In various systems such as industrial automation, intelligent monitoring, and IoT devices, sensors are the core components for perceiving external physical quantities. The stability of their output signals directly determines the operational reliability of the entire system. Compared to obvious faults like a complete lack of sensor output signal, issues such as signal anomalies, sudden jumps, and distortion are more insidious. These not only lead to data acquisition errors and control logic disorders but can also trigger chain reactions like equipment malfunctions, production accidents, and failure of monitoring data. When encountering such faults, many technicians often feel at a loss, either blindly replacing the sensor or repeatedly debugging software without finding the root cause, wasting time and increasing maintenance costs.

First, clarify the core manifestations of sensor signal anomalies: First, **signal jumps**, where values fluctuate irregularly, suddenly becoming significantly higher or lower than normal in a stable measurement environment. Second, **signal distortion**, where the output waveform does not match the actual change in the physical quantity. Analog sensors may exhibit sawtooth or square wave distortions, while digital sensors may experience data packet loss or garbled data. Third, **signal drift**, where the measured value slowly deviates from the true value, rising or falling on its own without external interference. Fourth, **signal lag**, where the sensor output delays responding to changes in the physical quantity, or the output is severely attenuated. These phenomena are not solely caused by a single sensor fault but involve multiple factors such as power supply, wiring, interference, mechanical installation, component aging, and software configuration. Troubleshooting should follow the principle of **"external before internal, hardware before software, simple before complex"** to gradually narrow down the fault scope.

**Unstable power supply** is the primary cause of sensor signal anomalies and the most easily overlooked issue. Sensors have strict requirements for the accuracy, ripple, and stability of the supply voltage. Whether it's the commonly used industrial two-wire 4-20mA sensors, three-wire 0-10V sensors, or digital I2C and RS485 sensors, voltage fluctuations can directly cause signal distortion. During troubleshooting, first measure the actual voltage at the sensor's power supply end and compare it with the rated parameters: the standard supply for two-wire transmitters is 24V DC, with an allowable fluctuation range of ±10%. If the voltage drops below 20V or exceeds 26V, the internal circuit may malfunction, causing signal jumps. If the power supply ripple is too high (exceeding 50mV), AC noise will superimpose on the DC signal, causing analog distortion. Also, check for loose connections or excessive voltage drop in the power supply circuit. Long-distance wiring with thin conductors or oxidized connectors can result in the voltage at the sensor end being much lower than at the power source end. For example, after a 24V power supply transmits through 100 meters of thin wire, the sensor end might only have 20V, directly causing signal instability. Solutions include replacing the power supply with a regulated one, adding power filters, using thicker transmission wires, and optimizing wiring connections to ensure a clean and stable power supply.

**Wiring and connection faults** are a frequent cause of signal anomalies and are often insidious, mostly manifesting as intermittent faults. Sensor wiring includes power terminals, signal terminals, and ground terminals. Poor contact, wiring errors, or damaged cores at any of these points can lead to signal anomalies. Common issues include: terminal screws not tightened, oxidized wire cores, incorrect grounding of the shield, reversed positive and negative signal wires, and shorts in multi-core wires. For example, with a 4-20mA analog sensor, a short circuit between the signal wire and the power wire can cause a full-scale signal jump. An improperly single-point grounded shield can introduce interference signals. Connecting the ground terminal to the same point as high-power equipment grounds can create potential differences, leading to signal drift. During troubleshooting, disconnect the sensor from the controller and use a multimeter's continuity test to check the wiring circuit for shorts, opens, or excessive contact resistance. Simultaneously, verify the wiring sequence against the diagram to ensure it meets the sensor manual's requirements. The shield must be single-point grounded and kept away from high-power equipment like variable frequency drives (VFDs) and power lines. Avoid running signal wires parallel to power cables. For digital sensors, check if the communication terminal crimps are secure and if the termination resistors on the RS485 bus are correctly matched to prevent data packet loss and garbled data leading to signal distortion.

**Electromagnetic Interference (EMI)** is a core external factor causing sensor signal anomalies in industrial environments and one of the most challenging issues to troubleshoot. Equipment like VFDs, motors, contactors, welders, and high-voltage lines in industrial sites generate strong electromagnetic fields. These fields interfere with sensor signals through space radiation or coupling into wires, causing jumps and distortion. Analog sensors are particularly sensitive to EMI; unshielded signal wires act like antennas, picking up interference. Digital sensors may experience communication interruptions or data errors due to interference. Troubleshooting interference first involves locating the source. Observe if the signal anomaly coincides with the startup of nearby equipment. For instance, if the sensor signal jumps immediately when a VFD starts, it's highly likely the VFD is the source. Solutions fall into three categories: First, **physical isolation**: Keep sensor signal wires at least 20cm away from high-power equipment and power cables, and avoid running them in the same cable tray. Second, **shielding optimization**: Use double-shielded signal cables and ensure the shield is reliably grounded at a single point. Third, **filtering**: Install magnetic cores or filters on the sensor's power supply end, and add resistor-capacitor (RC) filter circuits on the signal output end to attenuate high-frequency interference. In high-interference environments, consider using fiber optic signal transmission to fundamentally eliminate electromagnetic interference.