NJTY T28B Digital Multimeter User Manual

1. Introduction

The NJTY T28B is a high-precision digital multimeter designed for household and professional electrical measurements. It features True RMS measurement, a 6000-count display, and a wide range of functions including AC/DC voltage, AC/DC current, resistance, capacitance, frequency, temperature, diode, and continuity testing. This manual provides detailed instructions for safe and effective use of your multimeter.

Figure 1: NJTY T28B Digital Multimeter highlighting key features.

2. Safety Information

Always observe safety precautions when using this multimeter to prevent electric shock or personal injury. Improper use can damage the instrument or connected equipment.

• Read and understand all instructions in this manual before use.
• Do not exceed the maximum input values for any function.
• Ensure the test leads are in good condition and properly connected for the measurement being performed.
• Do not use the meter if it appears damaged or if the casing is open.
• Be cautious when working with voltages above 30V AC RMS, 42V peak, or 60V DC, as these pose a shock hazard.
• Always disconnect power to the circuit under test before connecting or disconnecting test leads for current measurements.
• Replace batteries when the low battery indicator appears to ensure accurate readings.
• The device is equipped with overload protection. However, avoid inputting voltage into current sockets to prevent damage.

3. Package Contents

Verify that all items are present in your package:

• NJTY T28B Digital Multimeter
• Test Probes (Red and Black)
• Temperature Probe
• User Manual

Figure 2: Included accessories: Multimeter, Test Probes, Temperature Probe, and User Manual.

4. Product Overview

Familiarize yourself with the components of your NJTY T28B Multimeter:

Figure 3: Front panel and input jacks.

• Display Screen: Shows measurement readings and indicators.
• Function Knob: Rotary switch to select measurement functions (e.g., V, A, Ω, Hz, °C, NCV).
• FUNC/HOLD Button: Short press to switch between functions within a mode (e.g., AC/DC, Hz/Duty Cycle). Long press for Data Hold.
• Hz/%/Δ Button: For Frequency/Duty Cycle measurements.
• RANGE Button: For manual range selection (Auto Range is default).
• Flashlight/Backlight Button: Activates the flashlight and display backlight.
• NCV Electric Field Induction Probe: For Non-Contact Voltage detection.
• Input Jacks:
• mA/μA Jack: For small current measurements (up to 500mA FUSED).
• 20A Jack: For large current measurements (up to 20A FUSED).
• COM Jack: Common (negative) input for all measurements.
• VΩHz°C Jack: Positive input for Voltage, Resistance, Frequency, Capacitance, Diode, Continuity, and Temperature measurements.

Figure 4: Multimeter with soft rubber casing for protection.

Figure 5: Multimeter with integrated kickstand for convenient viewing.

5. Setup

5.1 Battery Installation

The NJTY T28B Multimeter requires four 1.5V AAA batteries for operation. Batteries are not included.

1. Ensure the multimeter is turned OFF.
2. Locate the battery compartment on the back of the device.
3. Use a screwdriver to open the battery compartment cover.
4. Insert four 1.5V AAA batteries, observing the correct polarity (+/-) as indicated inside the compartment.
5. Replace the battery compartment cover and secure it with the screw.

Figure 6: Battery compartment requiring four 1.5V AAA batteries.

Figure 7: Correct battery insertion.

6. Operating Instructions

Before any measurement, ensure the multimeter is set to the correct function and the test leads are connected to the appropriate input jacks.

6.1 General Measurement Steps

1. Turn the function knob to the desired measurement mode.
2. Connect the black test lead to the COM jack.
3. Connect the red test lead to the appropriate positive input jack (VΩHz°C for voltage, resistance, etc., or mA/μA/20A for current).
4. Connect the test leads to the circuit or component under test.
5. Read the measurement value on the display.

6.2 AC Voltage Measurement

1. Turn the function knob to the 'V~' (AC Voltage) position.
2. Connect the black test lead to the COM jack and the red test lead to the VΩHz°C jack.
3. Connect the test leads in parallel across the AC voltage source.
4. Read the AC voltage value on the display.

Figure 8: AC Voltage Measurement. Ensure correct jack usage.

6.3 DC Voltage Measurement

1. Turn the function knob to the 'V=' (DC Voltage) position.
2. Connect the black test lead to the COM jack and the red test lead to the VΩHz°C jack.
3. Connect the test leads in parallel across the DC voltage source, observing polarity.
4. Read the DC voltage value on the display.

Figure 9: DC Voltage Measurement.

6.4 Current Measurement (AC/DC)

WARNING: Current measurements must always be made in series with the circuit. Never connect the multimeter in parallel across a voltage source when in current mode, as this will cause a short circuit and damage the meter or power source.

1. Turn the function knob to the 'A~' (AC Current) or 'A=' (DC Current) position.
2. Determine the expected current range. For small currents, connect the red test lead to the mA/μA jack. For large currents (up to 20A), connect the red test lead to the 20A jack. The black test lead always goes to COM.
3. Open the circuit where you want to measure current and connect the multimeter in series.
4. Read the current value on the display.

Figure 10: Current Measurement. Note the series connection.

6.5 Resistance Measurement

1. Turn the function knob to the 'Ω' (Resistance) position.
2. Connect the black test lead to the COM jack and the red test lead to the VΩHz°C jack.
3. Ensure the circuit or component is de-energized before measuring resistance.
4. Connect the test leads across the component.
5. Read the resistance value on the display.

Figure 11: Resistance Measurement.

6.6 Capacitance Measurement

1. Turn the function knob to the 'Cx' (Capacitance) position.
2. Connect the black test lead to the COM jack and the red test lead to the VΩHz°C jack.
3. Ensure the capacitor is fully discharged before measurement to prevent damage to the meter.
4. Connect the test leads across the capacitor terminals.
5. Read the capacitance value on the display. The meter can measure up to 100,000 μF.

Figure 12: Capacitance Measurement.

6.7 Frequency/Duty Cycle Measurement

1. Turn the function knob to the 'Hz/%' position.
2. Connect the black test lead to the COM jack and the red test lead to the VΩHz°C jack.
3. Connect the test leads across the signal source.
4. Press the 'Hz/%/Δ' button to toggle between Frequency (Hz) and Duty Cycle (%).
5. Read the value on the display.

6.8 Temperature Measurement

1. Turn the function knob to the '°C/°F' (Temperature) position.
2. Connect the temperature probe to the VΩHz°C and COM jacks, observing polarity if applicable.
3. Place the tip of the temperature probe on or near the object whose temperature you wish to measure.
4. The display will show the temperature in Celsius (°C) or Fahrenheit (°F). Use the FUNC button to switch between units.

Figure 13: Temperature Measurement with switchable units.

6.9 Diode Test

1. Turn the function knob to the 'Diode' position (often shared with Continuity).
2. Connect the black test lead to the COM jack and the red test lead to the VΩHz°C jack.
3. Connect the red test lead to the anode and the black test lead to the cathode of the diode.
4. The display will show the forward voltage drop. Reverse the leads; the display should show 'OL' (Open Loop) for a good diode.

Figure 14: Diode Voltage Drop Measurement.

6.10 Continuity Test

1. Turn the function knob to the 'Continuity' position (often shared with Diode).
2. Connect the black test lead to the COM jack and the red test lead to the VΩHz°C jack.
3. Connect the test leads across the circuit or component.
4. If the resistance is below a certain threshold (typically 50Ω), the buzzer will sound, and the display will show a low resistance value.

Figure 15: Continuity Buzzer Measurement.

6.11 Non-Contact Voltage (NCV) Detection

1. Turn the function knob to the 'NCV' position.
2. Hold the NCV Electric Field Induction Probe near a live AC voltage source (e.g., a wall outlet or live wire).
3. The meter will emit an audible beep and/or flash an indicator light, with the display showing 'NCV' and bars indicating signal strength, if AC voltage is detected.

Figure 16: Non-Contact Voltage (NCV) Detection.

6.12 Additional Features

• Data Hold: Press and hold the 'FUNC/HOLD' button to freeze the current reading on the display. Press again to release.
• Backlight/Flashlight: Press the 'Flashlight/Backlight' button to turn on the display backlight or the integrated flashlight. Press again to cycle or turn off.
• Auto Shutdown: The multimeter will automatically power off after approximately 15 minutes of inactivity to conserve battery life.
• Low Voltage Indication: An icon will appear on the display when the battery voltage is low, indicating that batteries should be replaced soon.
• Magnetic Attraction Feature: The back of the multimeter has a magnetic strip for convenient attachment to metal surfaces.

7. Specifications

The following table outlines the functional parameters and general specifications of the NJTY T28B Digital Multimeter:

Figure 17: Functional Parameters Table.

Figure 18: Device Dimensions.

8. Maintenance

8.1 Cleaning

Wipe the case with a damp cloth and mild detergent. Do not use abrasives or solvents. Keep the input terminals free of dirt and moisture.

8.2 Battery Replacement

When the low battery indicator appears on the display, replace the batteries as described in the 'Setup' section (5.1 Battery Installation). Remove batteries if the meter is not used for an extended period.

8.3 Fuse Replacement

If the current measurement function fails, the fuse may need replacement. Refer to the internal circuit board diagram for fuse locations. Always replace with a fuse of the specified type and rating (e.g., 500mA FUSED for mA/μA jack, 20A FUSED for 20A jack).

Figure 19: Internal circuit board for reference.

9. Troubleshooting

• No Display/Meter won't turn on: Check battery installation and ensure batteries are not depleted. Replace if necessary.
• 'OL' (Overload) displayed: The measured value exceeds the selected range or the meter's maximum capability. Switch to a higher range (if in manual range mode) or ensure the input is within the meter's limits.
• Incorrect Readings:
• Check if the function knob is set to the correct measurement type.
• Ensure test leads are properly connected to the correct input jacks.
• Verify that the test leads are not damaged.
• For resistance or capacitance, ensure the component is isolated from the circuit and fully discharged.
• Current measurement not working: Check the fuse for the selected current jack (mA/μA or 20A). Replace if blown.
• Buzzer not sounding during continuity test: The resistance may be too high, or the circuit is open.

10. User Tips

• Probe Quality: Always ensure your test probes are in good condition and rated for the maximum voltage and current you intend to measure. The included probes are designed for the meter's specifications, including the 20A current range.
• Preventing Damage: When measuring current, it is critical to connect the multimeter in series with the load. Never connect the current jacks directly across a voltage source (e.g., a battery or wall outlet) as this will immediately blow the fuse or damage the instrument.
• Capacitor Discharge: For capacitance measurements, always discharge capacitors before connecting the multimeter to avoid potential damage to the meter or inaccurate readings.
• Auto Range Convenience: The T28B features auto-ranging, which simplifies operation by automatically selecting the correct measurement range. You can use the 'RANGE' button to switch to manual ranging if needed for specific applications.

11. Warranty and Support

For warranty information or technical support, please refer to the seller's policies or contact the point of purchase. Keep your purchase receipt as proof of purchase.