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April 2000 Rosemount Analytical 245364-U

Model 755A Oxygen Analyzer

OTES

Summary of Contents for 755A

Page 1: ...Rosemount Analytical MODEL 755A OXYGEN ANALYZER INSTRUCTION MANUAL 245364 U ...

Page 2: ...nge without notice Manual Part Number 245364 U April 2000 Printed in U S A Rosemount Analytical Inc 4125 East La Palma Avenue Anaheim California 92807 1802 Teflon is a registered trademark of E I duPont de Nemours and Co Inc SNOOP is a registered trademark of NUPRO Co ...

Page 3: ...E AND FIELD SERVICE P 6 RETURNING PARTS TO THE FACTORY P 6 TRAINING P 6 DOCUMENTATION P 6 COMPLIANCES P 7 SECTION 1 INTRODUCTION 1 1 OVERVIEW 1 1 1 2 OXYGEN RANGE ON FRONT PANEL DIGITAL DISPLAY 1 2 1 3 OXYGEN RANGES FOR RECORDER READOUT 1 2 1 4 RECORDER VOLTAGE AND CURRENT OUTPUTS 1 3 1 5 AUTOMATIC PRESSURE COMPENSATION 1 3 1 6 ALARM OPTION 1 3 1 7 CASE MOUNTING OPTIONS 1 3 1 8 ELECTRICAL POWER OP...

Page 4: ...10 2 6 6 Corrosive Gases 2 11 2 7 LEAK TEST 2 11 2 8 PURGE KIT OPTIONAL 2 12 SECTION 3 INITIAL STARTUP AND CALIBRATION 3 1 SELECTION OF RECORDER OXYGEN RANGE 3 1 3 1 1 Recorder Oxygen Range Selection Procedure 3 1 3 1 2 Readout of Applied Zero Suppression Voltage on Digital Display 3 5 3 2 STARTUP PROCEDURE 3 6 3 3 CALIBRATION 3 7 3 3 1 Calibration Using Digital Readout for Oxygen Readout 3 7 3 3 ...

Page 5: ...5 6 5 3 ELECTRONIC CIRCUITRY 5 6 5 3 1 Detector Magnet Assembly 5 7 5 3 2 Control Board and Associated Circuitry 5 7 5 3 3 Case Board 5 9 5 3 4 Isolated Current Output Board Optional 5 10 5 3 5 Alarm Option 5 10 SECTION 6 ELECTRONIC CIRCUIT ANALYSIS 6 1 OVERVIEW 6 1 6 2 15VDC POWER SUPPLY 6 1 6 3 CASE HEATER CONTROL CIRCUIT 6 1 6 4 DETECTOR HEATER CONTROL CIRCUIT 6 6 6 5 DETECTOR LIGHT SOURCE CONT...

Page 6: ...7 3 7 3 DETECTOR COMPONENT REPLACEMENT 7 3 7 3 1 Detector Replacement 7 3 7 3 2 Source Lamp Replacement 7 5 7 3 3 Photocell Replacement and Adjustment 7 7 7 4 HEATING CIRCUITS 7 8 7 4 1 Case Heater Control Circuit 7 8 7 4 2 Detector Magnet Heating Circuit 7 9 SECTION 8 REPLACEMENT PARTS 8 1 CIRCUIT BOARD REPLACEMENT POLICY 8 1 8 2 SELECTED REPLACEMENT PARTS 8 1 GENERAL PRECAUTIONS FOR STORING AND ...

Page 7: ... Magnetic Field 5 2 5 2 Functional Diagram of Paramagnetic Oxygen Measurement System 5 3 5 3 Detector Magnet Assembly 5 4 6 1 Two Comparator OR Circuit 6 2 6 2 Ramp Generator 6 3 6 3 Case Heater Control Circuit 6 4 6 4 Case Heater Circuit 6 5 6 5 Detector Heater Control Circuit 6 7 6 6 Detector Light Source Control Circuit 6 8 6 7 Detector with First Stage Amplifier and Pressure Compensation Circu...

Page 8: ...TED IN REAR OF MANUAL 617186 Schematic Diagram Master Board Assembly Case 617731 Pictorial Wiring Diagram Model 755A 620434 Schematic Diagram 0 to 20 mA or 4 to 20 mA Current Output 632349 Installation Drawing Model 755A 652219 Schematic Diagram Control Board 652222 Schematic Diagram Transducer ...

Page 9: ...GER is used to indicate the presence of a hazard which will cause severe personal injury death or substantial property damage if the warning is ignored WARNING is used to indicate the presence of a hazard which can cause severe personal injury death or substantial property damage if the warning is ignored CAUTION is used to indicate the presence of a hazard which will or can cause minor personal i...

Page 10: ...ystem must be carefully leak checked upon installation and before initial start up during routine maintenance and any time the integrity of the sample containment system is broken to ensure the system is in leak proof condition Leak check instructions are provided in Section 2 7 Internal leakage of sample resulting from failure to observe these precautions could result in an explosion causing deat...

Page 11: ...more than 11 1 C 20 F 2 5 of fullscale per 24 hours with ambient temperature change over entire range BAROMETRIC PRESSURE COMPENSATION Oxygen readout automatically corrected to within 1 of fullscale for barometric pressure variations within 3 of target value and within 2 of fullscale for barometric pressure variations within 5 of target value The target may be set anywhere within range of 2 7 to 3...

Page 12: ... Hz POWER CONSUMPTION Maximum 300 watts Nominal 75 watts OUTPUT Standard Field selectable voltage output of 0 to 10mV 0 to 100mV 0 to 1V or 0 to 5VDC Optional Isolated current output of 0 to 20mA or 4 to 20mA with Current Output Board ALARM OPTION High Low Alarm Contact Ratings 5 amperes 240V AC resistive load 5 amperes 120V AC resistive load 5 amperes 28V DC resistive load SETPOINT Adjustable fro...

Page 13: ...pe Z purge WEIGHT Approximately 32 5 lbs 14 74 Kg DIMENSIONS Height 13 5 343 mm Width 11 5 294 mm Depth 7 12 181 mm 3 When installed with user supplied components meets requirements for Class I Division 2 locations per National Electrical Code ANSI NFPA 70 for analyzers sampling nonflammable gases Analyzers sampling flammable gases must be protected by a continuous dilution purge system in accorda...

Page 14: ... Unauthorized returns will be returned to the sender freight collect When returning any product or component that has been exposed to a toxic corrosive or other hazardous material or used in such a hazardous environment the user must attach an appropriate Material Safety Data Sheet M S D S or a written certification that the material has been decontaminated disinfected and or detoxified Return to ...

Page 15: ...nal Safety and Health Act OSHA of 1970 if installed in accordance with the requirements of the National Electrical Code NEC of the United States in non hazardous areas and operated and maintained in the recommended manner This product may carry approvals from a certifying agency or may be in compliance with EMC Directive If so the product will carry approval insignia like those shown here on the p...

Page 16: ...PREFACE P 8 April 2000 Rosemount Analytical 245364 U Model 755A Oxygen Analyzer NOTES ...

Page 17: ...of the oxygen content of a flowing gas sample Oxygen is strongly paramagnetic other common gases with only a few exceptions are weakly diamagnetic A front panel liquid crystal display provides direct digital readout of oxygen concentration In addition a field selectable voltage output is provided as standard An isolated current output of 0 to 20 mA or 4 to 20 mA is obtainable with the optional Cur...

Page 18: ...n SCALE EXPANSION Fullscale oxygen span for the recorder is switch selectable for 1 2 5 10 20 or 100 oxygen ZERO SUPPRESSION The desired zero suppression is obtained as the sum of a a jumper selectable fixed value of 0 20 40 60 or 80 oxygen and b a continuously adjustable value of 0 to 25 oxygen Thus the electronic circuitry provides the capability of setting the total zero suppression for any des...

Page 19: ...utput option Note Voltage and current outputs may be used simultaneously if desired 1 5 AUTOMATIC PRESSURE COMPENSATION The oxygen readout is automatically corrected for pressure variations within 3 of the target value which may be set anywhere within the range of 2 7 to 3 3 psig 3 psig 18 6 to 22 8 kPa 21 kPa 1 6 ALARM OPTION The analyzer has an alarm relay assembly consisting of two single pole ...

Page 20: ...1 Alarm Relay Assembly Alarm Option Case Board Case Heater Assembly AC Power TB1 Detector Magnet Assembly Detector Magnet Assembly Shock Mount Fuse AC Power Recorder Output TB2 Fuse Case Heater Transducer Location for Optional Current Output Board Control Board ZERO Control SPAN Control Span Jumper Select Recorder Output Jumper Select Zero Suppression CAL2 Adjustment Pressure Compensation CAL1 Adj...

Page 21: ... 7 C to 49 C Avoid mounting outside in direct sunlight or inside in a closed building where ambient temperature may exceed the allowable maximum Shock and mechanical motion can reduce instrument accuracy therefore mount the instrument in an area that is as vibration free as possible 2 3 VOLTAGE REQUIREMENTS Do not operate without doors and covers secure Servicing requires access to live parts whic...

Page 22: ... Electrical power is supplied to the analyzer via a customer supplied three conductor cable type SJT minimum wire size 18 AWG Route power cable through conduit and into appropriate opening in the instrument case see Installation Drawing 642349 Connect power leads to HOT NEUT AND GND terminals on TB1 see Figure 2 1 Connect analyzer to power source via an external fuse in accordance with local codes...

Page 23: ...utput Selection Jumper Figure 2 2 in position appropriate to the desired output 10 mV 100 mV 1V or 5V On TB2 Figure 2 1 connect leads of shielded recorder cable to MV AND COM terminals Connect free end of output cable to appropriate terminals of recorder or other potentiometric device For device with a span of 0 to 10mV 0 to 100mV 0 to 1V or 0 to 5V connect cable directly to input terminals of the...

Page 24: ...metric Recorder Input Terminals Make sure polarity is correct Voltage Divider Customer Supplied Position of Recorder Output Selector Plug Minimum Permissible Resistance for R1 R2 10 mV 1K Ohm 100 mV 10K Ohm 1 V 100K Ohm 5 V 2K Ohm R2 R1 R3 R4 R5 R6 R8 R9 CR2 U6 I G O U3 U2 1 2 3 4 I G O C5 C4 C2 U4 U5 I G O C3 CR1 C1 U1 J1 JP3 Control Board Current Output Board 5V 1V 0 1V 0 01V Recorder Output Vol...

Page 25: ...ultaneously if desired FIGURE 2 4 MODEL 755A CONNECTED TO DRIVE SEVERAL CURRENT ACTIVATED OUTPUT DEVICES 2 4 3 OUTPUT CONNECTIONS FOR DUAL ALARM OPTION If so ordered the analyzer is factory equipped with alarm output Alternatively the alarm feature is obtainable by subsequent installation of the 618083 Alarm Relay Kit ALARM OUTPUT CONNECTIONS The alarm output provides two sets of relay contacts fo...

Page 26: ...RM 2 Relay The ALARM 2 relay coil is de energized when the meter needle moves upscale through the value that corresponds to the setpoint plus deadband This relay coil is energized when needle moves downscale through the value that corresponds to setpoint minus deadband See Figure 2 5B Alarm Reset Normally both the ALARM 1 and ALARM 2 functions incorporate automatic reset When the meter reading goe...

Page 27: ... 115 VAC When input signal moves upscale through this point the coil of ALARM 1 relay K1 is energized providing continuity between the common and normally closed contacts of the relay ALARM 1 Setpoint When input signal moves downscale through this point the coil of ALARM 1 relay K1 is de energized providing continuity between the common and normally open contacts of the relay ALARM 2 Setpoint When...

Page 28: ...alibration point at or near the upper range limit If this range limit is 21 or somewhat above 21 the usual standard gas is dry air 20 93 oxygen 2 6 SAMPLE HANDLING Under no circumstances allow pressure to exceed 10 psig 69 kPa as irreparable damage to the detector may result Many different sample handling systems are available depending on the requirements of the individual user Most sample handli...

Page 29: ...ic pressure variations within 3 of the target value which may be set anywhere within the range of 2 7 to 3 3 psig 3 psig 18 6 to 22 8 kPa 21 kPa The basic rule for pressure of sample and standard gases supplied to the inlet is to calibrate the analyzer at the same pressure that will be used during subsequent operation and to maintain this pressure during operation The arrangement required to obtai...

Page 30: ...and through the analyzer Such operation necessitates special precautions to ensure accurate readout There is the basic consideration of supplying the standard gases to the analyzer at the same pressure that will be used for the sample during subsequent operation In addition any leakage will result in decreased readout accuracy as compared with operation at atmospheric pressure The minimum permissi...

Page 31: ...ch may be flammable If used for analysis of such gases the instrument must be either in an explosion proof enclosure suitable for the gas or protected by a continuous dilution purge system in accordance with Standard ANSI NFPA 496 Chapter 8 or IEC Publication 79 2 1983 Section Three If explosive gases are introduced into this analyzer the sample containment system must be carefully leak checked up...

Page 32: ... 2 1983 Section Three If explosive gases are introduced into this analyzer the sample containment system must be carefully leak checked upon installation and before initial start up during routine maintenance and any time the integrity of the sample containment system is broken to ensure the system is in leak proof condition Internal leaks resulting from failure to observe these precautions could ...

Page 33: ...ns through the case must be sealed thoroughly with the sealant supplied in the kit The sealant applied from the interior of the case must thoroughly cover all existing leads as well as the conduit fitting FIGURE 2 8 INSTALLATION OF PURGE KIT OPTIONAL 645835 Purge Outlet Fitting 190697 Purge Inlet Fitting Flow Indicator Purge Supply Analyzer Door Affix Warning Label 190697 Purge Inlet Fitting 64583...

Page 34: ...UNPACKING AND INSTALLATION 2 14 April 2000 Rosemount Analytical 245364 U Model 755A Oxygen Analyzer NOTES ...

Page 35: ...f fullscale Thus if the recorder output is to be the important display medium for the particular application expanded scale operation may be necessary to obtain the desired readout accuracy Such operation is obtained by an appropriate combination of scale expansion and zero suppression 3 1 1 RECORDER OXYGEN RANGE SELECTION PROCEDURE Refer to Table 3 1 and Figure 3 2 1 Verify that Recorder Voltage ...

Page 36: ...l Display Designation 1 Oxygen content of sample 0 00 to 100 00 NORM 2 Pressure Voltage CAL 1 CAL 1 3 Pressure Voltage CAL 2 CAL 2 4 Zero suppression applied to analog output circuit 0 00 to 10 00 VDC ZERO SUPPRESSION ZERO Control R13 Used to establish downscale calibration point on digital display or recorder chart With suitable downscale standard gas flowing through the analyzer the ZERO Control...

Page 37: ... Zero Suppression Fine Adjustment are adjusted for 0 oxygen Note The Zero and Span adjustments on the analyzer door are used only for the calibration of the digital readout for 0 to 100 oxygen The suppressed recorder ranges may only be set up after the digital readout has been calibrated When setting up a suppressed recorder range use only R41 R104 setpoint and R88 Span for adjustments DO NOT RE A...

Page 38: ... does not require readjustment except after replacement of detector 10 Response Time Adjustment R30 Provides adjustment range of 5 to 25 seconds for electronic response time 0 to 90 of fullscale Adjusting clockwise decreases response time 11 Response Ratio Timing Potentiometer R29 Permits compensation for slight gain changes that may result from adjustment of R20 At the factory R29 is adjusted to ...

Page 39: ...he position appropriate to the recorder 10 mV 100 mV 1 V or 5 VDC 2 Place the front panel TEST switch in position 4 thus disconnecting the signal input to permit display of the zero suppression voltage only 3 Temporarily place Recorder Oxygen Span Jumper in 100 oxygen i e 1X gain position The digital display will now read the applied zero suppression voltage in Refer to Table 3 1 for descriptions ...

Page 40: ...en thus Recorder Zero Suppression Jumper is set in 80 position and Recorder Zero Suppression Adj4ustments R41 and R104 are set for a reading of 99 00 volts on the digital display Recorder Oxygen Span Jumper is returned to 1 oxygen 100X gain position normal span setting for 99 to 100 oxygen range R88 may be used for fine span adjustment Set front panel TEST switch to position 1 3 2 STARTUP PROCEDUR...

Page 41: ...n If so almost any down scale and upscale standards may be used Typically the downscale standard will be an oxygen free gas such as nitrogen and the upscale standard will be some readily obtained gas such as dry air 20 93 oxygen or 100 oxygen Purity requirements will be dictated by the accuracy requirements of the application 3 3 2 CALIBRATION USING RECORDER FOR OXYGEN READOUT In some applications...

Page 42: ...or the calibration of the digital readout for 0 to 100 oxygen The suppressed recorder ranges may only be set up after the digital readout has been calibrated When setting up a suppressed recorder range use only R41 R104 setpoint and R88 Span for adjustments DO NOT RE ADJUST THE ZERO AND SPAN CONTROLS ON THE ANALYZER DOOR c Adjust ZERO Control so that the reading on the digital display or recorder ...

Page 43: ...o interaction has occurred 3 3 4 CALIBRATION OF AUTOMATIC PRESSURE COMPENSATION Oxygen readout is automatically corrected to within 1 of fullscale for barometric pressure variations within 3 of the target value and is corrected to within 2 of fullscale for variations within 5 of the target value The target value may be set anywhere within the range of 2 7 to 3 3 psig 3 psig 18 6 to 22 8 kPa 21 kPa...

Page 44: ...he same noted in step 5 9 Repeat steps 3 through 7 as many times as necessary to ensure repeatability of compensation calibration Note Although not mandatory it is desirable in order to obtain maximum accuracy that the oxygen concentration of the gas used during calibration be close to that of the process stream which is to be analyzed 3 4 COMPENSATION FOR COMPOSITION OF BACKGROUND GAS Any gas hav...

Page 45: ... MIXTURES The oxygen equivalent of a gas mixture is the sum of the contribution of the individual gas components Example At lower range limit i e 0 oxygen composition of sample is 80 CO2 20 N2 From Table 3 3 the oxygen equivalents are CO2 0 623 and N2 0 358 oxygen equivalent of the mixture 0 8 x 0 623 0 2 x 0 358 0 4984 0 0716 0 570 3 4 2 COMPUTING ADJUSTED SETTINGS FOR ZERO AND SPAN CONTROLS Duri...

Page 46: ... 0 623 0 358 When the ZERO gas is more diamagnetic than the background gas in the sample this difference is negative Use a recorder with below zero capability to set negative values GAS EQUIV AS O2 Acetylene C2H2 0 612 Allene C3H4 0 744 Ammonia NH3 0 479 Argon A 0 569 Bromine Br2 1 83 1 2 Butadiene C4H6 1 047 1 3 Butadiene C4H6 1 944 n Butane C4H10 1 481 iso Butane C4H10 1 485 Butene 1 C4H8 1 205 ...

Page 47: ...r reading exactly fullscale If the fullscale setting cannot be reached then set to a reading higher than the desired alarm setpoint 3 Set ALARM 1 calibration adjustment R63 to its clockwise limit Turn R63 counterclockwise the minimum required to energize ALARM 1 relay K1 Figure 3 4 Energization may be verified by connecting an ohmmeter to relay terminals on 638254 Alarm Relay Assembly Figure 2 1 C...

Page 48: ...o lower the output below the setpoint This will re energize the relay Turning R68 above the setpoint will energize the relay 3 5 2 SELECTION OF DEADBAND The desired deadband may be selected with the appropriate trimming potentiometer ALARM 1 R73 ALARM 2 R78 For any setpoint deadband is adjustable from 1 of fullscale counterclockwise limit to 20 of fullscale clockwise limit Deadband is essentially ...

Page 49: ...Figure 3 2 may be desirable to obtain the optimum compromise between response speed and noise 4 2 EFFECT OF BAROMETRIC PRESSURE CHANGES ON INSTRUMENT READOUT If the analyzer exhaust port is vented through a suitable absolute backpressure regulator and the installation site is at or near sea level barometric pressure changes do not affect the percent oxygen readout If conditions are otherwise the p...

Page 50: ...ROUTINE OPERATION 4 2 April 2000 Rosemount Analytical 245364 U Model 755A Oxygen Analyzer NOTES ...

Page 51: ...ed by a null balance system where the displacement torque is opposed by an equal but opposite restorative torque The restorative torque is due to electromagnetic forces on the spheres resulting from a feedback current routed through a titanium wire conductor wound lengthwise around the dumbbell In effect each sphere is wound with a one turn circular loop The current required to restore the test bo...

Page 52: ...test body are the basis of the oxygen measurement it is worthwhile to consider the force acting on one of these spheres alone and to disregard for the present the remainder of the detector A small sphere suspended in a strong non uniform magnetic field Figure 5 1 is subjected to a force proportional to the difference between the magnetic susceptibility of this sphere and that of the surrounding ga...

Page 53: ...ckel Alloy Suspension Ribbon Balancing Weight Balancing Weight Nitrogen Filled Hollow Glass Test Body Mirror Titanium Wire Conductor TEST BODY DETAIL Electromagnetic Axis Electromagnetic Axis Restoring Current Restoring Current Displacement Torque Restoring Torque CONTROL ASSEMBLY DETECTOR MAGNET ASSEMBLY Test Body Shaded Pole Pieces 4 Source Lamp DS1 Restoring Current Span Zero Dual Photocell BT1...

Page 54: ...eated to approximately the same temperature as the detector assembly Detector Assembly Mounting Screws 2 Optical Bench Assembly Magnet Assembly Sample Outlet Tube Sample Inlet Tube Sample Pre Heating Coil Connector J12 Dual Photocell Connector J12 Lamp Retaining Set Screw Photocell Lock Screws 2 Source Lamp Assembly Lamp Viewing Hole Dual Photocell Integral Temperature Sensor RT1 Integral 5 Micron...

Page 55: ...bench assembly Figure 5 3C the source lamp and the photocell plate are externally accessible permitting convenient replacement 5 2 VARIABLES INFLUENCING PARAMAGNETIC OXYGEN MEASUREMENTS Variables that influence paramagnetic oxygen measurements include operating pressure Section 5 2 1 sample temperature Section 5 2 2 interfering sample components Section 5 2 3 and vibration 5 2 4 5 2 1 PRESSURE EFF...

Page 56: ...s required See Section 3 4 2 5 2 4 VIBRATION EFFECTS INSTRUMENT DESIGN To minimize vibration effects the detector magnet assembly is contained in a shock mounted compartment Figure 1 2 INSTALLATION Avoid excessive vibration In making electrical connections do not allow any cable to touch the shock mounted detector magnet assembly or the associated internal sample inlet and outlet tubing This preca...

Page 57: ...UITRY The Control Board contains signal conditioning and control circuitry The Control Board is mounted on the inside of the analyzer door see Figure 1 2 The Control Board contains the following INPUT AMPLIFIER U1 This amplifier receives the error signal from the dual photocell of the detector assembly and drives amplifier U2 AMPLIFIER U2 AND ASSOCIATED ZERO ADJUSTMENT Amplifier U2 supplies the re...

Page 58: ...nsation Circuit above AMPLIFIER U10 U10 is an non inverting buffer amplifier that incorporates an anticipation arrangement in its input network thus providing slightly faster response time 90 of fullscale on the readout device s Potentiometer R30 provides a continuously variable adjustment of 5 to 25 seconds for the electronic anticipation time and is factory set for 20 seconds Since the anticipat...

Page 59: ...oltage regulator circuit utilizing U7 Q4 and Q5 15V POWER SUPPLY This circuit provides DC voltages required for various amplifiers and other circuits Fullwave rectifier bridge CR5 provides both positive and negative outputs Each is routed through an associated series type integrated circuit voltage regulator providing regulated outputs of 15V and 15V DETECTOR TEMPERATURE CONTROL This circuit maint...

Page 60: ...he Control Board assembly See Figure 1 2 The current outputs available by this board are 0 to 20 mA or 4 to 20 mA 5 3 5 ALARM OPTION The alarm option provides two sets of relay contacts for actuation of customer supplied alarm and or process control device s The alarm relay assembly has two single pole double throw relays one each for the ALARM 1 and ALARM 2 contacts Alarm output connections are o...

Page 61: ... left hand corner of the Case Board 19VAC should be measured with respect to ground at CR5 WO4 15VDC should be measured at the C27 lead and 15VDC at the C28 lead If the specified voltage measurements are obtained the power supply is working correctly 6 3 CASE HEATER CONTROL CIRCUIT The case heater control circuit utilizes four voltage comparators LM339 quad com parator An understanding of how one ...

Page 62: ... the transistor or comparator output is at whatever potential is then present on the collector When the non inverting terminal of comparator 2 is less positive more negative than the inverting terminal the transistor conducts and the output of the comparator is 15V This value is the output of the OR circuit Comparator 2 is biased at 0 volts on the inverting terminal Comparator 1 is biased at about...

Page 63: ...again 15V The output remains at 15VDC until the incoming signal crosses zero value and the positive signal causes the comparator 2 transistor to cease to conduct Summing the effects of the two comparators in the OR circuit results in no output from the comparators for about 4 of the sinewave 2 after the signal goes positive 0 to 2 and 2 before the positive signal reaches 180 178 to 180 During the ...

Page 64: ...ross C37 will vary almost linearly with time and form a ramp signal of about 6 Hz As the potential across C37 increases and decreases linearly it affects the potential at the top of the bridge circuit between R82 and R83 through R74 Because of the ramp action charging and discharging C37 the potential between R82 and R83 varies approximately from 1 85V to 1 92VDC The temperature sensing device RT1...

Page 65: ...iation from the desired temperature and the ramp value at the function of R82 and R83 The input from the OR circuit comparator See Figure 6 1 is either 15VDC or the ramp effect on the bridge When 15V the junction of R82 and R83 is also this value The error signal into comparator 4 is negatively large to the inverting terminal Comparator 4 output transistor does not conduct The base of Q6 is positi...

Page 66: ...ly part of each ramp and the number of pulses operating Q7 will be proportional to the amount of error sensed by the 6 Hz ramp The pulses arrive at Q7 just as the supply AC line voltage is passing the zero volt crossover point The purpose of C36 Figures 6 2 6 4 is to delay the timing pulse relative to line frequency so that a pulse arrives at the gate of Triac Q7 as the line potential just passes ...

Page 67: ...y cold would be about 20VAC and when controlling would be AC of very low amplitude As the temperature increases the resistance of RT1 decreases and the junction point between RT1 and R59 becomes less positive Terminal 3 of AR6 becomes less positive with respect to terminal 2 The output of AR causes Q2 and Q3 to conduct less When terminal 3 equals terminal 2 or is less than terminal 2 the output of...

Page 68: ... output AR7 will increase causing Q4 to conduct more current through R66 As the potential across R66 increases Q5 will conduct more current causing a further increase in current flow through DS1 The net result is that the voltage across DS1 will remain uniform and the operation of Q4 and Q5 will adjust the gain of AR7 to maintain the light emission from DS1 uniform for a long period of time Voltag...

Page 69: ...c field of the test assembly has to be flowing through the feedback loop in order to maintain balance and provide a reading of the oxygen content of the sample Resistances R5 R17 and the resistance of the wire in the feedback loop determine the gain of amplifier AR2 The mirror on the dumbbell is positioned by the amount of current in the feedback loop The mirror reflects light from the source DS1 ...

Page 70: ...utput from amplifier U8 will remain constant regardless of pressure variations within the specified range PRESSURE SIGNAL CIRCUIT Refer to Figure 6 8 The pressure signal circuit consists of the pressure sensor transducer and two associated amplifiers The sensor provides a voltage output that is proportional to pressure This signal is ratioed and combined with the negative voltage reference so as t...

Page 71: ... LOOP U4 R16 R5 R17 C1 0022uF 30K R44 200K R9 20K R13 20K 15V 15V 15V 15V DETECTOR COARSE ZERO FRONT PANEL ZERO U2 U6 Vx Vz To Digital and Analog Circuits 10V PRESS SENSOR U7 10V CAL 1 CAL2 U9 R98 R99 To Test Switch To Analog Divider U6 Reference Voltages REFERENCE 10 00V Reference Voltage Circuit R19 TRIM U3 REFERENCE U5 10 00V FIGURE 6 7 DETECTOR WITH FIRST STAGE AMPLIFIER AND PRESSURE COMPENSAT...

Page 72: ...its Digital Output Circuit Section 6 8 Analog Output Circuits for Recorder and Alarms Section 6 9 FIGURE 6 9 BUFFER ANTICIPATION AND DIGITAL OUTPUT CIRCUIT 6 8 DIGITAL OUTPUT CIRCUIT Refer to Figure 6 10 With front panel TEST Switch in position 1 the output signal from buffer amplifier U10 is routed through an attenuator and filter network to an integrating analog to digital converter It converts ...

Page 73: ...ired zero suppression is obtained as the sum of a a jumper selectable fixed value of 0 20 40 or 80 oxygen and b a continuously adjustable value of 0 to 25 oxygen Thus the total zero suppression may be set for any desired valued from 0 to 105 oxygen In order to establish the precise zero suppression required for the recorder output the actual applied zero suppression may be read on the digital disp...

Page 74: ...he Zero Suppression Potentiometer is set for 10 oxygen SECOND STAGE AMPLIFIER This amplifier is an inverting configuration that provides a signal attenuation of 2X thus reducing the 10 volt fullscale input signal to obtain a 5 volt fullscale output This output is routed to Recorder Output Resistor Network It provides a jumper selectable output of 0 to 10 mV 0 to 100 mV 0 to 1V or 0 to 5VDC for a p...

Page 75: ...To Recorder U13 Front Panel TEST 100X 50X 20X 1X U16 5V 1uF 10X 5X 2M To Alarm and V I Amplifier Gain Jumper Selectable Recorder Output Jumper Selectable 20K R50A 20K 1M 200K 100K 20K 2 3 4 Recorder Zero Suppression Jumper Selectable Continuously Variable Recorder Zero Suppression 0 to 25 Oxygen REF REF 20K 75K 17 8K 25K 80 8 33K 60 25K 25K 25K 40 20 1V 100mV 10mV Resistor Values are in Ohms ...

Page 76: ...ELECTRONIC CIRCUIT ANALYSIS 6 16 April 2000 Rosemount Analytical 245364 U Model 755A Oxygen Analyzer NOTES ...

Page 77: ...n of components may adversely affect safety of this product Use only factory documented components for repair The information provided in this section will aid in isolation of a malfunction to a particular assembly or circuit No detailed procedures for component service and maintenance are provided as they are beyond the scope of this manual A few detailed checks are included but only for location...

Page 78: ... electronics Verification that all circuits are operating properly should be performed before replacing detector 7 2 DETECTOR COMPONENT CHECKS 7 2 1 DETECTOR Before concluding that the detector is defective and must be replaced verify that all components and circuits that could cause erratic readings are operating properly To isolate the detector as a source of a problem the source lamp photocells...

Page 79: ... clockwise as viewed from the top and to the right as viewed through the window Failure to rotate indicates that the suspension has been damaged and that the detector assembly must be replaced See Section 7 3 1 7 3 DETECTOR COMPONENT REPLACEMENT 7 3 1 DETECTOR REPLACEMENT Prior to removal of the detector remove power from instrument and stop flow of sample gas 1 Remove the four screws securing the...

Page 80: ...ution from the slider of Coarse Zero potentiometer R9 to chassis ground With a steady flow of 50 to 500 cc min of nitrogen gas passing through the instrument adjust Coarse Zero R9 for zero volts 11 Connect the voltmeter between TP10 and circuit ground Adjust front panel ZERO control R13 for reading of exactly zero on voltmeter With all internal adjustments now properly set the instrument may be ca...

Page 81: ...GRN 18 BLK BLK WHT WHT RT1 Suspension Terminals A Connections to Source Lamp and Photocell B Connections to Suspension and Heater Circuits C Removal and Insertion of Pin Leads in Connector J12 C1 R13 R9 U2 Voltmeter Lead FIGURE 7 2 DETECTOR MAGNET ASSEMBLY WIRING FIGURE 7 3 DETECTOR ADJUSTMENT 7 3 2 SOURCE LAMP REPLACEMENT 1 Remove the four screws securing the detector assembly cover plate 2 Refer...

Page 82: ...d to the old style lamp and the other lead into the position for the blue lead of the old lamp See Figure 7 2A 9 Insert the lamp into the assembly After reassembly and application of power the lamp will have to be rotated to place the lamp filaments in proper orientation If the lamp assembly removed from the instrument has two wires proceed to step 13 If the lamp assembly removed from the instrume...

Page 83: ...l from the optical bench perform steps 1 through 5 in Section 7 3 2 2 Install replacement photocell by reversing removal procedure 3 The photocell must now be adjusted With zero gas flowing a Place a digital voltmeter on the wiper of the front panel ZERO control R13 and ground TP7 ground on the Control Board Adjust front panel ZERO control for 0 0 VDC b Place the voltmeter from the bottom of R10 a...

Page 84: ...it receives power via thermal fuse F2 76 C This fuse located on the Case Board can be checked for continuity Case heater element HR3 located on the heater fan assembly has a normal resistance of 20 ohms To verify heater operation place a hand beside the right hand side of the detector housing Heated air should be felt If it is not check the case heating circuit Temperature sensor RT1 has a cold re...

Page 85: ...ot remove pin leads 14 and 15 from the connector to measure the resistance of HR2 alone This resistance should be approximately 89 ohms If resistance the resistance of HR2 is correct and yet the combined resistance is incorrect heater HR1 may be open To reach the leads of HR1 remove the printed circuit board on the heater assembly Resistance of HR1 should be approximately 21 ohms To check operatio...

Page 86: ...ROUTINE SERVICE AND MAINTENANCE 7 10 April 2000 Rosemount Analytical 245364 U Model 755A Oxygen Analyzer NOTES ...

Page 87: ...board than to attempt isolation and replacement of the individual component The cost of test and replacement will exceed the cost of a rebuilt assembly As standard policy rebuilt boards are available on an exchange basis Because of the exchange policy covering circuit boards the following list does not include individual circuit board mounted components If circumstances necessitate replacement of ...

Page 88: ...EPLACEMENT PARTS 8 2 April 2000 Rosemount Analytical 245364 U Model 755A Oxygen Analyzer 652225 Transducer Assembly 621023 Current Output Board 0 to 20mA 4 to 20mA 631773 Case Board 652220 Control Board ...

Page 89: ... to be used 4 Avoid dragging rolling or sliding cylinders even for a short distance they should be moved by using a suitable hand truck 5 Never tamper with safety devices in valves or cylinders 6 Do not store full and empty cylinders together Serious suckback can occur when an empty cylinder is attached to a pressurized system 7 No part of cylinder should be subjected to a temperature higher than ...

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Page 91: ... or from any other cause All other warranties expressed or implied are hereby excluded IN CONSIDERATION OF THE HEREIN STATED PURCHASE PRICE OF THE GOODS SELLER GRANTS ONLY THE ABOVE STATED EXPRESS WARRANTY NO OTHER WARRANTIES ARE GRANTED INCLUDING BUT NOT LIMITED TO EXPRESS AND IMPLIED WARRANTIES OR MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE Limitations of Remedy SELLER SHALL NOT BE LIAB...

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Page 93: ...r Please have the following information when you call Model Number Serial Number and Purchase Order Number or Sales Order Number Prior authorization by the factory must be obtained before returned materials will be accepted Unauthorized returns will be returned to the sender freight collect When returning any product or component that has been exposed to a toxic corrosive or other hazardous materi...

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Rosemount 755A, Instruction Manual

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