Extech Instruments MS420 User manual

USER MANUAL
Digital 20MHz Oscilloscope
Model MS420 - 20MHz

2MS420-en-US_V6.0 2/23
INTRODUCTION
Congratulations on your purchase of the Extech Digital Oscilloscope. This manual is
divided into two sections: Section One for the Oscilloscope functions and Section
Two for the Multimeter functions. This meter is shipped fully tested and calibrated
and, with proper use, will provide years of reliable service.

3MS420-en-US_V6.0 2/23
TABLE OF CONTENTS
PRODUCT CONTENTS ····································································· 5
SUPPLIED EQUIPMENT SAFETY INFORMATION································· 6
Safety Symbols and Terms··········································································6
GENERAL SAFETY INFORMATION ···················································· 7
INPUT CONNECTIONS ····································································· 9
Input Connections ·····················································································9
FRONT PANEL AND KEYPAD OVERVIEW ·········································10
BASIC OSCILLOSCOPE FUNCTIONS ················································12
About this Chapter··················································································· 12
Powering the Oscilloscope ········································································ 12
Main Oscilloscope Display Screen······························································· 12
Menu Description ···················································································· 14
MANUALLY SETTING THE TRIGGER POSITION AND TIME BASE ········15
Recall the Factory Default Settings······························································ 18
OSCILLOSCOPE INPUT CONNECTIONS············································19
Measure Unknown Signals using the Auto-Set Feature ···································· 19
Auto Zero the Horizontal Trigger and Trigger Level Position ······························ 19
Automatic Measurement Ranging ······························································· 19
Data Hold (Freezing the Displayed Reading) ················································· 20
Using the Average Mode to Smooth Waveforms············································· 21
Persistence Mode (superimposing waveforms)··············································· 22
Using Peak Detection to Capture Glitches····················································· 23
Glossary of Terms ··················································································· 24
Selecting AC-coupling ·············································································· 24
Reversing the Polarity of the Displayed Waveform ·········································· 25
Using Mathematical Functions on Waveforms················································ 26
USB mass storage device / Save waveform data ············································ 27
ADVANCED OSCILLOSCOPE FUNCTIONS ········································28
Vertical Settings for CH1 and CH2 ······························································ 28
Setting the probe attenuation ····································································· 31
Invert a Waveform ··················································································· 31
WAVE MATH Function Menu Settings·························································· 31
Setting the Trigger System ········································································ 33
Triggering Control···················································································· 33
Edge Triggering ······················································································ 34
Video Triggering······················································································ 35
Glossary of Terms ··················································································· 41
Acquisition Mode····················································································· 41
Display Setting························································································ 42
Persistence ···························································································· 43
XY Mode ······························································································· 43
Storing Waveforms ·················································································· 44

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Function Setting Menu (refer to Table below)················································· 45
Automatic Ranging Measurements ······························································ 46
Cursor Measurements ·············································································· 51
Square wave output test signal (5V, 1 KHz)··················································· 54
System Status Menu ················································································ 55
Main Time Base Mode·············································································· 56
USING THE MULTIMETER································································58
About this Chapter··················································································· 58
Making Meter Connections ········································································ 58
Multimeter Display Window········································································ 58
MAKING MULTIMETER MEASUREMENTS ·········································60
Measuring Resistance ·············································································· 60
Measuring Diode Voltage ·········································································· 61
Continuity Test························································································ 62
Measuring Capacitance ············································································ 63
Measuring DC Voltage·············································································· 64
Measuring AC Voltage·············································································· 65
Measuring DC Current·············································································· 66
Measuring AC Current ·············································································· 67
Freezing the Readings (Data Hold)······························································ 69
Taking a Relative Measurement·································································· 69
Selecting the Automatic / Manual Range Modes ············································· 69
FAQ ······························································································71
APPENDICES ·················································································72
Appendix A: Specifications ········································································ 72
MULTIMETER ························································································ 76
GENERAL SPECIFICATIONS····························································78
Appendix B: Maintenance and Cleaning ······················································· 79
Appendix C: Charging the Instrument··························································· 80
Appendix D: Set the Real-time clock ···························································· 81
TWO-YEAR WARRANTY··································································82

5MS420-en-US_V6.0 2/23
PRODUCT CONTENTS
MS420 Instrument
1. AC Adaptor
2. Oscilloscope Probes (2); Grey in color
3. Multimeter test leads (2); One black, one red
4. USB mass storage connection cable
5. Extension module for low capacitance measurements
6. Probe adjustment tools
7. USB or Serial PC Communication cable
8. User manual
9. CD-ROM Software Program
10. Carrying Case

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SUPPLIED EQUIPMENT SAFETY INFORMATION
Please read the user manual before use to ensure safety and precision
SAFETY SYMBOLS AND TERMS
SAFETY SYMBOLS
THESE SYMBOLS MAY APPEAR IN THIS MANUAL OR ON THE INSTRUMENT:
WARNING:“WARNING”IDENTIFIES CONDITIONS &ACTIONS THAT
POSE A HAZARD TO THE USER
Caution: “Caution” identifies conditions and actions that may damage
the product or external equipment
SAFETY TERMS
The following terms may appear on the instrument:
Danger: The term “Danger” is used in this manual to indicate that
immediate personal injury can result
Warning: The term “Warning” is used in this manual to indicate that,
although immediate personal injury is not likely, caution should be taken
Notice: The term “Notice” is used in this manual to indicate that
damage to the meter or to other equipment can occur
DANGER:
High
Refer to
the
Manual
Protective
Conductor
Terminal
Chassis
Ground
Earth
(ground)
Terminal

7MS420-en-US_V6.0 2/23
GENERAL SAFETY INFORMATION
Carefully read the following safety information in order to avoid personal injury and
damage to this product or to products connected to it. This product must only be
used in the specified manner to prevent danger and hazard to products and persons.
Warning:
To avoid fire or electrical shock please use the proper power adapter. Use only the
power adapter recommended by the manufacturer.
Warning:
To avoid fire or electrical shock do not connect meter to more than 42V peak
(30Vrms) or on circuits of more than 4800VA:
●Use only the insulated voltage probes, test leads and adapter supplied with the
test tool, or as indicated by Extech as suitable for the Oscilloscope & Multimeter.
●Before use, inspect voltage probes, test leads and accessories for mechanical
damage. Replace the equipment when it appears damaged.
●Remove all probes, test leads and accessories when not in use.
●Always connect the power adapter first to the AC outlet before connecting it to
the Oscilloscope & Multimeter.
●Do not apply voltages that exceed 400 V from earth ground to any input when
measuring in a CAT II environment.
●Do not apply voltages that exceed 400 V to the isolated inputs when measuring in
a CAT II environment.
●Use caution when using 1:1 test leads since the probe tip voltage will be directly
transmitted to the Oscilloscope & Multimeter.
●Do not use exposed metal BNC or banana plug connectors.
●Do not insert metal objects into the connectors.
●Always use the Oscilloscope & Multimeter in the manner specified.
●Voltage ratings, mentioned in the warnings, are provided as “working voltage”
limits. They represent V ac rms (50-60Hz) for AC sine wave applications and as
V dc for DC applications. Overvoltage Category II refers to local level applicable
for appliances and portable equipment.
Only qualified technical personnel should perform maintenance on these devices.
Observe the nominal value limits for all terminals: To avoid fire or electric shock,
observe all nominal value limits, markings, and specifications for this product. Before
connecting to this product, carefully read the user’s manual.
Do no operate this instrument without the cover plate secured: If the cover plate
or panel has been removed, do not use this product.
Do not touch bare conductors

8MS420-en-US_V6.0 2/23
Do not use this meter in case of any undetermined failure: When in doubt consult
qualified repair personnel
Do not hinder the meter’s ventilation: Refer to the user manual for detailed
installation instructions and proper setup for adequate ventilation
Do not operate this meter in overly humid environments.
Do not operate this meter in potentially explosive environments.
Keep the meter’s surface clean and dry.
Use of this device in any manner inconsistent with the uses specified in this manual
can possibly compromise the safety protection provided by the meter.

9MS420-en-US_V6.0 2/23
INPUT CONNECTIONS
INPUT CONNECTIONS
See Figure 2 below
Figure 2
Description
1. The power adapter is use to supply AC power and for battery recharging
2. Multimeter test leads
3. Multimeter input jacks (L to R: Current 2A-10A input, mA Current input, COM
ground input, Voltage/Resistance/Capacitance input)
4. Oscilloscope probes
5. Oscilloscope channel inputs
6. Square wave output jack
6

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FRONT PANEL AND KEYPAD OVERVIEW
Figure 3
Description of Meter Front Panel and Keypad (Figure 3)
1. AC adapter Port
2. RS-232C Port
3. USB Port
4. USB Mass Storage Port

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5. Power switch
6. F1 – F5 Soft-key options
7. AUTO SET: In the Scope mode, the meter automatically selects the
horizontal/vertical scale and trigger level
8. COPY: Press to store the waveform data into a USB storage device
9. ▲ (Red): Adjust the horizontal scale for Channel 1
10. VOLTS POSITION (Red): Switch between voltage and horizontal scales for
Channel 1
11. ▼ (Red): Adjust the horizontal scale for Channel 1
12. ▲ (Blue): Adjust the horizontal scale for Channel 2
13. VOLTS POSITION (Blue): Switch between the voltage and horizontal scales
for Channel 2
14. ▼ (Blue): Adjust the horizontal scale for Channel 2
15. RUN/STOP: Start/Stop the waveform capture process
16. BACKLIGHT: Turn the display backlight ON and OFF
17. DMM/OSC: Operation mode (switch between oscilloscope and multimeter)
18. MENU ▲: Choose a higher item on a menu list
19. MENU: Show / Hide menu
20. MENU ▼: Choose a lower item on a menu list
21. OPTION: Used in combination with the four (4) yellow arrow keys. This button
is used to set the main time base, trigger horizontal position and trigger vertical
position. Also used to adjust the display multiplier factors and display vertical
position during waveform calculation. Further, it is used to adjust cursor 1 (V1
or T1) and cursor 2 (V2 or T2) position during cursor measurements
22. ▲(yellow): Oscilloscope UP arrow adjustment key
23. ▼(yellow): Oscilloscope DOWN arrow adjustment key
24. ►(yellow): Oscilloscope FORWARD adjustment key
25. ◄(yellow): Oscilloscope BACKWARD adjustment key
26. A: Selects DMM Current measurement mode
27. V: Selects DMM Voltage measurement mode
28. R: Selects DMM impedance, diode, continuity, capacitance measurement
mode
29. SET: Toggle AC/DC in the current or voltage multimeter measurement modes;
also switches between resistance, diode and capacitance modes while in the
resistance mode.

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BASIC OSCILLOSCOPE FUNCTIONS
ABOUT THIS CHAPTER
This chapter provides introductory Oscilloscope instructions. This introduction does
not cover all of the oscilloscope capabilities but provides basic examples of menu
navigation and operations. Detailed instructions are provided in the Advanced
Oscilloscope functions section.
POWERING THE OSCILLOSCOPE
Connect the oscilloscope to an AC power source using the supplied AC adaptor.
If the battery is charged, the oscilloscope may be powered by the supplied and
installed Li-ion battery. The meter will run for up to four (4) hours on a full charge.
Turn the oscilloscope on by pressing the power key.
Upon power up, the instrument performs a ‘self check’. The display will show the
“press any key to continue……” screen.
MAIN OSCILLOSCOPE DISPLAY SCREEN
Figure 4: Oscilloscope Display Screen
Description of Oscilloscope Display Screen (Figure 4)
1. Battery power status icon ( , , and )

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2. Auto measurement screen No. 1 (“f” for frequency, “T” for cycle, “V” for
average value, “Vp” is the peak-peak value and “Vk” is the root-mean-
square value
3. Auto measurement screen No. 2
4. Horizontal triggering position
5. The difference in time between the horizontal triggering position and the
screen’s centerline (zero when the pointer is in the center of the screen)
6. The trigger modes:
Auto: The oscilloscope is in the automatic mode and displaying the waveform
in the non-trigger mode
Trig’d: The oscilloscope has detected a trigger and is displaying the
information generated after the trigger
Ready: All pre-triggered data has been captured and the oscilloscope is ready
to receive trigger signals
Scan: The oscilloscope records and displays waveform data continuously
Stop: The oscilloscope has stopped collecting waveform data
7. Red and blue trigger pointer shows vertical position of alternate triggers.
The trigger pointer turns green when it reaches an edge trigger or a video
trigger
8. Hide or View the menu using the MENU key;
9. Menu setting options (vary with each function)
10. Trigger Voltage Level
11. Trigger signal source
12. Primary Time Base
13. The coupling mode for CH2; “~” AC, “-” DC, and ground
14. The vertical Voltage units scale for CH2
15. The coupling mode for CH1; “~” AC, “-” DC, and ground
16. Vertical Unit Scale for CH1

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17. The blue pointer shows the ground point of the waveform for CH2
(zero position). If this pointer is not shown, the channel has not been
opened.
18. OPTION (options vary with each function)
19. The red pointer shows the ground point of the waveform for CH1 (zero
position). If this pointer is not shown, the channel has not been
opened
20. Waveform display area. Red waveform represents CH1, blue
represents CH2
MENU DESCRIPTION
The following explains how to navigate the menus to select a function.
1. Press the MENU key to open the Function Menu. The Menu appears on the right
of the screen with the corresponding options available on the bottom of the
screen. Press MENU again to hide the Function Menu.
2. Use the MENU ▲ or MENU ▼ keys to navigate and select menu functions.
3. Use the soft-keys (F1…F5) to select an available option
Figure 5: Menu

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MANUALLY SETTING THE TRIGGER POSITION AND TIME BASE
Use the OPTION key to set the vertical trigger position, the main time base and the
horizontal trigger position during Edge triggering and Video Triggering or vertical
trigger position for Horizontal time base and vertical trigger position and horizontal
level position during an Alternate trigger.
The following example shows how to use the OPTION key to change a setting.
For triggering in edge and video trigger mode:
1. Press the OPTION key once; the following will appear at the screen’s bottom left:
◄/► – Time Base
▲/▼ – Trig
Figure 6
2. Press ◄ (yellow) or ► (yellow) to adjust the main time base. Press ▲ (yellow)
or▼ (yellow) to adjust the trigger horizontal position.
3. Press OPTION again and the following will appear:
◄/► – Time
▲/▼– Trig

16 MS420-en-US_V6.0 2/23
Figure 7
4. Press ◄(yellow) or ►(yellow) to adjust time base horizontal position, press▲
(yellow) or ▼ (yellow) to adjust trigger position.
5. Use the OPTION key to toggle between the two modes described above.
When triggering in the Alternate trigger mode:
7. Press OPTION and the following will appear:
—Time
—Trig 2
Figure 8:

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7. Press ◄(yellow) or ►(yellow) to adjust the time base horizontal position and
press ▲ (yellow) or ▼ (yellow) to adjust the trigger horizontal position for Channel 2.
8. Press OPTION again to display the following:
— Time Base
— Trig 1
Figure 9:
9. Press ◄(yellow) or ►(yellow) to adjust the main time base and press ▲
(yellow) or▼ (yellow) to adjust the trigger horizontal position for Channel 1.
10. Press OPTION again to return to step 6 above.
Glossary of Terms
Vertical scale factor: The voltage amplitude represented by a division in the
vertical direction of the display area, through the adjustment of which the user can
amplify or attenuate the signal and thus regulate the signal amplitude so that it is
placed in the expected measurement range.
Vertical zero position: Ground point, through the adjustment of which the user
can regulate the display position of the waveform on the screen.
Main time base: The time value represented by a division in the horizontal
direction of the display area.

18 MS420-en-US_V6.0 2/23
Trigger horizontal position: The time difference between the actual trigger point
and the screen central line, which will be displayed as 0 at the center point of the
screen.
Trigger level position: The voltage difference between the actual trigger level
and the zero position of the triggering signal source channel.
RECALL THE FACTORY DEFAULT SETTINGS
To reset the Oscilloscope to the factory default settings, refer to the following:
1. Press the MENU key; the function menu will appear on the right side of the
screen
2. Press the MENU ▲ or MENU ▼ key to select a FUNCTION; three options will be
visible at the bottom of the screen.
3. Press F1 (Recall Factory) to recall the factory settings.
4. Press F2 to select “Auto calibration”. If the ambient temperature varies from the
specified operating temperature by more than 5 degrees Celsius, an Auto
Calibration should be performed.
Refer to Figure 10:
Figure 10: Resetting the Oscilloscope

19 MS420-en-US_V6.0 2/23
OSCILLOSCOPE INPUT CONNECTIONS
The Oscilloscope has two (2) signal inputs (located on the lower right side) for CH1
and CH2 measurements.
Isolated inputs allow for independent floating measurements between Multimeter and
Scope functions.
MEASURE UNKNOWN SIGNALS USING THE AUTO-SET FEATURE
The Auto-Set feature allows the Oscilloscope to measure and display unknown
signals automatically. This function optimizes position, range, time-base, and
triggering. It also assures a stable display of virtually any waveform. Auto Range is
especially useful for quickly checking several signals.
To enable the Auto-Set feature, perform the following steps:
1. Connect the test probe to the circuit or device under test.
2. Press the AUTO SET key; the test signals will appear on the screen.
AUTO ZERO THE HORIZONTAL TRIGGER AND TRIGGER LEVEL POSITION
To configure the instrument so that the horizontal trigger and the trigger level position
automatically return to zero.
1. Press the Vkey; the horizontal trigger position will automatically return to zero
2. Press the Rkey; the trigger level position will automatically return to zero
AUTOMATIC MEASUREMENT RANGING
The Oscilloscope offers five (5) ranges that adjust automatically as measurements
are taken. Two numeric readings can be displayed: MEAS SET1and MEAS SET2
(selectable independently); the measurements can be performed on the CH1 or CH2
waveform inputs.
To choose a frequency for CH1, perform the following procedure:
1. Press the MENU key; the function menu will appear on the right side of the
screen.
2. Press MENU ▲ or MENU ▼ to select MEAS SET 1. Five selectable options
will then be visible at the bottom of the screen.

20 MS420-en-US_V6.0 2/23
3. Press the F1 key and select Freq CH1 from the root mean square (RMS)
option. The MEAS SET 1window color will change to red and display CH1
frequency.
To choose Peak-Peak measurements for the CH2 input, refer to the following:
1. Press the MENU key; the function menu will appear at the right side of the
screen.
2. Press MENU ▲ or MENU ▼ key to select MEAS SET 2. Five (5) selectable
options will appear at the bottom of the screen.
3. Press the F4 key to select PK-PK CH2 from the Peak-Peak option. The
MEAS SET2window color turns to blue and displays the peak-peak value for
the CH2 input.
Refer to Figure 11:
Figure 11: Automatic Scope Measurements
DATA HOLD (FREEZING THE DISPLAYED READING)
To freeze any displayed reading or waveform, follow these steps:
1. Press the RUN/STOP key to freeze the screen: STOP appears at the top
(right) of the screen.
2. Press the RUN/STOP key again to resume normal mode. Refer to Fig. 12: