TABLE OF CONTENTS
CHAPTER 1 INTRODUCTION ............................................................................................................................ 2
1.1 Introduction ............................................................................................................................................ 2
1.2 Definition of Signal Warning and Symbols ............................................................................................ 2
1.3 Safety Precaution .................................................................................................................................. 3
1.4 Service Facilities ................................................................................................................................... 3
1.5 Tools and Test Equipment Required ..................................................................................................... 4
1.6 Test Masses Required .......................................................................................................................... 4
1.7 Service Strategy .................................................................................................................................... 4
1.8 Physical Description: Model Defender Series Base .............................................................................. 4
1.9 Specifications ........................................................................................................................................ 5
1.10 How Load Cells Operate ....................................................................................................................... 9
1.11 Load Cell Connection .......................................................................................................................... 10
CHAPTER 2 TROUBLESHOOTING .................................................................................................................. 12
2.1 Troubleshooting ................................................................................................................................... 12
2.1.1 Checking Load Cells for Trouble ..................................................................................................... 12
CHAPTER 3 MAINTENANCE AND REPAIR PROCEDURES .......................................................................... 13
3.1 Preventive Maintenance ...................................................................................................................... 13
3.1.1 Preventive Maintenance Checklist .............................................................................................. 13
3.2 Replacing the Load Cell ...................................................................................................................... 13
3.3 Overload Stop Adjustment .................................................................................................................. 14
CHAPTER 4 TESTING ...................................................................................................................................... 17
4.1 Testing ................................................................................................................................................. 17
4.2 Load Cell Resistance Checks ............................................................................................................. 17
4.3 Calibration with an External Indicator .................................................................................................. 17
4.4 Consistency Check .............................................................................................................................. 18
4.5 Performance Tests .............................................................................................................................. 18
4.5.1 Off Center Load (Shift) Test ............................................................................................................ 19
4.5.2 Adjusting Off Center Load ............................................................................................................... 20
4.5.3 Full Load Test .................................................................................................................................. 21
CHAPTER 5 PARTS IDENTOFICATION ........................................................................................................... 22
5.1 Defender series Base: Carbon Steel model ........................................................................................ 22
5.2 Defender series Base: Stainless Steel model ..................................................................................... 24
APPENDIX A. GLOSSARY ................................................................................................................................ 26
Ohaus Corporation www.ohaus.com i Defender™ Series Bases Service Manual
CHAPTER 1 INTRODUCTION
1.1 Introduction
This service manual contains the information needed for diagnosis and repair of Ohaus Defender series Bases.
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 Parts Identification – Contains exploded views of Defender series Bases and parts, identifying all
serviceable components with parts lists.
Before servicing the Base, you should be familiar with the Instruction Manual which is packed with every base.
1.2 Definition of Signal Warning and Symbols
Safety notes are marked with signal words and warning symbols. These show safety issues and warnings.
Ignoring the safety notes may lead to personal injury, damage to the instrument, malfunctions and false results.
Signal Words
WARNING For a hazardous situation with medium risk, possibly resulting in injuries or death if not
avoided.
CAUTION For a hazardous situation with low risk, resulting in damage to the device or the property or in
loss of data, or injuries if not avoided.
Attention For important information about the product.
Note For useful information about the product.
Warning Symbols
General Hazard Electrostatic discharge sensitive
Electric Shock Hazard
Ohaus Corporation www.ohaus.com 2 Defender™ Series Bases Service Manual
1.3 Safety Precaution
For AC mains powered models:
- Verify that the local AC power supply is within the input voltage range printed on the equipment’s data
label. - Only connect the AC power cord to a compatible grounded electrical outlet.
For AC adapter powered models:
- Verify that the local AC power supply is within the input voltage range printed on the AC adapter’s
data label. - Only connect the AC adapter to a compatible grounded electrical outlet.
Do not position the scale such that it is difficult to disconnect the power cord from the power
receptacle.
This equipment is intended for indoor use and should only be operated in dry locations.
Operate the equipment only under ambient conditions specified in the user instructions.
Do not operate the equipment in hazardous or unstable environments.
Disconnect power from the equipment before cleaning or servicing the equipment.
Service should only be performed by authorized personnel.
Use electrostatic protection measures when handling the printed circuit board.
Only use original replacement parts and accessories.
1.4 Service Facilities
To service a scale Base, the service area should meet the following requirements:
Clean and level environment.
Away from magnetic fields such as motors or large transformers.
Free of vibrations such as fork lift trucks close by, large motors, etc.
Stable and level work surface.
Not exposed to direct sunlight or radiating heat sources.
Ohaus Corporation www.ohaus.com 3 Defender™ Series Bases Service Manual
1.5 Tools and Test Equipment Required
Platform – Stainless Steel
Scale Base – Carbon Steel or Stainless steel
Load Cell – Aluminum
Corner Loading –1/2 to 2/3 of Full Capacity
Safe Overload – 150% of Full Capacity
Ultimate Overload – 300% of Full Capacity
Ambient temperature: -10º C to +40º C
Relative humidity: up to 80% at 31º C, decreasing linearity to 50% at
40º C
Height above sea level: Up to 2,000m
Operability is assured at ambient temperature -10º C to + 40º C
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 5000, or equivalent commercial indicator
7. A calibrated Torque Wrench N.m. – Ft/Lbs
1.6 Test Masses Required
The masses required to test the Ohaus Defender series Bases when connected to an Indicator must meet the
requirements of ASTM Class or OIML. Mass values 3kg to 600kg, depending on the Base model. The full
scale rated capacity of the Base should be used for Span calibration.
1.7 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.
The Defender series Base contains the following basic replaceable assemblies: Platform, Load Cell with
Connecting Cable, and Down Stop 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 its original factory specifications.
1.8 Physical Description: Model Defender Series Base
Ohaus Corporation www.ohaus.com 4 Defender™ Series Bases Service Manual
1.9 Specifications
NTEP and Measurement Canada 5000e
Stainless Steel platform with painted steel frame and rubber leveling feet
350 Ohm, aluminum, single point
Complete specifications for the Ohaus Defender series Bases are listed in Table 1-1. 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 SERIES BASES
Ohaus Corporation www.ohaus.com 5 Defender™ Series Bases Service Manual
NTEP and Measurement Canada 5000e
600 x 800 mm
24 x 31.5 in
Stainless Steel platform with painted steel frame and rubber leveling feet
350 Ohm, aluminum, single point
Ohaus Corporation www.ohaus.com 6 Defender™ Series Bases Service Manual
NTEP and Measurement Canada 5000e
Stainless Steel platform with stainless steel frame and rubber leveling feet
350 Ohm, stainless steel, single point
Ohaus Corporation www.ohaus.com 7 Defender™ Series Bases Service Manual
NTEP and Measurement Canada 5000e
Stainless Steel platform with stainless steel frame and rubber leveling feet
350 Ohm, stainless steel, single point
Ohaus Corporation www.ohaus.com 8 Defender™ Series Bases Service Manual