OHAUS Defender D15HR User manual

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 [phone]

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 Page No.
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 H-Q-W Bases ..........................................................1-2
1.7 Specifications.............................................................................................................1-3
1.8 How Load Cells Operate............................................................................................1-6
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 H-Q-W Bases.............................................................................................5-2
APPENDIX A: GLOSSARY
A-1 Glossary.................................................................................................................... A-1
LIST OF TABLES
1-1 Specifications for Defender Rectangular Bases (Regular)....................................1-3
1-2 Specifications for Defender Rectangular Bases (Large).......................................1-3
1-3 Specifications for Defender Square Bases (Regular)............................................1-4
1-4 Specifications for Defender Square Bases (Large)...............................................1-4
1-5 Specifications for Defender Square Washdown Bases (Regular).........................1-5
1-6 Specifications for Defender Square Washdown Bases (Large)............................1-5
3-2. Overload Gap Settings For Defender H-Q-W Bases.............................................3-3
4-1 Load Cell Resistance Readings............................................................................4-1
4-2 Load Cell Output Readings...................................................................................4-3
5-1 Defender H-Q-W Bases: Housing & Internal Parts ...............................................5-3
(continued next page)
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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
2-1 Removing plastic shipping tabs.............................................................................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 Overload Gap Setting............................................................................................3-2
3-4 Location of top Overload Stops.............................................................................3-2
3-5 Location of bottom Overload Stops.......................................................................3-3
4-1 Resistance elements on H and Q series Bases....................................................4-1
4-2 Positions A, B, C and D are Centered...................................................................4-4
4-3 Off Center Load adjustment points........................................................................4-5
5-1 Defender H-Q-W Bases: Housing & Internal Parts ...............................................5-2
Defender™ H-Q-W 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 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 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, 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 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
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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)
MODEL: H Series D15HR D30HR D60HR
Capacity 15 kg / 30 lb 30 kg / 60 lb 60 kg / 150 lb
Standard Resolution 1:15000 1:15000 1:12000
Approved Resolution (nmax) 1:3000 1:3000 1:3000
Safe Overload Capacity 150% of capacity
Load Cell Protection/ 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 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 12 x 14 in. / 30.5 x 35.5 cm
TABLE 1-2. SPECIFICATIONS FOR DEFENDER RECTANGULAR BASES (Large)
MODEL: H Series D60HL D100HL D150HX D300HX
Capacity 60 kg / 150 lb 100 kg / 250 lb 150 kg / 300 lb 300 kg / 600 lb
Standard Resolution 1:12000 1:10000 1:15000 1:15000
Approved Resolution (nmax) 1:3000 1:3000 1:3000 1:3000
Safe Overload Capacity 150% of capacity
Load Cell Protection/
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 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 15.7 x 19.7 in. / 40 x 50 cm 16.5 x 21.6 in. / 42 x 55 cm
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CHAPTER 1 INTRODUCTION
1.7 SPECIFICATIONS
TABLE 1-3. SPECIFICATIONS FOR DEFENDER SQUARE BASES (Regular)
MODEL: Q Series D10QR D15QR D25QR D30QR D50QR
Capacity 10 kg / 25 lb 15 kg / 30 lb 25 kg / 50 lb 30 kg / 60 lb 50 kg / 100 lb
Standard Resolution 1:10000 1:15000 1:12500 1:15000 1:10000
Approved Resolution (nmax) 1:5000 1:3000 1:5000 1:3000 1:5000
Safe Overload Capacity 150% of capacity
Load Cell Protection/
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 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 12 x 12 in. / 305 x 305 mm 18 x 18 in. /
457 x 457 mm
TABLE 1-4. SPECIFICATIONS FOR DEFENDER SQUARE BASES (Large)
MODEL: Q Series D60QL D100QL D150QL D250QX D300QX
Capacity 60 kg / 150 lb 100 kg / 250 lb 150 kg / 300 lb 250 kg / 500 lb 300 kg / 600 lb
Standard Resolution 1:12000 1:10000 1:15000 1:12500 1:15000
Approved Resolution (nmax) 1:3000 1:5000 1:3000 1:5000 1:3000
Safe Overload Capacity 150% of capacity
Load Cell Protection/ 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 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 18 x 18 in. / 457 x 457 mm 24 x 24 in. / 61 x 61 cm
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CHAPTER 1 INTRODUCTION
1.7 SPECIFICATIONS
TABLE 1-5. SPECIFICATIONS FOR DEFENDER SQUARE WASHDOWN BASES (Regular)
MODEL: W Series D10WR D15WR D25WR D30WR D50WR
Capacity 10 kg / 25 lb 15 kg / 30 lb 25 kg / 50 lb 30 kg / 60 lb 50 kg / 100 lb
Standard Resolution 1:10000 1:15000 1:12500 1:15000 1:10000
Approved Resolution (nmax) 1:5000 1:3000 1:5000 1:3000 1:5000
Safe Overload Capacity 150% of capacity
Load Cell Protection/
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 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 12 x 12 in. / 305 x 305 mm 18 x 18 in. /
457 x 457 mm
TABLE 1-6. SPECIFICATIONS FOR DEFENDER SQUARE WASHDOWN BASES (Large)
MODEL: W Series D60WL D100WL D150WL D250WX D300WX
Capacity 60 kg / 150 lb 100 kg / 250 lb 150 kg / 300 lb 250 kg / 500 lb 300 kg / 600 lb
Standard Resolution 1:12000 1:10000 1:15000 1:12500 1:15000
Approved Resolution (nmax) 1:3000 1:5000 1:3000 1:5000 1:3000
Safe Overload Capacity 150% of capacity
Load Cell Protection/
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 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 18 x 18 in. / 457 x 457 mm 24 x 24 in. / 61 x 61 cm
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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
Beam
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.)
Force
Wheatstone Bridge Circuit
Strain Gauge
+
+
Strain Gauge –
Strain Gauge
Strain Gauge
–
Printed Circuit Board (PCB )
completing 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.
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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.
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.
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
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CHAPTER 1 INTRODUCTION
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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.
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.
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.
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CHAPTER 2 DIAGNOSTIC GUIDE
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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 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.
Figure 3-1. Four Mounting Bolts that secure
the Top Frame to the Load Cell.
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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 Cell 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.
Figure 3-3. Overload Gap Setting.
Figure 3-4. Location of top Overload Stops.
Jam Nut
Overload Sto
p
Set Screw
Gap
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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
Model Overload Stop (Corner) Overload Stop (Center)
D15HR 2mm (0.78in.) 0.5mm(0.02in.)
D30HR 2mm (0.78in.) 0.5mm(0.02in.)
D60HR 3mm (0.118in.) 0.5mm(0.02in.)
D60HL 3mm (0.118in.) 0.75mm(0.03in.)
D100HL 3mm (0.118in.) 0.75mm(0.03in.)
D150HX 4mm (0.157in.) 1mm (0.04in.)
D300HX 4mm (0.157in.) 1mm (0.04in.)
D10QR 2mm (0.78in.) 0.8mm (0.3in.)
D25QR 2mm (0.78in.) 0.8mm (0.3in.)
D50QL 3mm (0.11in.) 1mm (0.4in.)
D100QL 4mm (0.157in.) 1mm (0.4in.)
D250QX 6mm (0.23in.) 1mm (0.4in.)
D10WR 2mm (0.78in.) 0.8mm (0.31in.)
D25WR 2mm (0.78in.) 0.8mm (0.31in.)
D50WL 3mm (0.11in.) 1mm (0.04in.)
D100WL 4mm (0.157in.) 1mm (0.04in.)
D250WX 6mm (0.23in.) 1mm (0.04in.)
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CHAPTER 3 MAINTENANCE AND REPAIR PROCEDURES
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