NPN vs PNP sensors

How to wire PNP and NPN sensors? What’s the difference and why should anyone care? If you’re confused by the terms PNP and NPN, then hopefully this post will shed some light on the differences between the two.  In the context of this post, they refer to the construction of a sensor’s transistor and whether it has a p-type or n-type semiconductor. The “N” stands for “Negative” and the “P” stands for “Positive”.  With respect to sensors, an NPN device is one that can switch the negative side of the circuit while a PNP device switches the positive side. The […]

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Strain Gauge Transducers

Strain gauges are used in many instruments that produce mechanical strain because of the affect being measured. In their own right, they are used to measure the strain in a structure being stretched or compressed. The strain gauge element is a very thin wire that is formed into the shape shown. This produces a long wire all in one direction but on a small surface area. The element is often formed by etching a thin foil on a plastic backing. The completed element is then glued to the surface of the material or component that will be strained. The axis […]

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Types of Level Guages

Level gauges measure the depth or level of liquids and powder in tanks. They use a variety of principles and produce outputs in electrical and pneumatic forms. The type to use depends on the substance in the tank. Here are a few The ultrasonic system reflects sound waves from the surface and determines the depth from the time taken to receive the reflected sound. The electronic version uses a variety of electrical affects including conduction of the fluid and capacitance. The pneumatic version bubbles air through the liquid and the pressure of the air is related to the depth. A […]

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Types of Position Sensors

Position sensors are essential elements in the control of actuators. The position of both linear and rotary actuators is needed in robotic type mechanisms. There are three principle types. · Resistive · Optical · Inductive Resistive type A potentiometer is a variable electrical resistance. A length of resistance material has a voltage applied over its ends. A slider moves along it (either linear or rotary) and picks off the voltage at its position or angle. The tracks may be made from carbon , resistance wire or piezo resistive material. The latter is the best because it gives a good analogue […]

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Types of Force Sensors

The main types of force sensors are · Mechanical types. · Hydraulic types. · Electrical strain gauge types. Mechanical type Mechanical types are usually complete measuring systems involving some form of spring such as in a simple spring balance or bathroom scale. It is a basic mechanical principle that the deflection of a spring is directly proportional to the applied force so if the movement is shown on a scale, the scale represents force. Hydraulic type Hydraulic types are often referred to as hydraulic load cells. The cell is a capsule filled with liquid. When the capsule is squeezed, the […]

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Types of Flow Transducers

There are many hundreds of types of [ithoughts_tooltip_glossary-glossary]flow[/ithoughts_tooltip_glossary-glossary] meters depending on the make and application. They may be classified roughly as follows.     Positive Displacement Type Inferential Type Variable Type Differential Pressure Type Positive Displacement Type These types have a mechanical element that makes the shaft of the meter rotate once for an exact known quantity of fluid. The quantity of fluid hence depends on the number of revolutions of the meter shaft and the flow rate depends upon the speed of rotation. Both the revolutions and speed may be measured with mechanical or electronic devices. Some of the most common listed below. […]

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Types of Speed Transducers

Speed transducers are widely used for measuring the output speed of a rotating object. There are many types using different principles and most of them produce an electrical output.   Optical types These use a light beam and a light sensitive cell. The beam is either reflected or interrupted so that pulses are produced for each revolution. The pulses are then counted over a fixed time and the speed obtained. Electronic processing is required to time the pulses and turn the result into an analogue or digital signal. Magnetic Pick ups These use an inductive coil placed near to the rotating body. A […]

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Types of Pressure Transducers

Pressure sensors either convert the pressure into mechanical movement or into an electrical output. Complete gauges not only sense the pressure but indicate them on a dial or scale. Mechanical movement is produced with the following elements. · Bourdon Tube. · Spring and Piston. · Bellows and capsules. · Diaphragm. Bourdon tube The Bourdon tube is a hollow tube with an elliptical cross section. When a pressure difference exists between the inside and outside, the tube tends to straighten out and the end moves. The movement is usually coupled to a needle on a dial to make a complete gauge. It can […]

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Types of Temperature Transducers

Thermocouples When two wires with dissimilar electrical properties are joined at both ends and one junction is made hot and the other cold, a small electric current is produced proportional to the difference in the temperature. Seebeck discovered this effect. It is true no matter how the ends are joined so the cold end may be joined at a sensitive millivolt meter. The hot junction forms the sensor end. The picture shows a typical industrial probe with a flexible extension and standard plug. Thermocouples come in several forms. They may be wires insulated from each other with plastic or glass fibre materials. For high temperature […]

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