Module 1 and 2 - Introduction to Sensors - Sensor Characteristics (PDF)

MODULE 1 Introduction to Sensors Sensors signals and systems, classifications, and units of measurement. ENGR. RENDELL JASON M. LAGMAN What is a Detector? A detector is a device designed to identify the...

MODULE 1 Introduction to Sensors Sensors signals and systems, classifications, and units of measurement. ENGR. RENDELL JASON M. LAGMAN What is a Detector? A detector is a device designed to identify the presence or absence of a specific substance, condition, or phenomenon. Example: Smoke detector identifies the presence of smoke, signaling a potential fire. “a Detector might trigger an alarm, while a Sensor would provide a specific reading of the detected condition” What is a Transducer? A transducer is a device that converts one form of energy into another, a process known as transduction. Typically, a transducer transforms a signal from one state or type of energy to another. For example, a transducer might convert electrical energy into mechanical movement. What is a Transducer? General term for any device converting energy from one form to another. Transducers are commonly used in various applications, including measurement systems, control systems, and automation. What is a Transducer? Transducers are a broad category encompassing all devices that convert energy from one form to another. Sensors are transducers that detect changes in the environment and provide a readable signal, typically electrical. “While all sensors are transducers, not all transducers are sensors.” Categories of Transducers Transducers can be classified into different categories based on various parameters, such as the nature of the energy they convert and the type of operation they perform. Classification by Type of Energy Conversion Mechanical Transducer: – Converts a physical quantity into its mechanical counterpart. – Example: Pressure gauge, which converts pressure into mechanical displacement. Electrical Transducer: – Converts a physical quantity into its electrical counterpart. – Example: Thermocouple, which converts temperature into an electrical voltage. Classification by Type of Operation Input Transducer: – Converts a physical quantity or parameter into a readable signal, usually in electrical form. – Example: Microphone, which converts sound waves into electrical signals that can be amplified or processed. Output Transducer: – Converts an electrical signal into another form of energy. – Example: Lamp, which converts electrical energy into light. Sensors A device that converts a physical phenomenon into an electrical signal. Convert a Signal or Stimulus (Representing a Physical Property) into an Electrical Output Represents part of the interface between the physical world and the world of electrical devices such as computers. Stimulus The quantity, property, or condition that is received and converted into an electrical signal. Actuator Converts energy from one form to another. Converts electrical signals into physical phenomena. IMPORTANCE OF SENSORS IMPORTANCE OF SENSORS Process Diagram Input Output Process Diagram showing sensors’ role in converting inputs to outputs in control systems Process Control Loop Input Output Actuator Process Sensor Controller Sensors provide feedback to the controller, which then adjusts the actuators to maintain the desired system output. Process Control Loop Sensor Data Sheet A marketing document typically designed to highlight a positive attributes of a particular sensor and emphasize some of the potential uses of sensor. Sensor Classifications Sensor Classifications - Nature of Output. - Requirement of power source. - Input being measured. Nature of Output Analog Sensor Digital Sensor Analog Sensor Analog sensors are the devices that produce analog output in correspondence to the quantity being calculated. These sensors also observe the change in external factors such as light intensity, speed of the wind, and solar radiation, and others. And the output ranges between 0V to 5V. Converts a variable physical quantity into a signal that the control system can understand – voltage or current. Continuously measures and outputs varying signals over time. Unlike digital sensors that output discrete values (like 0s and 1s), analog sensors provide a smooth, continuous range of values. TYPES OF ANALOG SENSORS Examples: Accelerometers, Light Sensors, Sound Sensors Types of Analog Sensors Accelerometers Type of analog sensors where those can be utilized to detect changes in acceleration applied on the sensor. Sample applications: Smartphones and wearable devices. Types of Analog Sensors Light Sensors These are the kind of photoelectric devices where the detected light energy is converted to that of electrical energy which means that photons are converted as electrons. Mostly, light sensors are implemented for robotic intelligence and motion lights. Light Sensors Types: Photovoltaic Light Dependent Photo Diode Proximity Types of Analog Sensors Sound Sensors Sound sensors are considered as the modules to find out sound waves by the intensity and converting those into electrical signals. Sample applications: Door alarms, Music systems, Burglar alarms, Computers Types of Analog Sensors Pressure Sensors Pressure sensors measure the pressure levels of liquids or gases by converting the physical pressure into an electrical signal, typically a continuous, varying voltage or current that corresponds directly to the pressure level. They are considered analog sensors because their output is proportional to the measured pressure and provides a continuous range of values rather than discrete steps. Pressure sensors can also function as pressure switches, where they trigger an "On" or "Off" state when a specific pressure threshold is reached. However, their primary role as analog sensors lies in their ability to provide detailed, variable measurements across a range of pressures. Types of Analog Sensors Analog Temperature Sensor These sensors deliver analog output voltage or current signals in linear to the temperature levels. The usage of these devices is so simple, and no need for complicated circuits to construct. Converts Temperature to voltage Digital Sensor Digital sensors are the kind of electrochemical or electrical sensors where the information is converted to digital form and then transmitted. The output of a digital sensor is the distinct digital signal of the quantity which is being measured. The output is in the form of 1’s and 0’s where ‘1’ represents ON condition and ‘0’ represents OFF condition. Examples: Digital accelerometers, Digital temperature sensors  Digital sensors output data in binary form, which is either a high state (1) or a low state (0). The image shows a waveform that could represent a digital signal output, where the high voltage (5V/3.3V) represents a binary "1" and the low voltage (Ground) represents a binary "0." This type of signal is crucial in conveying information from the sensor to a microcontroller or processing unit. Types of Digital Sensors Digital accelerometers Digital Temperature Sensor  Requirement of Power Source Active Sensors: These require an external source of excitation. Examples include resistor-based sensors like thermistors, RTDs (Resistance Temperature Detectors), and strain gauges. These sensors need a current to be passed through them, and the resulting voltage is measured to determine their resistance value. Alternatively, they can be used in bridge circuits, but an external current or voltage is still necessary. Requirement of Power Source Passive Sensors: Also known as self-generating sensors, these produce their own electrical output signal without needing external voltages or currents. Examples include thermocouples and photodiodes. Thermocouples generate thermoelectric voltages, while photodiodes produce photocurrents. These outputs are independent of external circuits. Requirement of Power Source Input being measured TYPES OF INPUTS Displacement Sensors Velocity Sensors Force Sensors Temperature Sensors Light Sensors Input being measured Displacement Sensors Used to measure travel range between where an object is and a reference position. Input being measured Velocity Sensors A velocity or speed sensor measures consecutive position measurements at known intervals and computes the time rate of change in the position values. Input being measured Force Sensors It converts an input mechanical force such as load, weight, tension, compression or pressure into another physical variable, in this case, into an electrical output signal that can be measured, converted and standardized. Input being measured Temperature Sensors A temperature sensor is a device that detects and measures hotness and coolness and converts it into an electrical signal. Input being measured Light Sensors Light sensors are a type of photodetector (also called photosensors) that detect light. Different types of light sensors can be used to measure illuminance, respond to changes in the amount of light received, or convert light to electricity. UNITS OF MEASUREMENTS MODULE 2 SENSORS CHARACTERISTICS Static vs. Dynamic Characteristics Importance in sensor performance ENGR. RENDELL JASON M. LAGMAN SENSORS CHARACTERISTICS Static Characteristics - Properties when the sensor is in a steady state. Dynamic Characteristics - Behavior during changes in the input before reaching a steady state. SENSORS CHARACTERISTICS Static Characteristics - Properties when the sensor is in a steady state. Static Characteristics - Accuracy Accuracy – Ability of a sensor to produce results close to the true value of the measured quantity. Static Characteristics - Precision Precision –Ability of a sensor to consistently produce the same results under the same conditions. Static Characteristics - Linearity Linearity – Extent to which the sensor’s output is directly proportional to its input. – Graphically represented as a straight line. Voltage Output of TMP36 (V) Temperature of the water bath (T)  Static Characteristics - Sensitivity Sensitivity – Ratio of change in the sensor’s output to the change in the input it measures. It focuses on how much the output changes in response to changes in the input signal. – For example, Sensor A can detect a change as small as ¹⁄₂°F, while Sensor B can only detect a change of 1°F. Therefore, Sensor A is twice as sensitive as Sensor B. Static Characteristics - Resolution Resolution – Smallest detectable change in the input signal that causes a detectable change in the output. – Example: For a temperature sensor with a resolution of 0.01°C, it can detect changes in temperature as small as 0.01°C. Static Characteristics - Transfer Function Transfer Function – Often represented as a graph. – The transfer function shows the functional relationship between physical input signal and electrical output signal. Static Characteristics - Calibration Calibration – Process of adjusting the sensor to ensure its output matches a known standard. Static Characteristics - Error Error – Difference between the measured value and the true value. – Types: Systematic and Random Errors. TYPES OF ERROR Random error refers to unpredictable fluctuations in measured data Systematic error stems from consistent biases in measurement.  Static Characteristics - Span (Input Range) Span (Input Range) – The range of input values that a sensor can accurately measure. – The range of input physical signals that may be converted to electrical signal by the sensor – Signals outside of this range are expected to cause unacceptably large inaccuracy. Static Characteristics - Saturation Saturation – Point where increasing input no longer changes the output, indicating the sensor’s limit. Static Characteristics - Excitation Excitation – External signal (voltage or current) required for sensor operation. – Stability of this signal affects sensor performance. Static Characteristics - Reliability Reliability – Probability that a sensor will function without failure for a specified time under stated conditions.  SENSORS CHARACTERISTICS Dynamic Characteristics - Behavior during changes in the input before reaching a steady state. Dynamic Characteristics - Response Time Response Time – Time taken by a sensor to respond to a change in input and reach a steady state. Dynamic Characteristics - Dynamic Error Dynamic Error – Delay between the change in input and the sensor’s output response.  The dynamic characteristics of control elements are the properties during changing conditions. Response time is how quickly an element reacts to a change in the measured variable or produces a 100% change in the output signal due to a 100% change in the input signal. For example, the response time of a temperature sensor determines how quickly it indicates or records a change in temperature. Dynamic error is the difference between a changing value and the momentary instrument reading or the controller action. Dynamic Characteristics - Bandwidth Bandwidth – Range of frequencies over which the sensor can accurately track changes in input. – The bandwidth of the sensor is defined as the range between these upper and lower cutoff frequencies. This range indicates the frequencies within which the sensor can effectively and reliably operate. Dynamic Characteristics - Settling Time Settling Time – Time required for the sensor’s output to stabilize within a specific range after an input change.