Multiple Tariff Meters or TOU Meters
Time of use metering facilitates load control and planning on the part of utilities. This is efficiently achieved using a concept known as Time of Usage (TOU) metering. This includes dividing the day, month and year into tariff slots and along with higher rates at peak load periods and low tariff rates at off-peak load periods. Electric utilities might charge customers different tariffs at different times of the day along with the help of this category of metering. This is because there is commonly a surplus of electrical generation capacity at times of low demand, such as during the night. Such multiple tariffs could be made applicable only through time of use (TOU) meters, that incorporate or are connected to a time switch and that have multiple registers.
Domestic variable-rate meters generally permit only one (uniform) or two tariffs ("peak" and "off-peak") and in like installations an easy electromechanical time switch might be used. Large commercial and industrial premises might use electronic meters that record power usage in blocks of half an hour or less. This is since most electricity grids have demand surges throughout the day and the power company might wish to provide incentives to large customers to decrease demand at these times. Some multiple tariff meters use various tariffs for various amounts of demand. These are commonly industrial meters.
The multiple tariff rates might also be dependent of frequency, also called as availability based tariff (ABT), deployed in grid substations and inter- utility transfer points for bulk transfer of energy. This is based on the premise in which the system frequency is inversely proportional to the current load. This also causes self-regulation since the rates are higher when the system frequency is low, eventually bringing down the demand. ABT compliant meters also called as Special Energy Meters (SEMs) record and store data on electrical quantities in blocks of 15 minute period, that are downloaded for billing reasons at the time of meter reading.