Product Service Manual - American Weigh Scales Inc
Contents
1. Figure 5 2 Defender Square Q amp W Bases Parts Ohaus Corporation www ohaus com 5 4 Defender H Q W Series Service Manual CHAPTER 5 PARTS LISTS amp DIAGRAMS 5 2 DEFENDER SQUARE Q amp W BASES PARTS TABLE 5 1 DEFENDER SQUARE Q amp W BASES PARTS Pan Defender H Q W Series Service Manual 5 5 Ohaus Corporation www ohaus com CHAPTER 5 PARTS LISTS amp DIAGRAMS Ohaus Corporation www ohaus com 5 6 Defender H Q W Series Service Manual APPENDIX A GLOSSARY APPENDIX A GLOSSARY Ohaus Load Cells contain a specification label on the Load Cell itself Compensated Temperature Range The range of temperatures over which the output from the cell is compensated If used outside this range the output cannot be guaranteed to follow the specifications Environmental Protection IP rating against moisture and dust for example IP 65 Excitation Voltage applied to the Exe and Exe leads of the load cell Input Resistance The resistance measured across Exe and Exe with load cell disconnected and no load Insulation Resistance Normally measured at 50 V dc this is the minimal resistance between the metal body of the load cell and any of its electrical connections Mechanical Failure The load at which the cell is likely to fail mechanically that is break or deform mV V Usually the output from a load cell will be approximately Om V at zero load though typically there may be a2. At zero load all strain gauges are unstressed Weight placed on the Platform bends the beam causing two gauges to stretch and two to compress in opposition changing the electrical resistance of the circuit Ohaus Corporation www ohaus com 1 6 Defender H Q W Series Service Manual CHAPTER 1 INTRODUCTION 1 8 HOW LOAD CELLS OPERATE The difference in the output signal before and after the mass was placed on the platform is taken interpreted and displayed Strain Gauges Excitation Tension Supply LOADCELL Ga INPUT volts pression Compression 4 strain gauges __ Excitation connected as a Supply Wheatstone Bridge i cig Figure 1 3 Route of electrical Load Cell input and output through Wheatstone Bridge circuit A Load Cell is a force sensor which receives a voltage excitation from a regulated power source in the Indicator and sends back a low voltage milli volt mV relative to the force applied The Load Cell signal is read by the Indicator which converts it to a numeric value and shows it visually This output value increases as weight is loaded to the Load Cell For example a 500kg Load Cell with 2mV V output and 5V excitation would have a change of 0 02mV per kg change in the load that is 10mV 500 0 02mV per kg At a load of 250kg the signal voltage would thus increase by 5mV from the value measured at no load Defender H Q W Series Service Manual 1 7 Ohaus Corporation w
3. Load Cell Rated Output 2 mV V 10 Load Cell Excitation Voltage Maximum 20V AC DC Recommended 5 15V AC DC Load Cell Input Output Resistance TABLE 1 2 SPECIFICATIONS FOR DEFENDER RECTANGULAR BASES Large Safe Overload Capacity 150 of capacity Load Cell Protection Accuracy Class IP67 single point C3 Load Cell Rated Output 2 mV V Load Cell Excitation Voltage Load Cell Input Output Resistance Operating Temperature 14 F to 104 F 10 C to 40 C Base Dimensions 15 7 19 7 in 40 50 cm 16 5 21 6 in 42 55cm Defender H Q W Series Service Manual 1 3 Ohaus Corporation www ohaus com Maximum 20V AC DC Recommended 5 15V AC DC 410 10 ohms 350 4 ohms CHAPTER 1 INTRODUCTION 1 7 SPECIFICATIONS TABLE 1 3 SPECIFICATIONS FOR DEFENDER SQUARE BASES Regular Capacity Load Cell Protection l Accuracy Class IP67 single point C3 Load Cell Rated Output 2 mV V Load Cell Excitation Voltage Maximum 20V AC DC Recommended 5 15V AC DC Load Cell Input Output Resistance 410 10 ohms 350 4 ohms Operating Temperature 14 F to 104 F 10 C to 40 C 18 18 in Base Dimensions 12 12 in 305 x 305 mm 457 x 457 mm TABLE 1 4 SPECIFICATIONS FOR DEFENDER SQUARE BASES Large Capacity Approved Resolution nmax 1 3000 1 5000 1 3000 1 5000 Safe Overload Capacity 150 of capacity Load Cell Protection Accuracy Class
4. NOTE In all cases where a part is replaced the base must be thoroughly checked after the replacement is made The base MUST meet the parameters of all applicable specifications in this manual further technical information is needed please contact your local Ohaus office or Ohaus Corporation www ohaus com 19A Chapin Road P O Box 2033 Pine Brook NJ 07058 2033 USA Tel 973 377 9000 Fax 973 593 0359 In the United States call toll free 800 526 0659 between 8 00 a m and 6 00 p m EST Defender H Q W Series Service Manual 5 1 Ohaus Corporation www ohaus com CHAPTER 5 PARTS LISTS amp DIAGRAMS 5 1 DEFENDER RECTANGULAR H BASES PARTS Had Q a 7 io 7 ee a 0 Figure 5 1 Defender Rectangular H Bases Parts Ohaus Corporation www ohaus com 5 2 Defender H Q W Series Service Manual CHAPTER 5 PARTS LISTS amp DIAGRAMS 5 1 DEFENDER RECTANGULAR H BASES PARTS TABLE 5 1 DEFENDER RECTANGULAR H BASES PARTS Pan When replacement parts are needed refer to the spare part list for the model you are servicing Parts lists are available from your local Ohaus office or visit Ohaus com Defender H Q W Series Service Manual 5 3 Ohaus Corporation www ohaus com CHAPTER 5 PARTS LISTS amp DIAGRAMS 5 2 DEFENDER SQUARE Q amp W BASES PARTS Oe O Q
5. SERVICE MANUAL Defender Bases Rectangular H Series Square Q Series Square Washdown W series Ohaus Corporation 19A Chapin Road P O Box 2033 Pine Brook NJ 07058 2033 973 377 9000 2 SERVICE MANUAL Defender Bases Rectangular H Series Square Q Series Square Washdown W series The information contained in this manual is believed to be accurate at the time of publication but Ohaus Corporation assumes no liability arising from the use or misuse of this material Reproduction of this material is strictly prohibited Material in this manual is subject to change Copyright 2008 Ohaus Corporation all rights reserved TM Registered trademark of Ohaus Corporation TABLE OF CONTENTS CHAPTER 1 INTRODUCTION CHAPTER 2 TROUBLESHOOTING 2 1 Troubleshooting CHAPTER 3 MAINTENANCE AND REPAIR PROCEDURES 3 1 Preventive Maintenance 3 1 1 Preventive Maintenance Checklist 3 2 Replacing the Load Cell 3 3 Overload Stop Adjustments CHAPTER 4 TESTING 4 1 Testing 4 2 Load Cell Resistance Checks 4 3 Calibration with an External Indicator 4 4 Consistency Check 4 5 Performance Tests 4 5 1 Off Center Load Shift Test 4 5 2 Adjusting Off Center Load 4 5 3 Full Load Test CHAPTER 5 DRAWINGS AND PARTS LISTS 5 1 Defender H Q W Bases APPENDIX A GLOSSARY A 1 Glossary LIST OF TABLES 1 1 Specifications for Defender Rectangular Bases 4600 8 1 2 Specifications for Defender
6. H Q W Series Service Manual CHAPTER 4 TESTING 4 1 TESTING Before and after servicing a Defender Base conduct Load Cell Resistance Checks Calibration using an external Indicator and Performance Tests to confirm that the base meets specifications Allow time for the base to stabilize after moving from an area which is at a different temperature than the area where it is to be operated Allow one hour for each 5 F 2 7 C temperature change before using the base The following tests require a Digital Multimeter an Indicator and hand tools The Digital DC Voltmeter should have a reading range from 1 mV to 50 V full scale It should be capable of reading differences of one micro volt per increment The indicator can be either the Ohaus Defender 5000 or an equivalent commercial indicator NOTE A N Make sure the test area is free from drafts and that the base rests on a level and vibration free surface 4 2 Load Cell Resistance Checks Use an ohm meter to measure across each pair of wires and compare the results with Table 4 1 The Load Cell must be completely disconnected from the Indicator and at no load when these tests are made Note The cable fitting for the H and Q series Bases has seven pins as shown in Figure 4 1 Pin 1 is EX Pin 3 is S Pin 5 is S Pin 7 is EX The wires are color coded on the W series The Load Cell label shows the wire color code for the Load Cell Figure 4 1 Resistance elements on
7. H and Q series Bases In addition to the four resistance elements which make up the Wheatstone Bridge there are commonly one or two resistors in the excitation lines The resistance across the excitation wires is usually the highest resistance measured across any two wires the resistance readings are in the range specified skip to the next section If they are incorrect for example outside the expected range open circuit or short circuit across any two wires the likely causes are a damaged or faulty Load Cell or incorrect or faulty wiring If the Load Cell is defective replace it See Chapter 3 TABLE 4 1 LOAD CELL RESISTANCE READINGS in Ohms Modes Ex ox 5 105 Erto S Defender H Q W Series Service Manual 4 1 Ohaus Corporation www ohaus com CHAPTER 4 TESTING 4 3 Calibration with an External Indicator 1 Install the Load Cell See Section 3 2 2 Connect the excitation signal shield and sensing wires if provided to the Indicator Calibrate the Indicator to read the load in the units required for example kilograms or grams Consult the Indicator instruction manual for calibration procedures For calibration mass weights see Table 1 1 in Chapter 1 3 Check that the Indicator is reading correctly over a range of values 4 4 Consistency Check To check the system prior to installation make the following measurements Also make these checks the Load Cell will not cal
8. Rectangular Bases Large 1 3 Specifications for Defender Square Bases Regular 1 4 Specifications for Defender Square Bases Large pp 1 5 Specifications for Defender Square Washdown Bases Regular 1 6 Specifications for Defender Square Washdown Bases Large 3 2 Overload Gap Settings For Defender H Q W BaseSs 4 1 Load Cell Resistance Readings pp 4 2 Load Cell Output Readings ee 5 1 Defender H Q W Bases Housing amp Internal 88 L2 SONICO FACIES eami ee er ee 1 3 Tools and Test Equipment Required pp 1 4 3 1 5 SENCE 1 6 Physical Description Defender H Q W Bases pp 127 een ee ern 1 8 OW LOG 0 2 1 1 Checking Load Cells for Trouble pp continued next page Ohaus Corporation www ohaus com i Defender H Q W Series Service Manual TABLE OF CONTENTS Page No LIST OF ILLUSTRATIONS 1 1 Typical Strain Gauge Load 1 4 1 2 Downward force on the Platform bends the beam pp 1 4 1 3 Route of electrical Load Cell input and output uusnnsseeennennen nennen nennen 1 5 2 1 REMOVING PlaStiG Shipping tabs ine sea Ba ees 2 1 3 1 Four Mounting Bolts that secure the Top Frame to the Load Cell 3 1 3 2 Four Mounting Bolts that secure the Bottom Frame to the Load Cell 3 2 3 3 OverloadGap SONG eNA 3 2 3 4 Location Of 10p Overload STOPS u hen 3 2 3 5 Lecationor Dotto Overload Sl6
9. Shift Test is made before and after a Base has had the Load Cell replaced and adjustments have been made that affect its performance The Shift Test verifies that all sections of the Base weigh within specified tolerance If the Base does not pass the Shift Test verify that the Overload Stops are properly set See Section 3 1 If the Shift Test cannot be passed the Load Cell must be replaced Prior to starting this test the Base must be connected to a properly functioning Indicator with capacity and readability values set according to the specifications for the Base under test 1 Place test weights equal to one third of the Base s capacity sequentially at each of the positions A B C and D as shown in Figure 4 1 Note the indicator reading at each position For Base capacity see Table 1 1 2 Check the variation between mass weights and indicator reading against specified Shift Tolerance in Table 1 1 Figure 4 2 Positions A B C and D are centered at each quarter of the base platform Ohaus Corporation www ohaus com 4 4 Defender H Q W Series Service Manual CHAPTER 4 TESTING 4 5 2 Adjusting Off Center Load the Off Center Load Shift is excessive perform adjustment as follows 1 Top view of Load Cell Side view of Load Cell Figure 4 3 Off Center Load adjustment points Place the test weight in the center of the Platform Tare the indicator Move the weight to point A and record the re
10. base 1 2 SERVICE FACILITIES To service a Base the service area should meet the following requirements e Clean and level surface e Away from magnetic fields such as motors or large transformers e Free of vibrations such as fork lift trucks close by large motors etc e Stable and level work surface e Not exposed to direct sunlight or radiating heat sources Defender H Q W Series Service Manual 1 1 Ohaus Corporation www ohaus com CHAPTER 1 INTRODUCTION 1 3 TOOLS AND TEST EQUIPMENT REQUIRED 1 Common hand tools 2 Standard electronics tool kit 3 Digital Voltmeter DVM capable of reading from 1 mv to 50 V dc 4 Megohmeter 50 Volt dc maximum test voltage 5 Desk magnifier on a stand 6 Ohaus Indicator Defender 3000 5000 7000 or equivalent commercial indicator 7 A calibrated Torque Wrench N m Ft Lbs 1 4 TEST MASSES REQUIRED The masses required to test the Ohaus Defender H Q W Series Bases when connected to an Indicator must meet the requirements of ASTM Class 4 or OIML F2 Mass values 3kg to 300kg depending on the Base model The full scale rated capacity of the Base should be used for Span calibration 1 5 SERVICE STRATEGY The Load Cells used in Ohaus Bases are non repairable The repair method for the Base is direct replacement of Load Cells with connecting cable and hardware Each base contains the following basic replaceable assemblies Platform Load Cell with Connecting Cable and Down Stop
11. small offset voltage at zero load Over the full rated capacity of the load cell the mV output will change The amount by which it changes depends upon the resistance change in the cell and on the excitation voltage applied Since the load cell manufacturer does not know what excitation voltage will be applied to the cell rather than quote the V output over full range they will quote the milli Volt output per volt of excitation or in its short form mv V Most Ohaus Indicators provide an excitation voltage of 5 Volts dc Output Resistance The resistance measured across S plus and S with load cell disconnected and no load Overload Capacity The maximum load that can be applied without permanent damage Loads in excess of maximum capacity will cause damage to the load cell Rated Capacity The maximum load over which the load cell will operate within its specifications Rated Output The nominal mV V output of the load cell Ultimate Capacity This is a percentage setting usually 300 of full capacity Zero Balance The output of the load cell at no load normally quoted as a percentage of full load Also known as zero offset Defender H Q W Series Service Manual A 1 Ohaus Corporation www ohaus com APPENDIX A GLOSSARY Ohaus Corporation www ohaus com A 2 Defender H Q W Series Service Manual x 8 0 25 2 5 9 6 P N 80252596 SERVICE MANUAL DEFENDER H Q W SERIES BASES
12. IP67 single point C3 Load Cell Rated Output 2 mV V 10 Load Cell Excitation Voltage Maximum 20V AC DC Recommended 5 15V AC DC Load Cell Input Output Resistance Operating Temperature 14 F to 104 F 10 C to 40 C 0 Shift Tolerance Maint Base Dimensions 18 18 in 457 457 mm 24 24 in 61 61cm 410 10 ohms 350 4 ohms Ohaus Corporation www ohaus com 1 4 Defender H Q W Series Service Manual CHAPTER 1 INTRODUCTION 1 7 SPECIFICATIONS TABLE 1 5 SPECIFICATIONS FOR DEFENDER SQUARE WASHDOWN BASES Regular Capacity Load Cell Protection l Accuracy Class IP67 single point C3 Load Cell Rated Output 2 mV V Load Cell Excitation Voltage Maximum 20V AC DC Recommended 5 15V AC DC Load Cell Input Output Resistance 410 10 ohms 350 4 ohms Operating Temperature 14 F to 104 F 10 C to 40 C 18 18 in Base Dimensions 12 12 in 305 x 305 mm 457 x 457 mm TABLE 1 6 SPECIFICATIONS FOR DEFENDER SQUARE WASHDOWN BASES Large Capacity Approved Resolution nmax 1 3000 1 5000 1 3000 1 5000 Safe Overload Capacity 150 of capacity Load Cell P rotection l Accuracy Class IP67 single point C3 Load Cell Rated Output 2 mV V 10 Load Cell Excitation Voltage Maximum 20V AC DC Recommended 5 15V AC DC Load Cell Input Output Resistance Operating Temperature 14 F to 104 F 10 C to 40 C 0 Shift Toleranc
13. ading Move the weight to point B and record the reading Move the weight to point C and record the reading Move the weight to point D and record the reading the reading at point A is negative file at points 1 and 4 AT AN ANGLE the reading at point B is negative file at points 1 and 2 STRAIGHT ACROSS O o Se eee 9 the reading at point C is negative file at points 2 and 3 AT AN ANGLE 10 If the reading at point is negative file at points 3 and 4 STRAIGHT ACROSS A N Note It is not recommended that you try to adjust more than 5 counts if the beam has been filed already If the beam has not been filed previously you can adjust 10 counts Remember when filing you are weakening the beam File a little at a time Defender H Q W Series Service Manual 4 5 Ohaus Corporation www ohaus com CHAPTER 4 TESTING 4 5 3 Full Load Test 1 After the Off Center Load Test has been passed test the Base s full capacity according to the Specification Tables 1 1 through 1 6 The Base must meet all specifications as listed 2 If the Base fails the Full Load Test check and set the Overload Stops See Section 3 3 Ohaus Corporation www ohaus com 4 6 Defender H Q W Series Service Manual CHAPTER 5 PARTS LISTS amp DIAGRAMS This section of the manual contains exploded views for the Defender H Q W Bases The exploded view drawings are designed to identify the parts which can be serviced in the field
14. and mounting hardware There is an exploded view drawing of the Base and associated parts list in Chapter 5 This service manual contains sufficient information to isolate the problem replace the component test and restore the Base to specifications 1 6 PHYSICAL DESCRIPTION DEFENDER BASES Construction H and Q Series General Purpose Bases Platform Stainless steel Frame Painted Carbon Steel Load Cell IP 67 Aluminum W series Washdown Bases Platform Fabricated stainless steel Scale Base Formed and welded stainless steel Load Cell IP 67 Stainless steel Overloading Corner Loading 100 of Full Capacity Safe Overload 150 of Full Capacity Ultimate Overload 300 of Full Capacity Operating Environment Designed to meet OIML 3000e and NTEP 5000d requirements to operate at a temperature range from 10 C to 40 C 14 F to 104 F 0 to 95 relative humidity Ohaus Corporation www ohaus com 1 2 Defender H Q W Series Service Manual CHAPTER 1 INTRODUCTION 1 7 SPECIFICATIONS Complete specifications for the Ohaus Defender H Q W Series Bases are listed in Tables 1 1 through 1 6 When a Base has been serviced it must meet the specifications listed in the table Before servicing the Base determine what specifications are not met TABLE 1 1 SPECIFICATIONS FOR DEFENDER RECTANGULAR BASES Regular Safe Overload Capacity 150 of capacity Load Cell Protection Accuracy Class IP67 single point C3
15. e Maint Base Dimensions 18 18 in 457 457 mm 24 24 in 61 61cm 410 10 ohms 350 4 ohms Defender H Q W Series Service Manual 1 5 Ohaus Corporation www ohaus com CHAPTER 1 INTRODUCTION 1 8 HOW LOAD CELLS OPERATE Load Cells are devices that convert force into a signal Defender Bases have a Strain Gauge Load Cell which is made from a metal beam with holes drilled in it Strain gauges are affixed to the beam at the top and bottom to measure changes in the beam due to deflection The gauges are bonded very securely to the metal where they sense very small deflections in the metal caused by the load being applied to the cell Because the signal levels are very small the circuit is protected from all outside influences such as moisture physical damage or electrical interference Attachment points to Platform Strain Gauges Printed Circuit Board completing Wheatstone Bridge circuit Holes drilled in Strain Gauge Load Cell Figure 1 1 Strain Gauge Load Cell The strain gauges are wired into a Wheatstone Bridge Circuit See Figure 1 2 Strain Gauge Strain Gauge Strain Gauge Strain Gauge Printed Circuit Board PCB completing Wheatstone Bridge circuit Wheatstone Bridge Circuit Figure 1 2 Downward force on the Platform bends the beam causing two gauges to stretch and two to compress in opposition changing the electrical resistance of the circuit
16. ell assembly can now be removed from the Lower Frame 5 Install the new Load Cell following steps 1 through 4 in reverse order Figure 3 2 Four Mounting Bolts that secure the Bottom Frame to the Load Cell 3 3 Overload Stop Adjustments The Overload Stop gaps must be checked and reset if the Load Cell is replaced 1 Remove the Platform and loosen the Jam Nuts first on the four Overload Stops on the top side of the Frame then on the bottom See Figures 3 3 3 4 and 3 5 2 Use the appropriate size feeler gauge in the Gap see Table 3 1 and turn the set screws until a slight drag is felt on the feeler gauge Set Screw Jam Nut Overload Stop Figure 3 3 Overload Gap Setting SS Figure 3 4 Location of top Overload Stops Ohaus Corporation www ohaus com 3 2 Defender H Q W Series Service Manual CHAPTER 3 MAINTENANCE AND REPAIR PROCEDURES 3 3 Overload Stop Adjustments 3 Tighten the Jam Nut and re check the Gap 4 Re adjust if necessary 5 Cover the Platform and check for full capacity See Table 3 1 for Gap settings Figure 3 5 Location of bottom Overload Stop TABLE 3 1 OVERLOAD GAP SETTINGS FOR DEFENDER H Q W BASES esi Tet Sop Comen Own Sp a S25 D100WL 4mm 0 157in D250WX 6mm 0 23in Defender H Q W Series Service Manual 3 3 Ohaus Corporation www ohaus com CHAPTER 3 MAINTENANCE AND REPAIR PROCEDURES Ohaus Corporation www ohaus com 3 4 Defender
17. ibrate or if the Indicator does not read correctly or is giving unstable readings 1 Using a voltmeter measure and record the excitation voltage supplied by the Indicator Most Ohaus indicators supply 5 volts dc for the excitation voltage 2 Using an mV meter measure and record the signal voltage with no load on the base CAUTION A N IN THE NEXT STEP DO NOT OVERLOAD THE BASE BEYOND FULL CAPACITY RATING 3 Using an mV meter measure and record the signal voltage at the loads shown in Table 4 2 4 Compare the measured output readings with the theoretical values from the Load Cell data See Table 4 2 Ohaus Corporation www ohaus com 4 2 Defender H Q W Series Service Manual CHAPTER 4 TESTING 4 4 Consistency Check TABLE 4 2 LOAD CELL OUTPUT READINGS in mV with 5V Excitation Defender H Q W Series Service Manual 4 3 Ohaus Corporation www ohaus com CHAPTER 4 TESTING 4 5 Performance Tests Accurate performance of the Defender Bases is determined by two tests Compare the displayed readings with the tolerances listed in the Specifications Tables in Chapter 1 NOTE The following performance tests are used to evaluate base operation before and A N after repairs The base must meet the requirements specified in each test as well as the specifications listed in Table 1 2 Before proceeding with the following tests the indicator should be calibrated See Section 4 3 4 5 1 Off Center Load Shift Test The
18. ps nanena ce tcc at saci te elects 3 3 4 1 Resistance elements on H and Q series Bases 4 4 1 4 2 Positions A B C and D are Centered pp 4 4 4 3 Off Center Load adjustment pointS 4 4 5 5 1 Defender H Q W Bases Housing amp Internal Parts pp 5 2 Defender H Q W Series Service Manual 1 Ohaus Corporation www ohaus com CHAPTER 1 INTRODUCTION 1 1 INTRODUCTION This service manual contains the information needed for diagnosis and repair of Ohaus Defender Square Rectangular and Square Washdown Bases the H Q W Series The contents of this manual are contained in five chapters Chapter 1 Introduction Contains information regarding service facilities tools and test equipment test masses specifications service strategy and the mechanical and electronic operation of the Base Chapter 2 Troubleshooting Provides guidelines for evaluating the condition and performance of a Base unit and a standard troubleshooting methodology to follow as well as a diagnostic guide Chapter 3 Maintenance Procedures Contains preventive maintenance procedures and disassembly repair and replacement procedures Chapter 4 Testing Contains guides for operational and performance tests and adjustments Chapter 5 Drawings and Parts Lists Contains exploded views of the Defender Bases and parts identifying all serviceable components Before servicing the Base you should be familiar with the Instruction Manual which is packed with every
19. r Check for a bent or twisted Load Cell Place the top surface and then each of the sides of the Load Cell on a flat surface to see if it rests flat and even A gap indicates a bent or twisted Load Cell Examine the Load Cell for corrosion due to high humidity or exposure to chemicals A Load Cell that is even slightly bent or corroded should be replaced 2 Perform a Resistance Test to determine if the Load Cell is severely damaged or a short circuit to the frame has occurred See Chapter 4 for details 3 Perform an Output Voltage Test Measure the no load 50 load and full load output The reading should meet the Load Cell specifications See Chapter 4 The Load Cell output should be very close to linear over its capacity range Defender H Q W Series Service Manual 21 Ohaus Corporation www ohaus com CHAPTER 2 DIAGNOSTIC GUIDE Ohaus Corporation www ohaus com 2 2 Defender H Q W Series Service Manual CHAPTER 3 MAINTENANCE AND REPAIR PROCEDURES 3 1 PREVENTIVE MAINTENANCE Ohaus bases should be carefully handled stored in a clean dry area and cleaned periodically Follow these precautionary steps When a base has had chemicals or liquids spilled on it all exterior surfaces should be cleaned as soon as possible with warm water on a damp cloth Do not leave a mass on the base when it is not in use Allow time for the base to stabilize after moving it from an area which is at a different temperature
20. than the area where it is to be operated Allow one hour for each 5 F 2 7 C temperature change before using the base 3 1 1 Preventive Maintenance Checklist The scale should be inspected and checked regularly as follows 1 Clean the base 2 Remove the Platform to inspect and clean the area beneath the Platform CAUTION A N DO NOT USE CHEMICAL CLEANERS OR SOLVENTS OF ANY TYPE SOME CLEANERS ARE ABRASIVE AND MAY AFFECT THE BASE S FINISH 3 Check the Load Cell cable for broken or damaged insulation 4 Make a visual inspection as detailed in Chapter 2 3 2 Replacing the Load Cell A Load Cell that is even slightly bent or corroded should be replaced The Load Cell may also need to be replaced because of instability or because the scale does not calibrate or repeat or because it is physically broken 1 Remove the scale Platform and disconnect the Base from the Indicator d DZ Er AD etendi Sue _ 2 Remove the four Load Cell Mounting Bolts and washers that secure the Top Frame to the Load Cell 3 Set the Top Frame and the Load Cell Spacer aside 5 Basal Dr A L Figure 3 1 Four Mounting Bolts that secure the Top Frame to the Load Cell Defender H Q W Series Service Manual 3 1 Ohaus Corporation www ohaus com CHAPTER 3 MAINTENANCE AND REPAIR PROCEDURES 3 2 Replacing the Load Cell 4 Remove the bottom Load Cell Mounting Bolts washers and spacer The Load C
21. ww ohaus com CHAPTER 1 INTRODUCTION Ohaus Corporation www ohaus com 1 8 Defender H Q W Series Service Manual CHAPTER 2 DIAGNOSTIC GUIDE 2 1 TROUBLESHOOTING This section of the manual provides guidelines for evaluating the condition and performance of a scale Base and a standard troubleshooting methodology to follow 2 1 1 Checking Load Cells for Trouble 1 Visual Check Remove the plastic shipping tabs from between the upper and lower Housings if present Clean the unit before evaluating any mechanical problems In some cases debris may have accumulated inside the Base Housing Make sure there is no buildup of any foreign material Figure 2 1 Removing plastic shipping tabs Examine the Base Housing for dents bent Platform or signs of physical abuse that could cause the Base to malfunction Make sure that the proper Platform is supplied with the Base Replace all damaged parts See Chapter 5 for parts identification Remove the Platform from the Base Check that the Overload Stops are not touching the Top Plate See Figure 5 1 Chapter 5 This would restrict movement causing improper operation of the Base If the Overload Stops are improperly set adjust them See Section 3 3 Check the metal surfaces of the Platform All surfaces should be parallel the platform is deformed it should be replaced Check the cables leading to the Load Cell for cuts abrasions or other signs of excessive wear and tea
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