OHAUS DEFENDER SERIES User manual

DefenderSeries Base
Service Manual
99 Washington Street
Melrose, MA 02176
Phone [phone]
Toll Free 1-800-517-8431
Visit us at www.TestEquipmentDepot.com

i Defender™Series Bases Service Manual
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

2 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

3 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.

4 Defender™Series Bases Service Manual
1.5 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 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
Construction
Platform –Stainless Steel
Scale Base –Carbon Steel or Stainless steel
Load Cell –Aluminum
Overloading
Corner Loading –1/2 to 2/3 of Full Capacity
Safe Overload –150% of Full Capacity
Ultimate Overload –300% of Full Capacity
Operating Environment
Ambient temperature: -10ºC to +40ºC
Relative humidity: up to 80% at 31ºC, decreasing linearity to 50% at
40ºC
Height above sea level: Up to 2,000m
Operability is assured at ambient temperature -10ºC to + 40ºC

5 Defender™Series Bases Service Manual
1.9 Specifications
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
MODEL
D12RQR
D25RQR
D50RQR
D12RTR
D25RTR
D50RTR
D50RQL
D125RQL
Capacity
25 lb /
12.5 kg
50 lb /
25 kg
100 lb /
50 kg
25 lb /
12.5 kg
50 lb /
25 kg
100 lb /
50 kg
100 lb /
50 kg
250 lb /
125 kg
Approved Resolution
NTEP and Measurement Canada 5000e
Safe Overload
Capacity
150% of capacity
Pan Dimensions
305 x 305 mm
12 x 12 in
305 x 355 mm
12 x 14 in
457 x 457 mm
18 x 18 in
Base Construction
Stainless Steel platform with painted steel frame and rubber leveling feet
Load Cell Capacity
22 kg
50 kg
100 kg
22 kg
50 kg
100 kg
100 kg
200 kg
Load Cell Cable
2 m L x 6-wire
Load Cell Type
350 Ohm, aluminum, single point
Load Cell Excitation
5-15V DC/AC
Load Cell Rated
Output
2mV/V
Load Cell Protection
IP67
Net Weight
6.kg / 13.2 lb
7 kg / 15.4 lb
11.5 kg / 25.4 lb
Shipping Weight
7 kg / 15.4 lb
8 kg / 17.6 lb
13.5 kg / 29.8 lb

6 Defender™Series Bases Service Manual
MODEL
D50RTX
D125RTX
D250RTX
D50RQV
D125RQV
D250RQV
D500RQV
D125RTV
D250RTV
D500RTV
Capacity
100 lb /
50kg
250 lb /
125 kg
500 lb /
250 kg
100 lb /
50 kg
250 lb /
125 kg
500 lb /
250 kg
1000 lb /
500 kg
250 lb /
125 kg
500 lb /
250 kg
1000 lb /
500 kg
Approved
Resolution
NTEP and Measurement Canada 5000e
Safe
Overload
Capacity
150% of capacity
Pan
Dimension
s
457 x 610 mm
18 x 24 in
610 x 610 mm
24 x 24 in
600 x 800 mm
24 x 31.5 in
Base
Constructi
on
Stainless Steel platform with painted steel frame and rubber leveling feet
Load Cell
Capacity
100 kg
250 kg
500 kg
100 kg
250 kg
500 kg
750 kg
250 kg
500 kg
750 kg
Load Cell
Cable
2 m L x 6-wire
Load Cell
Type
350 Ohm, aluminum, single point
Load Cell
Excitation
5-15V DC/AC
Load Cell
Rated
Output
2mV/V
Load Cell
Protection
IP67
Net
Weight
21.5 kg / 47.4 lb
31 kg / 68.3 lb
39.2 kg / 86.4 lb
Shipping
Weight
24 kg / 52.9 lb
34 kg / 75.0 lb
42.7 kg / 94.1 lb

7 Defender™Series Bases Service Manual
MODEL
D2WQS
D5WQS
D12WQS
D12WQR
D25WQR
D50WQR
D25WQL
D50WQL
D125WQL
Capacity
5 lb /
2.5 kg
10 lb /
5 kg
25 lb /
12.5 kg
25 lb /
12.5 kg
50 lb /
25 kg
100 lb /
50 kg
50 lb /
25 kg
100 lb /
50 kg
250 lb /
125 kg
Approved
Resolution
NTEP and Measurement Canada 5000e
Safe
Overload
Capacity
150% of capacity
Pan
Dimensions
254 x 254 mm
10 x 10 mm
305 x 305 mm
12 x 12 in
457 x 457 mm
18 x 18 in
Base
Construction
Stainless Steel platform with stainless steel frame and rubber leveling feet
Load Cell
Capacity
6 kg
10 kg
30 kg
30 kg
50 kg
100 kg
50 kg
100 kg
200 kg
Load Cell
Cable
1 m L x 4-wire
2 m L x 6-wire
2.5 m L x 6-wire
Load Cell
Type
350 Ohm, stainless steel, single point
Load Cell
Excitation
5-15V DC/AC
Load Cell
Rated
Output
2mV/V
Load Cell
Protection
IP67
Net Weight
4.5 kg / 9.9 lb
6 kg / 13.2 lb
12.5 kg / 27.6 lb
Shipping
Weight
6 kg / 13.2 lb
7 kg / 15.4 lb
14 kg / 30.9 lb

8 Defender™Series Bases Service Manual
MODEL
D50WTX
D125WTX
D250WTX
D50WQV
D125WQV
D250WQV
D500WQV
Capacity
100 lb /
50 kg
250 lb /
125 kg
500 lb /
250 kg
100 lb /
50 kg
250 lb /
125 kg
500 lb /
250 kg
1000 lb /
500 kg
Approved Resolution
NTEP and Measurement Canada 5000e
Safe Overload Capacity
150% of capacity
Pan Dimensions
457 x 610 mm
18 x 24 in
610 x 610 mm
24 x 24 in
Base Construction
Stainless Steel platform with stainless steel frame and rubber leveling feet
Load Cell Capacity
150 kg
300 kg
500 kg
150 kg
300 kg
500 kg
750 kg
Load Cell Cable
2 m L x 6-
wire
2.5 m L x 6-wire
2 m L x 6-
wire
2.5 m L x 6-wire
Load Cell Type
350 Ohm, stainless steel, single point
Load Cell Excitation
5-15V DC/AC
Load Cell Rated Output
2mV/V
Load Cell Protection
IP67
Net Weight
24 kg / 52.9 lb
31.5 kg / 69.4 lb
Shipping Weight
26 kg / 573 lb
35.5 kg / 78.3 lb

9 Defender™Series Bases Service Manual
1.10 How Load Cells Operate
Load Cells convert force into a signal. The Defender 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.
Figure 1-1. Typical Strain Gauge Load Cell.
The strain gauges are wired into a Wheatstone Bridge Circuit. (See Figure 1-2.)
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.
The difference in the output signal before and after the mass was placed on the platform is measured,
interpreted and displayed.
Force
Wheatstone Bridge Circuit
Strain Gauge
+
+
Strain Gauge
–
Strain Gauge
Strain Gauge
–
Printed Circuit Board (PCB )
completing Wheatstone
Bridge circuit
Strain Gauges
Internal PCB
Beam
Attachment
points to
Platform