Spot-Weldable Strain Gauges

VW Spot-Weldable Strain Gauges

Designed to measure strain in steel, this vibrating wire strain gauge is spot-welded to the surface of the steel. A sensor is then fixed atop the gauge. Readings are obtained with a VW readout or with a data logger.

Applications

Spot-weldable strain gauges are used with strain gauge sensors and a vibrating wire indicator or data logger to monitor strain in steel members. Typical applications include:

  • Monitoring structural members of buildings and bridges during and after construction.
  • Determining load changes on ground anchors and other post-tensioned support systems.
  • Monitoring load in strutting systems for deep excavations.
  • Measuring strain in tunnel linings and supports.
  • Monitoring areas of concentrated stress in pipelines.
  • Monitoring distribution of load in pile tests.
Spot-Weldable Strain Gauges

Operation

The spot-weldable strain gauge, with its tensioned wire inside, is welded to the structural member, so that an increase in tensile strain increases tension in the wire, and a decrease in tensile strain decreases tension in the wire. A strain gauge sensor is mounted on top of the strain gauge.

On flat surfaces, the sensor is typically held in place by weld-down straps. On reinforcing and tieback bars, the sensor is often secured by cable-ties and tape.

The strain gauge sensor uses an electromagnet to pluck the strain gauge and then returns a frequency signal to the readout or data logger, where it is converted to units of microstrain or period. The VW strain gauge sensor also incorporates a temperature sensor, which supplies data for temperature compensation.
 

Advantages

Very Low Profile

The vibrating wire element is positioned only 0.96 mm (0.038 inch) above the measured member. This patented, low-profile design reduces errors caused by bending of the structural member.

Pre-Tensioned Wire

Durham Geo Slope Indicator's arc-weldable strain gauges are delivered pre-tensioned, ready for spot welding. Pre-tensioned gauges eliminate the time-consuming, process of tensioning the vibrating wire element in the field. Gauges can be ordered in three tension ranges to match virtually any application.

Full-Length Welding Flange

The full length welding flange allows reliable coupling of the gauge to the structural member and prevents misalignment of the end points of the gauge, a common problem with other strain gauges.

Stainless Steel Construction

The welding flange and the protective tube that seals the vibrating wire are constructed from stainless steel for corrosion resistance. The wire itself is steel, selected to match the thermal characteristics of structural steel.

Limitations

Requires spot-welder, not suitable for high-speed dynamic measurements.

For more information

Please download the datasheet and manual for the VW Spot-Weldable Strain Gauges. These documents can be viewed and printed with Adobe Acrobat Reader.

Spot-Weldable Strain Gauges Specifications

SPOT-WELDABLE STRAIN GAUGE
Gauge Set Midrange 52602100
Gauge for Compressive Strain 52602101
Gauge for Tensile Strain 52602102
Range Approximately 2,500 microstrain
Gauge Length 62 mm (2.45")
Height of Wire 0.96 mm (0.038") above measured member
Thermal Coefficient 10.8 x 10-6 per °C, 6 x 10-6 per °F
Materials Stainless steel flange and tube, steel wire
Dimensions 66.7 x 7.6 x 1.8 mm, (2.65 x 0.3 x.07 inch)
VW STRAIN GAUGE SENSOR
Strain Gauge Sensor 52623000 VW strain gauge sensor is a pluck-type vibrating wire sensor for spot-weldable strain gauge. Includes a thermistor or RTD for temperature measurements and two stainless steel welddown straps for fixing sensor to structure. Does not include signal cable
Frequency Range 0.8 to 2.4 kHz
Temp Rating -29 to 105 °C, -20 to 220 °F
Waterproof Rating 10.4 bar, 150psi
Materials Resin-filled ABS plastic case
Dimensions 80 x 26 x 16 mm, 1 x 3.17 x 0.64"
Weight 28 g (1 oz)
SIGNAL CABLE
Signal Cable 50613824 Shielded cable with four 22-gauge tinned-copper conductors and polyvinyl chloride (PVC) jacket that is rated for 80 °C (176 °F). Attached to sensor at the factory
Universal Connector 57705001
Universal Terminal Box 57711600 Provides connections for 12 sensors and an indicator. Sensors selected by rotary switch. Weatherproof fiberglass box measures 290 mm wide x 345 mm high x 135 mm deep (11. 5 x 13.5 x 5.25")
INSTALLATION ACCESSORIES
Scotchkote 06700019 For applying moisture barrier. 440 ml (15oz) can. Note that Scotchkote is flammable and may not be shipped via air freight. In addition, a hazardous materials shipping surchage will be added to the freight cost for ground shipments
Spare Weld-Down Straps 52623110 Two weldable stainless steel straps designed to hold sensor onto structure
Protective Cover 52623120 Formed stainless steel cover for sensor
3M Mastic Pad 06700180 Self-vulcanizing sealing material
Spot Welder, 115VAC 52602550 Includes tip, hand piece, welding unit, battery, and case
Spot Welder, 220VAC 52602560 Includes tip, hand piece, welding unit, battery, and case
READOUTS
Compatible readouts include the VW Data Recorder and other pluck-type VW readouts. See separate data sheets for features and specifications
DATA LOGGERS
VW MiniLogger for 1 Sensor 52613310
4-Channel V-Logger 52615140
8-Channel V-Logger 52615180
Campbell Scientific Data Loggers VW strain gauges connect directly to the VW MiniLogger, V-Logger and Campbell Scientific CR6. Campbell Scientific CR800 or CR1000 require an AVW200 vibrating wire adapter. See separate data sheets