Proportional Band - Fluke Dry-Well 9103 User Manual

Proportional Band

In a proportional controller such as this, the heater output power is proportional to the well temperature
over a limited range of temperatures around the set-point. This range of temperature is called the
proportional band. At the bottom of the proportional band, the heater output is 100 %. At the top of the
proportional band, the heater output is 0. Thus, as the temperature rises the heater power is reduced,
which consequently tends to lower the temperature back down. In this way the temperature is
maintained at a constant level.
The temperature stability of the well and response time depend on the width of the proportional band. If
the band is too wide, the well temperature deviates excessively from the set-point due to varying
external conditions. This is because the power output changes very little with temperature and the
controller cannot respond very well to changing conditions or noise in the system. If the proportional
band is too narrow, the temperature may swing back and forth because the controller overreacts to
temperature variations. For best control stability, the proportional band must be set for the optimum
width.
The proportional band width is set at the factory as printed on the Report of Calibration. The
proportional band width can be altered by the user if desired to optimize the control characteristics for a
particular application.
The proportional band width is easily adjusted from the front panel. The width can be set to discrete
values in degrees C or F depending on the selected units. The proportional band adjustment is
accessed within the secondary menu. Push SET and EXIT to enter the secondary menu and show the
heater power. Then push SET to access the proportional band.
SET+EXIT
12.0 P
SET
PrOP
15.0
To change the proportional band push UP or DOWN.
4.0
To store the new setting push SET. Push EXIT to continue without storing the new value.
SET
15
Access heater power in secondary menu
Heater power in percent
Access set-point voltage
Flashes PrOP and the setting
Proportional band setting
New proportional band setting
Accept the new proportional band setting
Dry-Well
Controller Operation