Microcontroller Based Maximum Demand Indicator

SKU: 010354


Power is measured in instantaneous quantities, while energy is the integral of power over time. For example, a 100 W light bulb absorbs 100 W of power. If operated for one hour, that light bulb absorbs 100 W – hours of energy. Maximum demand is the maximum instantaneous power consumed over a specified window of time. In the case of that 100 W bulb, as it is switched on and off, the instantaneous demand goes from zero to 100 W to zero, etc. Not very interesting. But if that bulb is operated in parallel with a second 100 W light bulb that is left on all the time, the demand will switch instantaneously between 100 W and 200 W, and the maximum demand of the combination will be 200 W. Now, the way this is applied is that electric distribution utilities often include demand as one of the factors used to determine the bill the consumer receives. In addition to measuring integrated energy consumption over the billing period (typically a month), they also measure demand. Rather than measure truly instantaneous values, they actually measure energy over a short window of time, and then divide the energy consumed during that interval by the length of the interval to arrive at an effective peak value for the interval. This is done because truly instantaneous measurements can be distorted by common events such as starting a motor (ElSayed, 1999). So, for example it is fairly common to see demand referred to as 'fifteen minute demand' because it is the effective peak value over a fifteen minute window of time. The reason for measuring and charging for demand is that the distribution utility has to build out its infrastructure to be able to support the peak consumption by its customers. Measuring and billing for maximum demand is a way of assessing the degree to which the needs of individual customers are driving the expansion of the infrastructure that supports all customers
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