AstroAI AM33D Digital Multimeter User Manual

Introduction

Thank you for purchasing the AstroAI Digital Multimeter. The AstroAI Digital Multimeter is designed to be safely and accurately used in schools, laboratories, factories, and other social/industrial settings. This user manual provides all the safety information, operation instructions, specifications, and maintenance information for the meter. This tool can test AC/DC Voltage, DC Current, Resistance, Diodes, and Continuity.

Thank you again for choosing AstroAI. If you have any questions or concerns regarding your product, please contact support@astroai.com.

Note: Please fully read and understand this manual before using this product and keep it for future reference.

Warning

To avoid possible electric shocks, personal injury, and damage to the meter or the equipment being tested, adhere to the following rules:

• Use the meter strictly in accordance with this manual. Otherwise, the protection function provided by the meter may be damaged or weakened.
• Be especially careful when measuring over 60 V DC, 30 V AC RMS, or 42 V peak value, as there is an increased risk of electric shocks.
• Do not apply more than the rated voltage marked on the meter, between the terminals or between any terminal and grounding.
• Check whether the meter is working normally by measuring a known voltage. Do not use it if the readings are incorrect or if the meter is damaged.
• Before using the meter, check for cracks or damage to the meter's plastic casing. Do not use the meter if any part of the exterior casing is damaged.
• Use the meter according to the measurement category, voltage, or current rating specified on the meter or manual.
• Comply with local and national safety regulations. Wear personal protective equipment (such as approved rubber gloves, masks, and flame-retardant clothing, etc.) to prevent injury from electric shocks and arcs when hazardous live conductors are exposed.
• Replace the battery as soon as the low-battery indicator appears to avoid measurement errors.
• Do not use the meter around explosive gas, steam, or humid environments.
• When using the test leads, keep your fingers behind the finger guards.
• When measuring, connect the neutral/ground wire first, then connect the live wire. When disconnecting, disconnect the live wire first and then disconnect the neutral/ground wires.
• Before opening the case or battery cover, remove the test leads from the meter. Do not use the meter when it is disassembled or when the battery cover is opened.
• The meter can only be safely used with the equipped test leads. Before using the meter, please check the test leads. If they are damaged and need to be replaced, only replace them with the same model and the same electrical specifications.

Package Includes

• User Manual x 1
• Pair of Test Leads x 1
• AstroAI Digital Multimeter x 1

Electric Symbols

• AC (Alternating Current)
• DC (Direct Current)
• V Voltage
• A Current
• Square Wave
• Double Insulation
• CE Compliant with EU Standards
• Low Battery Symbol ?
• Audible Continuity Test ?
• Diode Test ⚡
• Ω Resistance Test
• Earth Ground ⏚
• Warning ⚠️

Diagram

The multimeter features the following components:

• 1 LCD Screen: Displays measurement readings.
• 2 OFF: Rotary switch position to turn off the meter.
• 3 Hold Button: Press to hold or cancel the current reading.
• 4 DC Voltage Test: Rotary switch position for DC voltage measurements.
• 5 Rotary Switch: Selects the measurement function and range.
• 6 Resistance: Rotary switch position for resistance measurements.
• 7 10 A Terminal: Input for measuring high DC current (up to 10A).
• 8 VΩmA Terminal: Input for voltage, resistance, continuity, diode, and low current measurements.
• 9 Backlight Button: Press to turn on/off the LCD backlight.
• 10 AC Voltage Test: Rotary switch position for AC voltage measurements.
• 11 DC Current Test: Rotary switch position for DC current measurements (mA range).
• 12 Square Wave Output: Output terminal for square wave signals.
• 13 Continuity Test/Diode Test: Rotary switch position for continuity and diode tests.
• 14 COM Terminal: Common (negative) input for test leads.
• 15 Test Leads: Probes for connecting to the circuit under test.

Dimensions

The multimeter measures approximately 2.9 inches (7.3 cm) in width, 5.12 inches (13.0 cm) in height, and 1.6 inches (3.7 cm) in depth.

Button Functions

Hold Button

Press the HOLD Button to hold or cancel the data. Pressing this button during a test freezes the reading on the screen. Pressing it again turns off the hold function. The screen will display 'H' when the data hold function is active.

Backlight Button

Press the Backlight Button to turn on the screen's backlight for better visibility in dim environments. The backlight dims slowly when turned off. Press the button again to illuminate it. To quickly turn off the backlight, move the rotary switch to the OFF position.

Instructions

General Precautions:

• To avoid damaging the meter, do not measure voltages exceeding 600 V.
• This is a manual range multimeter; ensure you select the correct measuring range to prevent damage.
• Pay special attention to safety when measuring high voltages to avoid electric shock or personal injury.
• Before use, confirm the meter's functions work properly by testing a known voltage or current.

Measuring DC Voltage

1. Insert the red test lead into the “VΩmA” terminal and the black test lead into the “COM” terminal.
2. Turn the rotary switch to the continuity test (? symbol) and touch the red and black test leads together. The buzzer will beep if the test leads are normal.
3. Turn the rotary switch to the DC Voltage (“V=”) area. The screen will display “000”.
4. Connect the test leads to the circuit being tested in parallel to the power supply or circuit.
5. If the reading is negative, the positive and negative poles of the test leads are reversed; switch the test leads.
6. After the reading stabilizes, record the reading from the LCD screen.
7. Turn the rotary switch to the OFF position to turn off the meter.

Note: The test unit is “V”. If the number is followed by “m”, the unit is “mV”. “HV” is displayed for the maximum range (600 V setting).

Measuring AC Voltage

1. Insert the red test lead into the “VΩmA” terminal and the black test lead into the “COM” terminal.
2. Turn the rotary switch to the continuity test (? symbol) and touch the red and black test leads together. The buzzer will beep if the test leads are normal.
3. Turn the rotary switch to the AC Voltage (“V~”) area. The screen will display “000”.
4. Connect the test leads to the circuit being tested in parallel to the power supply or circuit.
5. After the reading stabilizes, record the reading from the LCD screen.
6. Turn the rotary switch to the OFF position to turn off the meter.

Voltage Tips:

How to find a live wire in a socket:

1. Switch to the voltage test setting.
2. Connect the black test lead to the grounded wire or terminal. Connect the red test lead to one of the terminals to be measured.
3. Check both terminals. One should have a reading, and the other should remain at or near zero. The live wire will be the one with the reading.

Voltage Notes:

• When measuring an unknown voltage, choose the 600 V setting. After the initial measurement, select an appropriate range based on its voltage.
• Do not measure voltage exceeding 600 V DC or 600 V AC CAT II.
• If the AC setting is used to measure DC or vice versa, an overflow symbol will be displayed. This may damage the meter and components.
• Voltage readings may fluctuate depending on the power supply. Fluctuations of ±10 V are normal and not indicative of inaccuracy.

Measuring DC Current

1. Disconnect the power supply of the circuit under test.
2. Insert the red test lead into the “VΩmA” terminal and the black test lead into the “COM” terminal.
3. Turn the rotary switch to the continuity test (? symbol) and touch the red and black test leads together. The buzzer will beep if the test leads are normal.
4. Insert the black test lead into the “COM” terminal and the red test lead into the 10 A terminal.
5. Turn the rotary switch to the 10 A setting of the “A-” area. The screen will display “000” for DC current from 200 mA to 10 A.
6. Connect the meter to the circuit under test in series and then turn on the circuit's power supply.
7. After the reading stabilizes, record the reading from the LCD screen.
8. Turn the rotary switch to the OFF position to turn off the meter.

Note: Start with the 10 A setting when measuring unknown current. The test unit is “A”. If followed by “m”, it’s “mA”. If followed by “μ”, it’s “μA”.

Automotive Parasitic Battery Drain:

1. Check if battery voltage (approx. 12.7 V) and power generation (approx. 14 V) are within the normal range.
2. Turn off all electrical accessories inside and outside the car and close the doors.
3. Remove the battery's negative electrode. Set the multimeter to the maximum current level and connect the meter in series to the battery.
4. Connect the red test lead to the negative line and the black test lead to the battery terminal.
5. Adjust the meter to a lower range if necessary.
6. Wait for about 30 minutes for vehicle modules to enter sleep state. Read the static discharge current (typically 0.02 A or 20 mA, but can vary; normally not exceeding 50 mA).
7. If the drain is larger than 50 mA, check fuses individually to identify the circuit drawing excess load. Removing a fuse that reduces the draw below 50 mA indicates that circuit is the source.

Current Notes:

• When measuring unknown current, start with a higher maximum rating setting and then select an appropriate range based on the result.
• If using the 10 A terminal, ensure the test lead is returned to the “VΩmA” terminal before the next operation to prevent damage.
• For high current tests, limit each measurement to less than 10 seconds, with at least 15 minutes between tests.
• A load must be present in the circuit when testing current. Connecting the multimeter in series without a load can damage the meter.
• Do not apply current exceeding the meter's range.

Measuring DC A Current

1. Disconnect the power supply of the circuit under test.
2. Insert the red test lead into the “VΩmA” terminal and the black test lead into the “COM” terminal.
3. Turn the rotary switch to the continuity test (? symbol) and touch the red and black test leads together. The buzzer will beep if the test leads are normal.
4. Turn the rotary switch to the “A-” area with yellow font. The screen will display “000” for DC A current from 2000 μA to 200 mA.
5. Connect the meter to the circuit under test in series and then turn on the circuit's power supply.
6. After the reading stabilizes, record the reading from the LCD screen.
7. Turn the rotary switch to the OFF position to turn off the meter.

Measuring Resistance

1. Insert the red test lead into the “VΩmA” terminal and the black test lead into the “COM” terminal.
2. Turn the rotary switch to the continuity test (? symbol) and touch the red and black test leads together. The buzzer will beep if the test leads are normal.
3. Turn the rotary switch to the “Ω” area with yellow font. The screen will display “1” (or OL) indicating resistance measurement.
4. Connect the test leads to both ends of the circuit or resistor under test in parallel.
5. After the reading stabilizes, record it from the LCD screen.
6. Turn the rotary switch to the OFF position to turn off the meter.

Note: The test unit is “Ω”. If followed by “M”, it’s “MΩ”. If followed by “K”, it’s “KΩ”.

Resistance Notes:

• Do not change resistance while measuring, as it may damage the meter and affect results.
• Do not test parallel circuits; accuracy may be affected.
• Do not directly measure the internal resistance of micrometers, galvanometers, batteries, or other instruments.

Continuity Test

1. Insert the red test lead into the “VΩmA” terminal and the black test lead into the “COM” terminal.
2. Turn the rotary switch to the continuity test (? symbol). Touch the red and black test leads together. The buzzer will beep if the test leads are normal.
3. Connect the test leads to both ends of the circuit or resistor under test in parallel. If the resistance is less than 50 Ω, the buzzer will emit a beep sound.
4. If the circuit or resistor is disconnected, or the resistance value is greater than 30 Ω ± 20 Ω, the LCD screen will display “1” (or OL).
5. Turn the rotary switch to the OFF position to turn off the meter.

Diode Test

1. Insert the red test lead into the “VΩmA” terminal and the black test lead into the “COM” terminal.
2. Turn the rotary switch to the diode test (⚡ symbol). Touch the red and black test leads together. The buzzer will beep if the test leads are normal.
3. Connect the red test lead to the anode of the diode under test and the black test lead to the cathode of the diode. (Usually, the anode is the longer end).
4. The LCD screen will display the approximate voltage drop reading of the diode (unit: “mV”). If the test leads are connected in reverse, “1” will be displayed. Switch the test leads and measure again.
5. Turn the rotary switch to the OFF position to turn off the meter.

Diode Test Tips:

• Forward Conduction: If the red lead is connected to the positive pole and the black lead to the negative pole, the diode should conduct, displaying the forward voltage drop.
• Normal Diode Forward Voltage Drop: Silicon diodes: 0.5-0.7 V. Germanium diodes: 0.15-0.3 V.
• Reverse Bias: If the red lead is connected to the negative pole and the black lead to the positive pole, the diode should block, displaying “1”.

Polarity Judgment Method:

1. Switch the multimeter to the Resistance setting.
2. Connect the two test leads to the two electrodes of the diode.
3. Measure one result, then swap the positions of the test leads and measure the second result.
4. The larger result is the reverse resistance, and the smaller result is the forward resistance. The smaller resistance occurs when the black test lead is connected to the positive end of the diode and the red lead to the negative end.

Square Wave Output

1. Insert the red test lead into the “VΩmA” terminal and the black test lead into the “COM” terminal.
2. Turn the rotary switch to the continuity test (? symbol). Touch the red and black test leads together. The buzzer will beep if the test leads are normal.
3. Turn the rotary switch to the “OUT” setting. The screen will display “1” indicating square wave output.
4. Connect the test leads in parallel to both ends of the power supply or circuit being tested.
5. After the reading stabilizes, record the reading from the LCD screen.
6. Turn the rotary switch to the OFF position to turn off the meter.

Maintenance

Cleaning the Meter

If there is dust or humidity in the terminals, it may produce erroneous measurements. Clean the meter as follows:

1. Turn off the meter and remove the test leads.
2. Turn the meter over and shake out accumulated dust. Wipe the case with a damp cloth or mild detergent. Wipe the contacts in each terminal with a clean cotton swab dampened in alcohol.

Replacing the Battery and Fuse

Battery Replacement

1. Turn off the meter and remove the test leads.
2. Unscrew the battery cover screws with a screwdriver and remove the cover.
3. Remove the old battery and replace it with a new battery of the same specification.
4. Put the battery cover back to its original position and affix it with the removed screws.

Battery Type: 1 x 9 V Battery NEDA 1604/6F22/006P.

Fuse Replacement

1. Turn off the meter and remove the test leads.
2. Unscrew the battery cover screws with a screwdriver and remove the cover and batteries.
3. Remove the insulating sleeve and screws on the back cover of the meter.
4. Remove the blown fuses and replace them with new fuses of the same specification. Ensure the fuses are loaded into the fuse clip and clamped tightly.
5. Replace the insulation cover, battery, and battery cover, then secure with screws.

Fuse specifications:

• Fuse 1: F500 mA/600 V fuse; Size: Ø5 × 20 mm.
• Fuse 2: F10 A/600 V fuse; Size: Ø5 × 20 mm.

Specifications

• Digital Display: 2000, 3 1/2 digits
• Sampling Speed: 2 Times/Second
• LCD Dimensions: 1.93 x 0.67 Inches / 49 x 17 mm
• Range Selection: Manual
• Polarity Indication: “-” Automatically Displayed
• Overload Indication: “1” Displayed
• Work Environment: 32–104 °F; 0–40 °C, at <80%RH
• Storage Temperature: 14–122 °F; -10–50 °C, at <85%RH
• Power: 1 x 9 V Battery NEDA 1604/6F22/006P
• Weight: 0.32 lb / Approximately 145 g
• Dimensions: 5.12 x 2.87 x 1.46 Inches / 130 x 73 x 37 mm
• Low Battery Indication: “?” Displayed when battery voltage is lower than normal

Detailed Specifications

Accuracy is guaranteed for 1 year, with storage conditions of 23 °C ± 5 °C, less than 80%RH.

DC Voltage

AC Voltage

DC Current

Measured Voltage Drop: 200 mV.

Resistance

Maximum Open Circuit Voltage: 3 V.

Continuity Test

Recycling

You may dispose of the product when its service life has ended. Please recycle the recyclable parts according to local guidelines.

Warranty Period

3-Year Limited Warranty from AstroAI.

Each AstroAI Digital Multimeter will be free from defects in material and workmanship. This warranty does not cover fuses, disposable batteries, and damage from neglect, misuse, contamination, alteration, accident, or abnormal conditions of operation or handling, including over-voltage failures caused by use outside the meter's specified rating, or normal wear and tear of mechanical components. This warranty covers the original purchaser only and is not transferable.

Questions or concerns? Please contact support@astroai.com.