Mastech MS8251A Digital Multimeter User Manual

1. Introduction

Thank you for purchasing the Mastech MS8251A Digital Multimeter. This device is a portable, professional measuring instrument with a large LCD display, providing clear and easy-to-read results. It is designed for use in laboratories, factories, and homes, offering a wide range of functions including AC/DC voltage, AC/DC current, resistance, capacitance, frequency, duty cycle, temperature, diode, continuity, and non-contact voltage (NCV) detection.

Please read this manual thoroughly before using the meter to ensure safe and proper operation. Keep this manual for future reference.

2. Safety Information

WARNING: To avoid possible electric shock or personal injury, and to avoid possible damage to the meter or to the equipment under test, follow these instructions:

• Always ensure the meter is in the correct function and range for the measurement being performed.
• Do not apply more than the rated voltage, as marked on the meter, between the terminals or between any terminal and earth ground.
• Use caution with voltages above 30V AC RMS, 42V peak, or 60V DC. These voltages pose a shock hazard.
• Before making current measurements, ensure the meter's fuses are intact and the test leads are connected to the correct input jacks.
• Disconnect the circuit power and discharge all high-voltage capacitors before testing resistance, continuity, diodes, or capacitance.
• Do not use the meter if it is damaged or if the case (or part of the case) is removed. Inspect the meter before use.
• Do not operate the meter around explosive gas, vapor, or dust.
• When servicing the meter, use only specified replacement parts.
• Always use approved test leads.
• Do not use the meter if the battery cover is not properly closed.
• Remove the test leads from the meter before opening the battery cover.

3. Key Features

• Display: 6600 counts
• Auto Ranging and Manual Ranging capabilities
• Automatic Power Off function to conserve battery life
• Relative Measurement mode
• Non-Contact Voltage (NCV) Detector for safety
• Diode Open Voltage: 3.2V
• Continuity Buzzer for quick circuit checks
• MAX/MIN value recording
• Data Hold function to freeze readings
• Low Battery Display indicator
• Display Backlight for visibility in low-light conditions

Figure 3.1: Overview of Mastech MS8251A features, main applications, and included contents. This image illustrates the versatility of the multimeter across domestic, industrial, and electronics applications, highlighting its core functionalities and what comes in the box.

4. Product Components and Overview

The Mastech MS8251A Digital Multimeter is designed for ease of use and durability. Familiarize yourself with its main parts:

• LCD Display: Shows measurement readings, units, and function indicators.
• Function Buttons: REL△, RANGE, MAX/MIN, HOLD, FUNC, NCV, Backlight.
• Rotary Switch: Selects the desired measurement function (e.g., V~, V—, Ω, A~, A—, Temp, Diode, Continuity, Hz%).
• Input Jacks:
• COM: Common terminal for all measurements.
• VΩHz%Temp→←: Input for voltage, resistance, frequency, duty cycle, temperature, diode, and continuity measurements.
• mAμA: Input for milliampere and microampere current measurements.
• 10A: Input for 10 Ampere current measurements (fused).

Figure 4.1: Front view of the Mastech MS8251A Digital Multimeter, showing the LCD display, function buttons, rotary switch, and input jacks. This image provides a clear visual reference for identifying the various parts of the device.

5. Setup

5.1. Battery Installation

The Mastech MS8251A requires 2 LR44 batteries (included). To install or replace batteries:

1. Ensure the meter is turned OFF and disconnect all test leads from the input terminals.
2. Locate the battery compartment on the back of the meter.
3. Use a screwdriver to loosen the screw(s) on the battery cover.
4. Remove the battery cover.
5. Insert the 2 LR44 batteries, observing the correct polarity (+ and -).
6. Replace the battery cover and tighten the screw(s).

5.2. Connecting Test Leads

Always connect the common (black) test lead to the COM jack. Connect the red test lead to the appropriate input jack based on the measurement you intend to make:

• For Voltage, Resistance, Capacitance, Frequency, Duty Cycle, Temperature, Diode, and Continuity measurements, connect the red lead to the VΩHz%Temp→← jack.
• For milliampere (mA) or microampere (μA) current measurements, connect the red lead to the mAμA jack.
• For 10 Ampere (10A) current measurements, connect the red lead to the 10A jack.

6. Operating Instructions

Before any measurement, ensure the test leads are correctly connected and the rotary switch is set to the desired function.

6.1. General Operation

• Power ON/OFF: Turn the rotary switch from OFF to any function to power on. Turn to OFF to power off.
• Auto Power Off: The meter will automatically power off after approximately 15 minutes of inactivity to save battery. Press any button or turn the rotary switch to wake it up.
• Backlight: Press the ★ button to turn the display backlight on or off.
• Data Hold: Press the HOLD button to freeze the current reading on the display. Press again to release.
• MAX/MIN: Press the MAX/MIN button to enter MAX/MIN recording mode. The meter will display the maximum or minimum reading detected. Press again to cycle between MAX, MIN, and current reading. Hold to exit.
• RANGE: In auto-ranging mode, press RANGE to switch to manual ranging. Press repeatedly to cycle through available ranges. Hold to return to auto-ranging.
• REL△ (Relative Measurement): Press REL△ to store the current reading as a reference value. Subsequent readings will be displayed as the difference from this reference. Press again to exit.
• FUNC: In multi-function positions (e.g., Diode/Continuity/Temp), press FUNC to cycle through the available sub-functions.

6.2. Specific Measurement Functions

Below are common measurement procedures. Always refer to the specifications for ranges and accuracy.

6.2.1. DC Voltage Measurement (V—)

1. Set the rotary switch to the V— position.
2. Connect the black test lead to the COM jack and the red test lead to the VΩHz%Temp→← jack.
3. Connect the test leads across the component or circuit to be measured in parallel.
4. Read the voltage value on the display.

6.2.2. AC Voltage Measurement (V~)

1. Set the rotary switch to the V~ position.
2. Connect the black test lead to the COM jack and the red test lead to the VΩHz%Temp→← jack.
3. Connect the test leads across the component or circuit to be measured in parallel.
4. Read the voltage value on the display.

6.2.3. Resistance Measurement (Ω)

1. Set the rotary switch to the Ω position.
2. Connect the black test lead to the COM jack and the red test lead to the VΩHz%Temp→← jack.
3. Ensure the circuit is de-energized before measuring resistance.
4. Connect the test leads across the resistor or component.
5. Read the resistance value on the display.

6.2.4. Continuity Test (→←)

1. Set the rotary switch to the →← position. Press FUNC if necessary to select continuity.
2. Connect the black test lead to the COM jack and the red test lead to the VΩHz%Temp→← jack.
3. Ensure the circuit is de-energized.
4. Connect the test leads across the circuit or component. If resistance is less than approximately 50Ω, the buzzer will sound, indicating continuity.

6.2.5. Diode Test (→←)

1. Set the rotary switch to the →← position. Press FUNC if necessary to select diode test.
2. Connect the black test lead to the COM jack and the red test lead to the VΩHz%Temp→← jack.
3. Ensure the circuit is de-energized.
4. Connect the red test lead to the anode and the black test lead to the cathode of the diode. The display will show the forward voltage drop. Reverse the leads; the display should show OL (Open Loop) for a good diode.

6.2.6. Non-Contact Voltage (NCV) Detection

1. Set the rotary switch to the NCV position.
2. Move the top end of the meter close to the AC voltage source (e.g., a live wire).
3. The meter will beep and the NCV indicator light will flash if AC voltage is detected. The frequency of beeps and flashes increases with stronger signals.

For other functions like Current (AC/DC), Capacitance, Frequency, Duty Cycle, and Temperature, follow similar steps, ensuring the rotary switch is set to the correct function and test leads are connected to the appropriate input jacks.

7. Maintenance

7.1. Cleaning

Wipe the case with a damp cloth and mild detergent. Do not use abrasives or solvents. Keep the terminals free from dirt or dust, which can affect readings.

7.2. Battery Replacement

When the low battery indicator appears on the display, replace the batteries immediately to ensure accurate readings. Refer to Section 5.1 for battery installation instructions.

7.3. Fuse Replacement

If the meter fails to measure current, the fuse may be blown. To replace the fuse:

1. Ensure the meter is turned OFF and disconnect all test leads.
2. Open the battery compartment as described in Section 5.1.
3. Locate the fuse(s). The MS8251A typically uses a 10A fuse for the 10A input and a 600mA fuse for the mA/μA input.
4. Carefully remove the old fuse and replace it with a new fuse of the same type and rating.
5. Replace the battery cover and tighten the screw(s).

Note: Always use fuses with the specified voltage and current ratings for safety and proper operation.

8. Troubleshooting

9. Specifications

9.1. General Specifications

• Product Dimensions: 7.87 x 5.91 x 9.84 inches (200 x 150 x 250 mm)
• Item Weight: 2.2 Pounds (1 Kilogram)
• Color: Blue
• Power Source: Battery Powered (2 LR44 batteries, included)
• Manufacturer: MASTECH
• Model Number: YQ-MS8251A
• Safety Rating: CAT III 600V, CAT II 1000V

9.2. Electrical Specifications

Figure 9.1: Detailed electrical specifications for the Mastech MS8251A, including ranges, resolutions, and accuracy for various measurement functions such as DC Voltage, AC Voltage, DC Current, AC Current, Resistance, Capacitance, Frequency, and Duty Cycle.

Figure 9.2: Comparison table highlighting features and specifications across various Mastech digital multimeters, including the MS8251A, providing context on its capabilities relative to other models.

10. Warranty

The Mastech MS8251A Digital Multimeter comes with a 1-year limited warranty from the date of purchase. This warranty covers defects in materials and workmanship under normal use. It does not cover damage caused by misuse, accident, unauthorized repair, neglect, or modification. Please retain your purchase receipt as proof of purchase for warranty claims.

11. Support

For technical support, troubleshooting assistance, or warranty inquiries, please contact Mastech customer service. You can find more information and contact details on the official Mastech website or through the retailer where you purchased the product.

Visit the Mastech Store on Amazon for additional product information and support resources.