ALLPCB
Overview
In geotechnical monitoring, stable operation of the VWD-A vibrating-wire soil settlement meter is essential. Cable continuity directly affects the accuracy of monitoring data, so field diagnostic skills for cable faults are important for maintaining system reliability. The following outlines practical methods to identify short circuits and open circuits on VWD-A settlement meters.
Basic continuity test
For on-site diagnosis, use a multimeter set to the resistance (ohms) range for basic checks. Measure the frequency wires (red and black). A normal resistance is about 300 ohms. A significantly higher reading or infinity indicates an open circuit, while a near-zero reading indicates a short circuit. Measure the temperature wires (green and white); at 25°C the expected resistance is approximately 3 kΩ. Abnormal readings on these cores usually indicate a wiring fault. If resistance values appear normal but there is no signal output, consider possible internal instrument faults or water ingress.
Insulation testing
Insulation should also be checked. Use a 100 V DC megohmmeter to measure insulation resistance between the cores and the shield/ground. A normal value is not less than 50 MΩ. When insulation resistance drops below 5 MΩ, this typically indicates moisture ingress at cable joints, which can cause measurement fluctuations or temperature readings that are abnormally low by 10–20 °C.
Troubleshooting and repair steps
When abnormal resistance is found, first inspect the nearest junctions and other easily damaged sections. If insulation has degraded due to moisture, cut out the damp cable section and remake waterproof joints. During measurements, connecting the shield/ground to the meter's black lead clip improves interference immunity. Regularly inspect cable conduits to ensure there is no crushing or sharp bending; this preventive maintenance helps avoid mechanical damage to cables.
Maintenance recommendations
Establishing a standardized cable testing procedure improves maintenance efficiency. It is recommended to perform system-wide checks quarterly and to intensify insulation inspections after storm seasons. These measures help ensure the VWD-A settlement meter continues to provide accurate and reliable monitoring data throughout the project lifecycle.
