wtw DIQ/S 182-MOD System Operating Manual page 94

Relay outputs
Frequency output
6 - 10
Switching frequency output is used, e.g. for controlling dosing pumps.
In contrast to the pulse-width output, not the pulse width is modulated
with 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 switched more often or less often.
Relay
t = 0.3 s
On
On
Off
T
Fig. 6-5 Relay output of frequency output
While the selected switching duration (t
constant, the switching frequency at which the relay switches changes
depending on the measured value.
 If the measured value is at the end of the proportional range (End
value), the switching frequency is higher.
 If the measured value is at the beginning of the proportional range
(Start value), the switching frequency is low.
Time [s]
= 0.3 s) always remains
on
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System 182
04/2012