Emerson 1154, 00809-0100-4514 manual Demodulator, Linearity Adjustment

Page 33

Reference Manual

00809-0100-4514, Rev BA January 2008

Rosemount 1154

Figure 4-2. Electrical Block

Diagram.

SENSOR

DEMODULATOR

CURRENT

 

 

-

 

 

DETECTOR

 

 

 

 

 

 

TEST

 

 

 

CURRENT

 

+

 

 

 

LIMITER

+

OSCILLATOR

 

 

 

 

SIGNAL

 

 

 

 

 

 

 

CURR.

-

 

 

OSC.

 

 

 

 

 

CONTROL

 

 

 

CONTROL

VOLTAGE

REVERSE

 

 

AMP.

 

 

AMP.

REGULATOR

 

 

POLARITY

 

 

 

 

 

 

 

 

 

 

 

 

 

PROTECTION

 

 

 

 

CURRENT

 

 

 

 

 

CONTROL

 

 

THE δ-CELLSENSOR Process pressure is transmitted through an isolating diaphragm and silicone oil fill fluid to a sensing diaphragm in the center of the δ-Cell. The reference pressure is transmitted in like manner to the other side of the sensing diaphragm.

The position of the sensing diaphragm is detected by the capacitance plates on both sides of the sensing diaphragm. The capacitance between the sensing diaphragm and either capacitor plate is approximately 150 pf. The sensor is driven through transformer windings by an oscillator at roughly 32 kHz and 30 Vp-p.

DEMODULATOR

The demodulator consists of a diode bridge that rectifies the ac signal from

 

the sensor cell to a dc signal.

The oscillator driving current, Iref (the sum of the dc currents through two transformer windings) is controlled to be a constant by an integrated circuit amplifier.

The dc current through a third transformer winding is a current directly proportional to pressure, i.e.,

Idiff = fVp p(C2C1)

LINEARITY ADJUSTMENT

The diode bridge and span temperature compensating thermistor are located inside the sensor module. The effect of the thermistor is controlled by resistors located in the electronics housing.

Linearity is adjusted by a variable-resistance network, capacitor, and diodes. The currents generated through this part of the circuit are summed into the inputs of the oscillator control circuit. This provides a programmed correction that raises the oscillator peak-to-peak voltage to compensate for first-order nonlinearity of capacitance as a function of pressure.

4-3

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Contents Reference Manual RosemountImportant Notice -- Errata Rosemount 1154 Alphaline Nuclear Pressure Transmitter Return of Material Revision Status Changes From June 1999 to JanuaryNew Old Changes Rosemount Table of Contents Maintenance Troubleshooting Specifications Reference DataSection TOC-3 TOC-4 Overview About the Transmitter Section IntroductionRosemount Overview General Considerations Section InstallationProcess Connections Mechanical ConsiderationsRosemount Electrical Considerations ConduitTransmitter Wiring Connections Installation ProceduresMechanical Range Code Pressure DimensionElectrical Liquid ServiceTransmitter Terminal Block Rosemount Span Adjustment Zero Adjustment Section CalibrationOverview Calibration Zero and Span Adjustment Calibration ProceduresZero and Span Adjustment Screws Linearity Adjustment Linearity and Damping Adjustment Damping AdjustmentRosemount Calculate zero adjustment correction in terms of pressure Rosemount Overview Transmitter Operation Section OperationΔ-Cell Demodulator Linearity AdjustmentFV Iref Overview Maintenance TroubleshootingTest Terminals Board Checkout Safety MessagesSensing Module Checkout Process Flange Removal Disassembly ProcedurePart Description Rosemount 1154 Parts ListReassembly Procedure Rosemount Process Flange Reassembly Post Assembly Tests Symptom Potential Source Corrective ActionOn Next Check for adequate voltage to the transmitter Nuclear Specifications Specifications and Reference DataPerformance Specifications Range Code Overpressure Effect Functional Specifications Range Code Static Pressure Zero EffectRange Code Response Time 25 to 0-150 inH2O 0-6.22 to 0-37.3 kPa Range Code Pressure RangesRange Code Overpressure Limit Physical SpecificationsRosemount Ordering Information Rosemount 1154DP 1154HP 1154GP Part Description Order No Rosemount 1154DP, 1154HP, and 1154GP Spare PartsFor use with existing N0026 transmitter only Spare Parts Shelf Life Important Notice Rosemount Current Control Current Limit Index-2 Page ¢00809-XXXX-XXXX ¤