Rockwell Automation 1756-XXXX ControlLogix Digital I/O Modules - Manual (Page 104)

104 Rockwell Automation Publication 1756-UM058G-EN-P - November 2012
Chapter 5 Fast Module Features
4. In the Pulse Width Modulation area, complete the fields as described in
the table below.
Field Description 1756-OB16IEF Tag Name 1756-OB16IEFS Tag Name
Enable Pulse Width Modulation
(PWM) Check the checkbox to enable PWM. If this checkbox is cleared, all other PWM
fields are unavailable, and the PWM On time and cycle time for the point are
ignored.
By default, PWM is disabled. C:Pt[x].PWMEnable C:PWM.Enable
PWM On Time (view only) Displays the length of time that a pulse is active, as defined in the PWMOnTime
output tag.
By default, this value is defined in seconds with a range of 0.0002…3600.0.
However, you can define the value as 0…100 percent of the cycle time by
clicking On Time in Percent below.
IMPORTANT: Before PWM will function, you must enable PWM during
configuration and define the PWM cycle time and On time in the PWMCycleTime
and PWMOnTime output tags.
If PWM is enabled (C:PWMEnable = 1) and the output is instructed to turn On
(O:Data = 1), the output generates a PWM signal. O:Pt[x].PWMOnTime O:PWM.OnTime
PWM Cycle Time (view only) Displays the duration of each pulse cycle, as defined in the PWMCycleTime
output tag. This value is always displayed in seconds with a range of
0.001 …3600.0 seconds.
IMPORTANT: Before PWM will function, you must enable PWM during
configuration and define the PWM cycle time and On time in the PWMCycleTime
and PWMOnTime output tags.
If PWM is enabled (C:PWMEnable = 1) and the output is instructed to turn On
(O:Data = 1), the output generates a PWM signal. O:Pt[x].PWM CycleTime O:PWM.CycleTime
Minimum On Time Type the minimum length of time required for the output to turn On. This value
must be defined in seconds.
For example, if a heating coil requires a minimum of 2 seconds to heat up, and
you enter a value of 2.000 in this field, the shortest pulse allowed is never less
than 2.000 seconds.
The default value of zero disables the feature. C:Pt[x].PWMMinimumOnTime C:PWM.MinimumOnTime
Extend Cycle to Accommodate
Minimum On Time Check or clear this checkbox to determine the output behavior when the On time
is less than the minimum On time:
• Check the checkbox to increase the duration of the pulse cycle to maintain
the On time to Cycle time ratio while taking into account the minimum On
time.
Note: Extending the cycle time is typically useful only when the On time is a
result of a calculation.
• Clear the checkbox if you do not want to increase the duration of the pulse
cycle. In this case, the output will not turn On if the On time is less than the
minimum On time.
By default, the checkbox is cleared, and cycles will not extend.
C:Pt[x].PWMExtendCycle C:PWM.ExtendCycle
Stagger Output to Adjust Cycle
Phase to Minimize Simultaneous
Outputs Check the checkbox to minimize the load on the power system by staggering
output transitions. See
Figure 18 on page 102 .
By default, this checkbox is cleared and staggering is disabled. When staggering
is disabled for an output point, the output always turns On at the beginning of a
pulse cycle.
C:Pt[x].PWMStaggerOutput C:PWM.StaggerOutput
On Time in Seconds
or
On Time in Percent To define PWM On time in seconds, click On Time in Seconds.
To define PWM On time as a percentage of the cycle time, click On Time in
Percent.
By default, the On time is defined in seconds. C:Pt[x].PWMOnTimeInPercent C:PWM.OnTimeInPercent