Industrial sensors are a key part of factory automation and Industry 4.0. Motion, environmental and vibration sensors are used to monitor the health of equipment, from linear or angular positioning, tilt sensing, leveling, shock or fall detection.
Dedicated industrial motion sensors based on micromachined sensing (MEMS) elements are suitable for Industry 4.0 applications with a wide mechanical frequency sensing bandwidth, high reliability, stable measurements and accurate operation up to 105°C.
An industrial sensor system is often powered by a 24V DC source, which is very different from a sensor in a consumer system that is powered by a 3V or 5V source. As a result, industrial sensor systems require additional power management to effectively drive the sensors. These use digital outputs such as IO-Link direct to a microcontroller or even to the wireless transceiver. The analog data output is usually conditioned by an op-amp and linked to the analog-to-digital converter (ADC) in a microcontroller.
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ST offers a range of MEMS motion and environmental sensors, 8-bit STM8 and 32-bit STM32 microcontrollers and an extensive range of connectivity – wired or wireless including IO-Link - solutions to help sensor system designers successfully meet these challenges.
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There are several types of industrial sensors, including:
Temperature sensors
Temperature sensors can vary from positive to negative coefficient type devices as well as RTD (Resistance Temperature Detector).
Positive Temperature Coefficient (PTC) thermistors are resistors with a positive temperature coefficient so that the resistance increases with temperature. These are often built with silicon to give a linear characteristic. In contrast, switching type PCT thermistors have a non-linear temperature measurement curve. As the thermistor heats up, the resistance decreases until a critical temperature is reached, after which it increases.
These are used in the windings of the electric motors in industrial equipment along with a monitoring relay to provide overtemperature protection to prevent insulation damage. The non-linear response curve has the resistance increase dramatically at the maximum allowable winding temperature, triggering the relay to prevent overheating. This can then be linked to the wireless sensor network.
Negative Temperature Coefficient (NTC) thermistors, where the resistance decreases with temperature, have precision accuracies over wide temperature ranges of +/- 0.1°C or +/- 0.2°C from 0°C to 70°C with excellent long term stability.
These are often used in thermistor probe assemblies across the IIoT and smart factories for fault diagnosis. The thermistor sensing element can be used to monitor all kinds of systems, linked to the wireless sensor system back to the cloud.
Analog and digital temperature sensor ICsProximity sensors
Inductive proximity sensors can detect metal close by, allowing human machine interfaces (HMI) to be safer. There are 2 and 3 wire DC versions as well as sensors with a separate amplifier for high-speed operation.
Laser ranging (lidar) sensors can be used in a 1D topology for object detection, on a conveyor line as an infrared motion sensor for example. 2D lidar sensors can be used as a position sensor to identify the positioning of parts in the production line.
Proximity and ranging ToF sensorsVibration sensors
Vibration sensors can use MEMS accelerometer elements or piezoelectric crystals to measure the frequency of vibration, tuned to the harmonics of the system being monitored. Vibration sensors provide vital data collection for fault diagnosis, while accelerometers can be used as motion sensors to provide tilt, fall and shock measurements.
Accelerometers Gyroscopes Inertial Measurement Units (IMU) e-CompassesOther sensors: pressure, pH, flow, humidity, ultrasonic, PIR, photoelectric sensors
Other sensors used in automation include pressure sensors, pH sensors for measuring the acidity of a liquid, as well as flow sensors, humidity sensors and ultrasonic sensors for monitoring actuators. PIR sensors, photoelectric sensors and rotary encoders can be used as limit switches for threshold measurements in industrial automation systems.
All these IoT sensors are linked though industrial sensor networks, either wired or wireless, back to a gateway and then back to the Internet of Things to provide real time analysis and conditional monitoring.
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Industrial wireless sensor networks use a wide range of protocols, from short range Bluetooth and Zigbee to Wi-Fi.
For long range, Industrial Wireless Sensor Networks (IWSN), the low power sub-GHz LORA wireless communication can be used.
Cellular modems are a higher cost option for wireless sensor networks, but offer telecommunication network reliability. This can be significant with the higher data rates delivered by machine vision systems. The video can be sent back to the cloud for analysis as part of the IoT.
Energy consumption is a key consideration for industrial sensor networks, as thousands of sensor nodes and their wireless transceivers can consume significant amounts of power. Some wireless routing protocols inherently consume less energy, mostly through lower duty cycles. Sometimes higher power is needed in heavy duty applications to overcome interference to ensure reliable data acquisition and network reliability.
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