Demodulator; Oscillator; Voltage Regulator - Emerson Rosemount 2151N Reference Manual

Reference Manual
00809-0000-4851 Rev AD
December 2023
Figure 4-2 – The Sensor Cell

DEMODULATOR

OSCILLATOR

VOLTAGE REGULATOR

Operation
The demodulator consists of a diode bridge that rectifies the
ac signal from the sensor cell to a dc signal. The oscillator
driving current, I (the sum of the dc currents through two
ref
transformer windings), is kept constant by an integrated circuit
operational amplifier (op amp). The output of the demodulator
is a current directly proportional to pressure, i.e.,
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The diode bridge and temperature compensation circuits are
located inside the sensor module.
The oscillator frequency is determined by the capacitance of
the sensing element and the inductance of the transformer
windings. The sensing element capacitance is variable.
Therefore, the frequency is variable about a nominal value of
110 kHz. An operational amplifier acts as a feedback control
circuit and controls the oscillator drive voltage such that:
The transmitter uses a zener diode, transistors, associated
resistors and capacitors to provide a constant reference
voltage of 3.2 Vdc and a regulated voltage of 7.4 Vdc for the
oscillator and amplifiers.
Rosemount 2151N
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