Sensors

Classified in Electronics

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Appointed censors T °, pressure, flow, weight and Ph. and define C / u of them.

The sensors: it is a primary element is the measurement that senses changes in the value of the variable measured or controlled, or also in the process variable signal assuming mechanical, electrical or similar.

Temperature sensors:
Type bulb, resistance RTDs, thermistors and thermocouples.
MEASUREMENT PRINCIPLE of operation: RTD resistance is based on the property of metals vary its electrical conductivity by the temperature change.
Lame:
Platinums -200 to 900 ° C within 1 hundredth of 1% pressure is 0.01 ° C.
Nickel -150 to 120 ° C 5 tenths accuracy of 0.5 0.5 ° C
-200 To 120 Copper | ° C accuracy of 1 tenth 0.1 ° C
Advantages: high accuracy, rapid response, good stability.
Disadvantages: more expensive than the thermocouple and termitor, fragile and heat itself can be a problem.

Thermocouple
MEASUREMENT PRINCIPLE of operation:
Based on the effect of seebebeck is the current flow of a closed circuit composed of two different metals whose junctions are kept distinct T °.
Application: gas-electric industrial furnaces, boilers moving grates.

Ranges: -200 to 1700 ° C depending on the alloy.

Advantages: small, cheap, fast, easy to assemble.
Disadvantages: cold junction compensation, these are the simplest and most used in sensors to measure T ° in exactly when you need a remote indication and when several points should be measured, no other method can compete on cost-benefit type material J, K, T, R, O, S

These pressure sensors are:
· Bourdon Tube
· Cells of strain or load
· Capacitive transducers
· Piezoelectric transducers


· Bourdon Tube
Operating Principle: Based on the physical law that the reflective flexible bodies by the action of pressure.

Application: liquid and vapor (steam mixed with chip)
Ranges: 0.5 to 6,000 bar with an accuracy of + / - 0.5 to + - 1% for type C
0.5 to 2500 bar, accuracy + - 0.5 to + - 1% for the spiral
0.5 to 5000 bar helical type with the same pressure
Advantages: wide availability of tubes Boudon
The helical and spiral types have a greater range of movement, ideal for registrars.
Small size, great length
Disadvantages: higher cost of construction depends on the construction material for each process area.

· Piezoelectric transducers
Operating Principle: Based on the generation of an EMF when certain crystals are deformed because of pressure applied at its ends, generating an electrical signal.
Ranges: the measuring range is between 0.1 to 600 kg / cm 2 with an accuracy of + - 1%.
Advantages: high frequency response, self-generation, small size, robust, linear
Low sensitivity to vibration
Disadvantages: sensitive to changes in T °, high output impedance, low output, poor stability, zero change after an extreme shock.

Flow sensors:

· Orifice Plate
· Rotametro
· Turbine
· Ultrasound
· Magnetic


· Orifice Plate
Operating Principle: the flux passing through a pipe with a restriction creates a pressure differential between inlet and outlet plate.
Application: gas, liquid, vapor, solid and combined them.
Flow measurement interval with a pressure of 1%.
Advantages: different types of hole that used to vapors, gases and liquids. They are simple, relatively low cost adaptable to any size pipe.
Disadvantages: high pressure drop, are not suitable for highly viscous fluids or dirty, non-linear but rather quadratic, are not suitable for small flows.
Types of Holes: concentric, eccentric segment.

Weight Sensor

· By hydraulic cells
· With strain gages system
· With pneumatic cell system

· Strain Gages

Operating Principle: Based on the use of Strain-Gauges to be installed in each of the ends of the platform weight. These elements as they deform under the effect of the pressure of the material changes its electrical resistivity and a direct reading using a Wheatstone bridge.
Application: Belt conveyor (pesometro)
Ranges: 20 kg - 150 ton and with an accuracy of + / - 0.2%
Advantages: protected against corrosion, not connected with the material though.
Disadvantage: needs understanding by T º, relatively high cost.


· Hydraulic load cells

Operating Principle: Based on a piston which exerts pressure on hydraulic fluid.
Ranges: Practical 40 kg - 90 ton and accurate fluid + - 0.2%
Advantages: simple installation, fast response, vibration resistant, supports up to 40% overload explosion proof, remote indicators.
Disadvantages: relatively high cost.


Pneumatic load cells ·

Operating Principle: Based on the weight on the platform load is compared with the effort exerted by a diaphragm powered by an adjustable set pressure.
Application: Generally for static weighing.
Ranges: Practice 10 kg - 10 ton and a precision + / - 0.2%
Advantages: Fits well controlled pneumatic remote indication.
Disadvantages: Requires compressed air instrumentation.


Censor PH: analytical measurement is a
Principle of Operation: glass tube is sealed on its inner surface with a glass membrane is particularly sensitive to hydrogen ions PH.
Application: acid and neutral solutions
Ranges: values of 0 -14 and accuracy is + - 0.25 to + - 1%
Advantages: simple installation, quick responses
Disadvantages: Requires permanent maintenance, the variation of T º influences the pH measurement.

Formulas change temperatutas

Degrees F = (5 / 9 * degrees Celcios) +32

Degrees C = 9 / 5 * (degrees F-32)

Kelvin = 273

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