Industrial Temperature sensor - Resistance Temperature Detector (RTD), Thermistor, Inductive, Capacitive

Basic Concept

•       RESISTANCE OF ANY METAL CHANGES WITH ITS TEMPERATURE CHANGE.

•       RTDs ARE

 POSITIVE TEMPERATURE CO-    EFFICIENT DEVICES 

   i.e. THEIR EFFECTIVE RESISTANCE INCREASES WITH THE INCREASE IN TEMPERATURE

         Pt 100 RESISTANCE VALUE AT 0 DEGREE CELSIUS.ITS RESISTANCE IS 100 OHM.

TEMPERATURE RANGE

•       - 200 degree Celsius     to  850 degree Celsius

ACCURACY

+/-  0.3 OHM at 100 degrees

       CELCIUS

Resistance Temperature Detectors / RTD / RTDs

1.      Resistance Temperature Detectors (RTD) are sensors used to measure temperature by correlating the resistance of the RTD element with temperature. Most RTD elements consist of a length of fine coiled wire wrapped around a ceramic or glass core. The element is usually quite fragile, so it is often placed inside a sheathed probe to protect it. The RTD element is made from a pure material whose resistance at various temperatures has been documented. The material has a predictable change in resistance as the temperature changes; it is this predictable change that is used to determine temperature
2.   The RTD is one of the most accurate temperature sensors. Not only does it provide good accuracy, it also provides excellent stability and repeatability. 
3. RTDs are also relatively immune to electrical noise and therefore well suited for temperature measurement in industrial environments, especially around motors, generators and other high voltage equipment.

Common Resistance Materials for RTDs:

•      Platinum (most popular and accurate)

•      Nickel

•       Copper

•      Balco (rare)

•       Tungsten (rare)

RTD ELEMENT

The RTD element is the simplest form of RTD. It consists of a piece of wire wrapped around a ceramic or glass core. Because of their compact size, RTD elements are commonly used when space is very limited.

A surface element is a special type   of RTD element. It is designed to be as thin as possible thus providing good contact for temperature measurement of flat surfaces.

RTD Probes

•       The RTD probe is the most rugged form of RTD. A probe consists of an RTD element mounted inside a metal tube, also known as a sheath. The sheath protects the element from the environment.

THERMISTER

Thermistor is a temperature-sensing element composed of sintered semiconductor material which exhibits a large change in resistance proportional to a small change in temperature.

•       THERMISTOR ARE

 NEGATIVE TEMPERATURE CO-    EFFICIENT DEVICES 

   i.e. THEIR EFFECTIVE RESISTANCE DECREASES WITH THE INCREASE IN TEMPERATURE

TEMPERATURE RANGE

Thermistor are fairly limited in their temperature range, working only over a nominal range of 0°C to 100°C .

ACCURACY

Thermistor are one of the most accurate types of temperature sensors having an accuracy of ±0.1°C or ±0.2°C

STABILITY

Thermistor are chemically stable and not significantly affected by aging.

Types of Thermistor

•       Thermistor Elements

•         Linear Response Thermistor Elements

•          Thermistor Probes

•         Solid State Temperature Sensor

Thermistor Elements

The Thermistor element is the simplest form of Thermistor. Because of their compact size, these are commonly used when space is very limited. Since Thermistor are non-linear, the instrument used to read the temperature must linearize the reading.

Linear Response Thermistor Elements

These consist of a Thermistor element for temperature sensing and an resistor  for linearizing.

Thermistor Probes

The bare thermistor element is relatively fragile and can not be placed in an industrial environment. In order to protect them, thermistor element is embedded in metal tubes.

Solid State Temperature Sensor

Converts temperature  into a proportional current output. The size and responsiveness of the AD590 make it perfect for uses where size is a consideration, such as on PC boards or heat sinks.

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Inductive Sensors

          Inductive sensors are used for controlling, regulating, automating, positioning and monitoring of work processes. Applications include machine tools, plastics machinery, assembly lines, and anywhere processes need to be automated!

Different Inductive Sensors

Capacitive sensors

They detect the change in capacitance caused by the approach of an object. Their advantage lies in the ability to detect virtually any material, from metals to oils

                        

Automatic Cable Cutter Positioning

            A wire and cable manufacturer needed a quicker and more precise method of spooling and cutting cable to customer-specified lengths on an adjustable cutting and crimp machine. Manual adjustment using a fixed scale and pointer to re-position cable grippers and cutters was time consuming and often inaccurate. Llinear position sensor solved this problem!

Hot-glass automated   product detection

            A glass manufacturer needed a reliable method of counting defect-free hot ashtrays, candle holders, bookends and more upon removal from a molding machine. Differing product sizes and shapes eliminated the use of typical thru-beam and diffuse sensors.  Infrared sensors solved this problem!

Color variance detection

             An automotive grille manufacturer needed to ensure the precise orientation of emblems before permanent fixation to the grille. The emblem's clear, curved lexan cover and reflective chrome background made it a difficult solution. See how a color mark scanner solved this problem! 

                

Confirmation of grease application

         An automotive interior components manufacturer needed a way to confirm that grease was applied in the assembly of interior headrests. A luminescence detector solved this problem.

  





As i got mail from readers after starting Industrial Sensors, On their demand i posted RTD(Temperature Sensor) blog in between Angular displacement Industrial Sensor.