Sensors in Automation: Encoders and Thermostats

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Questions and Answers

What is the primary function of an incremental encoder?

To provide continuous analog output signals

To process mechanical motion into digital information (correct)

To convert light signals into digital patterns

To measure temperature variations

What type of incremental encoder provides only position and velocity information?

Photoelectric encoder

Absolute encoder

Single channel encoder (correct)

Quadrature encoder

How does a quadrature encoder determine the direction of rotation?

By counting the total number of rotations

By analyzing input voltage levels

By noting which output channel produces an output first (correct)

By measuring resistance changes in its circuits

Which output signals are produced by a quadrature encoder?

Two separate sine and cosine output signals Signup and view all the answers

What is a disadvantage of incremental encoders?

They need external counters to determine absolute angle Signup and view all the answers

Which application typically utilizes a single channel encoder?

Vehicle speed and position tracking Signup and view all the answers

What is the relationship between the two channels in a quadrature encoder?

They are offset from each other by 90 degrees Signup and view all the answers

Which of the following best describes what happens when the shaft of an incremental encoder is rotated?

It provides output exclusively when rotated Signup and view all the answers

What is one advantage of resistive temperature devices (RTD) compared to thermocouples?

Linear output for accurate temperature measurements Signup and view all the answers

What is the main disadvantage of Platinum Resistance Thermometers (PRT)?

High cost of platinum material Signup and view all the answers

How does the resistance of an RTD change with temperature?

Increases with temperature rise Signup and view all the answers

What is one application of a Wheatstone bridge in connection with RTDs?

To avoid reading errors caused by resistance variation Signup and view all the answers

What characteristic makes thermocouples a popular choice for temperature sensing?

Simplicity and speed of response Signup and view all the answers

What range of temperatures can thermocouples typically measure?

-200 to +2000°C Signup and view all the answers

Which component is included in a typical RTD setup?

Measuring instrument Signup and view all the answers

What is the behavior of RTDs in terms of temperature coefficient?

They have a positive temperature coefficient Signup and view all the answers

Which material is primarily used in thin-film RTDs?

Platinum Signup and view all the answers

What is the resistance value of a commonly available Pt100 sensor at 0°C?

100Ω Signup and view all the answers

What is the main function of a snap action bi-metallic strip thermostat?

To produce an instantaneous ON/OFF action. Signup and view all the answers

What is a significant disadvantage of snap action type thermostats?

They have a large hysteresis range. Signup and view all the answers

How does a creep-action type thermostat respond to temperature changes?

It gradually unwinds or coils up. Signup and view all the answers

What principle do bulb and capillary thermostats operate on?

Capillary action of fluid expansion or contraction. Signup and view all the answers

What characteristic defines thermistors?

They are sensitive to temperature and change resistance accordingly. Signup and view all the answers

What materials are commonly used in the construction of thermistors?

Two or three metal oxides including zinc oxide. Signup and view all the answers

Which type of thermostat is ideal for use in temperature gauges and dials?

Creep-action type. Signup and view all the answers

Which statement about the resistance of thermistors is true?

Their resistance decreases as temperature rises. Signup and view all the answers

What occurs when two dissimilar materials in a thermocouple are at different temperatures?

A voltage difference is generated. Signup and view all the answers

Which effect is responsible for generating current when heat is applied to one of the junctions in a thermocouple?

Seebeck Effect Signup and view all the answers

What happens in the Peltier Effect?

Heat is absorbed when a current is applied. Signup and view all the answers

In a thermocouple, what is kept at a constant temperature?

The Cold junction Signup and view all the answers

What is generated across a conductor when two different metals are combined and a temperature difference exists?

Voltage Signup and view all the answers

What is the primary purpose of the Seebeck Effect in thermocouples?

To measure temperature differences Signup and view all the answers

Which of the following statements is true regarding the Thomson Effect?

Temperature differences lead to voltage generation across a conductor. Signup and view all the answers

When using a thermocouple, what determines the potential difference produced?

The temperature difference between the junctions Signup and view all the answers

What is the nominal impedance range of a moving coil loudspeaker?

4 to 16 Ω Signup and view all the answers

Which of the following materials is necessary for the production of sound in a voice coil loudspeaker?

Copper wire Signup and view all the answers

When designing a circuit system including a sensor and a transducer, what is primarily required?

Signal conditioning Signup and view all the answers

What would likely happen if a loudspeaker is connected to a circuit with an impedance lower than its nominal range?

It may overheat or get damaged. Signup and view all the answers

Which of the following is an example of a transducer?

Microphone Signup and view all the answers

What is typically the role of a potentiometer in a circuit?

To regulate resistance Signup and view all the answers

In the context of loudspeakers, what is the primary function of a voice coil?

To convert electrical energy into mechanical energy Signup and view all the answers

Which resource would typically be consulted for understanding electronic devices?

Electronic Devices textbook Signup and view all the answers

Study Notes

Incremental Encoders

Incremental encoders are frequently used sensors for converting mechanical motion into digital information.
They provide output only when the shaft of the encoder is rotated.
Single channel encoders are generally called tachometers and provide position and velocity information.
Quadrature or sine wave encoders use two photo detectors to produce two separate sine and cosine output signals.
They are used to determine the direction of rotation.
The disadvantage of incremental encoders is that they require external counters to determine the absolute angle of the shaft.

Bi-metallic Strip Thermostats

Bi-metallic strip thermostats are used to control temperature.
Snap action type: Produce an instant ON/OFF action at a set temperature point.
- They are commonly used in homes to control ovens, irons, immersion hot water tanks and heating systems.
- They have a larger hysteresis range, meaning there is a difference between the temperature at which the contacts open and close.
Creep-action type: Gradually change position as the temperature changes.
- They consist of a bi-metallic coil that slowly unwinds or coils up as the temperature changes.
- More sensitive to temperature changes than snap action types.
- Ideal for temperature gauges and dials.

Bulb and Capillary Thermostats

Use capillary action of expanding or contracting fluid to make or break electrical contact.

Thermistors

Thermistors: Thermally sensitive resistors.
- The electrical resistance changes based on their temperature.
- Made of a combination of metal oxides with zinc oxide embedded in a ceramic base.
Thermistors are available in two types based on temperature coefficient.

Resistive Temperature Devices (RTD)

These devices measure and control temperature.
Consist of a sensing element, connecting wires, and a measuring instrument.
RTDs are available in thin-film form.
- These devices have a thin film of platinum paste deposited onto a white ceramic substrate.
- Produce very accurate temperature measurements because the output is linear.
They have poor thermal sensitivity, meaning a change in temperature only produces a very small output change, such as 1Ω/oC.

Platinum Resistance Thermometer (PRT)

The most common type of RTD.
Commonly available in Pt100 sensors, with a standard resistance value of 100Ω at 0oC.
Platinum is expensive, making this type of device costly.
Typical RTD resistance:
- 100Ω at 0oC, increasing to about 140Ω at 100oC.
- Operating temperature range: -200 to +600oC.
RTD is usually connected to a wheatstone bridge network to avoid errors caused by variations in resistance from the current flow.

Thermocouples

Most commonly used type of temperature sensor due to their simplicity, ease of use and speed of response to temperature changes.
Have the widest temperature range of all temperature sensors, from below -200oC to well over 2000oC.
Consist of two junctions of dissimilar metals, such as copper and constantan, welded or crimped together.
One junction (reference/cold junction) is kept at a constant temperature while the other (measuring/hot junction) is exposed to the target temperature.
A voltage is generated across the junction based on the temperature difference, which is used to measure the temperature.

Principles of a Thermocouple

The Seebeck Effect: When two different metals at different temperatures are connected, heat provided to one metal will cause electrons to flow from the hot metal to the cold metal, generating current and a potential difference.
The Peltier Effect: The reverse of the Seebeck Effect. Applying a potential difference between two different metals creates a temperature difference between them.
The Thomson Effect: When two different metals are combined, two junctions are created. A voltage is generated based on the temperature difference.

Moving Coil Loudspeaker

Nominal impedance of loudspeaker – 4 to 16 Ω.

Performance Tasks

PT 1:
- Determine the wavelength of light in a material if the energy in a photon is 1 eV.
- Determine the output voltage of a 75% potentiometer position sensor.
PT 2:
- Design a simple circuit using a sensor and a transducer. Explain how it works.

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Description

Explore the fascinating world of automation sensors through this quiz on incremental encoders and bi-metallic strip thermostats. Learn how these devices convert physical actions into digital signals and control temperatures in various applications. Perfect for students and professionals in engineering and technology.