What is a LVDT | linear variable differential transducer

 The full name of LVDT is linear variable differential transducer or (transformer linear variable differential transducer or transformer). Basically, this reciprocal inductance is the type transducer. It consists of one primary coil P and two secondary ones S1 and S2. This transducer has variable coupling between two secondary coils.

LVDT  Is a passive transducer.  It is used to measure the displacement of the object in its direction and volume positions.

(A)

Principle -

LVDT , Works on the principle of variable inductance. According to this, when the AC in the primary horoscope When a signal is applied, a voltage is generated in the secondary coil. In this, the flux of primary and secondary coil is related to each other due to the winding in the magnetic core.

Construction –

In the picture

(A) LVDT The structure of is displayed. Accordingly, one primary coil and two secondary coils are coiled above a hollow cylindrical one. The two coils located around the primary coil are called secondary ones. The number of turns in the secondary coil is equal. Primary Horoscope A AC Attaches to the source. There is an iron core between these coils. This core is displaced. LVDT Converts displacement and force into electrical voltage signals. The measured amount is used on the center core. The iron core acts as a displacement detector. In the picture 

(B) LVDT A graph is displayed between the measured displacement of the transducer and the output voltage.

Working –

LVDT When the core is in normal or zero state, equal voltage is produced in both secondary coils. The frequency of alternating voltage used in the primary coil varies from 50 Hz to 20 kHz.

The output voltage of the coil S1 and the output voltage E2 of the coil S2 is E2 To convert the output voltage generated from both secondary coils into a single signal voltage, they are connected in series and counterclockwise, as shown in Fig. (B). Hence the output voltage Vo of the transducers is equal to the difference between the output voltage of the primary and secondary coil V₀ output voltage 

(B)

V₀ = E1 – E2

When the core is in the middle, the induced output voltage E1 and E2 are in the same and opposite direction. The associated flux and electric carrying force are produced in both secondary coils. In this case the value of the output voltage is zero. Now if the core moves to the left in the zero position, more of the coil S1 and less flux is produced in the coil. Accordingly, the output voltage of the coil S1 E1 will be higher than the output voltage E2 of the secondary coil S2 In this, the resulting output voltage is in phase. 

(C)

LVDT In E2 when the core moves from the applied force towards the coil, S2 the value of E1 increases, which decreases the magnitude of E1 although these are opposite phases from each other. Therefore, the resulting voltage in the phase of E1 is E1 - E2 Thus the magnitude of V₀ depends on the distance traveled by the core. Its polarity or phase indicates in which direction it is moving. If the core is connected to the moving object, the magnitude of V₀ indicates the position of the object. According to Fig. (C), the output voltage is the linear function of core displacement in a limited range of motion.

Advantages of LVDT – 

• In this, the relationship between input displacement and output voltage is linear.
• In this, the change in the value of output voltage is continuous, as there is no mechanical element to replace it. Even for 1–10 -³ millimeter resolution LVDT The construction work is satisfactory
• The higher the sensitivity of this transducer. 
• The design and structure of this transducer is simple
• This transducer accepts power of much lower value (less than 4 watts) than the power supply
• This transducer has a lower hysteresis loss
• In this transducer there are no sliding parts in contact. Hence the effect of friction and noise is less
• This transducer is used at alternating current voltages, which can be converted to sufficient frequency range.

Application of LVDT 

• in the measurement of thickness of material in hot strip or slab steel mills
• in accelerometer
• in controlling jet engine for the released gases
• in measuring rotational position
• for displacement measurement
• in measuring force, pressure, load etc
• as primary transducer

Disadvantages –

• For higher values ​​of differential output, the core tends to displace more
• Undesirable magnetic fields have a greater effect on input
• LVDT on vibration. The value of the result obtained from is many times a defect
• It is susceptible to the stray magnetic field
• Its dynamic response is limited
• Transducer operation is affected due to temperature change

Limitations –

• It measures displacement from 12 inches to a few millimeters
• It works only in a wide range of temperature from -265 ° C to 600 ° C
• The magnetic core attached to the rod should be bent
• LVDT  The required alignment for should be correct

Specifications –