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1SVC 440 795 M1100
Function of the pulse width modulation function block
h
The pulse width modulation function block must be
enabled so that it can work. Coil PW...EN is active. If coil
PW...EN is not active, the entire function block is
deactivated and reset. The output value is set to zero.
The manipulated variable at function block input >SV is
converted to a pulse string with a constant period duration.
The pulse width is proportional to the manipulated variable
>SV. The period duration and the minimum on duration can
be selected as required within the specified limits.
The function block causes a direct output of the pulse to the
corresponding output. The output image of the circuit
diagram is always updated.
h
The following applies if the output of a pulse width
modulator is used as a coil in the circuit diagram:
The state of the output is not refreshed from the circuit
diagram.
h
The following applies to the minimum on duration:
• The minimum on duration is equal to the minimum off
duration.
• The minimum on duration must not exceed 10 % of the
period duration. The ratio of period duration/minimum
on duration (P/M) determines which percentage of the
manipulated variable has no effect. The minimum on
duration must be set as low as possible so that the P/M
ratio is as high as possible. If the minimum on duration
must not be too low, due to the output relay, the period
duration must be increased accordingly.
• The minimum on duration is 1 ms.
• If the actual value of the pulse length is less than the
minimum on duration, the minimum on duration has the
effect of the pulse time. The status of the PW..E1
contact must be observed.
• If the off duration of the pulse is less than the minimum
off duration, outputs Q1 and Q2 are continuously in
operation. Note the state of the contact PW...E1.
Function blocks
243
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