Ruoshui 81D Digital Multimeter User Manual

Introduction

The Ruoshui 81D Digital Multimeter is a high-precision, multi-function instrument designed for accurate electrical measurements. It features a clear LCD display with 18.9mm text height and 3 3/4 digital counts, offering stable performance and high reliability. This multimeter is capable of measuring DC voltage, AC voltage, DC current, AC current, resistance, temperature, capacitance, frequency/duty cycle, diode, and performing on-and-off tests. It also includes unit symbol display, automatic/manual range switching, automatic power off, and an alarm function. Built with an integrated circuit, it directly drives an 8-bit microprocessor and double-integrating A/D switching for high resolution and precision, making it an ideal tool for various applications from laboratories to home use.

Safety Considerations

Before operating the instrument, please read and understand the following safety guidelines to prevent electric shock and damage to the meter:

• When measuring DC voltage above 30V, AC voltage above 25V, or current above 10mA, especially with inductive loads or power line fluctuations, be aware of electric shock hazards.
• Always ensure the measurement function switch is in the correct position before measurement. Verify that the test leads are reliably contacted, correctly connected, and well-grounded to avoid electric shock.
• Use only the matched meter pens provided to meet safety standards. If the test lead line is damaged, replace it with one of the same model or electrical specification.
• Do not use unconfirmed or disapproved protector tubes or batteries. Replace them only with the same model or electrical specification. Before replacement, ensure test leads are disconnected from the measuring point and no signal is present at the input terminal.
• Avoid direct contact with the ground, uncovered metal terminals, output ports, or lead clamps during electrical measurements. Use dry clothes, rubber shoes, and other insulating materials to keep your body insulated.
• Do not store or use the meter in high-temperature, high-humidity, inflammable, or strong magnetic field environments.
• Measuring voltage values beyond the permitted ultimate voltage can damage the meter and endanger the operator. Never exceed the marked standard values.
• If test leads are inserted into the current socket, do not measure any voltage to prevent damage to the meter and ensure operator safety.
• Do not attempt to calibrate or repair the meter unless you are qualified professional personnel with special training or approval.
• Ensure the measurement function aligns with the LCD display during measurement. Disconnect test leads from the measured object and ensure no input signal before switching function/range.
• If "BATTERY" symbol is shown on the LCD, replace the battery immediately to maintain measurement precision.
• Do not insert test leads into the current terminal to measure voltage.
• Do not modify the meter's circuits freely.

Safety Symbols

• Δ: Caution, refer to manual
• ⚠: Dangerous Voltage
• ⚡: Double Insulation
• CAT III 600V: Overvoltage Category III, 600 Volts
• CE: Conforms to European Union directives

Setup

Unpacking and Accessories

Carefully open the package box and remove the multimeter. Check the contents against the list below. If any items are missing or damaged, contact your distributor immediately.

• Digital Multimeter: 1 PC
• Instruction Manual: 1 copy
• Test Leads: 1 pair
• Temperature Probe (K-Thermocouple): 1 PC
• AAA (1.5V) 7# batteries: 2 PCs
• Holster: 1 PC

Product Overview

Familiarize yourself with the components and controls of your Ruoshui 81D Digital Multimeter.

Instrument Panel & Button Functions:

• Instrument Model Number: RuoShui 81D.
• LCD Display: Displays measured data and units.
• Function Buttons:
  • SELECT: Used to switch between DC/AC and other functions like continuity/diode.
  • RANGE: Toggles between auto-ranging and manual ranging. Press for >2 seconds to return to auto-range mode.
  • HOLD: Freezes the current display reading. Press again to clear.
  • REL (Relative Value Measurement): Performs relative measurements for all functions except Hz/Duty.
• Knob Switch: Used to select the measurement function and range (e.g., Ṽ, V—, Ω, Ã, A—, Hz, ℃/℉, Diode, Capacitance).
• Input Terminals:
  • COM: Common (negative) input terminal for all measurements.
  • VΩmA: Input terminal for Voltage, Resistance, Diode, Capacitance, Frequency, and current up to 400mA.
  • 10A: Input terminal for current measurements up to 10A.
  • TEMP: Input terminal for the K-type thermocouple temperature probe.

Operating Instructions

Always ensure the correct function is selected and test leads are properly connected before making any measurements.

DC Voltage (DCV) Measurement

1. Turn the knob switch to the "V—" Range.
2. The meter will be in automatic range status, indicated by "AUTO" symbol.
3. Connect the test leads to the testing point. The voltage and polarity will be displayed.

Caution: Do not measure voltage over 600V. Special attention should be given to personal safety when measuring high voltage.

Input Impedance: About 10MΩ. Overload Protection: 600V DC or 600V AC Peak Value.

AC Voltage (ACV True RMS) Measurement

1. Insert the black test lead into "COM" and the red one into "VΩmA".
2. Rotate the function switch to the "Ṽ" gear, then press "SELECT" to choose AC measurement mode.
3. The meter will be in automatic range status, indicated by "AUTO" symbol.
4. Connect the test leads to the testing point. The voltage will be displayed.

Caution: Do not measure voltage over 600V. Special attention should be given to personal safety when measuring high voltage.

Input Impedance: About 10MΩ. Overload Protection: 600V DC or 600V AC Peak Value. Frequency Response: (50~200) Hz. Display: Average value response (RMS of sine wave).

DC Current (DCA) Measurement

1. Insert the black test lead into "COM" and the red one into "VΩmA" (for max 400mA) or "10A" (for max 10A).
2. Rotate the function switch to the "A—" gear. The meter will be in automatic range status, indicated by "DC" symbol.
3. Connect the test leads in series with the circuit. The current value and polarity will be displayed.

Caution: If "OL" is displayed, the current exceeds the range limit. Select a higher range. Max input value is 400mA or 10A depending on the terminal used.

Max measurement voltage drop: Full Range mA is 0.4V, A is 100mV. Max input current: 10A (less than 15 seconds). Overload Protection: 0.4A/250V restorable fuse, 10A/250V fuse.

AC Current (ACA True RMS) Measurement

1. Insert the black test lead into "COM" and the red one into "VΩmA" (for max 400mA) or "10A" (for max 10A).
2. Rotate the function switch to the "Ã" gear, then press "SELECT" to choose AC measurement mode.
3. Connect the test leads in series with the circuit. The current value and polarity will be displayed.

Caution: If "OL" is displayed, the current exceeds the range limit. Select a higher range. Max input value is 400mA or 10A. Overrated current can melt the fuse or damage the meter.

Max measurement voltage drop: Full Range mA is 0.4V, A is 100mV. Max input current: 10A (less than 15 seconds). Overload Protection: 0.4A/250V restorable fuse, 10A/250V fuse. Frequency Response: True RMS response (50~200)Hz.

Resistance (Ω) Measurement

1. Insert the black test lead into "COM" and the red one into "VΩmA".
2. Rotate the Range to "Ω" gear.
3. Cross-connect the test leads to the resistor.
4. When measuring low resistance, short-circuit the meter pens first to test wire resistance, then deduct it from the actual resistance.

Caution: If "OL" is displayed, the resistance exceeds the range limit. Select a higher range. When measuring resistance >1MΩ, the reading may take several seconds to stabilize. Ensure power is off and capacitors are discharged completely when measuring in-line resistors.

Overload Protection: 250V DC or AC Peak Value.

Diode and Continuity Test

1. Insert the black test lead into "COM" and the red one into "VΩmA".
2. Rotate the Range to "Diode/Continuity" gear. Press "SELECT" to choose Diode measurement mode.
3. Forward Measurement: Connect the red lead to the diode's positive polarity and the black lead to its negative polarity. The approximate forward voltage drop will be displayed.
4. Backward Measurement: Connect the red lead to the diode's negative polarity and the black lead to its positive polarity. "OL" symbol should be displayed. If the result does not match, the diode is bad.
5. Press "SELECT" again to choose Continuity measurement mode.
6. Connect the meter pens to two points of the circuit. If the built-in buzzer sounds, the resistance between the points is less than 50Ω.

CAUTION: DO NOT INPUT VOLTAGE AT THIS RANGE!

Overload Protection: 250V DC or AC Peak Value.

Capacitance (C) Measurement

1. Rotate the function switch to the "Capacitance" gear.
2. Insert the black test lead into "COM" and the red one into "VΩmA".
3. Connect the tested capacitor using the test leads to the "COM" and "VΩmA" input terminals. The capacitance parameter will be displayed. Relative measurement can be performed by pressing the "REL" button.

Caution: Fully discharge the tested capacitor before measurement to prevent damage to the meter. When measuring in-line capacitors, ensure the power is off and all capacitors are completely discharged.

Overload Protection: 250V DC or AC Peak Value. Note: It takes about 30 seconds to input stable reading at 1000uF Range.

Frequency (F) Measurement

1. Connect test leads and shielded cable to "COM" and "VΩmA" terminals.
2. Rotate function switch to "Hz" gear.
3. Connect test leads and the cable to the signal source or tested load. The signal will show on the screen.

Caution: When inputting AC RMS over 10V, excess vibration may appear. It is recommended to test weak signals with shielded cable. Press "Hz/DUTY" to choose frequency or duty cycle mode in the frequency range. Do not input voltage over 250V DC or AC peak value.

0.1-99.9% For your reference. Input Sensitivity: >1V RMS. Overload Protection: 250V DC or AC Peak Value.

Temperature (℃/℉) Measurement

1. Rotate function switch to the "℃/℉" gear.
2. Insert the cathode (black pin) of the thermocouple into "COM" jack and the anode into "VΩmA" terminal.
3. Place the working end of the thermocouple on the surface or inside the object to be tested. The temperature will be displayed in Centigrade.

Caution: Do not input voltage at this range. Do not change the temperature probe randomly. Do not measure voltage at temperature range.

Sensor Type: K Thermocouple (Nickel-chromium-nickel silicon) (banana plug).

Automatic Power Off

The meter will automatically shut down (enter sleeping mode) after 15 minutes of inactivity to save power. To reactivate, press any function button or rotate the knob switch. This feature can be cancelled by pressing the SELECT button to turn the instrument on.

Product in Use Video

Maintenance

The Ruoshui 81D is a precision instrument and should not be modified. Follow these guidelines for proper maintenance:

• Keep the instrument away from water, dust, and shock.
• Do not store or operate the meter in high-temperature, high-humidity, combustible, explosive, or strong magnetic environments.
• Wipe the case with a damp cloth and mild detergent. Do not use abrasives or alcohol.
• If the instrument will not be used for a long time, remove the batteries to prevent leakage.
• Pay attention to the 1.5V battery status. When the "BATTERY" symbol flashes on the LCD, the battery should be replaced.

Battery Replacement

When the low battery indicator appears, replace the batteries to ensure accurate measurements.

1. Loosen the screw on the back cover that secures the battery door and remove the battery door.
2. Remove the two old 1.5V AAA batteries and replace them with two new ones. Alkaline batteries are recommended for longer operation life.
3. Mount the battery door and tighten the screw.

Precaution:

• Do not input voltage higher than DC 1000V or AC Peak Value.
• Do not measure voltage at current, resistance, diode, and buzzer ranges.
• Do not use the instrument if the battery is not properly mounted or the back cover is not tightened.
• Before replacing the battery or fuse, remove the meter pens from the measuring point and switch off the meter.

Troubleshooting

If the instrument does not work properly, try the following tips. If problems persist, contact the maintenance center or distributor.

The company is not liable for any accidents or hazards resulting from user mal-operations.

Specifications

General Specifications

• Display: LCD, 3999 counts (3 3/4 digits) with automatic polarity and unit display.
• Measuring Method: Dual integral A/D converter.
• Sampling Rate: Approximately 3 times/second.
• Over Range Indication: "OL" displayed.
• Low Battery Indication: "BATTERY" symbol appears.
• Operating Environment: 0℃ to 40℃, Relative Humidity: <80%.
• Storage Environment: 0℃ to 50℃, Relative Humidity: <80%.
• Power: 2 x 1.5V AAA batteries (Battery not included).
• Dimensions (Size): 145 x 74 x 36mm.
• Weight: Approx. 190g (including 2pcs 1.5V batteries).
• Accessories: Instruction Manual, Holster, Test Leads, K-Thermocouple.
• Certification: CE
• DIY Supplies: Electrical
• Operating Mode: Auto Range

Measurement Ranges and Accuracy

User Tips

• For optimal readability, especially in low-light conditions, consider using the multimeter in a well-lit environment as the display may not feature a backlight.
• Always double-check the function switch and lead connections before taking measurements to ensure accuracy and safety.
• When measuring capacitance, ensure the capacitor is fully discharged to prevent damage to the multimeter.

Warranty and Support

This instruction manual is subject to change without further notice. The content is considered correct, and in case of errors or missing parts, please contact the manufacturer.

For detailed information and additional support, please refer to the official user manual PDF available at: Ruoshui 81D Digital Multimeter User Manual (PDF).