DESCRIPTION AND OPERATION
LVDT OSCILLATOR
2 - 8
I-E96-315B
®
the LVDT secondary inputs (which are out of phase) and the
result is a DC offset that represents the actuator position. The
position feedback signal passes from the demodulator output
to the sample hold circuit.
Sample Hold Circuit
The sample hold circuit samples the demodulator output 1000
times per second. The position feedback travels directly from
the sample hold output to the position error circuit, completing
the control portion of the feedback loop.
Analog-to-Digital Converter
This portion of the position feedback circuitry converts the
analog feedback signal to a digital value. The position feedback
passes from the ADC converter to the data buffers, to the
microcontroller, to the slave expander bus and finally to the
MFP.
LVDT OSCILLATOR
The LVDT oscillator (frequency selectable) supplies an excita-
tion voltage to the LVDT primary. See Figure
. The excita-
tion voltage on the primary causes the secondary of the LVDT
to induce a differential voltage indicating actuator position.
This output has selectable gains. Setting a dipswitch adjusts
the operating range of the LVDT excitation voltage to allow a
maximum range of output voltage on the LVDT secondaries.
Figure 2-4. Position Feedback Circuit
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LVDT
BUFFER
SUMMING
AMP
SAMPLE/
HOLD
ADC
POSITION
FEEDBACK
TO MICRO-
CONTROLLER
TP25047B
TO POSITION ERROR CIRCUIT
(PROPORTIONAL AMP)
ACTUATOR
DEMODULATOR
DEMODULATOR
GAIN
1, 2.5 OR 10 KHZ
LVDT
OSCILLATOR
CORE
