The heart of Industrial Automation that keeps manufacturing lines beating is a new generation of advanced intelligent sensors connected via low-latency and real-time networks to high-performance Programmable Logic Controllers (PLC) and Human-Machine Interface (HMI) systems.

In Industrial Automation, sensors play a very important role in making the products intelligent and highly automatic. Machines can detect, process, analyze, and measure different position, height, appearance, length, and any displacement in production sites. These sensors also cater to the needs of multiple sensing applications.

What are Industrial Sensors?

Sensor/Detectors/Transducers are electronic or electrical devices. These special electronic sensitive materials sense, measure, and detect changes in the position, temperature, displacement, electrical current, and multiple parameters of industrial equipment.

Many types of sensors, transducers, and detectors are available, including those for detecting a physical presence such as flame, metals, leaks, levels, or gas and chemicals. A few are designed to sense physical properties, and others to detect motion or proximity. Various technologies are used to achieve these objectives, including inductive, magneto-resistive, ultrasonic, optical pressure, and capacitive.

The uniqueness of industrial sensors is the applications and environments they are used in. They need to pump out excellent performance in extreme conditions, including harsh and inaccessible environments like very high or very low temperature, vibrations, high humidity, etc.

Criteria for selection

Choosing the right sensor is critical to control system design. Accuracy, output type, response time, connectivity are a few features to be factored in during selection.

As shown in the following figure, various sensors make an industrial control system. They connect to the main controller via an interface module. This module has a signal conditioning component, and an Analog gain amplifier to amplify the signal strength. Analog sensor interfaces generate continuous output signals ranging from a few micro-volts (uV) to several milli-volts (mV), proportional to the quantity being measured. An analog-to-digital (ADC) converter converts the analog signal into a digital format to increase precision and accuracy. The logic controller is the brain of a control system. It receives the sensor signal, processes it as per application requirements, and transmits a control signal via an actuator to the output devices. These include a stepper motor control or conveyor belt motor drive, or any other mechanically operated devices.

Block diagram of sensors
Figure1: Block diagram of various sensors connected in industrial control system

The following industrial sensors find use in Industrial Automation systems and manufacturing processes. Multiple kinds of sensor are sprinkled across Industrial Automation. element14 partners with industry-leading suppliers catering to a wide range of industrial sensors portfolio. We will discuss a few of the different sensor technologies. (For more information on industrial sensor products, please click here)

Position & Velocity Sensor

Velocity and Position measurement is frequently required in feedback loops, positioning, and velocity control. It measures the distance travelled by any device starting from the device's reference position or by 'angular movement'/rotation. For more information on Position sensor click here & for Velocity Sensor products click here.

The Potentiometer is a type of of ‘position sensor’ and it is most commonly used to measure the displacement or distance of an object in a rotary or linear motion. It consists of a wiper contact attached to a mechanical shaft. This shaft can be either linear (slider type) or angular (rotational) in movement, thereby causing the resistance value among the two end connections and the wiper/slider to change. The consequence is an electrical signal output with a proportional relationship between the resistance value and the actual wiper position on that resistive track. Potentiometers work as voltage dividers and are analog sensors. The following figure shows the common types of potentiometers, including wire-wound, cermet, and plastic film. A positive aspect of the potentiometer is that it needs an analog signal for low-cost control. Please click here for more information on products.

Potentiometer Analog Sensor
Figure2: Basic operation of Potentiometer Analog Sensor

Linear Position Sensor is synonymous with precision position and plays a vital role in automation control. The sensors measure the device's linear position. An excellent example of such a sensor type is the Linear Variable Differential Transformer (LVDT). The sensor consists of a moving magnetic core inside a cylinder. The cylinder sleeve comprises an oscillating voltage-driven primary coil. The sleeve includes two secondary coils that detect this oscillating voltage having a magnitude equal to displacement. This automatic nulling, achieved through the use of two coils, makes LVDTs accurate in submillimetre. LVDT Signal Conditioning utilizes AC modulation, phase comparison, and demodulation. The highly accurate LVDT can function in any demanding environment. More information on products please click here.

Optical Encoders are digital sensors. They are commonly used to provide actuators position feedback. These sensors are made from a glass or plastic disc rotating between a light source (LED) and a photodetectors pair. The disk is encoded with alternate dark and light sectors. The rotation of that disk produces a pulse. click here for more information on products.

Pulses from LEDs in incremental encoders are counted to provide a rotary position. Two detectors are used to determine the direction, and an index pulse denotes the start point. Absolute encoders' unique code can detect every angular position, in 'grey code', a binary code of minimal change. These compact and rugged Encoders demand accurate position information along with a digital feedback loop.

The tachometer instrument measures a disk or shaft's rotation speed in any machine. This device uses a calibrated analog dial to display the revolutions per minute (RPM), but digital displays are increasingly common.

Proximity Sensor

These sensors, consisting of a sensor head (optical, inductive, and capacitive), amplifier, detector circuit, and an output circuit (TTL, solid-state relay), detect closed objects' presence and sense any physical contact. These are found in Industrial Automation latched to conveyor lines, machine tools with digital sensors to detect an object's presence or absence. Please click here for more information on Proximity sensor products.

Optical Proximity sensors comprise a light source (LED) and a light detector (phototransistor). The signal is modulated to minimize the ambient lighting conditions. Generally used in box-counting, stack height control, and fluid level control, these sensors work in three operational modes: a) beam mode of 20 m range, b) retro-reflective with a 1-3 meters, and c) diffuse-reflective mode with a 12-300 millimeter range. These sensors are non-contact and insensitive to vibration and shock. They have zero moving parts. For better understanding of such products and their information click here.

Ultrasonic proximity sensors use a 40 kHz-2MHz frequency range sound pulse to measure the time of flight and amplitude. They are employed as an approach warning before probable collisions and detect solid and liquid levels. As shown in the following figure 3, these sensors detect objects where the normal photocells cannot be employed for level measurement of solids and liquids, diameter or loop detection for materials like sheet iron, paper, and transparent objects detection like plastic, plastic filters, and glass bottles etc. For more information on products click here.

Operation Ultrasonic proximity Sensor
Figure3: Operation Ultrasonic proximity Sensor

Capacitive and Inductive Proximity Sensors: The basic difference between the two sensors is that inductive sensors use local magnetic field changes to detect the metal presence, and capacitive sensors use local capacitance changes due to non-metallic objects. Both are reliable and robust. Please click here for more information on Capacitive Sensors & here for Inductive proximity sensor products.

Pressure & Force Sensor

Multiple methods exist to measure pressures and forces. The force is frequently converted into a length change or spring height. The dimension difference is subsequently measured using an LVDT, and piezoelectric materials produce a current when deformed, and strain gauges.

Pressure sensors find use in multiple types of equipment, inclusive of but not restricted to nitrogen and oxygen gas tanks. They are also used in HVAC equipment, process controls, and compressors, among others. A few come in various sizes, types, and specifications; some equipment requires light-weight, compact-sized pressure sensors. Please click here for more information on products.

Force/Torque sensors are classified into two types: Quantitative sensor measures force and constitute its value regarding an electrical signal. And Qualitative sensor indicates the presence of an adequately strong force if applied or not. Force sensors are used in multiple industrial applications to discern load and compression, robotic end-effectors, invariable tension control, and wire bonding equipment. For more information on products click here.

Acceleration & Vibration Sensor

Accelerometers are full-contact transducers generally mounted on high-frequency devices. Accelerometers use the piezoelectric effect. Acceleration sensors are also employed to detect vibration. Sensors embedded in industrial applications like axial compressors and gas turbines, detect high-frequency vibration signals, connected to bearing supports, foundation and casing resonances, etc. They detect static shaft displacements, unbalance response, misalignment, dynamic instabilities, etc. click here for more information on acceleration products.

Vibration monitoring sensors assist in locating machine damage and prevent expensive consequential damage. Vibration is often measured using a ceramic piezoelectric sensor or accelerometer. Please click here for more information on products.

Temperature and Humidity Sensors

Temperature sensor gathers information connected to temperature from a particular source and subsequently changes it to a form decipherable by an observer or any device. Humidity sensors detect the air's humidity level. Humidity and Temperature sensors are frequently coupled together. The combination of high temperature and water will result in water molecules vaporizing, escalating humidity. Different temperature sensors are available, depending on the particular environment and medium being sensed, the ubiquitous being thermocouples, resistance temperature detectors (RTDs), thermistors, thermometers, and infrared sensors.

The data algorithms embedded in automated processes detect any overheating which may have occurred and take corrective action to stop the overheating sense without human intervention. Please click here for more information on Temperature Sensor & here for Humidity Sensor Products.

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