Turn a pulse count into energy or volume, and check that the pulse rate, pulse width and counter size suit the meter at its highest flow.
Energy in 3,600 pulses
3.6kWh
Check the values to see a result.
Meter output limits, minimum off time and debounce are in the meter and input datasheets.
Total = pulses ÷ Kpulse rate f = maximum rate × K ÷ 3600counter capacity = 2bits ÷ K
3,600 pulses at 1,000 imp/kWh is 3.6 kWh. At 72 kW the meter sends 20 Hz, within the input’s 40 Hz.
Tip: Use the pulse constant configured on the pulse output, not the LED constant printed on the meter face, unless the LED is what you count.
A pulse output sends one pulse for a fixed amount of energy or volume: the meter’s pulse constant, such as 1,000 pulses per kWh or 100 pulses per m³. To turn pulses into kWh or m³, divide the count by the constant. To check the counting input, work out how fast the pulses arrive at the meter’s highest load and compare that with the input’s maximum frequency.
total = pulses ÷ K
K is the pulse constant in pulses per kWh, per m³ or per unit. 3,600 pulses at 1,000 imp/kWh is 3.6 kWh.
f = maximum rate × K ÷ 3600
The maximum rate is in kW for electricity or m³/h for water and gas. Dividing by 3,600 turns pulses per hour into pulses per second (Hz).
pulse width < 1000 ÷ f (ms)
At the highest rate each pulse and the gap after it must fit inside one period. A 30 ms pulse at 20 Hz leaves 20 ms off in a 50 ms period.
capacity = 2bits ÷ K
An unsigned counter wraps to zero after 2bits pulses. A 16-bit counter holds 65,536 pulses, only 65.54 kWh at 1,000 imp/kWh.
Choosing the constant is a trade. A higher K gives finer resolution, which matters for interval data, but a faster pulse rate at full load. Pick the highest constant whose rate at maximum load stays within the counting input, with some margin.
3,600 pulses at 1,000 imp/kWh is 3.6 kWh. At the circuit’s 72 kW maximum the meter sends 72 × 1000 ÷ 3600 = 20 Hz, within a 40 Hz input, and a 30 ms pulse fits the 50 ms period.
Energy in 3,600 pulses 3.6 kWh Open in the calculator
2,500 pulses at 100 imp/m³ is 25 m³. At 6 m³/h the rate is 6 × 100 ÷ 3600 = 0.1667 Hz, one pulse every six seconds, far inside a 4 Hz battery-powered input.
Volume in 2,500 pulses 25 m³ Open in the calculator
The same 72 kW circuit with the output set to 10,000 imp/kWh sends 200 Hz at full load, eight times faster than a 25 Hz input can count. Pulses would be lost exactly when the load is highest. Setting the output to 1,000 imp/kWh brings it back to 20 Hz. The finer resolution was not buying much: at 10,000 imp/kWh, 36,000 pulses are still only 3.6 kWh.
Energy in 36,000 pulses 3.6 kWh Open in the calculator
The pulse frequency an electricity meter sends at its maximum load, for three common pulse constants. For water or gas, read the load column as m³/h and the constants as pulses per m³.
| Maximum load (kW) | 100 imp/kWh (Hz) | 1,000 imp/kWh (Hz) | 10,000 imp/kWh (Hz) |
|---|---|---|---|
| 5 | 0.139 | 1.39 | 13.9 |
| 10 | 0.278 | 2.78 | 27.8 |
| 20 | 0.556 | 5.56 | 55.6 |
| 50 | 1.39 | 13.9 | 139 |
| 72 | 2 | 20 | 200 |
| 100 | 2.78 | 27.8 | 278 |
| 150 | 4.17 | 41.7 | 417 |
| 200 | 5.56 | 55.6 | 556 |
| 300 | 8.33 | 83.3 | 833 |
| 500 | 13.9 | 139 | 1,389 |
| 1,000 | 27.8 | 278 | 2,778 |
Divide the number of pulses by the pulse constant. At 1,000 imp/kWh, each pulse is 1 Wh and 1,000 pulses are 1 kWh. At 800 imp/kWh, each pulse is 1.25 Wh.
Not always. The LED on an electricity meter often flashes at a different rate from its pulse output, and many meters let you set the output constant. Use the constant configured on the output you are counting.
Usually missed pulses at high load, contact bounce counted as extra pulses, or the wrong constant. Compare the count with two register readings some days apart. The pulse meter commissioning guide covers the checks.
A dry (volt-free) contact opens and closes a switch and needs the counting input to supply the voltage. An active pulse output drives a voltage itself. The input has to match; see dry pulse and active pulse.
A ZPC counts pulse outputs from existing meters and sends the counts to the Gateway. The battery-powered versions accept up to 4 Hz and the mains-powered versions up to 40 Hz, with pulses at least 10 ms long and 10 ms apart.
