61
SOR USAGE submenu. The thermal shock algorithm needs to know only the type and range of the
sensor.
THERMAL SHOCK SETUP should be accessed only after all sensor and setpoints
have been setup.
LOW FIRE METHOD:
This method of cold start thermal shock protection is generally used on
Water Tube Boilers. The setpoints associated with this method of thermal shock protection is:
•
THERMAL EXIT
(Thermal Shock Exit Setpoint): The PPC4000 will hold the servo motors
at the low fire (LF) position, P03, until the steam pressure (or water temperature) reaches the
Thermal Shock Exit Setpoint (
THERMAL EXIT
). Once this steam pressure (or water tem-
perature) is reached, the firing rate motor is positioned according to the modulating control
algorithm. The units and range displayed are determined by the sensor type selected.
•
MIN. LOW FIRE
(Low fire minimum): Use this selection to set the servo positions are the
calculated firing rate position during the low fire method operation. The range is 0 to 100%
and the increments are 1%.
.
SEGMENT METHOD:
This method of cold start thermal shock protection is generally used with
Fire Tube Boilers. The setpoints associated with this method of thermal shock protection are:
•
THERMAL START
(Thermal Shock Start Point): Sets the start point for thermal shock pro-
tection. The firing rate is held at low fire, P03, until the thermal shock start point is achieved.
The units and range displayed are determined by the sensor type selected.
•
THERMAL EXIT
(Thermal Shock Exit Point): Sets the steam pressure or water tempera-
ture exit point for thermal shock protection. Once this steam pressure (or water temperature)
is reached, the firing rate is positioned according to the modulating control algorithm. The
units and range displayed are determined by the sensor type selected.
•
TIMED OVERRIDE
(Timed Override Per Segment Setpoint): Sets the maximum time the
PPC4000 holds the firing rate for each segment before automatically; increasing to the next
segment. The allowable range is 0 to 30 minutes. If 0 is selected the control will move to the
next segment only when the pressure or temperature reaches the next segment.
THERMAL START and THERMAL EXIT:
Once the burner cycle starts, the PPC4000 will hold
the firing rate in the low fire position until the steam pressure (or water temperature) reaches the
Thermal Shock Start Point (
THERMAL STRT
). The PPC4000 divides the difference between the
Thermal Shock Start Point (
THERMAL STRT
), low fire, and the Thermal Shock Exit Point
(
THERMAL EXIT
) into sixteen (16) segments. The PPC4000 will increase the firing rate position
by the value of one segment, and wait until the steam pressure (or water temperature) increases by
the amount of one segment before moving on to the next segment. Once the steam pressure (or water
temperature) increases by the calculated amount, the PPC4000 increases the firing rate by the value
