Pulse Meter Inputs from Revenue and Sub-Meters
Many revenue meters provide kWh consumption by way of a pulse output (dry contact relay closure). To log kWh from such a meter, you can simply hook the pulse output to one of the 4 pulse inputs DI 1-4 on the GRIDlink. The GRIDlink will take the raw pulse count and multiply by the user specified pulse weight to allow reporting of instant kW and kWh.
Locate the pulse output terminals on the utility meter. Wire the meter’s pulse output terminals to one of the 4 GRIDlink Digital Inputs as shown below. On Form C devices (KYZ), this is the K and Z terminals. (K-Y is normally closed).
Form A -vs- Form C
A power meter that is listed as Form A indicates that the meter has a pulse output providing a pulse with a two-terminal dry contact. This can be either a mechanical relay or a solid state device. These devices close the contact every time a unit of power has been measured by the meter. The contact is then opened at some interval of time thereafter. (100ms). A form A device is essentially a SPST switch that opens and closes to indicate power consumption.
Form C devices are a little different. A form C device has 3 terminals, often labeled K, Y, and Z. The device will act like a SPDT switch, where K is the common terminal, Z is the Normally Open position, and Y is the normally closed position. When a unit of power has been measured by the meter, the meter *changes* the status of the output relay. If the relay was closed, it is opened, or vice-versa. The meter does not close and re-open the relay automatically.
In the following chart, both Form A and C are shown:
Three pulses are shown, labeled 1, 2, and 3. Notice how the form A output closes and opens for each pulse, where the form C output simply changes state. If you have a Form C device (3 terminals, KYZ), takes this into consideration automatically.
Configuring the Meter Pulse Weight
From the Meter Configuration page:
- There are up to 4 meters available for GRIDlink MV. Enable each meter by clicking the gray “Enable” button.
- Select the Meter Type to 10. This is the direct connection of all KYZ outputs to GRIDlink on-board Digital Counter Inputs.
- Set the pulse weight. The pulse weight tells GRIDlink how many kWh per pulse the meter reports. For example, if the meter reports 1/10 kWh per pulse, set the pulse weight to 0.1.
- If your selected pulse weight calculates Watt-Hours (normally used on small loads) then click the gray “Read Watts” button. The default is kW.
- The KYZ Input Type default form is “A”. To configure a form”C” click the gray “KYZ input type” button.
The GE kV2c pulse meter shown to the right provides the user with two form C outputs, one form A output, and one Real Time Pricing input to the meter. Kt (is the manufacturer’s nomenclature) of 1.2 represents Watthours.
Using KYZ Pulses to Monitor Demand
Electric 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.
Since the GRIDlink is connected to K and Z, 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). GRIDlink uses the pulse weight and the duration of each pulse to determine the demand (instant kW) at any time.
The pulse weight (pulse Constant), Kp, is calculated from the formula where:
If kWh is given
- Kh = Watthour constant Wh/revolution (in this example represented by Kt 1.2)
- M = Current transformer ratio multiplier (in this example represented by CTR 400)
- PPR = Pulses per revolution, the number of KYZ pulses per revolution (in this example there is no actual disc so we assume PPR = 1)
In this example we are using the Form A pulse output. Answer: Kp = 1.2 x 400/ 1 * 1000 Kp = 0.48
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.
Typical KYZ Pulse Input Box