SELF TUNE FROM A COLD START
When you start your machine or process from a cold
start, the SELF TUNE program begins with 100% output
power until the temperature reaches approximately one-
half way to setpoint (Figure 4-2). The setpoint must be
at least 30 degrees F (17 degrees C) above ambient. If
it isnt, the controller automatically goes to manual tuning
displays At the half way point the controller shuts off the
output and monitors the process as it responds to the
loss of heat. The controller calculates appropriate PID
values and returns output power to quickly bring the
temperature to setpoint under three mode control.
SELF TUNE FOR HOT RESTART AND DURING OPERATION
Controllers with analog inputs can only use SELF TUNE from a cold start. SELF
TUNE from a hot start will yield erroneous results.
Anytime during operation or after a pause in operation the SELF TUNE program can be used when a thermocouple or
RTD input is being used. If the process or machine is at or close to operating temperature, the controller will shut off the
output to allow an approximate 20% drop in temperature (setpoint to ambient) while it calculates new PID values. The
output is then turned ON to return the temperature to setpoint.
The 50% point for cold start and the 20% drop for hot retune are factory set but can be changed if either of these values
causes process difficulties. Contact the factory for instruction on changing either value.
While the SELF TUNE is active, the yellow TUN indicator will flash and all keys but two are disabled. The RETURN key is
active to allow you to observe the OPERATOR loop displays using the POINTER technique explained in Section 4.6. The
STOP/START (Model 2003) or AUTO/MANUAL (Model 2004) key is also active to allow you to stop the SELF TUNE
program if required. The SELF TUNE program will select the most appropriate PID values within fixed limits. Manual
tuning allows broader tuning values as shown below.
When the SELF TUNE program is completed, the display automatically advances to show you the Proportional Band
ECLIPSE INSTRUMENTATION DIVISION