Figure 7 Bath Temperature Fluctuations At Various Proportional Band Settings - Fluke 6055 User Manual

8 Controller operation
Proportional band
tional band is too narrow the bath temperature may swing back and forth be-
cause the controller overreacts to temperature variations. For best control
stability the proportional band must be set for the optimum width.
The optimum proportional band width depends on several factors among which
are fluid volume, fluid characteristics (viscosity, specific heat, thermal conduc-
tivity), operating temperature, and stirring. Thus the proportional band width
may require adjustment for best bath stability when any of these conditions
change. Of these, the most significant factors affecting the optimum propor-
tional band width are the fluid viscosity and thermal noise due to difference in
temperature between the fluid and ambient. The proportional band should be
wider when the fluid viscosity is higher because of the increased response time
and also when noise is greater.
Proportional Band too Narrow Proportional Band too Wide
Optimum Proportional Band

Figure 7 Bath temperature fluctuations at various proportional band settings

The proportional band width is easily adjusted from the bath front panel. The
width may be set to discrete values in degrees C or F depending on the selected
units. The optimum proportional band width setting may be determined by
monitoring the stability with a high resolution thermometer or with the control-
ler percent output power display. Narrow the proportional band width to the
point at which the bath temperature begins to oscillate and then increase the
band width from this point to 3 or 4 times wider.
The proportional band adjustment may be 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.
S+E
Access heater power in secondary menu
Heater power in percent
12 Pct
S
Access proportional band
35