Strain Gauges

Spot Weldable Strain Gauges

///Spot Weldable Strain Gauges

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.

Applications

For monitoring of:

  • Pipelines and gas pipelines
  • Tunnel centering
  • Metal bridges
  • Reinforcement bars
  • Trusses
  • Metal structures

Features and Benefits

  • Wire tensioned mid-scale or as requested
  • Flange for long welding for better adhesion of the sensor
  • Robust
  • High sensitivity and reliability over time
  • No drift
  • Accuracy
  • Ease of installation
  • Integrated temperature measurement
  • Integration into centralized monitoring systems

Measuring Principle

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

Technical Features

With internal magnets

Range 3.500 µstrain
Sensitivity 1,0  µstrain
Linearity 0,25% f.s.
Temperature range -30+80 °C
Typical Frequency 850-1150Hz
Linear Expansion Coefficient 11×10-6/°C
Operating temperature -20 ; +85°C
Temperature Sensor NTC Thermistor 3KOhm
Accuracy of temperature measurement 0,5°C
Length 50,8mm
Material stainless steel

With Pick up

Type Vibratig Wire
Vibration Frequency 1600-2500Hz
Measuring Range 3000 microstrain
Resolution 0,1%F.S.
Linear Expansion Coefficient 10.8 x 10-6/°C
Sensitivity 1 µstrain
Operating Temperature -30 ~ 105°C
Temperature Sensor Thermistor NTC 3KOhm
Customizations Possibility of pre-tensioning of the wire on request, for large quantities

Related Products

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
DEC3000 Portable Datalogger
CUM3000 Multichannel Datalogger
MUX Multiplexer for the connection of different sensors to the Datalogger

Technical Assistance

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.