5756
The system behaves the same as in the standard process control diagram until the demand for heat
drops.
1. Heat demand suddenly and substantialy decreases. This could
be caused by a rapid decrease in flow by the line heater or a
sudden emptying of a tank heater.
2. The Process Temp rises sharply.
3. The High Temp Thermocouple temperature rises above the
High Temp ESD Setpoint, the system immediately shuts
down, and the High Temp Thermocouple temperature begins
to decrease slowly.
AUX TEMP MODE: TEMP MAIN CTL
When Aux Temp Mode is set to Temp Main Ctl, it enables the Auxiliary Temperature input. The Proc Temp
signal measures the outlet temperature of a line heater and the Aux Temp signal measures the bath
temperature. If the heat demand increases, the bath temperature may rise quickly. The Aux Setpoint
is used to shut off the Main Valves to protect the bath and fire tube in the event of excessive bath
temperature.
AUX TEMP MODE: TEMP ESD
If the Aux Temp Mode is set to Temp ESD, then the Aux Temp signal must be below the Aux Setpoint
or the system will shut down. Normally this happens independent of the High Temp ESD previously
described. However, it is possible for the High Temp ESD Setpoint and the Aux ESD Setpoint to both be
applied to the same thermocouple. This happens when Process Control is set to Aux TC and Aux Temp
Mode is set to Temp ESD. In this case, whichever setpoint is lower will be used.
In this mode, the Aux Setpoint is used as another ESD setpoint. It is always compared against the
Auxiliary Temperature signal which depends on the Process Control setting. The system will immediately
shut down if this signal exceeds this setpoint.
AUTOMATIC RESTART EVENTS
In all waiting states, the system turns off the burner and pilot and waits for some event to occur before
restarting. There are two other groups of waiting states which may be optionally enabled: Auto Restart
122
TIME˚C ˚F
EXTREME DROP IN HEAT DEMAND
1
2
3
PROCESS SETPOINT
HIGH TEMP ESD
SETPOINT
and Level Event Restart. Each of these states can be entered automatically from any other Process
Control state if the associated condition is satisfied.
Several waiting states are enabled when the Auto Restart feature is enabled. The conditions and the
triggering states are as follows:
Waiting on Low Voltage - System Voltage below Low Alarm
Waiting on High Voltage - System Voltage above High Alarm,
Waiting on Low Pressure - Low Pressure Contact open or 4-20mA Pressure below Setpoint
One waiting state is enabled when the Level Event Restart feature is enabled:
Waiting on Low Level - Level Contact Open or 4-20mA Level below Low Setpoint
Once the triggering condition is cleared, the system will automatically restart via the Relight procedure.
RELIGHT PROCEDURE
After the system has been initially started, if it needs to be automatically relit, the system responds
based on the reason the pilot is off. If the event is a controlled one, the PF2100 follows the Process
Control sequence using the system settings. If the pilot goes out unexpectedly, the PF2100 checks to
see which mode it is in. In Manual mode, the system goes straight to shutdown; in Auto mode, the
system goes through Auto Mode Start Up. Note that the number of retries varies depending on the
reason for pilot being off, three for Process Control, none for Manual mode, and the user defined amount
in Auto mode.
4.3 | Contact Behavior
This section discusses the behavior of the PF2100’s input and output contacts and its response to
external signals.
STATUS OUTPUT
The Status Output Contact is generally used to remotely determine whether the system is operating
normally. It can be connected to a PLC and used to trigger a remote alarm so that a service technician
can be sent to the site in the event of trouble.
In general, the contact will be closed when the system is running and it will be open when the system is
not running. Five exceptions to this are as follows:
1. On Start: When the system is first started, the status contact
will remain open until after the pilot has been successfully lit.
2. Alarm Mode: If the Alarm Mode setting in menu 4 is No Alarm
When Off, the contact will remain closed if the system is
stopped because the Start Contact is open.
3. Low Temp Alarm: If the Low Temp Alarm feature is enabled in
menu 1 and the Process Temperature is currently below the
Low Temp Alarm Setpoint, the Status Contact will be open.
The contact will close again as soon as the temperature rises
above the Low Temp Alarm Setpoint.
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