Proportional Band - Fluke 9150 User Manual

9150
User's Guide

8.8 Proportional Band

In a proportional controller such a 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 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 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
excessively from the set-point due to varying external conditions. This deviation
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 to about 30.0°C. 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 can be accessed within the secondary menu.
Press "SET" and "EXIT" to enter the secondary menu and show the heater
power. Then press "SET" twice to access the proportional band.
  
  

 
To change the proportional band, press "UP" or "DOWN."
 
8-10
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+ Access heater power in secondary menu
Heater power in percent
Access set-point voltage
Set-point voltage in millivolts
Access proportional band
Flashes "" and then displays the setting
Proportional band
New proportional band setting
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