AMCI ANR2, User Manual

Page: 60 / 62

20 Gear Drive, Plymouth Ind. Park, Terryville, CT 06786

Tel: (860) 585-1254 Fax: (860) 584-1973 http://www.amci.com
60
APPENDIX A
T
HE
LVDT
AND
RVDT
What is an LVDT?
The LVDT, or Linear Variable Differential Transformer, is an analog sensor that measures linear position with
an accuracy that is limited only by the electronics attached to it. Each LVDT contains one input, or primary,
coil and two output, or secondary, coils. Some LVDT’s have the two secondary coils internally connected in
series opposition and appear to have only one secondary coil. A cut away view of a model LVDT is shown in
figure A.1 along with a schematic representation.
Figure A.1 LVDT Sensor
The Permeable Core is free to slide within the LVDT and is typically attached to what is being measured by a
non-magnetic rod. An excitation voltage is applied to the Primary Coil. The core couples energy from the
Primary Coil into the two secondary coils. When the core is centered in the LVDT, an equal amount of
energy is coupled into the secondary coils and their voltage outputs are equal. This is the “Null” position. As
the core moves towards Coil A, the amount of energy coupled into it increases, which appears as an increase
in voltage. Simultaneously, the amount of energy coupled into Coil B decreases, and its output voltage falls.
The same relationship occurs as the core moves towards Coil B. The voltage on Coil B increases while the
voltage on Coil A decreases.
When considering AC voltages, phase is important. One of the secondary coils produces a voltage that is in
phase with the excitation voltage and the other produces a voltage that is 180° out of phase with the excitation
voltage.
The vector difference of the induced voltages (V
A
– V
B
) is linear over most of the travel of the core. This
relationship is what makes the LVDT useful as an analog sensor.
This appendix explains how an LVDT works and the characteristics you must be
aware of when configuring the ANR2 to use your sensors.
Pe
rm
ea
ble
Co
re
Primary
Coil B Coil A