18
Heating Liquids.
Each power level is associated with a
volume range which acts as a guide when heating solutions
with heating mantles. When solutions are heated with
heating mantles set the power switch to the range that
includes the volume of solution being heated [Note: this
switch is set to the volume of solution, not the size of the
flask]. For example to heat 250 ml of toluene to 80o C in a
1 L round bottomed
Front Panel
Approx. % of
Volume Range
Full Power
1 - 10 mL
3
10 - 100 mL
10
50 - 500 mL
25
300 ml - 2 L
50
≥
2 L
100
flask choose the third power setting (50 - 500 ml) since the solution volume falls within this range. There
are situations when a power level other than that indicated on the front panel should be used:
Example
Power Setting
Explanation
80 ml toluene
100 ml flask
100 ml heating mantle
SP = 80o C
50 - 500 ml
(25% power)
Organic solvents heated to
≈
50 - 110o C are set to the
volume range on the front panel. When choosing between 2
power settings (i.e. 80 ml also falls within both the 10 - 100 ml
range and the 50 - 500 ml range) choose the higher setting.
80 ml collidine
100 ml flask
100 ml heating mantle
SP = 170o C
300 ml - 2 L
(50% power)
Even though the solvent volume is less than the range of this
power setting, it should be used because high temperatures
require additional power.
80 ml water
100 ml flask
100 ml heating mantle
SP = 80o C
300 ml - 2 L
(50% power)
While the setting 50 - 500 ml would work, since the heat
capacity of water is twice that of a typical organic solvent (1
cal/g/o K), a higher power setting can be used to compensate
for the higher heat capacity.
125 ml toluene
1 L flask
1 L heating mantle
SP = 80o C
10 - 100 ml
(10% power)
When the heating mantle size is substantially larger (
≥
5X)
than the volume being heated (i.e. the heating mantle has
excess heating capacity for the volume being heated), a lower
power setting gives better control.
150 ml toluene
250 ml flask
250 ml heating mantle
SP = 35o C
10 - 100 ml
(10% power)
Even though the solvent volume isn’t included in this power
setting, it should be used because low temperatures are better
regulated with less power.
Avoid switching between power levels while the controller is heating. Specifically, do not initially set the
controller on a high power level to rapidly heat the solution, then decrease the power level to the correct
setting as the solution approaches the set point. Changing power levels doesn’t damage the controller, but
it will reduce its heating performance.
Heating Equipment.
Two factors need to be considered when heating equipment (ovens, hot plates,
furnaces, HPLC columns, etc.); (1) placement of the temperature sensor (Section 2.4) and, (2) the
appropriate power setting. The best guide to the correct power setting for various pieces of equipment is
the researcher's experience. If your best guess is that the equipment needs 1/3 full power to heat to the set
point, set the power switch on the 300 ml - 2 L setting (i.e., 50% power, it’s usually better to have too much
power rather than too little). If the heater heats too slow, increase the power (to the >2 L setting), if it
heats too fast or has excessive overshoot, decrease the power (to the 50 - 500 ml setting). If the amount of
power seems to be adequate, but the heater doesn’t heat with stability, the controller probably needs to be
tuned (see Section 2). Section 3.8 shows the type of performance you should expect from the controller
with different pieces of equipment.
