AMCI ANR2, Руководство пользователя

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I
NTRODUCTION TO THE
ANR2
ADVANCED MICRO CONTROLS INC.
1
8
The ANR2 (continued)
LVDT Interface
The ANR2 incorporates a DSP controlled sine wave oscillator and power amplifier to generate the excitation
voltage for the LVDT. Fully programmable over a wide range of frequencies and amplitudes, the ANR2 can
be configured to run at the optimum frequency of your LVDT or RVDT sensor.
Many of signal conditioners on the market today use the differential measurement method, where the second-
ary windings are put in series opposition and the voltage across the two windings is measured. This condi-
tioning method is the simplest, compatible with all 4-, 5-, and 6-wire LVDT’s, and offers acceptable
performance for most applications. However, the accuracy of differential measurements can suffer from the
following:

Changes in excitation voltage and frequency caused by ambient temperature changes

Changes in sensor sensitivity caused by ambient temperature changes at the sensor

Electrical noise injected into the cabling from external sources.
A simple method used by the ANR2 eliminates measurement errors caused by changes in the ambient tem-
perature around the module. By feeding the excitation voltage (V
e
) back into the ANR2, the module can cal-
culate the ratio: {(V
A
– V
B
) / (V
e
)}. Dividing the differential measurement by the excitation voltage
eliminates changes in the excitation voltage as a source of error. However, this method does not eliminate
errors caused by changes in ambient temperature around the sensor.
Many LVDT/RVDT applications expose the sensor to large variations in temperature, and these applications
often require the most accurate measurements possible over the entire temperature range. For these demand-
ing applications, the ANR2 supports the
ratiometric measurement method. This method requires a five or six
wire sensor that is specifically manufactured to support ratiometric measurements. This method measures the
two secondary voltages separately and calculates the LVDT position as: {(V
A
– V
B
) / (V
A
+ V
B
)}. By consid-
ering the ratio of the outputs, any error caused by an increase or decrease in the absolute values of these volt-
ages is eliminated. This method also eliminates any common mode electrical noise that can be induced into
the sensor wiring from external sources.
Master/Slave Excitation Mode
Up to six ANR2 modules can be placed in a single AnyNET-I/O stack. When using multiple sensors in close
proximity, it is sometimes beneficial to synchronize the excitation voltages when the sensors use the same
excitation frequency. Synchronizing the excitation voltages avoids a phenomenon known as
heterodyning ,
which is commonly called beating .
In LVDT/RVDT applications, heterodyning can be considered a form of cross talk. If a small variance in
excitation frequency is coupled from one sensor into another, the result will be a dynamic change in output
signal that will affect the accuracy of the measurement. These effects are also compensated for in the ANR2
when using the ratiometric measurement method, but these effects can still be seen in differential measure-
ments.
All ANR2 modules ship as Master modules and generate their own excitation voltages. You change an
ANR2 to a slave module by changing a jumper on the front of the unit and programming a parameter in the
network data. External wiring is then used to connect the master module to the slaves. Any module in the
stack can be the master, but wiring will be easier if the module on the far left of the stack is the master.