Download Lab #7: LVDT - Montana State University

MONTANA STATE UNIVERSITY
DEPARTMENT OF MECHANICAL ENGINEERING
ETME 360 Spring 2017 – Measurements and Instrumentation Laboratory
Lab 7 - LINEAR VARIABLE DIFFERENTIAL TRANSFORMER
Investigating the Characteristics of an LVDT 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 5 kHz (5000 Hz.) Set sine wave
amplitude to a 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.
Vary the position of the core in ~0.10 inch increments 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, and dial
indicator positions, to compute the required results, below.
Perform the signal timing measurements necessary (as demonstrated and discussed in
lab!) to derive phase angle between input and output voltages as demonstrated in lab
and required in the results, below.
Results:
1.
Plot data to clearly show the two different methods commonly used to
characterize LVDT performance, as follows:
(a) voltage ratio (eo/ei) vs. core displacement for each of the two specified load
resistances, and
(b) voltage eo vs. core displacement for each of 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 one 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.