UNI-T UT171A/B/C Industrial True RMS Digital Multimeter

I. Overview

The UT171A/B/C DMM is a compact, handheld, automatic-ranging digital multimeter featuring a 4 3/4-4 5/6 digit true virtual value display. It offers comprehensive functions including AC/DC voltage and current, resistance, diode testing, circuit continuity, capacitance, frequency, duty ratio, temperature measurement, % (4-20mA) conversion, conductivity testing, Voltage to Frequency Converter (V.F.C.), Non-Contact AC Voltage Sensing (NCV), 600A AC/DC current measurement via calipers, square-wave output, data storage, misoperation alarm, and USB/Bluetooth interface configuration. It is designed as an essential portable instrument for users in design, research, and repair applications.

II. Accessories

Upon opening the packing box, please verify the presence and condition of the following accessories. Contact your supplier immediately if any items are missing or damaged:

• Operation Instruction (one copy)
• Probe (one pair)
• Point K-type (nickel-chromium nickel-silicon) thermocouple (configured for UT171B/C only, one piece)
• Lithium battery charger (configured for UT171B/C only, one piece)
• USB cable (one piece)
• Bluetooth interface (optional accessory)
• Current calipers (UT171C only, optional accessory)

III. Safety Operation Criterion

The UT171A/B/C is designed to meet safety standards IEC/EN61010-1, pollution level 2, and is rated for overvoltage categories CAT III 1000V and CAT IV 600V, with double insulation. Adhering to the following operational guidelines is crucial to prevent instrument damage and ensure user safety:

• Warning: Do not operate the instrument without the rear cover securely in place, as this poses an electric shock hazard.
• Before use, inspect the probe's insulation layer to ensure it is intact and free from any damage or broken wires.
• Replace the battery when the "□" symbol appears on the LCD to maintain measurement accuracy.
• Ensure the function range switch is set to the correct measurement position.
• Do not allow detected signals to exceed the specified limit values to prevent electric shock and instrument damage.
• Avoid changing the range switch settings while a measurement is in progress to prevent instrument damage.
• After completing a measurement, always disconnect the probe from the circuit under test. For current measurements, ensure power is disconnected and probes are removed from the circuit, especially when measuring high currents.
• Exercise caution when measuring voltages exceeding DC 30V or AC 30Vrms to prevent electric shock.
• Avoid using the instrument in environments with high temperature and humidity. Do not store it in a humid environment, as this can lead to performance degradation.
• Do not attempt to modify the internal wiring of the instrument, as this can cause damage and compromise safety.
• Clean the instrument casing using a damp cloth and mild detergent. Do not use abrasive cleaners or solvents.
• Utilize test probes that comply with CATIV 600V, CATIII 1000V standards or higher, as specified by IEC61010-31.

Electrical Symbols:

• Double insulation: [double-insulation symbol]
• Warning: [warning symbol]
• Grounding: [grounding symbol]
• CE: Indicates compliance with European Union directives.
• Intertek: Symbol signifies compliance with requirements in both the USA and Canada.

IV. Comprehensive Specification

V. Appearance Structure (Refer to Figure 1)

Diagram showing the appearance of the UT171A/B/C multimeter, illustrating the display, function knob, buttons, and input terminals. Key components include:

1. Shell
2. Displayer
3. Function key (3/4/7)
4. Range knob switch (5)
5. Input terminal for measuring (6)
6. Alarm luminous diode (8)
7. USB cable/Bluetooth interface/NCV sensing terminal (9)

The displayer (illustrated in Figure 2) shows various symbols such as Auto Peak, MIN AVG MAX H, AC+DC, Δ, µA, mS, VFC, LoZ, Hz, kHz, CoF, nS, °C, °F, etc., indicating measurement modes, units, and status.

VI. Displayer (Refer to Figure 2)

Illustration of various symbols displayed on the multimeter's screen, indicating measurement modes, units, and status. The displayer shows the following symbols and their specifications:

VII. Knob of Function Selection and Button

The function knob and buttons are used to control the instrument's operations:

Buttons:

• RANGE button: Switches between automatic and manual range modes. Press and hold for over 2 seconds to exit manual range mode (applicable to V~, Ω, I, Freq, Cap, and LoZ functions).
• STORE button: Short press to save data, indicated by "STO" flashing on the LCD. Long press to enter the automatic storage setting menu, where interval (1-240 seconds) and duration (minutes) for automatic storage can be set.
• RECALL button: Short press to enter recall mode, indicated by "D" or "VIEW" on the LCD. Use the REL or HZ button to navigate through stored data. The RANGE button deletes current data, and the HOLD button exits recall mode.
• MAX/AVG/MIN/Peak hold button: Short press to enter manual range recording modes (MAX, AVG, MIN). The automatic shutdown function is cancelled in these modes. Long press the "Peak hold" button to enter peak measurement mode (response time approx. 1mS).
• HOLD/: button (Data-hold/backlight): Short press to lock the displayed value, indicated by an "H" prompt. Press again to unlock. Long press to turn the backlight on/off (UT171A) or cycle through three backlight luminance levels (UT171B/C).
• RELA button (Direction selection/relative measurement): Short press to enter relative measurement mode, using the current displayed value as a reference. The difference between the measured value and the reference is shown on the main display. Press again to re-select the current value as the reference. Long press to exit REL mode (applicable to V~, Ω, I, °C/°F functions).
• Hz/%/Setup button: Use to switch between frequency and duty ratio measurements. Long press to enter the system setting menu, which allows adjustment of brightness, USB communication, buzzer, automatic light-off timer, automatic power-off timer, date/time settings (UT171C), and memory formatting.
• SELECT/ V.F.C. button: Used to select functions. Long press the V.F.C. button (in AC voltage mode) for 2 seconds or more to enter V.F.C. measurement mode. Long press SELECT in mV gear to enter or exit temperature measurement (UT171B/C only). Long press SELECT in mA gear to enter or exit % (4-20mA) measurement (UT171B/C only). Long press SELECT in µA gear to enter or exit square-wave function (UT171C only).

VIII. Measuring Operation Instructions

General Precautions:

• Check the built-in battery. If the "□" symbol appears on the LCD, replace or charge the battery promptly to ensure measurement precision. Low battery levels may force the instrument into sleep mode.
• Observe the "□" symbol near the probe sockets, which serves as a warning not to exceed the indicated voltage or current limits for safe measurement.

1. Measuring AC/DC Voltage (See Figure 3)

Diagram showing the correct probe connection for AC/DC voltage measurements. AC measurement displays the true virtual value. In AC voltage mode, pressing the Hz/% button allows selection of frequency or duty ratio for the auxiliary display. In DC voltage mode, pressing the SELECT button switches to AC+DC measurement mode, displaying the combined value on the main display. When in LoZ mode, the Hz/% button toggles the auxiliary display between Hz and duty ratio.

Caution:

• The instrument's input impedance is approximately 10MΩ. In high-impedance circuits, this can cause measurement errors. For circuits with impedance lower than 10kΩ, the error is generally negligible (0.1% or less).
• Do not input voltages exceeding 1,000Vrms. While higher voltages can be measured, it may result in instrument damage.
• Exercise extreme caution during high-voltage measurements to prevent electric shock hazards.
• Before use, test the instrument with a known voltage to confirm its correct functionality.

2. Measuring of Resistance/Conductivity (See Figure 4a)

Diagram illustrating probe connections for resistance and conductivity measurements. For measuring ultra-high resistance exceeding 40MΩ, it is recommended to use the nS range to measure conductivity (G=1/R, unit Siemens/nS). The instrument allows for self-checking of the built-in fuse through resistance measurement (refer to Figure 4b). The open-circuit voltage is approximately 1V.

Caution:

• The LCD will display "OL" if the resistance under test is open circuit or exceeds the instrument's maximum range.
• When measuring resistance within a circuit, ensure all power supply to the circuit is turned off and any residual electric charge in capacitors is discharged before proceeding with the measurement to guarantee accuracy.
• For low-resistance measurements, probe resistance can introduce an error of 0.1Ω-0.2Ω. To achieve accurate readings, short-circuit the probes and utilize the REL (relative measuring) function.
• If the probe resistance exceeds 0.5Ω when short-circuited, check the probes for looseness or other issues.
• When measuring high resistance, it is normal for the reading to take a few seconds to stabilize.
• Do not input voltages higher than DC 30V or AC 30V to prevent personal injury.

3. Measuring of Circuit Switching (See Figure 5)

Diagram showing probe connections for checking circuit continuity. If the resistance between two terminals is higher than 100Ω, it is considered an open circuit, and the buzzer will not sound. If the resistance is lower than 10Ω, it is considered a short circuit, and the buzzer will emit a continuous sound.

Caution:

• When inspecting in-circuit circuit switching, it is essential to disconnect all power supply from the circuit under test and discharge any residual electric charge in capacitors before measuring.
• Do not input voltages higher than DC 30V or AC 30V to prevent personal injury.

4. Diode Test (See Figure 6)

Diagram illustrating probe connections for performing a diode test. The test voltage range for diodes is approximately 0-3V. The auxiliary display shows "diod". For silicon PN junctions, a reading of 500-800mV is generally considered normal.

Caution:

• The display will show "OL" if the diode under test is open circuit or connected with reverse polarity.
• When testing a diode within a circuit, it is necessary to disconnect all power supply from the circuit and discharge any residual electric charge in capacitors before proceeding.
• Do not input voltages higher than DC 30V or AC 30V to prevent personal injury.

5. Measuring of Capacitance (See Figure 7)

Diagram showing probe connections for capacitance measurement. When no input is present, the instrument displays a fixed reading representing its inherent capacitance. For measurements in small capacitance ranges, this inherent value must be subtracted from the measured value to ensure accuracy. The instrument's REL (relative measuring) function can be used for automatic deduction.

Caution:

• The LCD will display "OL" if the metered capacitance is short-circuited or exceeds the instrument's maximum range.
• Measuring large capacitance values may take several seconds to complete.
• Before testing, it is crucial to discharge all residual electric charge from the capacitor, especially for high-voltage capacitors, to prevent damage to the instrument and personal injury.
• If the measured capacitance holds a charge, the screen may display "DISCHARGE" during the testing process.

6. Measuring of Frequency/Duty Ratio (See Figure 8)

Diagram showing probe connections for frequency and duty ratio measurements. In the frequency measurement gear, pressing the Hz/% button allows selection between period measurement for the auxiliary display and duty ratio measurement.

Caution:

• Do not input voltages higher than DC 30V or AC 30V to prevent personal injury.

7. Measuring Temperature (See Figure 9)

Diagram showing the connection of a K-type thermocouple for temperature measurement. Long press the SELECT button while in the mV gear to enter or exit the temperature measurement function. Short press SELECT within the temperature measurement function to switch between Celsius (°C) and Fahrenheit (°F) displays. This function requires a K-type thermocouple. The instrument displays "OL" until the temperature sensor is connected. The conversion formula is °F = 1.8°C + 32.

Caution:

• The K-type (nickel-chromium-nickel silicon) thermocouple provided in the accessories is suitable for measuring temperatures up to 230°C/446°F only.

8. Measuring AC/DC Current (See Figure 10)

Diagram illustrating probe connections for AC/DC current measurements. The AC measurement displays the true virtual value. When measuring AC current online, pressing the Hz/% button selects the auxiliary display for frequency/duty ratio measurement. Pressing SELECT switches to AC+DC measurement mode, showing the combined value on the main display. In the mA function, long pressing the SELECT button accesses the % (4-20mA) measurement function, displaying the percentile calibration of the measured current (4mA corresponds to 0%; 20mA corresponds to 100%) (applicable to UT171B/C only).

Note:

• Before connecting the instrument in series with the circuit to be tested, it is necessary to disconnect the power supply to the circuit.
• Ensure the correct input terminals and function gear are used. If the current magnitude is uncertain, start measurements from a higher range.
• Fuses are installed in the 10A and mA/µA input jacks. Never connect the probe test pins in parallel with any circuit, especially the power supply terminal, as this can damage the instrument and pose a safety risk. For currents exceeding 5A, limit each measurement to 10 seconds and ensure intervals of at least 15 minutes between measurements for safe operation.

9. 60A/600A ACA/DCA External Input Current Calipers Measurement (See Figure 11)

Diagram showing the connection of external current calipers for 60A/600A measurements. Press the RANGE button to switch between 60A and 600A measurement ranges. Use the SELECT button to choose between ACA and DCA function modes.

10. Non-contact AC Voltage Sensing (See Figure 12)

Illustration of the Non-Contact AC Voltage Sensing (NCV) function, showing the front of the instrument detecting voltage. When checking for the presence of AC voltage or electromagnetic fields, approach the front end of the instrument to the object being metered. The analog sensing capacity for AC voltage is as follows: if the voltage is less than or equal to the critical voltage V1, the main display shows "EF"; if it is higher than V1, the display shows "-". Five levels of "-" are indicated based on voltage segments (Vd), accompanied by buzzing sounds at different tempos to distinguish sensing voltage magnitude. Additionally, a red light flashes on the top of the instrument.

Caution:

• When the range switch is set to the "NCV" gear, no probe connection is required for sensing.
• If the electric field voltage exceeds 100 Vac, the instrument will provide acousto-optic prompts (within a distance of ≤10mm). If the distance is between 12mm and 50mm, acoustic prompting is optional. Beyond 50mm, sensing will not produce sound.

11. Square-wave Output (See Figure 13)

Diagram showing the output terminal for square-wave output. Long press the SELECT button to enter or exit the square-wave output interface. The square-wave frequency output can be selected using the RANGE and MAXMIN buttons. The square-wave duty ratio (%) can be selected using the REL (Hz/%) buttons. The square-wave output amplitude is approximately 0.8Vp, with a cycle/duty ratio range of 1%-100%.

Caution:

• The maximum square-wave output impedance is 500Ω.
• The positive or negative pulse width during duty ratio adjustment must be greater than 50µs.

12. Other Functions

• Error Display: After booting, if the instrument detects an error or low voltage in the EEPROM, it will display "ErrE".
• Automatic Shutdown: If the knob and buttons are not operated within the set time (5-30 minutes), the instrument will automatically shut down to conserve energy. The "APO" sign will flicker one minute before shutdown. If the "BEEP" function is enabled, the buzzer will sound three short beeps 40, 20, and 10 seconds before shutdown. The instrument can be woken up by pressing any button or turning the knob. The automatic shutdown function can be cancelled by pressing any button during the APO flicker countdown, or disabled entirely in the Setup menu (APO TIME: OFF).
• Buzzer: When the "BEEP ON" setting is active, the buzzer sounds "Beep" for valid button operations and two consecutive "Beep" warnings for invalid ones. The buzzer can be enabled or disabled in the Setup menu. Incorrect probe insertion into the jacket will cause continuous warning beeps.
• Low-voltage detection: If the internal VDD drops below 7.3V, the "□" low-voltage symbol will appear on the LCD (UT171B/C only), indicating the need to replace or charge the internal lithium battery. The instrument may enter sleep mode if low battery current is detected.
• Charging internal lithium battery (UT171B/C only): Diagram illustrating the connection of the power adapter for charging the internal lithium battery. Connect the provided charging adapter. A red indicator light shows charging status; it turns green when the charging voltage reaches the full value, and the instrument automatically cuts off the charging circuit.
• Caution: If the leads are disconnected or the lithium battery fails, the indicator light will flash red and green alternately (UT171B/C only).

IX. Technical Indexes

Accuracy is specified as ±(a% of reading + b counts) and is guaranteed for 1 year. Ambient temperature range for accuracy is 23℃±5℃ (73.4°F ±9°F), with relative humidity ≤75%.

Caution: For optimal accuracy, maintain the ambient temperature between 18°C and 28°C, with a fluctuation range of ±1°C. If the temperature falls outside this range, an additional temperature coefficient error of 0.1x (specified accuracy)/°C applies. Accuracy specifications are valid after 2 hours of stable temperature or battery charging.

1. Measuring of DC Voltage

2. Measuring of AC Voltage

3. Measuring of DC Current

4. Measuring of AC Current

5. Measuring of Resistance/Conductance (applicable to UT171B/C only)

6. Measuring of Capacitance

7. Measuring of Frequency/Duty Ratio/Cycle

8. Measuring of Temperature (applicable to UT171B/C only)

9. Measuring with current caliper (UT171C only)

10. Square-wave output (UT171C only)

X. Maintenance and Repair

Warning: Power off the instrument and disconnect probes before opening the rear cover.

1. General maintenance and repair: Clean the shell with a wet cloth and mild detergent. Avoid abrasives or solvents. Suspend operation if abnormality occurs. For calibration or repair, use qualified personnel or specific departments.
2. Replacement of battery or fuse tube (See Figure 15) Diagram showing the multimeter's rear cover, showing the location of the battery and fuse for maintenance.Operating steps:
   • Set power switch to "Off", disconnect probes from input jacks and remove protective jacket.
   • Unscrew the screw fixing the support with a screwdriver to remove the rear cover and battery support. Replace the used under-voltage battery (UT171A only) or blown fuse F1/F2.
   • For UT171B/C low voltage indication, connect the power adapter for charging (DC 10V, 500mA).