Emerson 755A - Manual (Page 4)

Instruction Manual
245364-V
May 2002
ii Contents Rosemount Analytical Inc. A Division of Emerson Process Management
Model 755A
3-0 OPERATION .........................................................................................................................3-1
3-1
Overview................................................................................................................................3-1
3-2 Selection of Recorder Oxygen Range...................................................................................3-1
a. Recorder Oxygen Range Selection Procedure...............................................................3-1
b. Readout of Applied Zero-Suppression Voltage on Digital Display .................................3-3
3-3 Startup Procedure .................................................................................................................3-4
3-4 Calibration..............................................................................................................................3-4
a. Calibration Using Digital Readout for Oxygen Readout..................................................3-4
b. Calibration Using Recorder for Oxygen Readout ...........................................................3-4
c. Calibration with Downscale and Upscale Standard Gases ............................................3-8
d. Calibration of Automatic Pressure Compensation ..........................................................3-8
3-5 Compensation for Composition of Background Gas .............................................................3-10
a. Oxygen Equivalent Values of Gases ..............................................................................3-10
b. Oxygen Equivalents of Gas Mixtures..............................................................................3-10
c. Computing Adjusted Settings for Zero and Span Controls.............................................3-10
3-6 Dual Alarm Option .................................................................................................................3-12
a. Initial Calibration and Selection of Setpoints for Alarms .................................................3-12
b. Selection of Deadband....................................................................................................3-13
3-7 Routine Operation .................................................................................................................3-14
3-8 Effect of Barometric Pressure Changes on Instrument Readout ..........................................3-14
3-9 Calibration Frequency ...........................................................................................................3-14
4-0 THEORY................................................................................................................................4-1
4-1
Principles of Operation ..........................................................................................................4-1
a. Magnetic Displacement Force ........................................................................................4-1
b. Physical Configuration of Detector/Magnet Assembly....................................................4-2
4-2 Variables Influencing Paramagnetic Oxygen Measurements ...............................................4-5
a. Pressure Effects..............................................................................................................4-5
b. Temperature Effects .......................................................................................................4-5
c. Interferents ......................................................................................................................4-5
d. Vibration Effects ..............................................................................................................4-5
4-3 Electronic Circuitry.................................................................................................................4-6
a. Detector/Magnet Assembly.............................................................................................4-6
b. Control Board and Associated Circuitry..........................................................................4-6
c. Case Board .....................................................................................................................4-7
d. Isolated Current Output Board (Optional) .......................................................................4-8
e. Alarm Option ...................................................................................................................4-8
5-0 CIRCUIT ANALYSIS.............................................................................................................5-1
5-1 Overview................................................................................................................................5-1
5-2 ±15VDC Power Supply..........................................................................................................5-1
5-3 Case Heater Control Circuit...................................................................................................5-1
5-4 Detector Heater Control Circuit .............................................................................................5-6
5-5 Detector Light Source Control Circuit....................................................................................5-7
5-6 Detector with First Stage Amplifier and Pressure Compensation Circuits ............................5-8
a. Pressure Compensation Circuit ......................................................................................5-9
b. Pressure Signal Circuit ...................................................................................................5-9
c. Positive and Negative Reference Voltage Circuits .........................................................5-9
5-7 Buffer Amplifiers U10 and Associated Anticipation Function ................................................5-11
5-8 Digital Output Circuit..............................................................................................................5-12
5-9 Analog Output Circuits for Recorder and Alarms ..................................................................5-12