A Manual on Experiments in Physics by R Srinivasan K R Priolkar and T G Ramesh

Author:R Srinivasan, K R Priolkar, and T G Ramesh
Language: eng
Format: epub
Publisher: Indian Academy of Sciences
Published: 2018-11-27T00:00:00+00:00

3. Apparatus Required

Signal generator, lock-in amplifier, two-channel oscilloscope, mutual inductance coil, and a DMM to measure DC output of lock-in amplifier to two decimal places in DC 20 V range.

4. Procedure

Since we are measuring an external signal, the switches SW1 and SW2 on the LIA front panel should be set to the positions marked EXT. The switch SW1 will point to the left and the switch SW2 to the right.

The red terminal on the signal generator is connected to the red terminal, and the black terminal on the signal generator to the black terminal, on the primary coil side of the insulating former. Connect the yellow and black terminals on the primary coil side of the insulating former to the RCA socket marked EXT REF on the front panel of the LIA.

Connect the red terminal on the secondary side of the insulating former to the red banana terminal marked EXT SIG on the LIA. Connect the black terminal on the secondary side of the insulating former to the black banana terminal marked EXT SIG on the front panel of the LIA.

Connect a DMM in the DC 20 V range to the RCA socket marked OUTPUT on the front panel of the LIA. Connect the two RCA sockets marked REF and REF′ on the front panel of the LIA to the two channels of an oscilloscope.

Switch on the signal generator. Set the peak-to-peak amplitude Vpp on its panel meter to 11 volts, and the frequency to 400 Hz. Switch on the lock-in amplifier and the oscilloscope. Put the toggle switch SW3 up. You will see two sinusoidal traces at the frequency of 400 Hz on the oscilloscope. When the phase-shift-adjust pot on the LIA is to the extreme right, the two traces will be in phase. Note that the DMM reading is small. Now turn the phase-adjust pot to the left. The trace of REF′ will shift relative to the trace of REF, and the DMM reading will increase. The sign of the DMM reading will be negative. The DMM takes some time to reach a steady value. So, turn the phase-adjusting pot little by little and wait for the DMM to reach a steady reading. The magnitude of the reading on the DMM will increase, and it will reach a maximum at one position of the phase-adjusting pot. A further turning of the phase-adjusting pot will reduce the magnitude of the reading. Keep the phase-adjusting pot at the position when you get the maximum negative reading on the DMM. On the oscilloscope screen, we see that the phase difference between the two traces is 90°. To show this more dramatically, press the XY button on the oscilloscope. Now one sees the Lissajous figure due to the signals REF and REF′. When the DMM shows the maximum value, this figure on the oscilloscope screen is a slightly distorted circle. The reference signal is in phase with the current. A maximum output of the LIA indicates that the phase-shifted reference signal is in phase with the mutual inductance emf.

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