VICI ITC - Manual (Page 17)

power is increased too abruptly, quickly driving the temperature up, out of reach. If
the heater size cannot be reduced, the bandwidth must be increased. Doing so
will decrease the rate of change in applied power, hopefully increasing stability.
Always allow ten to fifteen minutes after making each adjustment before making
another. This will allow the system enough time to reveal whether or not further
adjustment is required.
As a consequence of increasing the bandwidth, the user should be aware that the
controlled temperature is usually shifted upward, as well. This notion is most eas-
ily understood by noting the position of the 1% power point before and after adjust-
ment. Remember that the system will still require the same average power to
maintain a given temperature. Therefore, as the bandwidth is increased, the given
power point shifts upward, carrying with it, the controlled temperature.
Note that the controlled temperature shifts upward only if it was originally trying to
stabilize above the setpoint (50% power point). There usually is no stability
problem when the temperature is settling below the setpoint. However, we will
point out that in this situation, the temperature will shift downward when bandwidth
is increased.
The value of the bandwidth (in °C) can be determined by the following method:
1. Reduce the setpoint temperature until the HTR indicator is OFF continu-
ously. Make note of this temperature.
2. Increase the setpoint until the HTR indicator is ON continuously. Make note
of this temperature.
3. Determine the difference between the two temperatures. This value is the
bandwidth.
POWER APPLICATIONS
CONTROLLED TEMP
1
°
EXCURSION
TIME
POWER APPLICATIONS
CONTROLLED TEMP
1
°
EXCURSION
CONTROLLED TEMP
EXCURSION TEMP
3 °
6 °
Figure 9
15