MONTANA STATE UNIVERSITY 
DEPARTMENT OF MECHANICAL ENGINEERING                                   

ETME 360 Spring 2014 – Measurements and Instrumentation Laboratory

Variable Inductance Transducer Applications:
Investigation of Operating Characteristics of an LVDT -
LINEAR VARIABLE DIFFERENTIAL TRANSFORMER                         

R
. Larson

Goal:
Gain experience with Digital Storage Oscilloscope operation while investigating the  
input & output characteristics of a linear variable differential transformer (LVDT).

 References:
A. Wheeler & A Ganji, Introduction to Engineering Experimentation
ETME360 Lecture & laboratory instruction

 Equipment:
Linear Variable Differential Transformer, with Calibration Stand
Digital Storage Oscilloscope
Multi-function synthesizer or oscillator (sine wave generator)
Decade Resistor                                             

 Procedure:  
 
Assemble the circuit shown below.

   

Figure 1. LVDT Connection Schematic Diagram.

Adjust the A/C signal source to a frequency of 5KHz (5000 Hz.) Set sine wave amplitude to any known value between 1 to 5 volts. (Measure  the oscillator frequency and amplitude using appropriate oscilloscope functions, rather than assuming that oscillator settings are accurate.)

Two different load resistance cases will be examined:  

(a) Set load resistor RL=5,000 ohms.
(
b) Set load resistor RL=100 ohms.

Find the "null" position, i.e. the core position that gives the minimum voltage output for the particular LVDT, and rotate the outer rim of the dial indicator to re-define the “Zero” at this position.  

Incrementally vary the position of the core over the entire range of core displacements possible, both positive & negative from the null position, without exceeding the range of the dial indicator. Record all voltage inputs & outputs, dial indicator positions,  to compute the required results, below. 

Perform the signal timing measurements necessary to derive phase angle between input and output voltages as demonstrated in lab and required in the results, below.

Results:

1.         Create plots of:
(a)  
voltage ratio (eo/ei) vs. core displacement for each of the two specified load resistances, and
(b)  
voltage eo vs. core displacement for the two specified load resistances, at a given (recorded) input voltage.   

2.         Determine the sensitivity of the LVDT for each of the above cases and clearly present your findings. 

3.         Determine the phase angle between input and output voltages in two positions:
(a) At o
ne known, positive core displacement value and
(b)
at one known, negative core displacement value, for each of the load resistances.  Again, clearly present your findings.