OHAUS Defender D30BR User manual

SERVICE MANUAL
Defender™ Bases
– Dry-use (B Series)
– Wet-use (V Series)
Ohaus Corporation, 7 Campus Drive, Suite 310, Parsippany, NJ 07054 [phone]

SERVICE MANUAL
Defender™Bases
– Dry-Use (B Series)
– Wet-Use (V 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 2011 Ohaus Corporation, all rights reserved.
TM Registered trademark of Ohaus Corporation.

TABLE OF CONTENTS
Page No.
CHAPTER 1 INTRODUCTION
1.1 Introduction................................................................................................................1-1
1.2 Service Facilities........................................................................................................1-1
1.3 Tools and Test Equipment Required.........................................................................1-2
1.4 Test Masses Required...............................................................................................1-2
1.5 Service Strategy ........................................................................................................1-2
1.6 Physical Description: Defender B & V Bases ............................................................1-2
1.7 Specifications.............................................................................................................1-3
1.8 How Load Cells Operate............................................................................................1-4
CHAPTER 2 TROUBLESHOOTING
2.1 Troubleshooting.........................................................................................................2-1
2.1.1 Checking Load Cells for Trouble........................................................................2-1
CHAPTER 3 MAINTENANCE AND REPAIR PROCEDURES
3.1 Preventive Maintenance............................................................................................3-1
3.1.1 Preventive Maintenance Checklist .....................................................................3-1
3.2 Replacing the Load Cell.............................................................................................3-1
3.3 Overload Stop Adjustments.......................................................................................3-2
CHAPTER 4 TESTING
4.1. Testing.......................................................................................................................4-1
4.2 Load Cell Resistance Checks....................................................................................4-1
4.3 Calibration with an External Indicator........................................................................4-1
4.4. Consistency Check....................................................................................................4-2
4.5 Performance Tests ....................................................................................................4-2
4.5.1 Off Center Load (Shift) Test ...............................................................................4-3
4.5.2 Adjusting Off Center Load..................................................................................4-4
4.5.3 Full Load Test.....................................................................................................4-5
CHAPTER 5 DRAWINGS AND PARTS LISTS
5-1 Defender B & V Bases: Housing & Internal Parts......................................................5-2
APPENDIX A: GLOSSARY
A-1 Glossary.................................................................................................................... A-1
LIST OF TABLES
1-1 Specifications for Defender B & V Bases..............................................................1-3
4-1 Load Cell Resistance Readings............................................................................4-1
4-2 Load Cell Output Readings...................................................................................4-2
5-1 Defender B & V Bases: Parts List .........................................................................5-3
(continued next page)
Ohaus Corporation www.ohaus.com i Defender™ B & V Series Service Manual

TABLE OF CONTENTS
Page No.
LIST OF ILLUSTRATIONS
1-1. Typical Strain Gauge Load Cell.............................................................................1-4
1-2 Downward force on the Platform bends the beam................................................1-4
1-3 Route of electrical Load Cell input and output.......................................................1-5
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
3-2 Overload Stops .....................................................................................................3-2
4-1 Positions A, B, C and D are Centered...................................................................4-3
4-2 Off Center Load adjustment points........................................................................4-4
5-1 Defender B & V Bases: Housing & Internal Parts .................................................5-2
Defender™ B & V Series Service Manual ii 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 B & V 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 Drawings and Parts Lists – Contains exploded views of the Defender 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 SERVICE FACILITIES
To service a Base, the service area should meet the following requirements:
•Clean and level surface.
•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.
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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, 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 B & V 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 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 factory
specifications.
1.6 PHYSICAL DESCRIPTION: DEFENDER B & V Series BASES
Construction Wet-use (V Series): Stainless steel Pan,
Stainless steel Frame and
IP67 Stainless steel Load Cell
Dry-use (B Series): Stainless Steel Pan with painted carbon
steel Frame and aluminum IP67 Load Cell
Overloading Corner Loading – 100% of Full Capacity
Safe Overload – 150% of Full Capacity
Ultimate Overload – 300% of Full Capacity
Operating Environment Designed 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™ B & V Series Service Manual

CHAPTER 1 INTRODUCTION
1.7 SPECIFICATIONS
Complete specifications for the Ohaus Defender B & V 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 B & V SERIES BASES
MODEL: B Series D30BR D60BR D60BL D150BL D150BX D300BX
Construction 304 stainless steel pan, painted carbon steel tubular frame,
non-slip rubber leveling feet
Load Cell Protection/
Accuracy Class IP67, aluminum, single point / C3
MODEL: V Series D30VR D60VR D60VL D150VL D150VX D300VX
Construction 304 stainless steel pan and frame, non-slip rubber leveling feet
Load Cell Protection/
Accuracy Class IP67, stainless steel, single point / C3
Capacity 30 kg 60 kg 60 kg 150 kg 150 kg 300 kg
Maximum Resolution 6000d 6000d 6000d 7500d 7500d 6000d
Safe Overload
Capacity 125% of capacity
Load Cell Rated
Output 2 mV/V ± 10%
Load Cell Excitation
Voltage 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
Shift Tolerance new ±1d
Shift Tolerance
Maint. ±2d
Base Dimensions 305 x 355 x 75 mm 420 x 550 x 80 mm 500 x 650 x 90 mm
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CHAPTER 1 INTRODUCTION
1.8 HOW LOAD CELLS OPERATE
Load Cells convert force into a signal. The Defender B-V Series 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
Beam
Figure 1-1. Typical Strain Gauge Load Cell.
Internal PCB
The strain gauges are wired into a Wheatstone Bridge Circuit. (See Figure 1-2.)
–
Strain Gauge
+
Strain Gauge
Force
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.
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.
1.8 HOW LOAD CELLS OPERATE
The difference in the output signal before and after the mass was placed on the platform is
measured, interpreted and displayed.
Ohaus Corporation www.ohaus.com 1-4 Defender™ B & V Series Service Manual