ThermoWorks 9009-B INDUSTRIAL DUAL-BLOCK CALIBRATOR User Manual

Page 28

set-point. This range of temperature is called the proportional band. At the bot-
tom of the proportional band the heater output is 100%. At the top of the pro-
portional 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 fairly constant
temperature.

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 ex-
cessively 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 propor-
tional 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. The proportional band width
may be altered by the user if he desires to optimize the control characteristics
for a particular application.

The proportional band width is easily adjusted from the front panel. The width
may 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. Press
“SET” and “EXIT” to enter the secondary menu and show the heater power.
Then press “SET” to access the proportional band.

Access heater power in secondary menu

SEC

Flashes

for secondary menu and then displays the

heater power

13.0 P

Heater power in percent

Access proportional band

ProP

Flashes

and then displays the current setting

4.1

Current proportional band setting

To change the proportional band press “UP” or “DOWN”.

10.0

New proportional band setting

To accept the new setting press “SET”. Press “EXIT” to continue without stor-
ing the new value.

9009 Industrial Dual-Block Calibrator
User’s Guide