hello friends in this lecture I am going to explain about how LVDT means linear variable differential transformer works LVDT works on the principle of variation of mutual inductance it is one of the most popular type of device for measurement of linear displacement commercial LVD tees are available having full scale displacement range of plus minus 0.25 millimeters to plus minus 250 millimeters now look at construction of LVDT it consists of a cylindrical former it is surrounded by one primary winning called as primary coil at the center of the former the primary winding is excited by 1 to 10 volts AC voltage source and the 2 secondary windings are at both sides of primary coil are fixed called as secondary coil 1 and secondary coil 2 the number of terms in both secondary coils are equal and they are connected in series it consists of movable a ferromagnetic core which is freely moves through the former now see how LVDT works Here I am going to explain three positions for LVDT first condition core at null position that is at center second condition is core at left side of null position and third condition core ax right side of null position now let us see first case in details that is core at naught position the voltage induced in both for secondary coils are equal as EMF induced is same in both coils which results in net output is equal to zero thus from the measurement of the output voltage only one cannot predict the direction of the core movement so a phase sensitive detector is a useful circuit to make the measurement Direction sensitive it is connected at the output of the LVDT and compares the phase of the secondary output with the primary signal to judge the direction of movement case second when an external force is applied and if the iron core tends to move in the left-hand side direction then the EMF voltage induced in the secondary coil one is greater when compared to the EMF induced in the secondary coil two therefore the net output will give negative displacement case 3 when an external force is applied and if the iron core moves in the right hand-side direction then the EMF induced in the secondary coil 2 is greater when compared to the EMF voltage induced in the secondary coil first therefore the net output will give positive displacement LVDT having many advantages like one pad range the LVDT s have a very high range for measurement of displacement they can used for measurement of displacements ranging from 0.25 millimeters to 250 millimeters to no frictional losses as the core moves inside a hollow former so there is no loss of displacement input as frictional loss so it makes LVDT as very accurate device 3 high input and high sensitivity the output of LVDT is so high that it doesn't need any amplification the transducer possesses a high sensitivity which is typically about 40 volts per millimeter for low hysteresis LVDT s show a low hysteresis and hence repeatability is excellent under all conditions five direct conversion to electrical signals 6 they convert the linear displacement to electrical voltage which are easy 7 they can also acts as the secondary transducers for example LibDem tube which acts as a primary transducer and covered pressure into linear displacement then LVDT covers this displacement into electrical signal which after calibration gives the ideas of the pressure of fluid disadvantages of LVDT one LVDT is sensitive to stray magnetic fields so they always require a set up to protect them from stray magnetic fields to they are affected by vibrations and temperature thank you for listening carefully watch my next video on calibration of LVDT