Connection Of Test Meters

Electrical Measurements

  • Understanding the necessity of various electrical instruments for measuring different electrical quantities.

Key Electrical Quantities

  • Current: Amperes (A)

  • Voltage: Volts (V)

  • Resistance: Ohms (Ω)

  • Power: Watts (W)

  • Power Factor: Ratio of real power flowing to the load to the apparent power in the circuit.

Instruments Used

  • Current: Uses an Ammeter, connected in series.

  • Voltage: Uses a Voltmeter, connected in parallel.

  • Power: Uses a Wattmeter, measures both DC and AC power.

  • Resistance: Uses an Ohmmeter.

Measuring Current

  • Current measurement requires an ammeter placed in series with the circuit components.

  • Ammeters must have low resistance to avoid affecting the circuit.

  • In series circuits, current remains constant across all components.

Measuring Voltage

  • Voltage (potential difference) across components like lamps is measured using a voltmeter.

  • Voltmeters are connected in parallel to avoid significant current draw, allowing accurate voltage measurement without affecting circuit operation.

Measuring Power

  • Power measurement involves a wattmeter, combining functionalities of ammeter and voltmeter.

  • Essential for calculating power factor in a circuit.

Measuring Resistance

  • Resistance is measured in Ohms using an Ohmmeter.

  • Ohmmeters require internal power (battery) and must not be connected while power supply is on.

  • Low values should use low reading ohmmeters; high values require high reading ohmeters (e.g., insulation testers).

Measuring Energy Use

  • Energy measured in Joules; commonly expressed as kilowatt-hours (kWh).

  • Calculation:

    • Energy (kWh) = Power (kW) × Time (hours)

    • Example: A 3kW appliance used for 6.5 hours uses 19.5 kWh.

    • Cost calculation: 19.5 kWh × cost per unit (e.g., 16p/unit).

Summary of Connections

  • Series Connection: For ammeters measuring current.

  • Parallel Connection: For voltmeters measuring voltage.

  • Wattmeters: Typically connected to measure both current and voltage for power.

  • Ohmmeters: Can be connected in series or parallel, but not when a circuit is powered.