UNI-T UT33B/C/D Multimeter Operating Manual

Overview

This Operating Manual provides essential safety and caution information. Users are advised to read the relevant information carefully and strictly adhere to all Warnings and Notes.

Warning: To prevent electric shock or personal injury, read the "Safety Information" and "Rules for Safety Operation" thoroughly before using the Meter.

The UNI-T UT33B, UT33C, and UT33D Multimeters (referred to as "the Meter") are 3 1/2 digit instruments featuring steady operations, a fashionable design, and high reliability. They are capable of measuring AC/DC voltage, AC/DC current, resistance, temperature, diode, and continuity, making them ideal tools for maintenance.

Unless otherwise noted, the descriptions and instructions in this manual apply to all UT33B/UT33C/UT33D models.

Unpacking Inspection

Upon opening the package, carefully inspect the Meter and its contents for any missing or damaged parts. The package typically includes:

If any items are missing or damaged, please contact your dealer immediately.

Safety Information

This Meter complies with IEC61010 standards, including pollution degree 2, overvoltage category (CAT I 600V, CAT II 300V), and double insulation.

• CAT. I: Applies to signal level, special equipment, telecommunication, and electronic equipment with smaller transient overvoltages than CAT. II.
• CAT. II: Applies to local level, appliances, and portable equipment with smaller transient overvoltages than CAT. III.

Use the Meter only as specified in this operating manual to ensure the protection provided by the Meter is not impaired.

In this manual, a Warning indicates conditions or actions that pose hazards to the user or may damage the Meter or equipment under test. A Note highlights information that requires user attention.

International electrical symbols used on the Meter and in this manual are explained on page 10.

Rules For Safe Operation

Warning: To avoid electric shock or personal injury, and to prevent damage to the Meter or equipment under test, adhere to the following rules:

• Inspect the Meter's case before use. Do not use if the case is damaged or removed. Check for cracks or missing plastic and pay attention to connector insulation.
• Inspect test leads for damaged insulation or exposed metal. Check for continuity and replace damaged leads with identical models or specifications.
• Do not apply voltages exceeding the Meter's rated voltage between terminals or between a terminal and grounding.
• Ensure the rotary switch is in the correct position and avoid changing ranges during measurement to prevent Meter damage.
• When the Meter is working at voltages over 60V DC or 42V RMS AC, exercise special care due to the risk of electric shock.
• Use the correct terminals, function, and range for your measurements.
• Do not use or store the Meter in environments with high temperature, humidity, explosive, flammable materials, or strong magnetic fields, as this can degrade performance.
• Keep fingers behind the finger guards when using test leads.
• Disconnect circuit power and discharge high-voltage capacitors before testing resistance, continuity, diodes, and current.
• Before measuring current, check the Meter's fuses and turn off circuit power before connecting the Meter.
• Replace the battery immediately when the battery indicator appears. A low battery can lead to false readings, potentially causing electric shock or injury.
• Remove test leads and temperature probe, and turn off the Meter before opening the case.
• When servicing the Meter, use only replacement parts with identical model numbers or electrical specifications.
• Do not alter the internal circuit of the Meter to prevent damage or accidents.
• Clean the Meter's surface with a damp cloth and mild detergent. Avoid abrasive cleaners or solvents to prevent corrosion or damage.
• The Meter is suitable for indoor use only.
• Turn the Meter off and remove the battery when not in use for extended periods.
• Regularly check the battery for leaks. Replace a leaking battery immediately to prevent damage to the Meter.

International Electrical Symbols

The Meter Structure

The Meter consists of the following components (refer to figure 1):

1. LCD Display
2. HOLD Button
3. Display Backlight Button
4. Rotary Switch
5. COM Input Terminal
6. 10A Input Terminal
7. Other Input Terminals

(figure 1)

Functional Buttons

The following table describes the operations of the functional buttons:

Measurement Operation

A. DC Voltage Measurement

(see figure 2)

Warning: To avoid injury or Meter damage from electric shock, do not attempt to measure voltages higher than 500V, even if readings may be obtained.

The DC Voltage ranges are: 200mV, 2000mV, 20V, 200V, and 500V. To measure DC voltage:

1. Insert the red test lead into the VΩmA terminal and the black test lead into the COM terminal.
2. Set the rotary switch to the appropriate measurement position in the V range.
3. Connect the test leads across the object being measured.

The measured value will be displayed.

(figure 2)

Note:

• If the voltage to be measured is unknown, use the maximum measurement position (500V) and reduce the range step-by-step until a satisfactory reading is obtained.
• The LCD displays "1" when the selected range is overloaded, indicating a higher range is required for a correct reading.
• The Meter has an input impedance of approximately 10MΩ. In high impedance circuits, this loading effect can cause measurement errors. If the circuit impedance is less than or equal to 10kΩ, the error is negligible (0.1% or less).
• After completing DC voltage measurement, disconnect the connection between the testing leads and the circuit under test.

B. AC Voltage Measurement

(see figure 2)

Warning: To avoid injury or Meter damage from electric shock, do not attempt to measure voltages higher than 500Vrms, even if readings may be obtained.

The AC voltage measurement positions are: 200V and 500V. To measure AC Voltage:

1. Insert the red test lead into the VΩmA terminal and the black test lead into the COM terminal.
2. Set the rotary switch to the appropriate measurement position in the V~ range.
3. Connect the test leads across the object being measured.

The measured value, which is the effective value of a sine wave (mean value response), will be displayed.

Note:

• If the voltage to be measured is unknown, use the maximum measurement position (500V) and reduce the range step-by-step until a satisfactory reading is obtained.
• The LCD displays "1" when the selected range is overloaded, indicating a higher range is required for a correct reading.
• In each range, the Meter has an input impedance of approximately 5MΩ. This loading effect can cause measurement errors in high impedance circuits. If the circuit impedance is less than or equal to 10kΩ, the error is negligible (0.1% or less).
• The frequency response is 40Hz ~ 400Hz.
• When AC voltage measurement is completed, disconnect the connection between the testing leads and the circuit under test.

C. DC Current Measurement

(see figure 3)

Warning: Never attempt in-circuit current measurement if the voltage between terminals and ground exceeds 60V. Doing so may damage the Meter or cause operator injury if the fuse blows. Use proper terminals, function, and range. When connecting test leads to current terminals, do not parallel them across any circuit.

The Model UT33B has three current measurement positions on the rotary switch: 200μA, 200mA, and 10A.

The Model UT33C/UT33D has four current measurement positions on the rotary switch: 2000μA, 20mA, 200mA, and 10A.

To measure current:

1. Turn off power to the circuit and discharge all high-voltage capacitors.
2. Insert the red test lead into the VΩmA or 10A terminal and the black test lead into the COM terminal.
3. Set the rotary switch to the appropriate measurement position in the A range.
4. Break the current path to be tested. Connect the red test lead to the more positive side of the break and the black test lead to the more negative side of the break.
5. Turn on power to the circuit.

The measured value will be displayed.

(figure 3)

Note:

• If the current to be measured is unknown, use the maximum measurement position (10A) and reduce the range step-by-step until a satisfactory reading is obtained.
• When current measurement is completed, disconnect the connection between the testing leads and the circuit under test.
• At 10A Range: For continuous measurement, limit to ≤10 seconds with an interval of not less than 15 minutes.

D. Measuring Resistance

(see figure 4)

Warning: To avoid damage to the Meter or devices under test, disconnect circuit power and discharge all high-voltage capacitors before measuring resistance.

The Model UT33B/UT33C resistance measurement positions are: 200Ω, 2000Ω, 20kΩ, 200kΩ, and 20MΩ.

The Model UT33D resistance measurement positions are: 200Ω, 2000Ω, 20kΩ, 200kΩ, 20MΩ, and 200MΩ.

To measure resistance:

1. Insert the red test lead into the VΩmA terminal and the black test lead into the COM terminal.
2. Set the rotary switch to the appropriate measurement position in the Ω range.
3. Connect the test leads across the object being measured.

The measured value will be displayed.

(figure 4)

Note:

• Test leads can add 0.1Ω to 0.3Ω error to resistance measurements. For precision readings in low-resistance measurements (range of 200Ω), short-circuit the input terminals beforehand and record the reading (X). (X) represents the additional resistance from the test lead. Use the equation: measured resistance value (Y) - (X) = precision readings of resistance.
• For high-resistance measurements (>1MΩ), it may take several seconds to obtain a stable reading.
• When resistance measurement is completed, disconnect the connection between the testing leads and the circuit under test.

E. Diodes and Continuity Measurement

(see figure 5)

Testing Diodes

Warning: To avoid damage to the Meter or devices under test, disconnect circuit power and discharge all high-voltage capacitors before testing diodes.

Use the diode test to check diodes, transistors, and other semiconductor devices. The diode test sends a current through the semiconductor junction and measures the voltage drop across it. A good silicon junction typically drops between 0.5V and 0.8V.

To test a diode out of a circuit:

1. Insert the red test lead into the VΩmA terminal and the black test lead into the COM terminal.
2. Set the rotary switch to ⌡ (for Model UT33B) or ⎳⌡ (for Model UT33C/UT33D).
3. For forward voltage drop readings, place the red test lead on the component's anode and the black test lead on the component's cathode.

The measured value will be displayed.

(figure 5)

Note: In a circuit, a good diode should still produce a forward voltage drop reading of 0.5V to 0.8V. However, the reverse voltage drop reading can vary depending on the resistance of other pathways between the probe tips.

Testing for Continuity (UT33C/UT33D only)

To test for continuity:

1. Insert the red test lead into the VΩmA terminal and the black test lead into the COM terminal.
2. Set the rotary switch to ⎳⌡.
3. Connect the test leads across the object being measured.

The buzzer sounds if the resistance of the circuit under test is less than 70Ω.

Note: The LCD displays "1" indicating the circuit being tested is open.

When continuity testing is completed, disconnect the connection between the testing leads and the circuit under test.

F. Model UT33C: Temperature Measurement

(see figure 6)

Warning: To avoid injury or Meter damage, do not attempt to input voltages higher than 60V DC or 30V AC.

The Temperature measurement range is -40°C to 1000°C or -40°F to 1832°F. To measure temperature:

1. Insert the red temperature probe into the VΩmA terminal and the black temperature probe into the COM terminal.
2. Set the rotary switch to °C or °F.
3. Place the temperature probe on the object being measured.

The measured value will be displayed.

(figure 6)

Note:

• The Meter automatically displays the temperature value inside the Meter when there is no temperature probe connection.
• The included point contact temperature probe is rated for use up to 250°C (482°F). For measurements above this temperature, a rod type temperature probe must be used.
• When temperature measurement is completed, disconnect the connection between the testing leads and the circuit under test.

G. The Model UT33B: Battery Test

(see figure 7)

Warning: To avoid injury or Meter damage, do not attempt to input voltages higher than 60V DC or 30V AC.

To test the battery:

1. Insert the red test lead into the VΩmA terminal and the black test lead into the COM terminal.
2. Set the rotary switch to the appropriate measurement position in the ↕ range.
3. Connect the test leads across the battery being measured, ensuring correct polarity.

The measured value, which is the voltage between the cathode and anode of the battery, will be displayed.

(figure 7)

Note: When battery testing is completed, disconnect the connection between the testing leads and the circuit under test.

H. The Model UT33D: Square Wave Output

Warning: To avoid Meter damage, do not allow output terminals (red test lead) to reach higher than 10V.

To measure square wave output:

1. Set the rotary switch to ↕ OUT.
2. The square wave signal outputs between the VΩmA and COM Terminals.

Note:

• The frequency is approximately 50Hz.
• The output scope is higher than 3Vpp when loaded with 1MΩ.

When square wave output testing has been completed, disconnect the connection between the testing leads and the circuit under test.

General Specifications

• Maximum Voltage (including transient overvoltage) between any Terminals and Grounding: 500V rms.
• Fused Protection for VΩmA Input Terminal: 315mA, 250V fast type, φ5x20 mm.
• 10A Terminal: Un-fused.
• Range: Manual ranging.
• Maximum Display: 1999.
• Measurement Speed: Updates 2~3 times /second.
• Temperature:
  • Operating: 0°C~40°C (32°F~104°F).
  • Storage: -10°C~50°C (14°F~122°F).
• Relative Humidity: ≤75% @ 0°C - 30°C; ≤50% @ 31 - 40°C.
• Altitude: Operating: 2000 m; Storage: 10000 m.
• Battery Type: One piece of 9V Battery NEDA 1604 or 6F22 or 006P.
• Battery Deficiency: Display: ⏣.
• Negative reading: Display: — .
• Overloading: Display: 1.
• Dimensions (HxWxL): 130 x 73.5 x 35mm.
• Weight: Approx. 156g (battery included).
• Safety/Compliances: IEC61010 CAT.I 600V overvoltage and double insulation standard.
• Certification: CE

Accuracy Specifications

Accuracy: ±(a% reading + b digits), guarantee for 1 year.

Operating temperature: 23°C ± 5°C.

Relative humidity: <75%.

Temperature coefficient: 0.1 x (specified accuracy) / 1°C.

A. DC Voltage

Remark: Input impedance: 10MΩ.

B. AC Voltage

Remarks:

• Input impedance: approx. 5MΩ.
• Displays effective value of sine wave (mean value response).
• Frequency response 40Hz ~ 400Hz.

C. DC Current

Remark:

• At 10A Range: For continuous measurement ≤10 seconds and interval not less than 15 minutes.

D. Resistance

E. Diodes and Continuity Measurement

(Continuity test only for UT33C/UT33D)

F. The Model UT33C: Temperature

G. The Model UT33B: Battery Test

H. The Model UT33D: Square Wave Output

Remark:

• No overload protection.
• Make sure voltage output of calibrated equipment level is less than 10V to avoid damages to the meter.

Maintenance

This section provides basic maintenance information, including battery and fuse replacement instructions.

Warning: Do not attempt to repair or service the Meter unless you are qualified and have the necessary calibration, performance test, and service information. To avoid electrical shock or Meter damage, do not allow water to enter the case.

A. General Service

• Periodically wipe the case with a damp cloth and mild detergent. Do not use abrasives or solvents.
• Clean terminals with a cotton swab and detergent; dirt or moisture in the terminals can affect readings.
• Turn the Meter to the OFF position when not in use and remove the battery if storing for a long time.
• Do not store the Meter in environments with humidity, high temperature, explosive, flammable materials, or strong magnetic fields.

B. Replacing the Battery

(see figure 8)

Warning: To avoid false readings that could lead to electric shock or personal injury, replace the battery as soon as the battery indicator ⏣ appears.

To replace the battery:

1. Disconnect the testing leads from the circuit under test and remove them from the Meter's input terminals.
2. Turn the Meter to the OFF position.
3. Remove the screw from the case bottom and separate the bottom from the top case.
4. Remove the battery from the battery compartment.
5. Replace the battery with a new 9V battery (NEDA 1604 or 6F22 or 006P).
6. Rejoin the case parts and reinstall the screw.

(figure 8)

C. Replacing the Fuses

(See figure 8)

Warning: To avoid electrical shock, arc blast, personal injury, or Meter damage, use specified fuses ONLY according to the following procedure.

To replace the Meter's fuse:

1. Disconnect the testing leads from the circuit under test and remove them from the Meter's input terminals.
2. Turn the Meter to the OFF position.
3. Remove the screw from the case bottom and separate the bottom from the top case.
4. Gently pry one end of the fuse loose and remove it from its bracket.
5. Install ONLY replacement fuses with the identical type and specification: 315mA, 250V, fast type, φ 5x20mm. Ensure the fuse is firmly seated in the bracket.
6. Rejoin the case parts and reinstall the screw.

Replacement of fuses is seldom required. A blown fuse typically results from improper operation.