1. Common Electrical Instruments
1.1 Multimeter
Purpose: Used to measure DC/AC voltage, current, resistance, and in advanced models, capacitance, inductance, and power.
Main Components:
Indicator section: moving-coil meter (meter head).
Measuring circuits: shunt, divider, rectifier.
Switching device: selects measurement type and range.
Usage Guidelines:
Correctly connect test leads (red to “+”, black to “–”).
Select measurement type (voltage, current, resistance).
Choose proper range (reading should fall between 50–70% of scale).
Zero adjustment in resistance mode before each test.
Safety Notes:
Never measure resistance on a live circuit.
Avoid switching ranges while measuring high current/voltage.
After use, turn switch to highest AC voltage range for safety.
1.2 Megohmmeter (Insulation Tester)
Purpose: Measures high resistance and insulation resistance; units in megaohms (MΩ).
Selection Principle:
For equipment ≤500 V → choose 500 V or 1000 V tester.
For equipment >500 V → choose 1000–2500 V tester.
For insulators → choose 2500–5000 V tester.
Typical Applications:
Line-to-ground insulation.
Motor winding insulation.
Cable insulation.
Precautions:
Disconnect power before measurement and discharge equipment.
Rotate handle at ~120 rpm for stable readings.
Discharge test object immediately after measurement.
1.3 Ammeter
Types: DC, AC, or dual-purpose.
Selection:
Magnetic type for high sensitivity/accuracy (mainly DC).
Electromagnetic type for general AC/DC applications.
Use a current transformer (CT) for large AC currents.
Usage Notes:
Always connect in series with load.
Observe polarity when measuring DC.
With CT, secondary must be grounded and never open-circuited.
1.4 Voltmeter
Types: DC, AC, or dual-purpose.
Selection Principle:
Range must exceed expected circuit voltage.
Magnetic type offers higher sensitivity.
Usage Notes:
Always connect in parallel.
With potential transformer (PT), multiply indicated value by PT ratio.
Ensure PT secondary is protected (fuse installed).
1.5 Earth Resistance Tester
Purpose: Measures resistance of grounding electrodes and soil resistivity.
Measurement Steps:
Disconnect ground conductor from system.
Place two auxiliary ground rods (20 m and 40 m away).
Connect tester terminals: E → electrode, P → 20 m rod, C → 40 m rod.
Rotate handle, adjust dial, record reading × multiplier.
Best Practice: Take multiple readings in different directions and average.
2. Common Electrical Tools
2.1 Test Pen (Voltage Tester)
Purpose: Detects presence of voltage (60–500 V).
Usage Notes:
Finger must touch metal cap.
Observe neon lamp through window.
Approach object gradually; do not directly touch.
2.2 Electrician’s Knife
Purpose: Stripping insulation, cutting wire.
Safety Notes:
Never use on live circuits.
Cut with blade outward, avoid injury.
2.3 Screwdriver
Usage: Tightening/loosening screws.
Safety Notes:
Use insulated screwdrivers for live work.
Do not use full-metal shank tools.
2.4 Combination Pliers
Functions: Cutting, bending, twisting, gripping.
Safety Notes:
Check insulation before live use.
Never cut two conductors of different potential simultaneously.
2.5 Long-Nose Pliers
Purpose: For tight spaces, shaping small conductors, gripping small parts.
Safety Notes:
Confirm insulation integrity before live use.
Avoid contact with body or adjacent live parts.
3. Conclusion
Mastering the correct use of common instruments and tools is an essential skill for every control technician and electrician. Proper handling not only improves troubleshooting efficiency but also ensures personnel safety and equipment reliability.