Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 4-1 Transmitter Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 4-1The δ-Cell Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 4-3 Demodulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 4-3 Linearity Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 4-3 Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 4-4 Voltage Regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 4-4 Zero and Span Adjustments . . . . . . . . . . . . . . . . . . . . . . . page 4-4 Current Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 4-4 Current Limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 4-4 Reverse Polarity Protection . . . . . . . . . . . . . . . . . . . . . . . . page 4-4
This section provides brief descriptions of basic transmitter operations in the following order:
•Transmitter Operation
•The -Cell™Sensor
•Demodulator
•Linearity Adjustment
•Oscillator
•Voltage Regulator
•Zero and Span Adjustments
•Current Control
•Current Limit
•Reverse Polarity Protection
The block diagram in Figure 4-2 on page 4-3illustrates the operation of the transmitter.
The Rosemount 1154 Alphaline Pressure Transmitters have a variable capacitance sensing element, the δ-Cell (Figure 4-1 on page 4-2). Differential capacitance between the sensing diaphragm and the capacitor plates is converted electronically to a 2-wire 4–20 mA dc signal.
P = K | | ⎛ C2 | – C1⎞ |
1 | ⎜ -------------------- | ⎟ |
| ⎝ C1 | + C2⎠ |
Where:
Pis the process pressure.
