Spot Weldable Strain Gauges Description
The spot weldable strain gauge is generally used to control surface deformation in metal structures, such as centering, reinforcing bars , piles, pipes etc and in structural monitoring and load tests.
Easy to apply, by means of induction welding directly to the structure to be monitored, these instruments are measured from a distance with our portable Data Recorder units (DEC5 or DEC3000) or with our data acquisition systems and remote centralization (mod. DAC3000).
The spot weldable strain gauge comes ready positioned on a zero value in the middle of the scale; on request we can provide spot weldable strain gauges with a different value to zero and therefore with a different factory pretension.
For monitoring of:
- Pipelines and gas pipelines
- Tunnel centering
- Metal bridges
- Reinforcement bars
- Metal structures
Features and Benefits
- Wire tensioned mid-scale or as requested
- Flange for long welding for better adhesion of the sensor
- High sensitivity and reliability over time
- No drift
- Ease of installation
- Integrated temperature measurement
- Integration into centralized monitoring systems
Our spot weldable strain gauges are made of a stainless steel sealed tube containing an harmonic steel wire tensioned between the tube ends.
The steel tube, complete with pretensioned wire, is welded to a thin flange, the length of the tube, which is then spot welded to the metal structure to be monitored – this procedure guarantees perfect adhesion of the sensor, along its length, to the structure. Deformations of the structure are then transferred to the attached sensor, this causes wire deformation with consequent change to wire tension and frequency, with squared values proportional to the deformation.
Measurements are made via a coil mounted on a plastic support which excites the wire and acquires the resonance frequency. In the coil’s support, is an NTC sensor for reading the temperature, used for compensating deformation measurements.
Reading and acquisition of measurements can be made via portable units such as DEC5 and DEC 3000, or via dataloggers such as CUM3000 or automatic data acquisition systems such as technical VWBrick2.
Model with internal magnets
The strain gauges with integrated magnets have been projected to measure deformations over the steel structure surface.
This model is composed by a stretched steel wire between two fixing plates.
The two plates are fixed to the object to be monitored by weldings.
The deformation of the structure under load determines a movement between the two plates relative to one another with a consequent change in the strain of the vibrating wire and a corresponding variation of the resonance frequency of the same. The frequency of vibration of the wire is acquired by means of an electronic coil and the magnets which are housed on top of it.
Model with pick-up
As already said the “wire” group is fixed on the structure to be controlled by means of welding and the group “excitation coil” is applied on this metal band by means of screw or gluing.
Even these strain gauges, like all our other vibrating wire instruments are interrogated with the portable readout unit as our DEC5 or similar, as well as our automatic acquisition systems, which are connected by 4×0,32mm2 shielded cable.
The “coil assembly” can, in this case, be applied to the “wire” group also only at the time of measurement, and then be removed and applied on a second “wire” group for the control of a second point, and so on.
This possibility allows a considerable economization in the case of many points to be checked non-automatically; it is sufficient in this case to apply the wire group and then proceed to the various measures by moving, with the “coil” group, in the various points controlled.
For measurements with automatic data acquisition systems, they will be used complete units, at each point to check.
The thermal expansion coefficient of the entire instrument is very close to that one of the concrete and / or steel for which, in the case of application of these materials, the thermal variations do not alter the validity of the measure
With internal magnets
|Temperature range||-30+80 °C|
|Linear Expansion Coefficient||11×10-6/°C|
|Operating temperature||-20 ; +85°C|
|Temperature Sensor||NTC Thermistor 3KOhm|
|Accuracy of temperature measurement||0,5°C|
With Pick up
|Measuring Range||3000 microstrain|
|Linear Expansion Coefficient||10.8 x 10-6/°C|
|Operating Temperature||-30 ~ 105°C|
|Temperature Sensor||Thermistor NTC 3KOhm|
|Customizations||Possibility of pre-tensioning of the wire on request, for large quantities|
|Junction Boxes||Available in different models for the connection of different instruments|
|Selection and Measurement Box||Measure Box complete with MUX Cards for automatic selection|
|Measurement Box||Simple measurement Box|
|Multipolar Cable||Available with different conductors for the connection of different sensors to one cable|
|DEC5||Portable readout unit|
|MUX||Multiplexer for the connection of different sensors to the Datalogger|
If you have any requests or questions about our instruments or if you have special needs that require different solutions from the standard, please contact us. Our team will provide all the necessary information and will be very happy to work with you to study, develop and customize instruments and solutions suitable for your specific needs
All information in our datasheet is subject to change without prior notice.
Please check the datasheet/details carefully and contact Pizzi Instruments for further information.