YOKOGAWA 2768 User manual

2768
Precision Wheatstone Bridge
User's
Manual
IM 2768-01E
IM 2768-01E
4th Edition: Oct. 2017 (YMI)

IM 2768-01E
―i ―
Introduction
Thank you for purchasing our Precision wheatstone bridge.
This manual describes the specifications and handling precautions of the Precision wheatstone bridge.
Before using this product, thoroughly read this manual to understand how to use it properly.
Contact information of Yokogawa offices worldwide is provided on the following sheet.
PIM 113-01Z2: Inquiries List of worldwide contacts
Notice regarding This User’s Manual
• The information covered in this User’s manual is subject to change without prior notice.
• Every effort has been made to ensure accuracy in the preparation of this manual.
Should any errors or omissions come to your attention however, please inform YOKOGAWAaccordingly.
• YOKOGAWA is by no means liable for any damage resulting from the user’s mishandling of the product.
• This manual is intended to describe the functions of this product.
YOKOGAWA does not guarantee that these functions are suited to the particular purpose of the user.

IM 2768-01E
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Cautionary Notes for Safe Use of the Product
When operating the instrument, be sure to observe the cautionary notes given below to ensure correct and
safe use of the instrument.
If you use the instrument in any way other than as instructed in this manual, the instrument’s protective
measures may be impaired.
This manual is an essential part of the product; keep it a safe place for future reference.
YOKOGAWA is by no means liable for any damage resulting from use of the instrument in contradiction to
these cautionary notes.
■ The following safety symbols are used on the instrument and in the manual:
Danger! Handle with Care.
This mark indicates that operator must refer to an explanation in
the instruction manual in order to avoid risk of injury or death of
personnel or damage to the instrument.
This mark indicates earth (ground).
■ Since mishandling the instrument can result in an accident that may lead to
injury or death of the operator, such as an electric shock, be sure to observe
the following instructions.
WARNING
● Protective Measures
• If a crack appears in the instrument after it has been accidentally dropped or bumped,
the safety-purpose insulation may be damaged.
By all means do not use the instrument, but ask the manufacture for repair.
● Connection
• To avoid electric shock, be sure to apply protective grounding to the grounding terminal.
• Install a protection fuse as shown in the example of measurement.
● Measurement
• Always maintain the instrument within the limits for allowable current, voltage and power,
during operation.
If there is more than one limit for any of these parameters, the lowest limit takes precedence.
● External Power Supply
• Only operate the instrument on a supply voltage no greater than 60 VDC.
● Operating Environment
• Do not operate the instrument in a flammable or explosive gas atmosphere.
• Do not operate the instrument if there is any condensation on it.
● Do Not Remove the Case or Disassemble
• Do not open the case except when replacing batteries.
Only Yokogawa service personnel are authorized to remove the casing or disassemble or
modify the instrument.
Do not attempt to repair the instrument yourself, as doing so is extremely dangerous.

IM 2768-01E
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■ Since mishandling the instrument can result in an accident, such as an electric shock,
that may injure the operator or damage the instrument, be sure to observe
the following instructions.
CAUTION
● Batteries
Do not use a mixture of different types of batteries or a mixture of old and new batteries.
If the instrument will not be used for a prolonged period, remove the batteries before storage.
The battery fluid will leak more readily during long-term storage, resulting in instrument malfunction.

IM 2768-01E
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CONTENTS
Introduction.............................................................i
Cautionary Notes for Safe Use of the Product ..................................ii
1. GENERAL...........................................................1
2. SPECIFICATIONS.....................................................1
3. COMPONENT NAMES AND FUNCTIONS..................................4
4. MEASURMENT.......................................................6
4.1 Preliminary Procedure ..............................................6
4.2 Measurement.....................................................8
5. PRECAUTIONS ......................................................9
6. PRINCIPLE .........................................................10
7. FOR MORE EFFECTIVE USE OF THE INSTRUMENT .......................11
7.1 How to Use the Measuring Dial (Rs) ..................................11
7.2 To Connect ExternalAccessory Equipment
(Galvanometer and Power Source) ...................................11
(1) Connection of External Galvanometer..................................11
(2) Connection of External Power Source..................................11
(3) Caution..........................................................11
8. CIRCUIT DIAGRAM ..................................................13

IM 2768-01E
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1. GENERAL
Precision Wheatstone Bridge 2768 is an instrument designed for measuring DC resistance from
0.1 Ω to 110 MΩ.
This instrument is equipped with a galvanometer and a power source internally,
and the measured value is indicated in-line indication without using any additional equipment externally.
Moreover, this instrument is designed with maximum care for the precision and stability of
resistance elements and also for the insulation of the measuring circuit, and is provided with
a guard terminal and a ground terminal.
Therefore the precision measurement is accomplished with 2768.
2. SPECIFICATIONS
× 100 mΩ
× 1 Ω
× 10 Ω
× 100 Ω
× 1 kΩ
× 10 kΩ
× 100 kΩ
× 1 MΩ
× 10 MΩ
10 µΩ
100 µΩ
1 mΩ
10 mΩ
100 mΩ
1 Ω
10 Ω
100 Ω
1 kΩ
±0.5 mΩ
±(0.02% of setting + 0.5 mΩ)
±0.02% of setting
±0.01% of setting
±0.01% of setting
±0.01% of setting
±0.02% of setting
±0.02% of setting
±0.05% of setting
0.10000 to 1.11110 Ω
1.1111 to 11.1110 Ω
11.111 to 111.110 Ω
0.11111 to 1.11110 kΩ
1.1111 to 11.1110 kΩ
11.111 to 111.110 kΩ
0.11111 to 1.11110 MΩ
1.1111 to 11.1110 MΩ
11.111 to 111.110 MΩ
Accuracy: at 23 ± 5°C, less than 75%
Measuring Range and Accuracy:
Range Measuring Range AccuracyResolution

IM 2768-01E
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No. 1 Dial
No. 2 Dial
No.3 Dial
No. 4 Dial
No. 5 Dial
±0.006% (not included residual resistance.)
±0.01% (not included residual resistance.)
±0.1% (not included residual resistance.)
±0.5% (not included residual resistance.)
±5% (included residual resistance.)
1000 Ω × 10
100 Ω × 10
10 Ω × 10
1 Ω × 10
0.1 Ω × 10
At an ambient temperature of 23 ± 2°C, humidity of less than 75% R. H.
Residual resistance; Less than 0.02 Ω
(% of setting)
Measuring Arm:
Resistance Accuracy
× 100 mΩ
× 1 Ω
× 10 Ω
× 100 Ω
× 1 kΩ
× 10 kΩ
× 100 kΩ
× 1 MΩ
× 10 MΩ
±0.02%
±0.02%
±0.01%
±0.005%
±0.005%
±0.005%
±0.01%
±0.01%
±0.01%
10 Ω / 100 kΩ
10 Ω / 10 kΩ
100 Ω / 10 kΩ
1 kΩ / 10 kΩ
1 kΩ / 1 kΩ
10 kΩ / 1 kΩ
100 kΩ / 1 kΩ
100 kΩ / 100 Ω
100 kΩ / 10 Ω
*: At an ambient temperature of 23 ± 2°
C, humidity of 75% R. H. and resistance ratio.
Ratio Arm; 0.2 W continuous
Measuring Arm; 0.2 W / Element, continuous
Ratio Arm:
Maximum Allowable Input:
Range Resistance Ratio Accuracy*

IM 2768-01E
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operative for approx. 300 hours.
(Dry Cell UM-1, or SUM-1 4 each and 006P 1 each)
at ambient humidity of less than 75%
(not including a handle and mounts)
Between the case and the circuits; More than 1000 MΩat 250 VDC
User's Manual 1 each
Battery 1 set
Between the case and the circuits; 500 VAC, 1 minute
Maximum Sensitivity: Approximately 10µV / div.
Input Resistance: 9 kΩ
Max. Allowable Input Voltage: 5 V (peak value)
Power Source: 9 V (Dry Cell 006P) installed,
Galvanometer
Insulation Resistance:
Accessories:
Dielectric Strength:
Dimensions: Approx. 310
× 491 × 140 mm
Weight: Approx. 9.6 kg
Power Source: 1.5 V / 3 V / 6 V / 15 V

IM 2768-01E
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3. COMPONENT NAMES AND FUNCTIONS
[1]
[5]
[12] [11] [3] [4] [10] [13] [2]
[6] [7] [9] [8] [14]
Fig. 3.1 Front Panel
Galvanometer
5. 3
EXTGA
−EXTBA +
EXT
1.5V3V 6V 15V
POWER SUPPLY RANGE
EXT GAL H
×100 Ω
×10 Ω
×1 Ω
×1 kΩ
×10 kΩ
×10 MΩ
×1 MΩ
×100 kΩ
×100 mΩ
BCHECK
4 8 9
BA GA Rs
(kΩ)Rx GUARD YOKOGAWA
WHEATSTONE BRIDGE
2768
L H
OFF INT GA SENSITIVITY
GUARD
(Front Panel)
[1] Measuring Arm:
(Rs) Is composed of 5 dial type variable resistors, and is able to
change the resistance from 0.1 Ω till 11.111 kΩ in step of 0.1 Ω.
The resistance value indicated in the windows is connected to
the bridge circuit.
[2] Ratio Arm:
(Range)
Used to select a multiplying factor depending on
the resistance under test.
[3] Galvanometer Function Switch
INT. GA: Internal galvanometer is connected to the bridge circuit.
B CHECK: Used to check the power source for the internal galvanometer.
(If the pointer reaches to the blue zone, the batteries are normal.)
EXT. GA: Internal galvanometer is connected to the bridge circuit.
In this case, the power source for the galvanometer is set to OFF.

IM 2768-01E
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[4] Sensitivity Knob: Used to adjust the sensitivity of the internal galvanometer.
Turn the knob to increase the sensitivity.
[5] Power Supply Function Switch:
OFF: Power sources for the bridge circuit and the internal
galvanometer are switched off.
1.5 V to 15 V: Used to set the power supply voltage for the bridge circuit.
The power source for the internal galvanometer will be ON.
EXT: The external power source is connected to the bridge circuit,
and the power source for the internal galvanometer is set to ON.
[6] BA: This is a push button type switch used to switch the power source
for the bridge circuit ON and OFF during measurement.
[7] GA: This is a push button type switch used to connect
the galvanometer input to the bridge circuit.
[8] Rx Terminal: Used to connect the resistance under test.
[9] Rs Terminal: Used when the measuring dial (Rs) is employed as
a variable resistor.
[10] EXT. GATerminal: Used to connect the external galvanometer.
[11] EXT. BATerminal: Used to connect the external power source.
[12] Ground Terminal
[13] Galvanometer Guard Terminal
[14] Rx Guard terminal
Battery Case: The case is located on the bottom of this instrument.
Remove the cover by removing the screws to replace
the batteries.
The power source for the galvanometer is the dry cell battery
(006P) located at the end of the case.