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ABB proximity sensors are a general term for sensors designed to detect objects without physical contact, replacing contact-based detection methods such as limit switches. They convert information about an object's movement and presence into electrical signals. Detection methods that convert to electrical signals include those utilizing eddy currents generated in the metal body of the detection object due to electromagnetic induction, those detecting capacitance changes in the electrical signal caused by the approach of the detected body, and those using reed and guided switches.

ABB sensor detection principle

Detects magnetic losses caused by eddy currents generated on the surface of a conductor through the influence of an external magnetic field. This method involves generating an alternating magnetic field within the detection coil and detecting impedance changes caused by eddy currents produced in the metal body of the detected object. Additionally, other methods include aluminum detection sensors that detect frequency phase components, and all-metal sensors that detect only impedance change components through the operating coil. A transformer state occurs on the surfaces of both the detected object side and the sensor side.

ABB sensor classification

1) Capacitive proximity sensor: This is a capacitive proximity switch with an electrode as the detection terminal, consisting of a high-frequency oscillation circuit, detection circuit, amplification circuit, shaping circuit, and output circuit. Normally, there is a certain capacitance between the detection electrode and ground, which becomes part of the oscillation circuit. When the detected object approaches the detection electrode, the electrode, being voltage-biased, undergoes polarization due to electrostatic induction. The closer the object gets to the detection electrode, the more induced charge accumulates on it. Since the electrostatic capacitance of the detection electrode is C, the capacitance C increases as the charge increases. Because the oscillation frequency of the oscillation circuit is inversely proportional to the capacitance, the oscillation weakens or even stops when the capacitance C increases. These two states, oscillation and non-oscillation, are converted by the detection circuit into a switch signal for output. 2) Inductive proximity sensor: Consists of a high-frequency oscillation circuit, detection circuit, amplification circuit, shaping circuit, and output circuit. The sensitive element for detection is the detection coil, which is part of the oscillation circuit. The oscillation frequency of the circuit is . When alternating current flows through the detection coil, an alternating magnetic field is generated around it. When a metal object approaches the detection coil, eddy currents are generated in the metal object, absorbing magnetic energy and causing a change in the inductance L of the detection coil. This reduces the oscillation frequency of the circuit, potentially stopping oscillation. These two states, oscillation and non-oscillation, are monitored and converted into a switch signal for output. Note: Similar to capacitive proximity sensors, inductive proximity sensors detect metal conductors; non-metallic conductors cannot be measured using this method. Amplitude changes vary with the type of metal in the target object, so the detection distance also varies with the metal type. 3) Photoelectric proximity sensor: The beam axis of the light-emitting diode (or semiconductor laser tube) and the axis of the phototransistor lie in the same plane and form a specific angle, intersecting at a point in front of the sensor. When the surface of the detected object approaches this intersection point, the reflected light from the LED is received by the phototransistor, generating an electrical signal. When the object moves away from the intersection, the reflection area falls outside the phototransistor's field of view, and the detection circuit produces no output. Generally, the drive current supplied to the LED is not direct current but alternating current of a specific frequency. Consequently, the receiving circuit also obtains an alternating signal of the same frequency. Filtering the received signal to allow only signals of the same frequency to pass effectively prevents interference from other ambient light and can increase the luminous intensity of the LED.

ABB sensor applications

Proximity sensors are mainly used to detect object displacement and are widely applied in aviation, aerospace technology, and industrial production. In daily life, they are used in automatic doors and automatic heaters in hotels, restaurants, and garages. For security and anti-theft purposes, important locations such as archives, accounting departments, financial institutions, museums, and vaults are typically equipped with anti-theft devices composed of various proximity switches. In measurement technology, they are used for measuring length and position; in control technology, they are extensively used for measuring and controlling displacement, speed, and acceleration.

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