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Using KYZ Pulses to Monitor DemandElectric demand meters can have a module added to provide a contact indicating the meter disk has rotated a certain amount. Usually the meter output is a Form C relay called the KYZ relay. The K terminal is usually the common on the SPDT relay, the Y contact is Normally Open, and the Z contact is Normally Closed. The relay changes state between open and closed with each rotation or partial rotation, of the meter disk. Each change of state of the KYZ relay is called a pulse. Meters with a KYZ output are called Pulse Meters. The Dencor Controller is connected to K and Y or K and Z whichever is more convenient. The input to the Controller is then alternating between an open circuit and a closed circuit during successive revolutions or partial revolutions of the disk (successive pulses). The green light on the controller board will show these disk rotations. The light will be on during one pulse and off during the next. The computer uses the Pulse Constant and the duration of each pulse to determine the demand (kW) at any time. The Pulse Constant, Kp, is calculated from the formula where:
The instantaneous kW is given by:
where Tp is the duration of a pulse in seconds. Newer electronic meters may not have an actual rotating disk. However, the industry terminology still uses the term disk revolution. You may think of the meter as having a pseudo disk. When selecting a meter for an installation, a good value for Kp is given by:
where the highest billing kW is the highest previous billing demand in the building. This will give 2 seconds per pulse at the maximum instantaneous demand.
A Kp value between the maximum and minimum calculation above will produce good results.
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