Xylem WTW DIQ/S 281 Operating Manual page 86

Outputs
Pulse width output
Frequency output
86
The output of the pulse width is used, e.g. for controlling valves.
Pulse-width regulation changes the duration of operation (t
nal. Depending on the position of the measured value in the proportional range,
the relay is operated for a longer or shorter period.
Relay
t
On
On
Off
T
figure 6-4 Relay output of the pulse-width output
The cycle duration (T) is made up of the turn-on and turn-off switching
duration (t , t ) of the relay together. While the selected cycle duration
on off
(T) remains constant, the turn-on duration (t
the measured value and, with it, the pulse width (v). The pulse width can
be set from 0 % to 100 %.
v = (t / T) * 100 %
on
v = pulse width, T = cycle duration, t
 If the measured value is at the end of the proportional range (End value), the
turn-on duration (t
relay operates for a longer period.
 If the measured value is at the beginning of the proportional range (Start
value), the turn-on duration (t
spondingly shorter period.
If the duration of the closing or opening pulse is shorter than 0.1 s,
the relay remains open or closed for the complete cycle duration.
Switching frequency output is used, e.g. for controlling dosing pumps.
In contrast to the pulse-width output, the pulse width is not modulated with the
frequency output but the switching frequency of the output signal. Depending on
the position of the measured value in the proportional range, the relay is
t
Off
Time [s]
on
) is long, the turn-off duration is short. This means the
on
) is short, and the relay operates for a corre-
on
) of the output sig-
on
) changes depending on
on
= turn-on duration
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DIQ/S 281
08/2020