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.
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.
Advantages of the Spot-Weldable Strain Gauge include:
- Very Low Profile – The vibrating wire element is positioned only 0.96 mm (0.038 inches) above the measured member. This patented, low-profile design reduces errors caused by the bending of the structural member.
- Pre-Tensioned Wire – Durham Geo Slope Indicator’s arc-weldable strain gauges are delivered pre-tensioned, and 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.
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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 | 52623050 | VW strain gauge sensor is a pluck-type vibrating wire sensor for spot-weldable strain gauge. Includes a thermistor for temperature measurements and two stainless steel weld-down straps for fixing the sensor to the 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 the 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 surcharge will be added to the freight cost for ground shipments |
| Spare Weld-Down Straps | 52623110 | Two weldable stainless steel straps designed to hold the 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 |
Note – Requires spot-welder, not suitable for high-speed dynamic measurements.
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.
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.
