41 750-265
Fan Speed Modulation Parameters
These parameters are used only when fan speed is selected
as the modulation output.
Table 21. Modulation Output Parameters.
Parameter Comment
Modulation output Fan Speed, 4-20mA, 0-10V
This parameter selects the type of modulation output. The Falcon software responds by
driving the appropriate circuit to provide modulation of firing rate.
This parameter also affects the interpretation or the type of all parameters which specify
rates. These may be provided either as motor RPM or as percentage values, depending on
the type of modulation output selected.
The implementation of these two different types will share no common representations with
the exception of zero, which will mean both zero as an RPM and also zero as a percent
modulation (this provides a useful initial or default value). Any other non-zero value will be
legal only as a fan speed, or as a percent, but not both. Thus if a system is set up using fan
speed values, and then the modulation output parameter is changed to select one of the
analog outputs, then all of the fan speeds become “Invalid” except for those that are zero.
Similarly, parameters that were set up as percentages are invalid when interpreted as fan
speeds.
Whenever a function requires a rate parameter it will test this parameter for a legal value, and
if an invalid value is found it will respond by generating either an Alert or a Lockout, as
appropriate to the function, and by either suspending operation or operating in an alternative
manner, as appropriate to the function.
Prepurge rate RPM or %
This parameter specifies the analog output or fan speed used during prepurge.
Lightoff rate RPM or %
This parameter specifies the analog output or fan speed used during ignition.
Firing rate control Auto, Manual in Run, Manual in Run and Standby
If this parameter is set to either of the manual options, then the burner’s firing rate during
modulation in the Run state is the rate given by the Manual firing rate parameter. If the
Manual in Run and Standby option is chosen, the firing rate output is also controlled by the
manual firing rate parameter during the Standby condition; however this applies only to the
normal, idle Standby condition and not to a Standby Hold condition, wherein the burner is
preparing to fire but cannot leave standby because of something abnormal. In the latter case
the rate is driven by the burner control sequencer. However, a manual rate does not generate
demand—to fire at this rate demand must be present from another source. When set to
“Auto” the manual firing rate parameter is ignored.
Manual firing rate RPM or %
This parameter specifies the analog output or fan speed during burner modulation, when
firing rate control specifies manual mode.
CH Maximum modulation rate
DHW Maximum modulation rate
Minimum modulation rate
RPM or %
These parameters provide the limits of analog output, fan speed for CH, and fan speed for
DHW during modulation.
Postpurge rate RPM or %
This parameter specifies the analog output or fan speed used during postpurge.
Table 22. Fan Speed Modulation Parameters.
Parameter Comment
Absolute maximum fan speed RPM
The fan will never be proper to operate above the RPM provided by this parameter,
regardless of the rate request.
Absolute minimum fan speed RPM
The fan will never be proper to operate below the RPM provided by this parameter,
regardless of the rate request, except by commanding it to turn off.
PWM frequency 1000Hz, 2000Hz, 3000Hz, 4000Hz,
This parameter provides the frequency used by the PWM output to control the fan.
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