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What is a wattmeter?

All electrical equipment and systems consume power based on a set of known constants, which include rated voltage, the current usage measured in amps and the overall energy usage which is measured in watts. Some appliances and installations use far more energy than others of similar voltage ratings, and so we need to track and monitor this for cost reasons and for energy consumption reasons. A wattmeter allows for this power usage to be monitored in order to establish whether their inherent circuits are operating as they should be, to monitor the health of the circuit and to monitor the balance and consumption of the overall power supply.

So a wattmeter is a small handheld device which gives us a visual indication of the amount of electrical energy being supplied to a circuit, which is expressed in watts as this is the standard unit of measure for electrical energy supply and consumption. A wattmeter can also tell us the power consumption of a circuit over a period of time and provide data to estimate the cost of operating a device or a piece of equipment in a system using standard electricity rates.


How does a wattmeter work?

The wattmeter measures power by sampling amperes and volts several thousand times per second. These values are sampled and multiplied by one another to provide a wattage reading at any given time. There are two standard types of wattmeter, an analogue wattmeter and a digital wattmeter. Analogue wattmeters indicate the power supply via a needle and scale indicator, while digital wattmeters display results on an LCD screen. However, they each have different methods of calculating these results.

An analogue wattmeter consists of two coils, one is in series and the other is connected in parallel. The coil connected in series with the circuit is known as the current coil, while the other is known as the voltage or potential coil. These coils are named so because the current from the circuit passes through the current coil and voltage is dropped across the voltage coil. When this current passes through the current coil it creates an electromagnetic field around the coil. The strength of this electromagnetic field is directly proportional to the current passing through it.

Digital wattmeters use a simple microprocessor to measure the amperage and voltage values from the circuit, at a rate of several thousand samples per second. These samples are used to calculate the average power factor or power usage, and these are the results we see produced on the LCD display screen. In modern electrical testing almost all electrical engineers will use a digital wattmeter.


Where are wattmeters used?

There are many different applications in which a wattmeter might be used. These can include:

  • In electrical circuit measurements and debugging
  • In industries where you need to check the consumption of electrical equipment and appliances
  • Electromagnetic wattmeters can be used to measure utility frequencies
  • To measure the power rating of appliances such as refrigerators, electrical heaters and other equipment.


Please note that this section is for information purposes only. Anyone using equipment referred to in this section must be suitably qualified and/or experienced within the respective field. If in doubt before use, please consult a qualified electrician or engineer & thoroughly read all instruction booklets.

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