Application support holds the key to the development of new technologies. For instance, a liquid level sensor may be applied in industrial sectors ranging from chemical, paper and pulp, petroleum to food and beverage. Specific applications in these industries may include the use of sensors in cooling towers, fermentation vessels, fuel storage containers, blending and solvent level monitoring vessels, to name a few.
Automation, or automatic control, is the use of various control systems for operating equipment such as machinery, processes in factories, boilers, and heat-treating ovens, switching on telephone networks, steering, and stabilization of ships, aircraft, and other applications and vehicles with minimal or reduced human intervention.
The industry has always had an appetite for technology. From big data analytics to advanced robotics, the game-changing benefits of modern technologies are helping manufacturers reduce human intervention, increase plant productivity, and gain a competitive edge.
Sensor technology plays a variety of essential roles in machine automation. Sensors provide information about products during manufacturing. They deliver updates about the condition of the equipment, to help guide maintenance and prevent downtime. Sensors also provide feedback on the motion of the motor to ensure accurate positioning. A range of sensor technologies have been developed to address different applications and environments.
Sensors are part of an exploding market, and developments are occurring at a phenomenal rate. The technology is indispensable to a broad range of industries, providing critical information about such parameters as pressure, temperature, flow, gas and position, which can have a profound impact on a number of processes or systems.
Modern manufacturing puts the emphasis on maximizing operational equipment effectiveness (OEE) and increasing uptime. Condition monitoring is an essential tool for achieving this goal. Condition data provides insight into the health, operation, and performance of equipment, facilities, and even the products being manufactured. This typically encompasses factors like temperature, pressure, humidity, vibration, and current or voltage. An increase in the temperature of a motor might indicate lubricant breakdown, for example. The appearance of a spike in the vibration frequency spectrum of a pump might highlight erosion of the vanes. Increased current draw can indicate worn bearings or gears. With these types of insights, maintenance teams can troubleshoot faults more effectively and also help prevent them in the first place.
RFID sensor systems pass data from tagged objects to RFID readers. An RFID system consists of two parts: the RFID tag and the RFID reader or interrogator. Tags may be read only, write once read many, or read/write. Tags are classified as active, passive, or passive with battery assist. A passive tag needs to be interrogated by the RF signal from an active readout device. The readout device must be in proximity to the tag for a successful read. A passive tag with battery assist can send data over a greater distance. An active tag includes a power source so that the tag can broadcast its data to the reader.
Similarly, readout devices can be classed as active or passive. Typically, a passive tag is paired with an active reader and vice versa. For applications involving greater distances or interference, active tag-active sensor systems may be the best choice.
A piezoelectric vibration sensor (also known as piezo sensors) use the effect of mechanical strain caused by high-frequency motion of the equipment to detect acceleration and, hence, vibration. Certain materials such as quartz exhibit the piezoelectric effect, in which applying a mechanical stress to the material generates a positive or negative voltage. In a piezoelectric vibration sensor, the piezoelectric material is sandwiched between an unconstrained proof mass and the sensor frame. The sensor, in turn, is fixed to the device under test so that vibration of the motor or asset causes the sensor housing to move. The inertia of the proof mass causes it to apply stress to the piezoelectric material, generating a voltage.
In vibrating equipment, the sensor will generate a pulse stream. The signal can be presented as a time waveform or processed by FFT to convert the data into a frequency spectrum for additional vibration analysis.
Piezoelectric vibration sensors are effective and well-characterized. They operate with frequencies of up to 20 kHz and accuracies on the order of 1%. On the downside, they are expensive. The sensor engine alone costs between $300 and $500 for a single axis. In the case of a tri-axial vibration monitoring application, the sensors alone could cost more than $1500. The sensor alone is not enough, however.
Piezoelectric vibration sensors are inherently analog, so they require additional processing electronics to digitize the signal. On the upside, that enables the team integrating sensor engine and electronics to define the frequency properties through their choice of analog-to-digital converter. On the downside, the external electronics add both complexity and size, as well as increasing power consumption.
Higher power consumption can be an issue for wireless vibration sensors that are battery-powered. Changing the battery on a single sensor every few years might not be a hardship. Changing hundreds of batteries in wireless sensors deployed across the facility can consume a significant amount of time. This is a factor for industrial maintenance departments, which are typically oversubscribed as it is. MEMS-based accelerometers provide an alternative.