AU-31
MULTITESTERINSTRUCTION MANUALCONTENTS
AUTO-RANGE TYPE MULTITESTER MODEL AU-31 …………001[1] FEATURES ……………………………………………………001[2] SAFETY PRECAUTIONS:Before use, read the following safety precautions ……002[3] MEASURING RANGE AND PERFORMANCE ……………003[4] APPEARANCE AND NAMES OF COMPONENTS ………005[5] HOW TO READ SCALE PLATE ……………………………006[6] HOW TO FIX RANGE …………………………………………007[7] HOW TO SELECT RANGE MANUALLY …………………007[8] PREPARATION FOR MEASUREMENT ……………………008[9] MEASURING OF DC VOLTAGE ……………………………008[10] MEASURING OF AC VOLTAGE ……………………………010[11] MEASURING OF LOW FREQUENCY OUTPUT(dB) ……011[12] MEASURING OF RESISTANCE (auto range) ……………011[13] MEASURING OF DC CURRENT (fixed range)……………013[14] MEASURING OF AC CURRENT (fixed range)……………014[15] MAINTENANCE ………………………………………………015
15-1 Replacement of dry cells (Refer to Fig. 6): ………………015
15-2 Replacement of fuses (Refer to Fig. 6): …………………015
15-3 Cleaning and Storage………………………………………016[16] AFTER-SALES SERVICE ……………………………………016
16-1 Warranty and Provision ……………………………………016
16-2 Repair ………………………………………………………017
16-3 SANWA web site……………………………………………017

AUTO-RANGE TYPE MULTITESTERMODEL AU-31
This is a circuit tester developed for measurement of small capacity
electric circuits based on our advanced design and engineering
technology. Electric circuits that can be measured include small
communication equipment, household appliances, lighting lines(voltage), various batteries and other general electric circuits.
Before using your new tester, please read this instruction manualthat describes various useful methods of application and safe
operation.

[1] FEATURES
1. Auto range
A fully automatic range selector type eliminates a need for selectionof ranges for voltage or resistance measurement. The suitable
range is automatically set according to application.
2. Auto polarity
Both positive and negative polarities of DC voltage and current canbe automatically measured.
3. High input resistanceAn input resistance as high as 10MΩ for measurement of both DC
and AC voltage minimizes measurement loss.
4. Series capacitor input
When measuring AC voltage in a DC and AC superimposed circuit,the DC component can be cut and only AC voltage can be detected
and measured.
5. No need for 0Ω adjustment
There is no need for 0Ω adjustment, that is required when otherconventional testers are used.

— 1—[2] SAFETY PRECAUTIONS:Before use, read the following safety precautions
This instruction manual explains how to use your multitester AU-31,
safely.
Before use, please read this manual thoroughly. After reading it,
keep it together with the product for reference to it when necessary.
The instruction given under the heading
WARNINGCAUTION
must be followed to prevent accidental burn or electrical shock.
Warning Instruction for Safe Use

WARNINGTo ensure that the meter is used safely, be sure to observe theinstruction when using the instrument.
Please be careful that the protection circuit may be undermined byunjustifiable usage that does not follow the guidelines in the
instruction manual.
11. Never use the meter on the electric circuits that exceed 6kVA.
12. Pay special attention when measuring the voltage of AC 33
Vrms (46.7V peak) or DC 70V or more to avoid injury.
13. Never apply an input signals exceeding the maximum rating
input value.
14. Never use the meter for measuring the line connected withequipment (i.e. motors) that generates induced or surge
voltage since it may exceed the maximum allowable voltage.
15. Never use the meter if the meter or test leads are damaged or
broken.
16. Never use uncased meter.
17. Be sure to use a fuse of the specified rating or type. Never use asubstitute of the fuse or never make a short circuit of the fuse.
18. Always keep your fingers behind the finger guards on theprobe when making measurements.
19. Be sure to disconnect the test pins from the circuit whenchanging the function or range.
10. Before starting measurement, make sure that the function andrange are properly set in accordance with the measurement.
11. Never use the meter with wet hands or in a damp environment.
12. Never open rear case except when replacing batteries or fuse.
Do not attempt any alteration of original specifications.
13. To ensure safety and maintain accuracy, calibrate and checkthe tester at least once a year.
14. Indoor use.
— 2—[3] MEASURING RANGE AND PERFORMANCE
Table 1
Type ofMeasurement

Max. Scale
300mV

DC voltage±DCV

Allowance±3% of max.
scale.

Remarks
Input resistanceapprox.1MΩ

3/12/60/300/1000V ±3% of max.
scale.
±4% for 1000V

Input resistance
10MΩ min.

30kV(by use of
optional probe)±10% of max.
scale.

Probe resistance
1000MΩ

300mV±3% of max.
scale.
Frequency
characteristic
40Hz〜10kHz±5%.

Input resistanceapprox.1MΩ
Full wave
rectification

AC voltage
ACV

3/12/60/300/1000V ±3% of max.
scale.
±4% for 1000V

Input resistance
10MΩ min.
Full wave
rectificationLow
frequency
outputdB±3% of max.
-9/+11/+23/+37/
scale length.
+51/+62 dB
0dB=0.775V (1mW) ±4% for +62 dB(600Ω)

Input resistance
10MΩ min.
Full wave
rectification

DC current±DCA

300mA/3A±3% of max.
scale.

Shunt voltage
drop 220mV

300mA/3A±3% of max.
scale.

Shunt voltage
drop 220mV

Range Center Max ±3% of scalex1200Ω 20kΩ lengthx10
2kΩ 200kΩ
x0.1k 20kΩ
2MΩ
x1k 200kΩ 20MΩ
x10k 2MΩ 200MΩ

Terminal open
voltage 1.2VDC

AC current ACA
ResistanceΩ— 3—Standard working temperature: 23 ± 2˚CStandard working frequency: 50 Hz 〜 60 Hz
Standard working humidity: 45 〜 75% RH
Working temperature range: 0 〜 40˚C
Working humidity range: 80% RH max.
(No condensation)
Dimensions and weight: 110(W) x 124(D) x 48(H)mm,
290g
Accessories: Instruction manual,A pair of test leads (TL-61G type),
Fuse (5Φ x 20mm, 250V/0.5A)
Battery: R03(IEC)or UM-4
4 pieces
Life of dry cell
: Approx. 100 hours
when used 8 hours a day
built-in battery* AFactory-preinstalledbattery for monitoring is preinstalled before shipping, therefore it may
run down sooner than the battery life specified in the instruction manual.
The ”battery for monitoring” is a battery to inspect the functions andspecifications of the product.

Options: DC 30kV probe(HV-50 type),
Portable case(C-AU type)— 4—

[4] APPEARANCE AND NAMES OF COMPONENTS

Indicator
Pointer
Range display

Scale plate

Manual range
select switch

Zero point setterof indicator
Polarity display
LED

Range hold switch

Function switch
Measurement terminal( )Measurement terminal(-COM)

Measurement terminalfor 3A

Fig. 1 Tester

Test pins

Cords

Fig. 2 Test Leads— 5—

Red plug
Black plug[5] HOW TO READ SCALE PLATE
Unlike other conventional testers, this tester is of auto range typeand does not show a value in the current range corresponding to
the position of the switch, but instead shows it on the range
display.
First look at the line indicated by the function switch (V, Ω, mV •mA) and go down the column on which the range display LED islit. Then, read a value indicated by the pointer as follows.

Table 2
ColumnIndicatedby LED

Scale of
Scale Plate to
Read

Magnificationof Value
Read

Value toReadV

3 V scale 0 〜 13
0 〜 12
12
0 〜 6060
0 〜 13300
0 〜 1000
1000

x1
x1
x1
x 100
x1

0 〜 13V
0 〜 12V
0 〜 60V
0 〜 300V
0 〜 1000V

Ω

x l0k
x 1k
x 0.1k
x 10
x1

x 10k
x 1k
x 100
x 10
x1

Center 2MΩ
Center 200kΩ
Center 20kΩ
Center 2kΩ
Center 200Ω

x 100

0 〜 300mV, mA

mV • mA 300Ω scale

0〜∞
0〜∞
0〜∞
0〜∞
0〜∞

A scale 0 〜 3

Pointer
Scale for resistance (Ω)
Scale for DC, AC voltage (V)and current (A)dB scale
Battery check scaleFig. 3 Scale Plate— 6—

Range display LED
Range of DC, AC voltage (V)Range of resistance (Ω)
Range of DC, AC voltage (mV)and current (mA)

Fig. 4 Range Display and Example of Measurement(Example of measurement)
1. Function switch: Set to V
position
2. Range display: LED lit on 300 (Fig. 4)
3. Pointer of indicator: As in Fig. 3
How to read: A value to read is 0 〜 300V scale as show in Table
2 and the voltage is 250 VDC.

[6] HOW TO FIX RANGE
A range can be fixed with the range hold switch. This function isused for measurement of DCV, ACV and Ω.

Range is fixed.
Range is automatically selected.

[7] HOW TO SELECT RANGE MANUALLY
A range can be changed over by pressing the manual range selectswitch. This function is used for measurement of DCV, ACV and Ω.

Range is changed to right.
Range is changed to left.

— 7—

This switch is valid regardless of setting of the range hold switch
and is useful for reading in a different range. Note, however, that
this switch will not operate with the function switch at positions otherthan V〜 , Vand Ω .

[8] PREPARATION FOR MEASUREMENT
For safe operation, be sure to check the position of thefunction switch, terminals to use and condition ofconnection of the test leads to the tester before starting
measurement.
When measurement has been completed, be sure to return thefunction switch to POWER OFF to prevent unnecessary
consumption of the battery. As a countermeasure against a failure
to do this operation, the tester is designed to turn off the power
automatically when its indicator section is closed.
1. Check of the battery
The tester is driven by four dry cells R03. Before starting
measurement, check the remaining capacity. Turn the function
switch to INTERNAL BATT CHECK (a range to check thebattery). Then, the pointer deflects toward the right. The
capacity is sufficient when the pointer comes within the rangeof INTERNAL BATT GOOD at the lowest scale of the scale
plate. If the pointer stops on the left of this range, the dry cells
have been consumed and replace them in accordance with theprocedure described in [15] MAINTENANCE.
2. Zero adjustment of the indicator
If the pointer stays off the 0V line at the left end of the scale
plate, adjust it to the 0V line by turning the zero point setter ofindicator with a screwdriver.

[9] MEASURING OF DC VOLTAGE
Measurement of 0 〜 ±1000V DC (auto range)
Measurement of DC voltage below ±1000V max.
For safe measurement, never apply a voltage exceeding ±1000VDC.
Never apply an excessive voltage (more than 100 times the
maximum value of the applicable range) with the range held.
— 8—After preparation described in [8] PREPARATION FOR
MEASUREMENT has been completed, measure voltage as follows.
1. Connect the black plug of the test lead to the measurement
terminal (-COM) and the red plug to ( ).
2. Turn the function switch to V.
3. Set the range hold switch at AUTO .
4. Apply the test pins to an object.
5. Read the value as indicated on the range display. This is thevoltage you have measured.
(If the polarity display LED lights, it indicates that the +potential is applied to the measurement terminal (-COM) and potential to the( ).)6. After measurement, release the test pins from the object.
7. Return the function switch to POWER OFF .
Measurement of ±300mV (fixed range)
Measurement of DC voltage below ±300mV max.
Never apply an excessive voltage (over 100VAC or DC)
The measuring procedure is the same as for the above steps 1 to
7, except for the step 2 where the function switch should beturned to mV.
[NOTE] Influence of the electromagnetic field
ACV and DCV measurement functions may not work
properly in the electromagnetic field over 10kHz.

— 9—

[10] MEASURING OF AC VOLTAGE
Measurement of 0 〜 1000V AC (auto range)
Measurement of sine wave AC voltage below 1000V max.
For safe measurement, never apply a voltage above 1000V AC.
Never apply an excessive voltage (more than 100 times the
maximum value of the applicable range) with the range held.
After preparation described in [8] PREPARATION FOR
MEASUREMENT has been completed, measure voltage as follows.
1. Connect the plugs of the test leads to the measurement
terminals (-COM) and ( ).
(For AC voltage measurement, the red and black plugs neednot be distinguished.)
2. Turn the function switch to V〜 .
3. Set the range hold switch at AUTO .
4. Apply the test pins to an object.
5. Read the value as indicated on the range display. This is thevoltage you have measured.
6. After measurement, release the test pins from the object.
7. Return the function switch to POWER OFF .
Measurement of 300mV (fixed range)
Measurement of sine wave AC voltage below 300mV max.
Never apply an excessive voltage(above 100VAC or DC)
The measuring procedure is the same as for the above steps 1 to
7, except for the step 2 where the function switch should beturned to mV〜 .

— 10 —

[11] MEASURING OF LOW FREQUENCY OUTPUT(dB)
The dB value is scaled in the 3V AC range and only when the
impedance is 600Ω, 0dB is equal to 1mW and the output value canbe read directly. (0dB = 1mW = 0.775V at 600Ω)
1. The measuring procedure is the same as for measurement of
AC voltage.
2. Add the following dB values to dB values on the scale panel in
the ACV range.

Table 31
AC voltage range 300mV

3V

12V

60V

300V

1000V

dB value to add

0

+12

+26

+40

+52

-20

[12] MEASURING OF RESISTANCE (auto range)
Measurement of DC resistance below 200MΩ max.
Never apply an external voltage. Otherwise, the tester may bedamaged.
Caution:Be sure to turn off the power source switch of
measured circuit when the resistance in the circuit ismeasured.
Make sure that no voltage is applied to a resistor tomeasure.
After preparation described in [8] PREPARATION FOR
MEASUREMENT has been completed, measure resistance asfollows.
1. Connect the plugs of the test leads to the measurement
terminals (-COM) and ( ).
2. Turn the function switch to Ω .
3. Set the range hold switch at AUTO .
4. Apply the test pins to an object.
5. Read the value as indicated on the range display. This is theresistance you have measured.
6. After measurement, release the test pins from the object.
7. Return the function switch to POWER OFF .
— 11 —

0Ω setter(Refer to Fig. 6 in [16] MAINTENANCE) This tester
employs the constant voltage method for measurement ofresistance and there is no need of 0Ω adjustment for normal
measurement.
To cancel resistance of the test leads in measurement in the x 1Ω
range, turn the 0Ω setter in the battery case with the test pins
shorted CW or CCW to the 0Ω line at the right end of the Ω scale.
Also if the 0Ω point has moved over a long period of use, make0Ω adjustment in the same manner.
Applicable voltage and current in measurement of resistance
Measurement of resistance is conducted with the internal powersource. About 1.2V is output as follows: + to the (-COM) terminal
and - to the ( ) terminal. When this voltage is applied, thefollowing current flows. Refer to the following table whenmeasuring polarized resistors such as transistors and diodes orresistors whose values change according to intensity of current toflow.

Table 4
Range

x10k

x1k

Voltage(terminals open)
Current(terminals shorted)

x0.1k

x10

x1

600μA

6mA

1.2V constant
0.6μA

6μA

— 12 —60μA

[13] MEASURING OF DC CURRENT (fixed range)
Measurement of 0 〜 ±300mA(0 〜 ±3A)
To prevent damage to the tester and personal injury, do notmeasure current when the voltage exceeds ±600V.
After preparation described in [8] PREPARATION FOR
MEASUREMENT has been completed, measure current as follows.
1. Connect the black plug of the test lead to the measurement
terminal(-COM) and the red plug to ( ).
(For measurement of 0 〜 ±3A, connect the red plug to thespecial measurement terminal for 3A .)2. Turn the function switch to mA/3A.
3. Apply the test pins to an object.
4. Read the value as indicated on the range display. This is thecurrent you have measured.
(If the polarity display LED lights, it indicates that the + potential
is applied to the measurement terminal (-COM) and -potential
to the ( ).)5. After measurement, release the test pins from the object.
6. Return the function switch to POWER OFF .
Current measuring circuit (for both AC and DC):For measurement of current, connect the tester in series with anobject to measure as shown below.

Never make thisdangerous circuit.
○Correct circuit×Dangerous circuit

Fig. 5— 13 —

[14] MEASURING OF AC CURRENT (fixed range)
Measurement of 0 〜 300mA(0 〜 3A)
To prevent damage to the tester and personal injury, do notmeasure current when the voltage exceeds ±600V.
After preparation described in [8] PREPARATION FOR
MEASUREMENT has been completed, measure current as follows.
1. Connect the plugs of the test leads to the measurement
terminals (-COM) and ( ).
(For AC current measurement, the red and black plugs need not
be distinguished.)
2. Turn the function switch to mA/3A〜 .
3. Apply the test pins to an object.
4. Read the value as indicated on the range display. This is thecurrent you have measured.
5. After measurement, release the test pins from the object.
6. Return the function switch to POWER OFF .
Protection circuit:
As a safety measure against misoperation in measurement ofresistance and current, a fuse is set in the input section (but nofuse in the measurement terminal for 3A ). If the tester isoperated erroneously, this fuse is blown. Although this fuse canprotect the tester, the best practice is, of course, to operate thetester as instructed in this manual.

— 14 —

[15] MAINTENANCE
15-1 Replacement of dry cells (Refer to Fig. 6):
Replace dry cells if the pointer stays out of the range of
INTERNAL BATT GOOD when the function switch is turned to
INTERNAL BATT CHECK .
1. Remove the battery case lid.
2. Remove four old dry cells R03 and set new ones (UM-4SG).
(Pay attention to the polarity.)
3. Remount the battery case.

Fuse

Spare fuseDry cell0Ω setter

Battery case lid
Before removing the battery
case lid, be sure to disconnect
the test leads and turn thefunction switch to POWER
OFF .

Fig. 6 Layout of Dry Cells and Fuses
15-2 Replacement of fuses (Refer to Fig. 6):
1. Remove the battery case lid and replace fuses.
2. Use a mini fuse of 5φ x 20mm of rating of 250V AC/0.5A.

— 15 —

15-3 Cleaning and Storage

CAUTION
1. For cleaning, wipe lightly with a soft, and either dry or slightly
water-dampended cloth. Do not use volatile solvent such as
thinner or alcohol for panel, case, and meter cover.
2. The panel and the case are not resistant to heat. Do not place
the instrument near heat-generating devices (such as asoldering iron).
3. Do not store the instrument in a place where it may be subjected
to vibration or from where it may fall.
4. For storing the instrument, avoid hot, cold or humid places orplaces under direct sunlight or where condensation is
anticipated.

[16] AFTER-SALES SERVICE
16-1 Warranty and Provision
Sanwa offers comprehensive warranty services to its end-users andto its product resellers. Under Sanwa's general warranty policy, each
instrument is warranted to be free from defects in workmanship ormaterial under normal use for the period of one (1) year from the dateof purchase.
This warranty policy is valid within the country of purchase only, andapplied only to the product purchased from Sanwa authorized agent
or distributor.
Sanwa reserves the right to inspect all warranty claims to determine
the extent to which the warranty policy shall apply. This warranty shallnot apply to fuses, test leads, disposables batteries, or any product orparts, which have been subject to one of the following causes:
1. A failure due to improper handling or use that deviates from the
instruction manual.
2. A failure due to inadequate repair or modification by people
other than Sanwa service personnel.
3. A failure due to causes not attributable to this product such as
fire, flood and other natural disaster.
— 16 —

4. Non-operation due to a discharged battery.
5. A failure or damage due to transportation, relocation or
dropping after the purchase.
16-2 Repair
Customers are asked to provide the following information whenrequesting services:
1. Customer name, address, and contact information
2. Description of problem
3. Description of product configuration
4. Model Number
5. Product Serial Number
6. Proof of Date-of-Purchase
7. Where you purchased the product1) Prior to requesting repair,please check the following:
Capacity of the built-in battery, polarity of installation anddiscontinuity of the test leads.
2) Repair during the warranty period:
The failed meter will be repaired in accordance with the conditions
stipulated in 16-1 Warranty and Provision.
3) Repair after the warranty period has expired:
In some cases, repair and transportation cost may become higher
than the price of the product. Please contact Sanwa authorized
agent / service provider in advance.
The minimum retention period of service functional parts is 6 years
after the discontinuation of manufacture. This retention period is therepair warranty period. Please note, however, if such functionalparts become unavailable for reasons of discontinuation of
manufacture, etc., the retention period may become shorter
accordingly.
4) Precautions when sending the product to be repaired
To ensure the safety of the product during transportation, place theproduct in a box that is larger than the product 5 times or more involume and fill cushion materials fully and then clearly mark ”Repair
Product Enclosed” on the box surface. The cost of sending andreturning the product shall be borne by the customer.
16-3 SANWA web site
http://www.sanwa-meter.co.jp
E-mail: exp_sales@sanwa-meter.co.jp— 17 —SANWA ELECTRIC
INSTRUMENT CO., LTD.
Dempa Bldg, 4-4 Sotokanda2-Chome
Chiyoda-ku, Tokyo, Japan② 05.11 猯