulic cylinders, solenoids, etc. can be operated using PLCs.

Supervisory Control and Data Acquisition (SCADA)

SCADA

The industries consist of equipments and instruments placed at remote locations, these can be controlled remotely using the SCADA. It is a type of industrial control system in which supervisory system is combined with data acquisition system for acquiring information about the remote instruments or equipment with coded signals over different communication channels like wireless communication for transferring data to control panel.

Distributed Control System (DCS)

DCS Architecture

In industries control elements are located in a central location and also at distributed locations throughout the industry. Thus, for controlling these distributed subsystems a control system is required to operate at distributed locations called as distributed control systems. DCS is used for the automation of processes in various processes using computerized control system.

It is used to monitor and control various processes in industries such as nuclear power plants, water management system, oil refining plants, chemical plants, petrochemical industries, etc.

3. Actuators

Actuator

The actuator is used to control the mechanism or system based on the signal given to it by converting the electrical signal into powerful action. The output signal of the controllers or control systems like DCS or SCADA or PLCs used in industrial instrumentation are used for controlling the actuators.

Actuators are generally operated by the electric current, fluid pressure pneumatic pressure and this energy is converted into mechanical energy.
There are different types of actuators namely hydraulic actuator, pneumatic actuator, electric actuator and mechanical actuators.

These actuators are used for controlling the output devices such as motors, lights, valves, relays, contactors,  and so on.

Contactor

Contactor

The output of the PLC is used to close the Solenoid switch, resulting in switching on high currents, for example to switch on motor in industries.

Valves

Valves

The device used for controlling, regulating the flow of fluids by making open or close or partial obstruction of passageways or tubes. The flow of liquids or gases in industries can be controlled by using valves which can be controlled manually using handles or pedal or wheel and automatically driven according to the variations in pressure, flow and temperature.

The brief description regarding the industrial instrumentation is given in this article along with its major elements or processes. Do you want to know more information about the different instrumentation methods such as electronics instrumentation, mechanical instrumentation, electrical instrumentation? Then, post your queries to know about the advanced technologies in instrumentation by posting your comments below.

Credits: Edgefx.in

Temperature sensors

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Know about Various Types of Temperature Sensors

Types of Temperature Sensors

The most commonly measured physical parameter is temperature whether in process industry applications or in laboratory settings. Exact measurements are critical part of success. Exact measurements are needed for many applications such as medical applications, materials research in labs, studies of electronic or electrical components, biological research, and geological studies. Most commonly, temperature sensors are used to measure temperature in circuits which control a variety of equipment’s.

There are different types of temperature sensors used in the market today including resistance temperature detectors (RTDs), thermocouples, thermistors, infrared sensor , and semiconductor sensors. Each of them has a particular operating parameters. These sensors come in different varieties, but have one common thing: they all measure temperature by sensing a change in the physical characteristic.

What Is a Temperature Sensor?

Temperature Sensor

A temperature sensor is a device, usually an RTD (resistance temperature detector) or a thermocouple, that collects the data about temperature from a particular source and converts the data into understandable form for a device or an observer. Temperature sensors are used in many applications like HVand AC system environmental controls, food processing units, medical devices, chemical handling and automotive under the hood monitoring and controlling systems, etc.

The most common type of temperature sensor is a thermometer, which is used to measure temperature of solids, liquids and gases. It is also a common type of temperature sensor mostly used for non-scientific purposes because it is not so accurate.

Types of Temperature Sensors

There are different types of temperature sensors that have sensing capacity depending upon their range of application. Different types of temperature sensors are as follows:

• Thermocouples
• Resistor temperature detectors
• Thermistors
• Infrared sensors
• Semiconductors
• Thermometers

Thermocouples

Thermocouples

Thermocouple sensor is the most commonly used temperature sensor and it is abbreviated as TC. This sensor is extremely rugged, low-cost, self-powered and can be used for long distance. There are many types of temperature sensors that have a wide range of applications.

A thermocouple is a voltage device that indicates temperature by measuring a change in the voltage. It consists of two different metals: opened and closed. These metals work on the principle of thermo-electric effect. When two dissimilar metals produce a voltage, then a thermal difference exists between the two metals. When the temperature goes up, the output voltage of the thermocouple also increases.

This thermocouple sensor is usually sealed inside a ceramic shield or a metal that protects it from different environments. Some common types of thermocouples include K, J, T, R, E, S, N, and B. The most common type of thermocouples is J, T and K type thermocouples, which are available in pre-made forms.

The most important property of the thermocouple is nonlinearity – the output voltage of the thermocouple is not linear with respect to temperature. Thus, to convert an output voltage to a temperature, it requires mathematical linearization.

Resistor Temperature Detector (RTD)

Resistor Temperature Detector (RTD)

RTD sensor is one of the most accurate sensors. In a resistor temperature detector, the resistance is proportional to the temperature. This sensor is made from platinum, nickel, and copper metals. It has a wide range of temperature measurement capabilities as it can be used to measure temperature in the range between -270oC to +850oC. RTD requires an external current source to function properly. However, the current produces heat in a resistive element causing an error in the temperature measurements. The error is calculated by this formula:

Delta T=P*S

Where, ‘T’ is temperature, ‘P’ is I squared power produced and ‘S’ is a degree C/mill watt

There are different types of techniques to measure temperature by using this RTD. They are two wired, three-wired and four-wired method. In a two-wired method, the current is forced through the RTD to measure the resulting voltage. This method is very simple to connect and implement; and, the main drawback is – the lead resistance is the part of the measurement which leads to erroneous measurement.

Three-wired method is similar to the two-wired method, but the third wire compensates for the lead resistance. In a four-wired method, the current is forced on one set of the wires and the voltage is sensed on the other set of wires. This four-wired method completely compensates for the lead resistance.

Thermistors

Thermistors

Another type of sensor is a thermistor temperature sensor, which is relatively inexpensive, adaptable, and easy to use. It changes its resistance when the temperature changes like RTD sensor. Thermistors are made from manganese and oxides of nickel, which make them susceptible to damages. So, these materials are called ceramic materials. This thermistor offers higher sensitivity than the resistor temperature detectors. Most of the thermistors have a negative temperature coefficient. It means, when the temperature increases the resistance decreases.

Thermometers

Thermometers

A thermometer is a device used to measure the temperature of solids, liquids, or gases. The name thermometer is a combination of two words: thermo – means heat, and meter means to measure. Thermometer contains a liquid, which is mercury or alcohol in its glass tube. The volume of the thermometer is linearly proportional to the temperature – when the temperature increases, the volume of the thermometer also increases.

When the liquid is heated it expands inside the narrow tube of the thermometer. This thermometer has a calibrated scale to indicate the temperature. The thermometer has numbers marked alongside the glass tube to indicate the temperature when the line of mercury is at that point. The temperature can be recorded in these scales: Fahrenheit, Kelvin or Celsius. Therefore, it is always desirable to note for which scale the thermometer is calibrated.

Semiconductor Sensors

Semiconductor Sensors

Semiconductor sensors are the devices that come in the form of ICs. Popularly, these sensors are known as an IC temperature sensor. They are classified into different types: Current output temperature sensor, Voltage output temperature sensor, Resistance output silicon temperature sensor, Diode temperature sensors and Digital output temperature sensor. Present semiconductor temperature sensors offer high linearity and high accuracy over an operating range of about 55°C to +150°C. However, AD590 and LM35 temperature sensors are the most popular temperature sensors.

IR sensor

IR sensor

IR sensor is an electronic instrument which is used to sense certain characteristics of its surroundings by either emitting or detecting IR radiation. These sensors are non-contacting sensors. For example, if you hold an IR sensor in front of your desk without establishing any contact, the sensor detects the temperature of the desk based on the merit of its radiation. These sensors are classified into two types such as thermal infrared sensors and quantum infrared sensors.

Thus, this is all about different types of temperature sensors. The cost of the temperature sensor depends on the type of work it is intended for. However, the accuracy of the sensor will decide the price. So, the cost depends on the accuracy of the temperature sensor. Present temperature sensors intended at reducing the cost as well as efficiency. For more information regarding this type of sensors please visit our website Edgefxkits.com, also post your comments in the comment section below.

Credits: EDGEFX