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1. What is an LVDT ?
An LVDT (linear variable differential transformer) is a transformer device which produces an electrical output proportional to the displacement of a free moving core (separate movable core).
This type of transducer consists of a primary coil energized by an AC signal and two secondary coils.
When the core moves inside the coils, it induces voltage V1 and V2 in each secondary coil, porportional to its displacement.
The two secondary coils are connected in series and in opposite polarity, so that the output signal is the difference between these voltages.
In this configuration, the output voltage is null when the core is at the center.
When it moves from the center, the differential voltage increases.
This output voltage is then rectified in order to get a DC signal proportional to the displacement core. |
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2. Why choose an LVDT ?
- Contactless measurement
There is no physical contact between the core and the coil assembly. This allows both vibration measurements and testing of delicate materials.
- Unlimited life-time
The no-contact feature between the core and the coil assembly allows an infinite life time as well as exceptional reliability. These criteria allow fatigue testing use and severe environmental conditions such as space and military applications (servo-control)
- Infinite resolution
Being an inductive frictionless transducer, an LVDT has an infinite resolution only limited by the readability of the associated electronics. |
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3. Test report
With every sensor, a test report is provided indicating :
- Non linearity (% FSO)
- Sensitivity (mV/V/mm)
- Nul residual (mV rms)
Linearity defines the maximum deviation between calibration points and the best straight line drawn through all calibration points. It is expressed as a percentage of the Full Scale Ouptut.
Sensitivity : the LVDT sensitivity at constant temperature.
Nul residual : Sensor Null voltage at zero electrical point |
