Electrical Loads and Current Measurement

Electrical Loads

• A load is any electrical component that draws current, such as a lamp, stereo, motor, or heating element.
• Each load has a rated current limit that should not be exceeded to avoid excessive heat, insulation damage, component failure, and possible fire hazards.

Continuity Measurement

• Continuity is a quick check to see if a circuit is complete.
• Good fuses and closed switches have continuity.
• During a continuity measurement, the multimeter sends a small current potential through the circuit to measure the resistance of the circuit.
• Most multimeters indicate continuity from 0 to 50 ohms and may have an audible alarm.

Resistance Measurements

• Resistance is measured in Ohms (Ω).
• The circuit should be de-energized or turned off before measuring resistance to avoid damaging the meter.
• Most meters have overload protection on all ranges to prevent damage.
• Place the test leads on each side of the resistor to measure resistance.

Capacitance Measurement

• A capacitor is a device that stores energy.
• Multimeters can measure capacitance.

Multimeter

• A multimeter is a device that measures AC/DC voltage, current, and resistance.
• It is also called the Volti-Ohm Milliammeter (VOM) or a Multitester.
• Multimeters are used for various purposes, such as measuring DC and AC voltage, detecting short circuits, testing transistors, measuring capacitance, and frequency.

Types of Multimeter

• There are two types of multimeter: Analog Multimeter and Digital Multimeter.

Analog Multimeter

• Analog meters use a needle movement and calibrated scale to indicate values.
• The input impedance of an analog meter is expressed in Ohms per Volt.

Digital Multimeter (DMMs)

• Digital Multimeters feature a digital or liquid crystal display (LCD).
• Measurement readings are displayed as numerical values on the LCD Display.
• Digital Multimeters and Clamp meters use different techniques internally to measure AC, DC voltage, resistance, and amperes.

Parts of a Digital Multimeter

• A digital multimeter has three parts: LCD display, Selection knob, and Ports.
• Ports are the points where the probes (Red and Black) are plugged into for positive and negative connection.
• The knob is used for changing the parameter to be measured.

Measurement Functions

• Multimeters can measure various parameters, including voltage, current, resistance, and capacitance.
• Each parameter has a specific symbol and function on the multimeter.

Voltage Measurements

• Voltage measurements are perhaps the most common function used on a multimeter.
• Voltage is measured between two points, so solid contact is necessary at each point.
• The proper way to connect a meter is to connect the low or ground (black lead) first and the high (Red lead) next.

DC Voltage Measurements

• To measure DC voltage, place the Red lead into the V Ω COM port and turn the dial or switch to VDC or V.
• Set the range to the appropriate value (e.g., 20 V range for a 9V battery).

AC Voltage Measurement

• To measure AC voltage, place the Red lead into the V Ω port and black lead into the COM port.
• Turn the dial or switch to VAC or V ̴ and set the range to the appropriate value (e.g., 200 V range for a 120V outlet).

Current Measurements

• Current is the electron flow that causes electrical equipment to operate.
• When the equipment is turned on, it is considered a "load" on the circuit.