HRB1684301-11

Example calculations

This example calculation shows how to calculate power, pulse constants and maximum pulse frequency, and how to determine a pulse constant that reduces the maximum pulse frequency.
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A balanced 3-phase Wye system uses 480:120 volt VTs and 100:5 amp CTs. The signals at the secondary side are 119 volts line-to-neutral and 4.99 amps, with a power factor of 0.85. The desired pulse output frequency is 20 Hz (20 pulses per second).

  1. Calculate the typical total output power (Ptot):

  2. Calculate the pulse constant (K):

  3. At full load (200% of nominal current = 10 A) and power factor (PF = 1), calculate the maximum total output power (Pmax):

  4. Calculate the maximum output pulse frequency at Pmax:

  5. Check the maximum pulse frequency against the limits for the LED and digital outputs:

    • 47.2 Hz ≤ LED maximum pulse frequency (2.5 kHz)

    • 47.2 Hz > digital output maximum pulse frequency (25 Hz)

    NOTE: The maximum pulse frequency is within the limits for LED energy pulsing. However, the maximum pulse frequency is greater than the limits for digital output energy pulsing. Pulse output frequencies greater than 25 Hz will saturate the digital output and cause it to stop pulsing. Therefore in this example, you can only use the LED for energy pulsing.

Adjustments to allow energy pulsing at the digital outputs

If you want to use the digital output, you must reduce the output pulse frequency so it is within the limits.

Using the values from the above example, the maximum pulse constant for the digital output is:

  1. Set the pulse constant (K) to a value below Kmax, for example, 300 pulses/kWh. Calculate the new maximum output pulse frequency at Pmax:

  2. Check the new maximum pulse frequency against the limits for the LED and digital outputs:

    • 23.8 Hz ≤ LED maximum pulse frequency (2.5 kHz)

    • 23.8 Hz ≤ digital output maximum frequency (25 Hz)

    As expected, changing K to a value below Kmax allows you to use the digital output for energy pulsing.

  3. Set the new pulse constant (K) on your meter.

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