Difference between mechanical and digital meters

Update date:2018-04-27 Source:MAXGE

Difference between mechanical and digital meters

  The mechanical watt-hour meter is a current count meter, and the digital watt-hour meter is a power count meter. The readings of the two at the standard voltage (220v) should be the same. However, the allowable deviation of the power supply line in our country is ±5%, that is, the voltage fluctuation between 209V and 233V is possible.

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At different voltages, the readings of the two meters will be biased. The main reason is that the apparent power of the load changes. To facilitate the calculation, we use a 200V power supply as an illustration. Under the condition that the load is constant, the current of a consumer with a rated power of 220 watts is 1A, and if the voltage is insufficient, it is reduced to 200V, and the current becomes 0.91A. In this case, the mechanical watch power reading is 0.91×220=200 watts, one hour is 0.2 kWh, and the digital watt-hour meter power reading is 0.91×200=182 watts, and one hour is 0.182 kWh. The difference between the two is 9.89%. When the voltage is higher than 220 volts, the opposite is true. The digital watt-hour meter will have a higher power reading than the mechanical watt-hour meter. For example, with a 240-volt supply, the same load current becomes 1.1A, and the mechanical meter reads 232 watts, 0.232 kWh. The digital power meter has a count of 264 watts and 0.264 kWh per hour. The difference between the two is 13.79%. Therefore, when the low-voltage power supply is used, the user is disadvantaged, but although the calculated power of the mechanical power meter is lower than the rated power, although the watch is slow, the user still suffers. In the case of high voltage, although the reading of the mechanical watt-hour meter is higher than the rated wattage, it is still lower than the actual power consumption. Although the meter goes fast, the user of the mechanical watt-hour meter still earns. The basic digital power meter response is the real power, which is consistent with the usage.

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In simple terms, for a mechanical watch, if the supply voltage is low, the reading on the same load meter will be low, but the actual use of electricity is less, in fact the user is disadvantaged. On the contrary, if the supply voltage is high, then the meter will go faster, but the user's actual electricity consumption is much greater. Therefore, the user is actually earning.

Take the above figures, for appliances rated at 220 watts, if the 200 volt supply, users only use 182 watts, but the mechanical meter count is 200 watts, although the watch is slow, but the loss of 18 watts. That is, when the 200-volt power supply was used, the 220-watt light bulb used 182 watts of electricity, but it received 200 watts of money.

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If it is 240 volts, the user uses 264 watts, but the mechanical meter counts 232 watts. Although the watch is fast, the user earned 32 watts. That is, at 240 volts, the 220-watt light bulb used 264 watts of electricity, but it received only 232 watts of money.

For a digital meter, no matter how the supply voltage changes, it responds to the real power consumption. No matter if the reading is faster or slower, the user will not lose.

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www.maxge.com All Rights Reserved.

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