Sensors Overview
Many system applications require the measurement of a physical or electrical condition or the presence or absence of a known physical, electrical, or chemical quantity. Analog sensors are typically used to monitor the environmental condition by generating a change in an electrical property as a result of a change in the environmental condition.
Typical phenomena that are measured:
- Electrical signals and properties
- Magnetic signals and properties
- Temperature
- Humidity
- Force, weight, torque, and pressure
- Motion and vibration
- Flow
- Fluid level and volume
- Light and infrared
- Chemistry
Typical sensor applications involve the monitoring of sensor parameters and controlling actuators. The sensor signal chain, as shown below, consists of analog and digital domains. Typical sensors output very low amplitude analog signals. These weak analog signals are amplified and filtered and converted to digital values using op amps, Analog-to-Digital Converters (ADC), or voltage-to-frequency converters, and are processed at the PIC® MCU. The analog sensor output typically needs proper signal conditioning before it gets converted to a digital signal.
There are sensors that respond to these phenomena by producing the following electrical properties:
- Voltage
- Current
- Resistance
- Capacitance
- Charge
These electrical properties are then conditioned by analog circuits before being driven to digital circuits. In this way, the environmental condition can be quantified and the system can make decisions based on the results.
The MCU controls the actuators and maintains the operation of the sensor signal conditioning circuits based on the condition of the signal detection. In the digital-to-analog feedback path, Digital-to-Analog Converter (DAC), digital potentiometer, and Pulse-Width-Modulator (PWM) devices are most commonly used. A MOSFET driver is commonly used for the interface between the feedback circuit and actuators, such as motors and valves. Microchip offers a large portfolio of devices for signal chain applications.
Summary Of Common Physical Conditions and Related Sensor Types
This table provides an overview of typical phenomena, the type of sensor commonly used to measure the phenomena and electrical output of the sensor.
| Phenomena | Sensor | Electrical Output | |
|---|---|---|---|
| Magnetic | Hall Effect Magneto-Resistive | Voltage Resistance | |
| Temperature | Thermocouple RTD Thermistor IC Infrared | Voltage Resistance Resistance Voltage | |
| Humidity | Capacitive Infrared | Capacitance Current | |
| Force, Weight, Torque, Pressure | Strain Gauge Load Cell Piezoelectric Mechanical Transducer | Resistance/Voltage Resistance Voltage or Charge Resistance, Voltage, Capacitance | |
| Motion and Vibration | LVDT Piezoelectric Microphone Ultrasonic Accelerometer | AC Voltage Voltage or Charge Voltage Voltage, Resistive, Current Voltage | |
| Flow | Magnetic Flowmeter Mass Flowmeter Ultrasound/Doppler Hot-wire Anemometer Mechanical Transducer (turbine) | Voltage Resistance/Voltage Frequency Resistance Voltage | |
| Fluid Level and Volume | Ultrasound Mechanical Transducer Capacitor Switch Thermal | Time Delay Resistance/Voltage Capacitance On/Off Voltage | |
| Touch | Capacitance Inductance Resistance | Voltage Current Frequency | |
| Proximity | Capacitance Inductance Resistance | Voltage, Frequency Current, Frequency Voltage, Current | |
| Light | Photodiode | Current | |
| Chemical | pH Electrode Solution Conductivity CO Sensor Photodiode (turbidity, colorimeter) Ion Sensor | Voltage Resistance/Current Voltage or Charge Current Current | |