Operating Instructions 25
Operating Instructions
Pulse Outputs
The WattNode meter generates pulse outputs using one or more optoisolators (also called
photocouplers). These provide 5000 Vac of isolation using an LED and a photo-transistor. This
allows the meter to be interfaced to monitoring or data logging hardware without concerns about
interference, ground loops, shock hazard, etc.
Depending on the options selected, the Pulse WattNode meter can generate full-scale pulses at
output frequencies ranging from less than 1 Hz to 600 Hz. The standard full-scale pulse output
frequency is 4.00 Hz. The standard model provides two pulse streams for measuring bidirectional
power. With
Option P3
, there are three pulse channels for independently measuring each phase
or three single-phase circuits.
The pulse outputs are approximately square-waves, with equal on and off periods. The frequency
of pulses is proportional to the measured power. When the measured power is constant, the
pulse frequency is constant and the output is an exact square-wave. If the power is increasing
or decreasing, the output waveform will not be a perfect square-wave as the on and off periods
are getting longer or shorter. If you need a fixed or minimum pulse duration (closed period), see
Manual Supplement MS-17: Option PW (Pulse Width)
We define a “pulse” as a full cycle including both an Open
→
Closed and an Closed
→
Open
transition. You can choose either a rising or falling edge to start a pulse; the end of the pulse will
be the next matching edge. Some monitoring equipment or data loggers can be configured to
count
both
rising and falling edges: if your equipment is configured this way, you will count twice
as many pulses as expected. This can normally be corrected by reconfiguring the equipment or
adjusting the scale factors by a factor of 2.
Open
Closed
400ms
400ms
800ms
400ms
400ms
800ms
400ms
400ms
800ms
Figure 11: Output Pulses for Steady Power
Open
Closed
200
ms
200
ms
200
ms
200
ms
300
ms
400ms
500ms
500ms
1000ms
700ms
400ms
400ms
Figure 12: Output Pulses for Increasing Power
See
Connecting Pulse Outputs (p. 18)
and
Specifications - Pulse Outputs (p. 33)
for
more information.
