AMCI ANR2, Руководство пользователя

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
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T
HE
LVDT
AND
RVDT
A
61
What is an LVDT? (continued)
Internally, all LVDT’s have six wires except for half
bridge LVDT’s.
“Five-wire” LVDT have the two secondary coils tied in
series opposition and this connection is brought out as a
centertap. The sum and difference of the two voltages
can be determined with five and six wire sensors.
“Four-wire” LVDT’s are made by internally tying the
two secondary coils in series opposition and bringing
out the other two ends. This gives a fixed secondary
output of V
A
– V
B
. The sum of the two voltages cannot
be determined from a four wire sensor.
“Three-wire” LVDT’s are made by internally tying the
two secondary coils in series opposition and tying one
side of the primary to one end of the secondary coils.
This gives a fixed secondary output of V
A
– V
B
. The
sum of the two voltages cannot be determined from a
three wire sensor.
“Half bridge” LVDT’s have a single winding with a
centertap connection. These devices are typically mea-
sured by using two resistors to build a bridge circuit
with the LVDT as one side.
All of these configurations are shown in figure A.2. The ANR2 can interface with any of these wiring types.
What is an RVDT?
An RVDT, or Rotary Variable Differential Transformer, has electrical characteristics that are functionally
identical to the LVDT, but the mechanical construction is significantly different. An RVDT has the primary
and secondary coils located in the body of the RVDT and the permeable core is mounted on the shaft of the
sensor. As the shaft rotates, and the difference in induced voltages remains linear over a fixed range of
motion, typically ±30° to ±60°.
Important Characteristics

Sensor Type: This defines how the sensor is wired to the ANR2.

Input Voltage: Defines the nominal operating voltage for your sensor.

Input Frequency: Defines the nominal operating frequency of your sensor. This is sometimes speci-
fied as a range of acceptable values, with accuracy ratings listed at a specific frequency. Use this fre-
quency if it is available, or choose the center value from the range given.

Sensitivity: This parameter specifies the change in output that you can expect based on your Input
Voltage and change in position. V
o
= Sensitivity
x
Input Voltage
x
Change in position. For example,
assuming a sensitivity of 6.0 mV/V/0.001" and an Input Voltage of 4 Vrms, a change in position of
0.050 inches will result in an output change of 6.0 mV
x
4 V
x
(0.050"/0.001) = 1.2 Volts.

Stroke Length, or Nominal Range: Because of present manufacturing methods, the sensitivity of an
LVDT or RVDT decreases as the stroke length of the sensor increases. Therefore, the stroke length of
your sensor should match your expected travel as closely as possible. With this said, when program-
ming the ANR2, you should program in your expected travel length, especially if this length is signifi-
cantly less than the total stroke length of your sensor.
Figure A.2 LVDT/RVDT Wiring Types
Primary
Primary
Primary
Coil B
Coil B
Coil B
Coil A
Coil A
Coil A
6-Wire LVDT/RVDT
5-Wire LVDT/RVDT
4-Wire LVDT/RVDT
Primary
Coil B Coil A
3-Wire LVDT/RVDT
Half Bridge LVDT/RVDT