UNI-T UT502A Operating Manual

1. Overview

The UT502A Insulation Resistance Tester is designed with a new generation of integrated digital circuits. It measures insulation resistance, low resistance, and AC voltage with high accuracy and stable performance. It is ideal for measuring insulation resistance of insulating materials and various electrical equipment such as transformers, electric motors, cables, and switches, making it a valuable tool for electrical equipment maintenance and testing.

2. Safety Information

The instrument complies with the IEC61010 standard. Users must read and comprehend this manual before use. Incorrect operation can lead to accidents and damage to the instrument.

Danger: Indicates conditions and actions that may cause serious or fatal damage.
Warning: Alerts users to avoid electric shock or damage to the instrument.
Caution: Indicates conditions and actions that may cause damage to the instrument or affect accurate measurement.

Specific safety precautions include:

Do not measure circuits with voltage over 750VAC.
Do not test in flammable places due to the risk of explosion from sparks.
Ensure hands are dry when operating the instrument.
Do not touch conductive parts of test leads during measurement.
Do not press the TEST key when test leads are shorted and connected to the instrument.
Do not open the battery cover during testing.
Do not touch the tested line during insulation measurement.
If the instrument shows signs of malfunction (e.g., damage, exposed metal), stop using it immediately.
Exercise extreme caution when working with voltages exceeding 33Vrms, 46.7Vacrms, or 70Vdc, as these can cause electric shock.
Ensure circuits under test are discharged after high resistance measurements.
Do not replace the battery when the instrument is wet.
Ensure test leads are securely connected to the device's ports.
Shut down the instrument before opening the battery cover.
Ensure the circuit under test is completely discharged and isolated from the power circuit before measuring resistance.
If test leads or adaptors are damaged, replace them with components of the same model or electrical specifications.
Replace the battery when the low battery indicator ' ' appears. If the instrument will not be used for a long time, remove the battery.
Avoid operating or storing the instrument in environments with high temperature, high humidity, flammable materials, explosive substances, or strong electromagnetic fields.
Clean the instrument housing with a damp cloth and mild cleaning agent; avoid abrasives or solvents.
Dry the instrument before storage if it becomes wet.

3. Electrical Symbols

Risk of electric shock
Double insulation or reinforced insulation
AC
Grounding
CE: Comply with European Union standards

4. Technical Specifications

Accuracy is specified as ±(a% of reading + b digits), with calibration required annually.

Working conditions:

Temperature: 23±5°C
Humidity: 45~75%RH

Insulation Resistance Measurement

	500V	1000V	2500V
Rated voltage	DC 500V±10%	DC 1000V±10%	DC 2500V±10%
Measurement range	0.00MΩ ~ 5.00GΩ	0.00MΩ ~ 5.00GΩ	0.00MΩ ~ 20.0GΩ
Open circuit voltage	Under 500kΩ	Under 1MΩ	Under 2.5MΩ
Rated measurement current	1.00mA~1.10mA	1.00mA~1.10mA	1.00mA~1.10mA
Short circuit current	Approx. Less than 1.8mA
Accuracy range	0.00MΩ~99.9MΩ: ±(3%+5) 100MΩ~10GΩ: ±(5%+5) 10.0GΩ~20.0GΩ: ±(10%+5)

Polarization Index/Dielectric Absorption Ratio Measurement

PI Measurement	10min insulation resistance / 1min insulation resistance
PI Value	Greater than or equal to 4	4---2	Less than or equal to 1.0
Criterion	Best	Good	Bad

DAR Measurement	1min insulation resistance / 30s insulation resistance
DAR Value	Greater than or equal to 1.4	1.25--1.0	Less than or equal to 1.0
Criterion	Best	Good	Bad

Low Resistance Measurement

Open-circuit voltage	Approx. 5.0V
Measurement range	0.00Ω~2000Ω
Resolution ratio	0.01Ω
Accuracy	±(2%+3)Ω

Voltage Measurement

Measurement range	AC voltage 30~750V (50/60Hz)
Resolution	1V
Accuracy	±(2%+3)

5. Tester's Structure (Front View)

The front view of the UT502A includes:

EARTH: Sampling jack for insulation resistance measurement.
G: Negative jack for voltage measurement input.
V: Positive jack for voltage measurement input.
LINE: High voltage output jack for insulation resistance measurement.
Display: LCD screen.
Backlight button.
PI/DAR switch button.
TEST button.
Rotary knob.

LCD Display: Shows readings, units, and functions. Features include overload indication ('>22.0GΩ'), low battery indication (' '), automatic range, unit display, and backlight.

6. Buttons and Rotary Knob

PI/DAR button: Selects polarization index/dielectric absorption ratio measurement.
ZERO/LIGHT button: Turns on/off the backlight or resets the display to zero for low resistance measurement.
TEST button: Activates/deactivates insulation and low resistance measurements.
Rotary knob: Selects measurement functions: ACV for AC voltage, CONTINUITY for low resistance, and 500V/1000V/2500V for insulation resistance testing.

7. Preparations before Measurement

Replace the battery if the low battery indicator ' ' appears on the LCD.
Low voltage symbol indicates battery voltage is 7V or less.

8. AC Voltage Measurement

Refer to Figure 1:

Set the rotary knob to ACV.
Insert the red test lead into the "V" jack and the black test lead into the "G" jack.

Cautions:

Do not input voltage higher than 750Vrms, as it may damage the instrument.
Exercise extreme caution to avoid electric shock when measuring high voltages.
Disconnect test leads and tested circuits after measurement.
Do not perform measurements with the battery cover open.

9. Low Resistance Measurement

Refer to Figure 2:

Wiring method:

Before insulation resistance measurement, the circuit under test must be completely discharged and isolated from the power circuit.
Insert the red test lead into the EARTH port and the black test lead into the G port.
Connect the red and black alligator clips or test probes to the circuit under test.

With the instrument connected as described, turn the rotary switch to CONTINUITY and press TEST to conduct ground continuity measurement.

10. Insulation Resistance Measurement

Refer to Figure 3:

Cautions:

Ensure no electricity exists in the circuit under test before testing. Do not measure insulation of charged equipment or lines.
Do not short-circuit test leads when high voltage is output, or make insulation measurements after high voltage has been output.
Ensure the circuit under test is fully discharged and isolated from the power circuit before measuring insulation resistance.
Insert the red test lead into the "LINE" input port and the black test lead into the "EARTH" input port.
Connect the red and black alligator clips to the circuit under test; positive voltage output is from the LINE port.

Continuous measurement:

Set the knob to the desired test voltage (500V/1000V/2500V).
Press the TEST button to start continuous measurement. The instrument will lock, and the TEST button will light up.
Press the TEST button again to unlock and stop the measurement.

Polarization index measurement:

In insulation measurement mode, press the PI/DAR button once to select PI. The screen will display Time 1 (1min) / Time 2 (10mins). Press TEST to start PI measurement.

Dielectric absorption ratio measurement:

In insulation measurement mode, press the PI/DAR button twice to select DAR. The screen will display Time 1 (30s) / Time 2 (1min). Press TEST to start DAR measurement.
Press the TEST button a third time to select another DAR setting, showing Time 1 (15s) / Time 2 (1min). Press TEST to begin this DAR measurement.

Cautions:

Do not touch the circuit after testing. Stored capacity in the circuit may cause electric shock.
When red and black clips are connected, high voltage is output from the LINE jack and current from the EARTH jack.
Do not measure when the battery cover is opened.

11. Battery Replacement

Refer to Figure 4:

Danger: Remove wires from the instrument before replacing the battery to avoid electric shock.
Cautions:

Do not mix new and old batteries.
Observe battery polarity during installation.
Do not measure when the battery compartment is open.
Replace the battery when the ' ' symbol appears on the LCD.

Steps:

Turn off the instrument (set the knob to OFF) and disconnect test leads.
Loosen the screw on the battery cover, remove the cover, and replace the 6 batteries.
Ensure the screw is secured after replacing the batteries.

12. Maintenance

Cleaning the housing:

Clean the instrument surface with a soft cloth or sponge dampened with clean water.
Do not submerge the instrument in water.
Dry the instrument before storage if it becomes wet.

For verification or repair, please contact a qualified professional serviceman or the designated repairing department.

UNI-T

UNI-TREND TECHNOLOGY (CHINA) CO., LTD.

No.6, Gong Ye Bei 1st Road, Songshan Lake National High-Tech Industrial Development Zone, Dongguan City, Guangdong Province, China

Tel: (86-769) 8572 3888

http://www.uni-trend.com

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