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

10 Defender™Series Bases Service Manual
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.
1.11 Load Cell Connection
Type1. DxxxWxx Bases
FUNCTION
WIRE COLOR
+ Excitation
Green
- Excitation
Black
+ Signal
Red
- Signal
White
+ Sense
Blue
- Sense
Brown
Shield
Yellow
Tension
Tension
Compression
Compression
+Excitation
(Supply)
–Excitation
(Supply)
INPUT(volts)
LOADCELL
2 mV/V
Strain
Gauges
4 strain gauges
connected as a
Wheatstone
Bridge
OUTPUT (milli volts)
+Sig
–Sig

11 Defender™Series Bases Service Manual
Type2. DxxxRxx Bases
FUNCTION
WIRE COLOR
+ Excitation
Green
- Excitation
Black
+ Signal
White
- Signal
Red
+ Sense
Blue
- Sense
Brown
Shield
Yellow

12 Defender™Series Bases Service Manual
CHAPTER 2 TROUBLESHOOTING
2.1 Troubleshooting
This section of the manual provides guidelines for evaluating the condition and performance of a Base unit,
and a standard troubleshooting methodology to follow.
2.1.1 Checking Load Cells for Trouble
Visual Check: Examine the Load Cell for signs of bending, twisting or corrosion.
–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.
–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 list.
–Remove the Platform from the Base. Check that the Overload Stops are not touching the Top
Plate. 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.
If 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 tear.
–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.
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.)
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.

13 Defender™Series Bases 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 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
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.
2. Remove the 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.
4. Remove the bottom Load Cell Mounting Bolts, washers and spacer. The Load Cell assembly
can now be removed from the Lower Frame.
5. Install the new Load Cell following steps 1 through 4 in reverse order.

14 Defender™Series Bases Service Manual
3.3 Overload Stop Adjustment
The Overload Stop gaps must be checked and reset if the Load Cell is replaced.
Figure 3-1. Overload Stops on Defender series Base
1. Remove the Platform and loosen the Jam Nuts.
2. Use the appropriate size feeler gauge in the Gap (see Table 3-1), and turn the screws until a
slight drag is felt on the feeler gauge.
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.)
TABLE 3-1. OVERLOAD GAP SETTINGS FOR DEFENDER SERIES BASES
Base Model
Pan size
Overload Stop
Center (mm)
Overload
Stop Corner
(mm)
Shipping
Spacer
D2WQS
254 x 254
10" x 10"
0.8
2
Y
D5WQS
1.5
2
Y
D12WQS
2.5
3.5
Y
D6RQDR
305 x 305
12'' x 12''
0.8
1
N
D12RQR
1
1
N
D15RQDR
1.2
1.5
N
D25RQR
1
2
Y
D30RQR
1.5
2
Y
D50RQR
2.5
3.5
Y
D6WQDR
1
1.5
N
D12WQR
0.8
1.5
N
D15WQDR
0.6
2.5
Y
D15WQR
0.6
2.5
Y
D25WQR
0.8
2
Y
D30WQR
1
2
Y
D50WQR
1
3.5
Y
D12RTR
305 x 355
12'' x 14'
1
1.5
N
D25RTR
1.5
2
Y
D60RTR
2.5
3.5
Y
D50RTR
2.5
3.5
N

15 Defender™Series Bases Service Manual
D15RTDR
1.2
1.5
N
D30RTDR
1.5
2
N
D15RQDL
400 x 400
15.7" x 15.7"
1.5
2.5
Y
D30RQDL
1.5
3.5
Y
D60RQDL
2
5
Y
D15WQDL
0.6
3.5
Y
D15WQL
0.6
3.5
Y
D30WQDL
0.8
3.5
Y
D30WQL
0.8
3.5
Y
D60WQDL
2
6
Y
D60WQL
0.9
6
Y
D50RQL
457 x 457
18" x 18"
1
3.5
Y
D125RQL
2
6
Y
D25WQL
1
2
Y
D50WQL
1
3.5
Y
D125WQL
1.5
6
Y
D60RTDL
400 x 500
15.7" x 19.6"
1
1.5
N
D150RTDL
1.5
2.5
Y
D60WTDL
1
3.5
Y
D150WTDL
1.5
6
Y
D60RTL
1
1.5
N
D150RTL
1.5
2.5
Y
D60WTL
1
3.5
Y
D150WTL
1.5
6
Y
D50RTX
457 x 610
18" x 24"
0.8
1.5
N
D125RTX
1.2
2.5
Y
D250RTX
1.5
3.5
Y
D50WTX
0.8
3.5
Y
D125WTX
1
6
Y
D250WTX
1.5
9
N
D60RQDX
500 x500
19.6" x 19.6"
1
2
Y
D150RQDX
0.9
5
Y
D60WQDX
0.6
5
Y
D60WQX
0.8
5
Y
D150WQDX
0.8
6
Y
D150WQX
0.9
6
Y
D50RQV
610 x 610
24" x 24"
0.8
1.5
N
D60RQDV
0.6
1.5
N
D125RQV
1
2.5
Y
D150RQDV
1
3.5
Y
D250RQV
1.2
3.5
N
D300RQDV
1.4
5
N
D500RQV
1.8
6
N
D60WQDV
0.8
2
Y
D60WQV
0.5
2
Y
D150WQDV
0.7
5
Y
D150WQV
0.6
5
Y
D300WQDV
1
7
N
D50WQV
0.8
2
Y
D125WQV
1
5
Y
D250WQV
1.2
6
N
D500WQV
1.5
12
N

16 Defender™Series Bases Service Manual
D125RTV
600 x 800
23.6" x 31.5"
1.2
3.5
N
D150RTDV
0.9
3.5
N
D250RTV
1.8
5
N
D300RTDV
1.2
6
N
D500RTV
2.2
9
N
D600RTDV
2.2
8
N
D150WTDV
1
6
Y
D300WTDV
1.2
9
N
D600WTDV
1.5
12
N

17 Defender™Series Bases Service Manual
CHAPTER 4 TESTING
4.1 Testing
Before and after servicing a Defender series 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 it 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 3000 series, or an equivalent commercial indicator.
ARTTENTION: 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 in turn, 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.
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.
If 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)
Models
Ex+ to Ex–
S+ to S–
Ex+ to S–
Ex+ to S+
Ex–to S+
Ex–to S–
All Defender series
Bases
410 ±15
350 ±5
322.5 ±15
322.5 ±15
262.5 ±15
262.5 ±15
4.3 Calibration with an External Indicator
1. Install the Load Cell in position. (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.

18 Defender™Series Bases Service Manual
4.4 Consistency Check
To check the system prior to installation, make the following measurements. (Also make these checks if the
Indicator will not calibrate, 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:
IN THE NEXT STEP, DO NOT OVERLOAD THE BASE BEYOND FULL CAPACITY RATING.
3. Using an mV meter, measure and record the signal voltage.
4. Obtain the mV/V output figure from the Load Cell data supplied with the Load Cell, and
compare the signal changes seen with the theoretical values from the Load Cell data. (See
Table 4-2.)
TABLE 4-2. LOAD CELL OUTPUT READINGS
(in mV with 5V Excitation)
Zero Load
50% Load
100% Load
±0.1mv
4-6mv
9-11mv
4.5 Performance Tests
Accurate performance of the Defender series Bases is determined by two performance tests. The displayed
readings are compared with the tolerances listed in Table 1-1.
NOTE:
The following performance tests are used to evaluate base operation before and 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 base should be attached to an
indicator and calibrated.
(See Section 4.3.)

19 Defender™Series Bases Service Manual
4.5.1 Off Center Load (Shift) Test
The Off Center Load (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 Off Center Load Test verifies that all sections of
the Base weigh within specified tolerance.
If the Base does not pass the Off Center Load Test, verify that the Overload Stops are properly set. (See
Section 3.1.)
If the Off Center Load Test cannot be passed, the Load Cell must be adjusted or 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.
5. 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.)
6. Check the variation between mass weights and indicator reading against specified Shift
Tolerance in Table 1-1.
Figure 4-1. Positions A, B, C and D are centered
at each quarter of the base platform.
A
B
C
D