Arc-Weldable Strain Gauge
Designed to measure strain in steel, this vibrating wire strain gauge is held to the structure by mounting blocks are are arc-welded to the structure. Groutable mounting blocks are available for concrete structures. Readings are obtained from the arc-weldable strain gauge with a VW readout or data logger.
Vibrating Wire Arc-Weldable Strain Gauges are used to measure strain in steel or strain in concrete and masonry structures. Typical applications include:
- Monitoring structural members of buildings and bridges during and after construction.
- Monitoring load in struts used to brace deep excavations.
- Measuring strain in tunnel linings and supports.
- Monitoring areas of concentrated stress in pipes.
- Monitoring distribution of load in pile tests.
- Monitoring cracks in concrete (may require long-base strain gauge).
The strain gauge operates on the principle that a tensioned wire, when plucked, vibrates at its natural harmonic frequency, and by measuring that frequency, we can calculate the strain in the wire. The gauge is constructed so that a wire is held in tension between two mounting blocks that are welded to the structural member. Loading of the structural member changes the distance between the two mounting blocks and results in a change in the tension of the wire. An electromagnet is used to pluck the wire and measure the frequency of vibration. Strain is then calculated by applying calibration factors to the frequency measurement.
The strain gauge is supplied with two mounting blocks which are arc-welded to the steel surface. For applications on concrete, small holes are drilled into the structure and groutable mounting blocks are used.
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Arc-Weldable Strain Gauge Specifications
|ARC-WELDABLE STRAIN GAUGE
|Strain gauge with a thermistor. Anchors, clip-on pickup, and signal cable are ordered separately
|3,000 microstrain. User can set tension to maximize range for the application
|1 microstrain with VW Indicator
|± 0.5% FS
|11ppm / °C
|150 mm (5.875")
|-20°C to +80°C
|±0.5°C (at 0°C to 70°C)
|Two mounting-blocks with set-screws. Used if welding strain gauge to steel structures
|Two mounting blocks with 3" long groutable anchors attached. Used to mount strain gauge to concrete
|Kit includes one spacer rod, an Allen wrench, and two spare set screws.
|PICKUP AND SIGNAL CABLE
|VW Standard Clip-on Pickup
|Standard clip-on pickup includes 10 feet (3 m) of signal cable and a hose clamp
|VW Custom Length Clip-on Pickup
|Custom clip-on pickup includes the pickup and a hose clamp. Signal cable must be ordered separately and will be installed at the factory
|Shielded cable with four 22-gauge tinned-copper conductors and flexible polyvinyl chloride (PVC) jacket
|Terminal Box for 6 sensors
|Provides terminals for signal cable from 6, 12, or 24 sensors. Sensors are selected by rotary switch. Dimensions of 6-sensor box are 240 x 190 x 120 mm (9.5 x 7.5 x 4.75"). Dimensions of 12 and 24-sensor boxes are 290 x 345 x 135 mm (11.5 x 13.5 x 5.25")
|Terminal Box for 12 Sensors
|Terminal Box for 24 Sensors
|For terminating a single cable. Connector not required when sensors are connected to a terminal box, a data logger, or to the terminal posts on the VW Data Recorder
|VW Data Recorder
|The VW Data Recorder displays VW sensor readings in Hz or Hz2 /1000 and thermistor data in degrees C. It can also record the readings. See separate datasheet
|Jumper Cable for Terminal Box
|The jumper cable is required when the VW Data Recorder is to be connected to a terminal box or to a connector attached to signal cable
|The VW MiniLogger is a compact, low-cost data logger for one sensor. See separate datasheet
|Campbell Scientific Data Loggers
|Campbell data loggers with a VW interface and the AM16/32 multiplexer can accommodate 16 sensors with temperature readings or 32 sensors without temperature readings