50000 Counts Dual Display Digital Multimeter

The GDM-8245 is an economical bench-top DMM equipped with a rich set of features. The GDM-8245 has similar functions to the GDM-8246, but with slightly reduced DCV accuracy and no communication interfaces. The large 7 segment LED dual display features up to 50,000 counts and the ability to show two measurements at extensive list of measurement items - DC Voltage/Current, AC Voltage/Current with true RMS, Resistance, Capacitance, Frequency, Continuity (with beeper), Diode Test, and dBm.

Additional measurement functions, such as Max/Min hold, Relative value, and Compare ease setup and diagnosis burdens. With great range, good accuracy and able to accept up to 20A of current the

GDM-8245 is the perfect general purpose DMM.

GDM-8245 (50000 Counts)

FEATURES

* 50000 Counts Display

* Multi-Function ACV, DCV, ACA, DCA, R, C,

Hz, Continuity Beeper, Diode Test, Max/Min,

REL, Hold, dBm

* Dual Display Indicate ACV and Hz, DCV(ACV)

and dBm

* Manual or Auto Ranging

* 0.03% DCV Accuracy

* ACV Measuring Frequency Up to 50kHz

* AC True RMS or AC + DC True RMS

Rear Panel

GTL-117 Test Lead

For: GDM-8245/8246

GDM-8255A/8251A

CLC-9000

SPECIFICATIONS

DC VOLTAGE

Range

Accuracy

Input Impedance

500mV, 5V, 50V, 500V, 1000V 5 ranges

(0.03% rdg + 4 digits)

10M

AC VOLTAGE TRUE RMS (AC OR AC + DC TRUE RMS)

Range

500mV, 5V, 50V, 500V, 1000V 5 ranges

Accuracy

500mV ~ 50V 3 ranges :

20Hz ~ 45Hz : (1% rdg + 15 digits)

45Hz ~ 2kHz (0.5% rdg + 15 digits)

Input Impedance

2k~10kHz (1% rdg + 15 digits)

10kHz ~ 20kHz (2% rdg + 30 digits)

20kHz ~ 50kHz (5% rdg + 30digits)

500V,1000V range :

45Hz ~ 1kHz (0.5% rdg + 15 digits)

10M

DC CURRENT

Range

Accuracy

500 A, 5mA, 50mA, 500mA, 2A, 20A 6 ranges

500 A~500mA 4ranges: (0.02% rdg+2 digits); 2A~20A 2ranges: (0.3% rdg+2digits)

AC CURRENT TRUE RMS (AC OR AC + DC TRUE RMS)

Range

Accuracy

500 A, 5mA, 50mA, 500mA, 2A, 20A 6 ranges

500 A ~ 20A 6 ranges

20Hz ~ 45Hz : (1% rdg + 15 digits) ; 45Hz ~ 2kHz : (0.5%rdg + 15 digits)

500 A ~ 50mA 3 ranges

2kHz ~ 10kHz : (1% rdg + 15 digits) ; 10kHz ~ 20kHz : (2% rdg + 15 digits)

RESISTANCE

Range

Accuracy

500 ,5k ,50k ,500k ,5M ,20M 6 ranges

500 (0.1% rdg + 4 digits);

5k ~ 500k 3 ranges (0.1% rdg + 2 digits)

5M (0.2% rdg + 2 digits);

20M (0.3% rdg + 2 digits)

DIODE TEST

The one range can check the forward voltage of diode. Maximum forward voltage 1.5V open voltage 2.8V

CAPACITANCE

Range

Accuracy

5nF, 50nF, 500nF, 5 F, 50 F 5 ranges

(2% rdg + 4 digits)

FREQUENCY

Input Level

(Sine Wave)

FUNCTIONS

mV range :

10Hz ~ 50kHz : >120mV ; 50k ~ 150kHz : >200mV

5V ~ 50V range : 10Hz ~ 200kHz >1.2V ; 500V range : 20Hz ~ 1kHz >12V

Auto Manual/Range, Max, Min, dBm, REL, Hold

CONTINUITY BEEPER

Built in buzzer sounds when conductance is less than 5

DISPLAY

Dual Display 0.4" and 0.5", 7 segment LED display

POWER SOURCE

AC 100V/120V/230V 10%, 50/60Hz

DIMENSIONS & WEIGHT

251(W) x 91(H) x 291(D) mm, Approx. 2.6kg

ORDERING INFORMATION

GDM-8245 50,000 Counts Dual Display Digital Multimeter

ACCESSORIES :

User manual x 1, Power cord x 1, Test lead GTL-117 x 1

Made to Measure. Good Will Instrument Co., Ltd.

E8

DUAL DISPLAY DIGITAL

MULTIMETER

MODEL: GDM-8245

User Manual

Good Will Instrument Co., Ltd.

GW Part No. 82DM-82450MI

Declaration of Conformity

We

GOOD WILL INSTRUMENT CO., LTD.

No. 7-1, Jhongsing Rd, Tucheng City, Taipei County 236. Taiwan

GOOD WILL INSTRUMENT (SUZHOU) CO., LTD.

No.69 Lushan Road, Suzhou New District Jiangsu, China.

declares that the below mentioned product

GDM-8245

is herewith confirmed to comply with the requirements set out in the Council Directive on the Approximation of the Law of Member States relating to Electromagnetic

Compatibility (89/336/EEC, 92/31/EEC, 93/68/EEC) and Low Voltage Equipment

Directive (73/23/EEC, 93/68/EEC).

For the evaluation regarding the Electromagnetic Compatibility and Low Voltage

Equipment Directive, the following standards were applied:

◎ EMC

EN 61326-1:

Electrical equipment for measurement, control and laboratory use ––

EMC requirements (1997+A1: 1998)

Conducted and Radiated Emissions

EN55011 Group II class B: 1998

Current Harmonic

EN 61000-3-2: 1995

Voltage Fluctuation

EN 61000-3-3: 1995

Electrostatic Discharge

EN 61000-4-2: 1995

Radiated Immunity

EN 61000-4-3: 1996

Electrical Fast Transients

EN 61000-4-4: 1995

-------------------------

-------------------------

-------------------------

Surge Immunity

EN 61000-4-5: 1995

Conducted Susceptibility

EN 61000-4-6: 1996

Voltage Dips/ Interrupts

EN 61000-4-11: 1994

◎ Safety

Low Voltage Equipment Directive 73/23/EEC & amended by 93/68/EEC

IEC/EN 61010-1: 2001

DUAL DISPLAY DIGITAL MULTIMETER

USER MANUAL

TABLE OF CONTENTS PAGE

1.

SAFETY SUMMARY……………………………………………… 1

2.

INTRODUCTION…………………………………………………..

5

3.

SPECIFICATION…………………………………………………..

6

4.

OPERATION INSTRUCTION……………………………………. 11

5.

MEASUREMENT TUTORIAL…...………………………………. 14

6.

MEASUREMENT TECHNIQUES......…………………………… 18

7.

MAINTENANCE…………………………………………………... 22

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DUAL DISPLAY DIGITAL MULTIMETER

USER MANUAL

1.SAFETY SUMMARY

Please take a moment to review these safety terms and symbols which may appear in this manual or on Equipment to prevent damage to the instrument.

WARNING. Warning statements identify condition or practices that could result in injury or loss of life.

CAUTION. Caution statements identify conditions or practices that could result in damage to this product or other property.

Measurement category I is for measurements performed on circuits not directly connected to MAINS.

Measurement category II is for measurements performed on circuits directly connected to the low voltage installation.

Measurement category III is for measurements performed in the building installation.

Measurement category IV is for measurements performed at the source of the low-voltage installation.

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DUAL DISPLAY DIGITAL MULTIMETER

USER MANUAL

DANGER High Voltage

ATTENTION refer to Manual

Protective Conductor Terminal

(ground) Earth Terminal

Frame or Chassis Terminal

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DUAL DISPLAY DIGITAL MULTIMETER

USER MANUAL

FOR UNITED KINGDOM ONLY

NOTE: This lead/appliance must only be wired by competent persons

WARNING: THIS APPLIANCE MUST BE EARTHED

IMPORTANT: The wires in this lead are coloured in accordance with the following code:

Green/ Yellow: Earth

Blue: Neutral

Brown: Live(Phase)

As the colours of the wires in main leads may not correspond with the colours marking identified in your plug/appliance, proceed as follows:

The wire which is coloured Green & Yellow must be connected to the Earth terminal marked with the letter E or by the earth symbol or coloured Green or Green & Yellow.

The wire which is coloured Blue must be connected to the

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DUAL DISPLAY DIGITAL MULTIMETER

USER MANUAL terminal which is marked with the letter N or coloured Blue or

Black.

The wire which is coloured Brown must be connected to the terminal marked with the letter L or P or coloured Brown or

Red.

If in doubt, consult the instructions provided with the equipment or contact the supplier.

This cable/appliance should be protected by a suitably rated and approved HBC mains fuse : refer to the rating information on the equipment and/or user instructions for details. As a guide, cable of 0.75mm² should be protected by a 3A or 5A fuse. Larger conductors would normally require

13A types, depending on the connection method used.

Any moulded mains connector that requires removal

/replacement must be destroyed by removal of any fuse & fuse carrier and disposed of immediately, as a plug with bared wires is hazardous if a engaged in live socket. Any rewiring must be carried out in accordance with the information detailed on this label.

DUAL DISPLAY DIGITAL MULTIMETER

USER MANUAL

2. INTRODUCTION

This instrument is a portable, bench-type dual display digital multimeter with a good-performance 50000 counts designed for general purpose application. The dual display allows you to display two functions of the input signal being measured.

Features

z 50000 counts DMM z Multi-function ACV, DCV, ACA, DCA, R, C , Hz, Continuity Beeper,

Diode Test, MAX/MIN, REL, HOLD, dBm z Dual display Indicate ACV and Hz or DCV (ACV) and dBm z Manual or Autoranging z 0.03% DCV accuracy z 20A high current range z 1000V high voltage range z AC True RMS or AC+DC True RMS.

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3.SPECIFICATIONS

The specifications are operated under the essential conditions as follows: z A 1-year calibration cycle.

z An operating temperature of 18 to 28℃ (64.4 to 82.4℉) z Relative humidity not exceeding 75%

z

Accuracy is expressed as ±(percentage of reading + digits).

z

The AC specification is based on the 50% of duty cycle.

1. DC VOLTAGE

RANGE

500mV

RESOLUTION ACCURACY INPUT IMPEDANCE

10μV 10MΩ

5V

50V

100μV

1mV

0.03%+4

11.1 MΩ

10.1MΩ

500V 10mV 10MΩ

1000V 100mV 0.03%+9

10MΩ

Input Impedance

Approx. 10MΩ in parallel with <100pF, all ranges.

Normal Mode Rejection Ratio >60dB at 60Hz or 50Hz.

Common Mode Rejection Ratio >90dB at 60Hz or 50Hz.

Common Mode Voltage (Max.) 500V dc or peak ac.

Maximum Input

450V dc or peak ac continuous on 500mV range.

1000V dc or peak ac continuous on other range.

63.80 dBm ~-97.7 dBm dBm (ref 600Ω)

When the input exceeds the full scale of the selected range, the display will appear

“—OL—“ of over-range indication.

2. TRUE RMS AC OR AC+DC VOLTAGE

Accuracy between 2% of range and full range.

RANGE 20Hz-

45Hz

45Hz-

1kHz

1kHz-

2kHz

2kHz-

10kHz

10kHz-

20kHz

20kHz-

50kHz

500mV 1%+15

5V 1%+15

0.5%+15

0.5%+15

1%+15 2%+30 5%+30

1%+15 2%+30 5%+30

50V 1%+15 0.5%+15

500V 1%+15 0.5%+15

1000V 1%+15 0.5%+15

1%+15 2%+30 5%+30

—————————

—————————

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USER MANUAL

RANGE

500mV

RESOLUTION

10μV

INPUT IMPEDANCE

10MΩ

5V

100μV 11.1 MΩ

50V

500V

1000V

1mV

10mV

100mV

10.1MΩ

10MΩ

10MΩ

Input Impedance

Approx. 10MΩ in parallel with < 100pF,all ranges.

Maximum Input

450V dc or peak ac continuous on 500mV range.

1000V rms on other range.

dBm ( ref 600Ω)

63.8dBm ~ -97.7dBm

Crest Factor Range 3.0 at full scale.

When the input exceeds the full scale of the selected range, the display will appear

“—OL—“ of over-range indication.

3. FREQUENCY MEASUREMENT AT ACV RANGE

RANGE FREQUENCY INPUT LEVEL (SINE WAVE)

500mV 10Hz ~ 50kHz

≧ 120mV

5V

50V

500V

50k ~ 150kHz

10Hz ~ 200kHz

20Hz ~ 200kHz

20Hz ~ 1kHz

≧ 200mV

≧ 1.2V

≧ 1.2V

≧ 12V

AC+DC measurement does not support AC+Hz function.

500μA

5mA

50mA

500mA

2A

20A

0.01μA

0.1μA

1μA

10μA

100μA

1mA

0.2%+2

0.2%+2

0.2%+2

0.2%+2

0.3%+2

0.3%+2

ACCURACY

0.05%+1

0.05%+1

0.05%+1

0.05%+1

0.05%+1

Maximum Input 450V peak ac continuous on 500mV range.

500V peak ac continuous on the other range.

4. DC Current

RANGE RESOLUTION ACCURACY BURDEN VOLTAGE

0.7Vmax.

0.7Vmax.

0.7Vmax.

0.8Vmax.

0.8Vmax.

0.9Vmax.

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DUAL DISPLAY DIGITAL MULTIMETER

USER MANUAL

Protection

500μA,5mA,50mA,500mA,2A 5 ranges fuse protection.

20A range no fuse,15 seconds max.

When the input exceeds the full scale of the selected range, the display will appear

“—OL—“ of over-range indication.

5. TRUE RMS AC OR AC+DC CURRENT

Accuracy

RANGE

Between 2% of range and full range.

20Hz-45Hz 45Hz-2kHz 2kHz-10kHz 10kHz-20kHz

500μA

5mA

1%+15

1%+15

0.5%+15

0.5%+15

1%+15

1%+15

2%+15

2%+15

50mA

500mA

2A

1%+15

1%+15

1%+15

0.5%+15

0.5%+15

0.5%+15

1%+15 2%+15

—————————

—————————

—————————

20A 1%+15 0.5%+15

Protection

500μA,5mA,50mA,500mA,2A 5 ranges fuse protection.

20A range no fuse,15 seconds max.

Crest Factor Range 3.0 at full scale.

The burden voltage is the same as the DC current.

When the input exceeds the full scale of the selected range, the display will appear

“—OL—” of over-range indication.

6. FREQUENCY MEASUREMENT AT ACA RANGE

RANGE FREQUENCY INPUT LEVEL (SINE WAVE) ACCURACY

500μA 10Hz ~ 20kHz

5mA 10Hz ~ 20kHz

50mA 10Hz ~ 20kHz

500mA 10Hz ~ 20kHz

≧

90μA

≧

0.9mA

≧

≧

9mA

90mA

0.05%+1

0.05%+1

0.05%+1

0.05%+1

2A 10Hz ~ 2kHz

≧ 1A 0.05%+1

20A 10Hz ~ 2kHz

≧ 9A 0.05%+1

AC+DC measurement does not support AC+Hz function.

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DUAL DISPLAY DIGITAL MULTIMETER

USER MANUAL

7.RESISTANCE

RANGE

500Ω

RESOLUTION

0.01Ω

ACCURACY

0.1%+4

5kΩ 0.1Ω

0.1%+2

50kΩ 1Ω

0.1%+2

500kΩ 10Ω

0.1%+2

5MΩ 100Ω

0.2%+2

20MΩ 1kΩ

0.3%+2

Open-circuit Voltage

3.2 volts maximum on 500Ω, 1.3 volts maximum on all other ranges.

Protection 450V dc or peak ac continuous.

8. CAPACITANCE

RANGE:

5n *

50n

RESOLUTION

0.001n

0.01n

ACCURACY

≧1nF: 2%+10

<1nF & ≧0.5nF: 2%+20

≧10nF: 2%+10

<10nF & ≧5nF: 2%+30

500n

5μ

50μ

0.1n

1n

10n

2%+4

2%+4

2%+4

*5n range tends to be interfered by the test lead’s impedance and position. For the accuracy, please measure the range on the input terminal directly.

Protection

450V dc or peak ac continuous.

9. DIODE CHECK

Description

Display read forward voltage of diode.

Open Voltage

3.1V approx.

Maximum Forward

Voltage

1.5V

Protection 450V dc or peak ac continuous.

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DUAL DISPLAY DIGITAL MULTIMETER

USER MANUAL

10. CONTINUITY BEEPER

Description Built in buzzer sounds if conductance is less than 5 ohm.

Open Voltage

Protection

3 volts maximum.

450V dc or peak ac continuous.

11. ENVIRONMENTAL

Indoor use, altitude up to 2000m.

Ambient Temperature 0℃ to 50℃.

Operation

Environment

Relative Humidity 75% (Maximum).

Installation category II

Pollution Degree 2

Storage temperature

-40℃ to 70℃.

Relative Humidity

Up to 75%, 0℃ to 35℃, Up to 50%, 35℃ to 50℃, except the ranges of 2MΩ and 20MΩ which are up to 75% , 0℃ to 35℃.

12. GENERAL

Maximum Common

Mode Voltage

Warm Up

Power source

500V dc or peak ac ( low terminal potential with respect to power line ground ).

0.5 hours to achieve rated accuracy.

Accessories

Dimension

Weigh

AC 100V/120V/230V±15%, 50/60Hz, 8.0VA, 6.0W.

Test Lead × 1

Instruction manual × 1

251(W)×91(H)×291(D) m/m

Approx. 2.6 kg

WARNING：To avoid electrical shock, the power cord

protective grounding conductor must be connected to ground.

CAUTION：To avoid damaging the instrument, do not use

it in a place where ambient temperature exceeds

50℃

.

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DUAL DISPLAY DIGITAL MULTIMETER

USER MANUAL

4. OPERATION INSTRUCTIONS

4-1 Front panel and rear panel

The front panel, shown in Figure4-1, contains three main elements: the input terminals, the primary and secondary displays, and the push buttons.

The rear panel, shown in Figure 4-2, contains the AC power-line connector, and fuse & line voltage selector, and input fuse holder.

4-2 The [SHIFT] key and function keys

[SHIFT] button is used to enable the secondary function of certain function keys that with blue symbols printed above. The SHIFT LED will be on after pressed the [SHIFT] button. At this time, only the buttons with blue symbols are workable. To release SHIFT function, press [SHIFT] again. For example, to select DCmV function, press

[SHIFT], then press [DCV] ([DCmV]).

4-3 Warm up

The instrument requires half-an-hour warm up to achieve rated accuracy.

4-4 Over-range indication

An input is over-range if it exceeds the full scale of the selected range.

GDM-8245 indicates an input is over-range by lighting the “—OL—” pattern on display.

4-5 No specification indication

On AC+Hz measured mode, when an input is less sensitivity, the secondary display show “————”. When the frequency of an input exceeds 51kHz, the primary display will show “————”.

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DUAL DISPLAY DIGITAL MULTIMETER

USER MANUAL

z Figure 4-1 Front Panel z Figure 4-2 Rear Panel

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DUAL DISPLAY DIGITAL MULTIMETER

USER MANUAL

4-6 Input overload protection

The maximum allowable input is shown as table 4-1. Please proceed the measurement accordingly.

Table 4-1:

FUNCTION

DCV

ACV (AC+DC)

DCA,ACA(AC+DC)

DC,AC20A(AC+DC)

DC,ACmV (AC+DC)

OHM

CAPACITANCE

RANGE

5V~1000V

5V~1000V

500μA~2A

20A

500mV all ranges all ranges

MAXIMUN INPUT

1000Vdc or peak ac

1000V rms continuous &

10

7

V•Hz maximum fuse protected: 2A 250V no fuse protected

450V dc or ac peak

450V dc or ac peak

450V dc or ac peak

WARNING: To avoid shock hazard and/or instrument damage, do not apply input potentials that exceed the input overload limits shown in table 4-1.

4-7 Input connections to common

WARNING: To avoid shock hazard and/or instrument damage, do not connect the common input terminal to any source of more than 500 volts DC or peak AC above earth ground.

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DUAL DISPLAY DIGITAL MULTIMETER

USER MANUAL

5. MEASUREMENT TUTORIAL

5-1. Voltage measurements (DCV, ACV, DCmV, ACmV)

1).Press the button to select desired function.

2).Press [▲]or[▼]to the desired range (if you have no idea about the value of input, we suggest you always start at the highest range).

Press [AUTO/MAN] button for manual or auto-ranging selection.

3).Connect the test lead to the V and COM input terminals of the instrument.

4).Connect the test lead to the measuring points and read the displayed value.

NOTE: After measuring high voltage to 1000V dc, errors may

occur when the 100μV is measured. Allow up to one minute

prior to making low-level measurements

5-2. Current measurements (DCA, DC 20A, ACA, AC 20A)

1).Press the button to select function.

2).Press [▲]or[▼]to the desired range.(if you have no idea about the value of input. we suggest you always start at the highest range).Press [AUTO/MAN] button to change manual or autoranging.

3).Connect the test lead to the 2A or 20A and COM input terminals of the instrument.

4).Connect the test lead to the measuring points and read the displayed value.

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DUAL DISPLAY DIGITAL MULTIMETER

USER MANUAL

5-3. Resistance, capacitance, continuity beeper measurements

1).Press the button to select function.

2).Press [▲]or[▼]to the desired range. Press [AUTO/MAN] button to change manual or auto-ranging.

3).Connect the test lead to the Ω, and COM input terminals of the instrument.

4).Connect the test lead to the measuring points and read the displayed value.

5-4. Diode test measurements

1).Press the button to select function.

2).Connect the test lead to the instrument.

and COM input terminals of the

3).Connect the test lead to the semiconductor junction (diode or transistor) as shown in Figure 5-1,and read the displayed value.

z Figure 5-1

Connect to Connect to

“ ” “COM”

terminal. terminal

5-5. dBm measurements

This function converts a voltage measurement into dBm. The function can be selected only when a voltage function (volts ac, volts dc, or volts ac+dc) is selected. Press [dBm] button, the secondary display shows the dBm value that reposed on the voltage value showed in the primary display.

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DUAL DISPLAY DIGITAL MULTIMETER

USER MANUAL

For example, if [dBm] is pressed when measuring voltage in the max mode, the maximum value is converted to dBm. To release the dBm function, press [dBm] again. The dBm mode and AC+Hz mode are not selected concurrently.

The standard reference impedance of the instrument is 600Ω.

5-6. AC+Hz measurements

The function can be selected only when ac range is selected. Press

[SHIFT], then press [AC+Hz], the secondary display shows the frequency of the input signal that is higher than the sensitivity. The frequency measurement does not depend on the max/min, rel, or hold mode. In this mode, the reading rate of the DMM may be slower than the normal state.

To release the AC+Hz function, press [AC+Hz] again. The dBm mode and AC+Hz mode are not selected concurrently.

5-7 AC+DC measurements

The function can be selected only when voltage or current function is selected. Press [AC+DC] button, the primary display shows the true rms value of the input signal including the ac component and dc component. In this mode, the reading rate of the DMM is slower than the normal state.

To release the AC+DC function, press other function (voltage ac or dc, current ac or dc, R,C, Continuity Beeper, Diode Test) key.

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DUAL DISPLAY DIGITAL MULTIMETER

USER MANUAL

5-8 MAX/MIN measurements

The MAX/MIN mode causes the DMM to hold the lowest and highest readings. Press [MAX/MIN] button to the MAX mode. The highest will be displayed in continuous input. In the MAX mode, press

[MAX/MIN] button to the MIN mode. The lowest will be displayed in continuous input. In the MIN mode, press [MAX/MIN] button to release the MAX/MIN mode.

5-9. REL measurements

When the [REL] button is pressed, the meter stores the present reading and displays subsequent measurements as the difference between the measured value and the stored reading.

In the MAX/MIN mode, set [REL] button to the REL mode. The maximum or minimum reading will become the relative base.

5-10. HOLD measurements

The HOLD mode that allows you to keep your eyes fixing on the probes when taking measurements in difficult or hazardous circumstances, then read the display when it is convenient and safe.

Press the [HOLD] button the last reading is held on the display in all function. To release the HOLD function, press [HOLD] again.

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USER MANUAL

6.MEASUREMENT TECHNIQUES

6-1 dBm measurement technique

dBm is defined as above or below a 1mW reference. A voltage measurement is converted to dBm using the following formula: dBm=10*log

10

(1000*voltage value

2

/reference impedance.)

The standard reference impedance of the instrument is 600Ω.

For example, 0.7746V will be convert to 0 dBm.

6-2 True rms measurement

The true rms (root-mean-square) value of a waveform is equivalent to dc value that causes the same amount of heat to be dissipated in a resistor.

Since average-responding meters have been in use for so long, you may have accumulated test or reference data based on them. Figure 6-

1 illustrates the relationship between ac and dc components for common waveforms, and compares readings for true rms meters and average-responding meters. Figure 6-1 will help you convert between the two measurement methods.

DUAL DISPLAY DIGITAL MULTIMETER

USER MANUAL z Figure 6-1: Voltage Conversion

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6-3 AC+DC measurement

A signal includes an ac component and a dc level. The relationship between the total rms value of the signal and the ac component and the dc component is: rms total=

(

a

c component rms)

2

+

(dc component)

2

6-4 Crest factor

Crest factor is often overlooked in determining the accuracy of an ac measurement. Crest factor is defined as the ratio of the peak signal amplitude to the rms value of the signal.

If an input signal has a crest factor of 3.0 or less, voltage measurements will not be in error due to dynamic range limitations at full-scale.

The waveforms in Figure 6-2 show signals with increasing value of crest factor. As you can see from the series of waveforms, a signal with a crest factor above 3.0 is unusual.

DUAL DISPLAY DIGITAL MULTIMETER

USER MANUAL z Figure 6-2: Crest Factor

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7.MAINTENANCE

The following instructions are executed by qualified personnel only. To avoid electrical shock, do not perform any servicing other than the operating instructions unless you are qualified to do so.

7-1 Line fuse replacement

If the fuse blows, the DMM would not work. Try to determine and correct the cause of the blown fuse, then replace the fuse with correct rating and type shown as below:

FUSE RATING AND TYPE

100/120V T0.1A 250V

230V

F101 on PCB

T0.08A 250V

T0.5A 250V

7-2 Current fuse replacement

The current fuse protects the 500μA~ 2A range from an input current greater 2A.To replace the current fuse, perform the following steps:

1).Turn off the power, disconnect the power line and remove the test leads.

2).Place the end of a flat blade screwdriver into the slot of the fuse holder on the front panel. Push and carefully rotate the fuse carrier turn counterclockwise till remove the fuse and the fuse carrier off the front panel.

3).Remove the defective fuse and replace the correct fuse (F2A 250V).

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DUAL DISPLAY DIGITAL MULTIMETER

USER MANUAL

7-3 Line voltage conversion

The primary winding of the power transformer is tapped to permit operation from 100/120V, or 230V AC 50/60Hz line voltage.

Conversion from one line voltage to another is done by changing the line voltage selector switch as shown in Figure 4-2. The rear panel identifies the line voltage to which the unit was factory set. To convert to a different line voltage, perform the following procedure:

1). Make sure the power cord is unplugged.

2). Adjust the line voltage selector switch to the desired line voltage position.

3). A change in line voltage may also require a corresponding change of fuse value. Install the correct fuse value as listed on rear panel.

7-4 Cleaning

To keep the instrument clean, wipe the case with a damp cloth and detergent. Do not use abrasives or solvents.

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