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crack gauges
Kingmach crack gauges include the JMDL-31XXAT Smart Multipoint Displacement Meter for tunnels, rock slopes, foundation pits, and surrounding rock layers. This product is not used like a surface joint gauge. It is built for boreholes where movement must be separated by depth. The instrument group includes displacement gauges, PVC measuring rod protective tubes, anchor heads, and multipoint installation kits that support three to five points. During installation, the borehole is prepared, anchor heads are set at selected layers, and grouting fixes each anchor to its target rock or soil zone. Listed models include 50 mm, 100 mm, and 200 mm ranges, all with 0.01 mm resolution. The sensing circuit changes output frequency as the measuring rod moves through the coil, so each channel can report how one anchored layer moves relative to the reference head. This layout is useful when tunnel crown movement, slope slip, or foundation pit deformation may start at one depth before it appears elsewhere. Field records should emphasize borehole number, anchor depth, grout condition, channel order, and the direction of expected movement. During later review, engineers can compare shallow and deep anchors to judge whether the deformation is local relaxation, progressive sliding, or full-section movement. That layered view is the main reason to use a multipoint instrument instead of several unrelated surface gauges.
Application of crack gauges
In railway and highway subgrade monitoring, crack gauges are used to observe geogrid deformation, embankment movement, track foundation displacement, culvert joint movement, and settlement-related structural shifts. The field problem is that deformation may occur inside reinforced soil or pile-net foundations where visual inspection cannot reach after backfilling. Kingmach JMDL-24XXAT flexible displacement meters are designed for geogrid materials in reinforced soil and pile-net subgrade foundations. The bendable measuring rod can deform with the geogrid, while both ends are clamped using mounting brackets. Listed ranges are 30 mm and 50 mm, with 0.01 mm sensitivity, 0.5%FS accuracy, 20-point curve fitting, and a designed service life up to 30 years. For larger movement, JMLS-22XXADT wire rope sensors and JMDL-49XXAT formwork or steel wire meters can support long-distance displacement monitoring. These readings help maintenance teams connect settlement, traffic load, rainfall, and construction records. During operation, the monitoring team should keep the baseline, temperature, inspection notes, and nearby sensor behavior in the same review file. This makes it easier to tell whether a movement trend comes from normal service, a repair event, changing load, water influence, or developing structural risk. Clear records also help owners decide when a field inspection is needed instead of waiting for visible damage.
The future of crack gauges
The future of crack gauges will include more mixed measurement packages rather than single-sensor orders. A slope package may combine GNSS, multipoint displacement, crack gauges, pore pressure, rainfall, and tilt. A bridge package may combine differential displacement, strain gauges, load cells, accelerometers, temperature, and bearing inspection records. A tunnel package may combine multipoint displacement, convergence, lining strain, water pressure, and vibration. Kingmach already provides a broad product ecosystem across displacement, strain, load, settlement, tilt, environmental monitoring, acquisition equipment, cables, and software. The next step is project-specific packaging where the displacement instrument is selected together with its data logger, cable, cabinet, communication route, warning logic, and maintenance plan. That approach reduces mismatched hardware and makes the monitoring system easier to operate after handover. It also helps procurement teams compare complete monitoring functions instead of comparing sensor names alone. For complex infrastructure, the package should define which movement point answers which engineering question before hardware is ordered.
Care & Maintenance of crack gauges
For magnetostrictive crack gauges, maintenance should protect the non-contact sensing advantage by keeping wiring, power, and mounting clean. Kingmach JMCW-21XXADT lists DC24V input, RS485 communication, IP67 protection, reverse polarity protection up to -36V, and wiring colors for power and RS485 lines. Confirm red, yellow, blue, and green wires before energizing the device, and check grounding in cabinets where motors, pumps, or hydraulic equipment may create electrical noise. Because the sensor is used for absolute position measurement over 0 to 1000 mm, inspect mechanical alignment and travel stops so the moving part remains within range. Do not clamp the sensing body in a way that transfers bending force from the machine frame. During service, compare repeatability at known positions and review whether position drift appears after temperature swings, maintenance work, or hydraulic cylinder repair. Keep the installation photo, point number, zero value, and expected movement direction with the commissioning record for later review. If a reading changes after maintenance work, inspect the base, anchor, cable, and cabinet before assuming the structure itself has moved.
Kingmach crack gauges
When a monitoring plan is built around crack gauges, the first question should be the engineering decision behind the reading. If the purpose is crack control, the JMDL-22XXAT series focuses on crack width, joints, and expansion joints. If the purpose is rock layer movement, the JMDL-31XXAT multipoint meter anchors several depths and separates displacement by layer. If the purpose is bedrock or slope face movement, the JMDL-32XXAT embedded single-point meter uses an anchor head, tie rod, flange, and PVC pipe assembly. If the purpose is large travel or equipment position, the JMLS-22XXADT wire rope sensor and JMCW-21XXADT magnetostrictive meter provide longer range options. Kingmach's category is therefore a toolbox for movement diagnosis, not one product renamed many times. That distinction helps engineers set warning values that match the structure being observed. The point should be named on the drawing, linked with its cable route, and checked against the expected movement direction before the first automatic reading is accepted. For daily review, the reading should be compared with nearby points, recent weather, site operations, and any loading event that could explain the movement.
FAQ
Q: What are crack gauges used for?
A: They measure movement such as relative displacement, crack width, expansion joint travel, bedrock deformation, rock layer movement, geogrid deformation, formwork settlement, and equipment stroke.
Q: Which Kingmach models belong to this category?
A: Common models include JMDL-21XXAT, JMDL-22XXAT, JMDL-24XXAT, JMDL-31XXAT, JMDL-32XXAT, JMDL-49XXAT, JMDL-52XXADT, JMCW-21XXADT, and JMLS-22XXADT.
Q: What range should be selected first?
A: Start from the expected movement. Short joint monitoring may need 20 mm to 100 mm, while draw-wire or equipment travel may require 500 mm to 2000 mm.
Q: Can these products support remote monitoring?
A: Yes. Several Kingmach models support digital transmission, RS485 communication, automatic acquisition, integrated testers, or unattended monitoring systems.
Q: Why is the baseline reading important?
A: All later movement is compared against the starting point. The baseline should be recorded after the sensor, bracket, anchor, cable, and structure are stable.
Reviews
James Thompson
The tiltmeters and accelerometers are very sensitive and provide precise data. Perfect for our structural health monitoring system.
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The weir flow meter is well-built and delivers accurate measurements. Great value for water management applications.
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