resistive.pptx

Resistance types

1. RESISTANCE SENSORS SENSOR TECH

2. A resistive sensor is a transducer or electromechanical device that converts a mechanical change such as displacement into an electrical signal that can be monitored after conditioning. Thermistors, photoresistors, and potentiometers are some examples of common resistive sensors. FACTORS AFFECTING RESISTANCE- The resistance of a material depends on four factors: Cross-sectional area or thickness Length Temperature Conductivity

3. Based on the principle of resistive sensors, the conductor length is directly proportional to the resistance of the conductor and is inversely related to the area of the conductor.

4. R is the resistance of the conductor, A is the area of the conductor, l is the conductor’s length, and ρ is the resistivity of the conductor. If you need to change the resistance of a material, you should change the value of the above factors. When the length is modified, the change in resistance is direct. Doubling the material’s length will double the resistance as well. However, if you double the cross-sectional area of the wire, its resistivity will be cut in half. Changing the conductivity and temperature will not affect the resistivity.

5. DETECTING RESISTANCE CHANGES WITH RESISTIVE SENSORS Resistive sensors detect changes in resistance. There are different sensors available in the market which consider different factors in detecting resistance. Examples of some basic resistive sensors: Thermistors Flex sensors Force sensing resistors Light dependent resistors (photoresistors)

6. An example of a light-dependent resistor is shown in the schematic above. It consists of a length material whose resistance changes according to the light level. In this example, the brighter the light, the lower the resistance.

7. PHOTORESISTORS Also known as Light Dependent Resistors (LDR),  photoresistors  are light-sensitive devices. They are most often used to indicate the presence or absence of light. In low light, the resistance is very high and drops dramatically when exposed to light. It is made of a high-resistance semiconductor so that when the light of high enough frequency strikes the device, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. When that happens, the resulting free electron conduct electricity thereby lowering resistance.

8. The resistance of a photoresistor decreases as the light incident on the face of the photoresistor increases. By placing the photoresistor in the upper leg of a voltage divider, the output of the voltage divider increases as the light intensity increases.

9. THERMISTORS A  thermistor  is a temperature sensor made up of semiconductor material that executes a large modification in resistance in proportion to a tiny low modification in temperature.  It can be used to produce an analog output voltage with variations in ambient temperature referred to as a transducer. This creates a change in its electrical properties due to external and physical changes in heat.

10. TYPES OF THERMISTORS Negative Temperature Coefficient (NTC)  is the most common type of thermistor that has a resistance that falls as the temperature rises. It has a negative electrical resistance versus temperature (R/T) relationship. It means that even small changes in temperature can cause significant changes in their electrical resistance. This makes them ideal for accurate temperature measurement and control. Positive Temperature Coefficient (PTC)  has a resistance that increases with temperature.

11. CAPACITIVE SENSORS A capacitive  sensor  is an electronic device that can detect solid or liquid targets without physical contact.

12. To detect these targets, capacitive sensors emit an electrical field from the sensing end of the sensor. Any target that can disrupt this electrical field can be detected Types of materials capacitive sensors can detect Some examples of the solid materials a capacitive sensor can detect are all types of metal, all types of plastic, wood, paper, glass, and cloth.

13. Capacitive sensor main parts Capacitive sensors have four main parts, the sensor’s body, the sensing face, the indicator light, and the cable or cable connection end.

14. Adjustment screw If the sensor has an adjustable sensing range, it will also have an adjustment screw to adjust the sensing range

15. Sensor’s body Inside the sensor’s body is where the circuitry is that makes the sensor work.

16. Sensing face The sensing face is the part of the sensor that is used to detect the targets. Indicator light The indicator light is on the other end of the sensor from the sensing face. This light turns on when a target is within the sensors sensing range and turns off when the target is out of sensing range.

17. Sensing range The sensing range of a capacitive sensor is the max distance a target can be detected from the sensor sensing face.

18. An example of being within the sensors sensing range would be if the target is six millimeters away from the sensing face and the sensors sensing range is twelve millimeters.

19. The sensors sensing range can be found on the datasheet of the sensor Capacitive sensor’s outputs A capacitive sensor’s outputs can be a positive signal (or PNP) or a negative signal (or NPN). Depending on how the sensor outputs will be connected will determine what style of sensor outputs are needed.

20. Adjustable sensing range If the capacitive sensor has an adjustable sensing range it will have an adjustment screw. Turning the screw clockwise increases the sensitivity of the sensor and turning the screw counterclockwise decreases the sensitivity of the sensor.

21. Capacitive sensor applications Capacitive sensors can be used in many ways. They can be used for part detection on workstations, conveyors, and robots. They can also be used for counting and checking liquid levels. When these sensors are used for part detection, the sensor just sends a signal to the workstation, conveyor, or robot so they know when the part is there. A capacitive sensor can be set up on a conveyor to trigger a counter so that it can count how many parts have been built.

22. Capacitive sensors can also be used to check for high or low tank fluid levels and to trigger alarms for each.

23. What is an inductive sensor? An inductive  sensor  is an electronic device that can detect ferrous metal targets without physical contact. Inductive sensors will also detect non-ferrous metal targets like aluminum, brass, and copper. But using non-ferrous metal targets decreases an inductive sensor’s sensing range.

24. Sensing range The sensing range of an inductive sensor is the distance from the sensor’s face to the maximum distance the sensor can detect a metal target. The sensing distance can be found on the sensor’s  datasheet . The datasheet will also show some correction factors when you want to detect a non-ferrous metal. Non-ferrous metal is a type of metal that does not have a significant amount of iron in it. Brass, aluminum, and copper are examples of non-ferrous metals. This means these metals do not have a significant amount of iron within them.

25. Inductive sensor parts The four major external parts of an inductive sensor are the  body  of the sensor, the sensor’s  face , the  indicator light , and the  cable  end or cable connector end.

26. Inside the sensor’s body is where the circuitry that makes the sensor work is located.

27. he face is the part of the sensor that detects the targets.

28. The indicator light is usually near where the cable gets connected to the sensor. The indicator light turns on when the target is within the sensors sensing range. The sensor’s cable has three different colored wires in it, brown, blue, and black.

29. These sensors are available with a cable that is already attached or they can have a connector that the cable screws on to.

30. How does an inductive sensor work? How inductive sensors work is the sensor creates an electromagnetic field that emits from the sensor’s face. Putting a metal target near the sensor’s face will disrupt the electromagnetic field, causing the sensor’s output and indicator light to turn on.

31. Types of inductive sensors Inductive sensors are available in a lot of different configurations. They can be – AC or DC, – shielded or unshielded, – normally open or normally closed, –  NPN or PNP , just to name a few.

32. They also make inductive sensors for hazardous, high-temperature, and washdown locations.

33. For washdown locations , we need to use a shielded inductive sensor. The Advantages of an inductive sensor Here are some advantages of using inductive sensors compared to other types of sensors. Inductive sensors are solid-state and do not have any moving parts. This makes them very reliable because they usually only need to be replaced when they get physically damaged. Inductive sensors can get dirty and still work. Things like dirt, sawdust, oil, and grease will not affect how inductive sensors detect targets.

34. Inductive sensor mounting Inductive sensors can also be mounted in many different ways. Depending on the type, some of these sensors can be mounted by just bolting them in place or drilling and tapping a hole that is the same size and thread as the sensor.

35. For example, we will be using a general-purpose 24-volt DC twelve-millimeter inductive sensor, that is normally open and has a three-wire cable already attached. We will use a bolt to trigger the sensor. To connect the sensor to the tester, connect the brown wire to the sensor voltage + terminal, connect the blue wire to the sensor voltage – terminal, and connect the black wire to the sensor outputs #1 or #2 terminal.

36. Inductive sensor applications Now let’s talk about some examples of how inductive sensors are used with automation. Inductive sensors can be used to detect part in place at workstations, at conveyor stops, and even at robots.

37. They can be used to detect if an air cylinder is extended or retracted and if a pallet stop or chain transfer is raised or lowered.

38. Inductive sensors can be used to detect if a pallet is centered on a turntable before it starts to rotate.

39. Let’s say this turntable is rotated by a motor with a gearbox and the motor is controlled by a  VFD  (variable-frequency drive). Inductive sensors can be used to tell the VFD when to slow down and stop.

40. PROXIMITY SENSOR A proximity sensor is a non-contact  sensor  that detects the presence of an object (often referred to as the “target”) when the target enters the sensor’s field.  Depending on the type of proximity sensor, sound, light, infrared radiation (IR), or electromagnetic fields may be utilized by the sensor to detect a target. Proximity sensors are used in phones, recycling plants, self-driving cars, anti-aircraft systems, and assembly lines. There are many types of proximity sensors, and they each sense targets in distinct ways. The two most commonly used proximity sensors are the inductive proximity sensor and the capacitive proximity sensor.  

41. An inductive proximity sensor can only detect metal targets.  This is because the sensor utilizes an electromagnetic field. When a metal target enters the electromagnetic field, the inductive characteristics of the metal change the field’s properties, thereby alerting the proximity sensor of the presence of a metallic target.  Depending on how inductive the metal is, the target can be detected at either a greater or shorter distance

42. Capacitive proximity sensors, on the other hand, are not limited to metallic targets.  These proximity sensors are capable of detecting anything that can carry an electrical charge. Capacitive sensors are  commonly used in liquid-level detection .  Possible targets for capacitive sensors include but are but not limited to: glass, plastic, water, wood, metals, and a myriad of targets of other materials.

43. Another type of proximity sensor is called a  photoelectric proximity sensor .  There are two main types of photoelectric proximity sensors: reflective and through-beam.  Reflective proximity sensors detect objects when the light emitted from the sensor is reflected back at the photoelectric receiver.  Through-beam sensors detect targets when the target breaks the beam of light between the sensor’s emitter and receiver. 

44. Two other commonly used proximity sensors are the magnetic proximity sensors and ultrasonic proximity sensors.  Magnetic proximity sensors are only used to detect permanent magnets. Ultrasonic proximity sensors emit a high pitch sound. The distance between the sensor and the target is determined by how long the sound takes to reflect back to the sensor.