0
10
20
30
40
50
60
70
20
45
70
95
120
145
170
Temp
C
o
Time (min)
Conditions: 300 ml collidine
500 ml flask
500 ml heating mantle
Set point = 45 C
Power = 50 - 500 ml
(25% power)
o
Set point = 100 C
Power = 300 ml - 2 L
(50% power)
o
Set point = 155 C
Power = > 2 L
(100% power)
o
Graph 3
Another factor affecting the
choice of power setting is the set
point temperature. For set points
near room temperature a low
power level is adequate. For
average temperatures (50 - 100
o
)
the volumes printed on the front
of the controller is a good guide.
For high temperatures, the next
higher power setting might be
needed to supply the heater with
additional power.
The power reduction circuit limits the total amount of power delivered to the heater. In this sense it works
like a variac and can be used like one. If the heater isn’t getting enough power, turn the power level up
one notch, if it’s getting too much power, turn it down.
3.8
Do's and Don'ts When Using Your Controller.
The controller, heater and thermocouple form a
closed loop feedback system (see Fig. 2 in Section 4.1). When the controller is connected to a heater, the
feedback loop should not be broken at any point.
Don't
remove either the thermocouple or heater from the solution without setting the power level to the
"Heat Off". With the thermocouple or heater separated from the solution, as the thermocouple
cools the controller turns the heater on. Since this heat is never fed back to the controller it heats
continuously.
Don't
use the controller to regulate an exothermic process.
The controller has no capacity for cooling. If an exotherm is expected, it must be controlled in
another way.
Do
use an appropriate size flask and heater for the volume being heated.
Use the smallest flask and heating mantle that accommodates the reaction. This ensures that the
heating power of the heating mantle closely matches the volume being heated. This also allows
the solution to radiate excess heat to minimize temperature overshoots.
Do
place the thermocouple directly in the solution.
Place at least the first 1/4” of the thermocouple directly into the solution. If a corrosive mixture is
heated, use a Teflon-coated thermocouple (or use the external thermocouple method; Section 4.2).
Do
avoid exposure of the controller to corrosive gases and liquids.
The atmosphere of a research hood is corrosive to all electronics. Place the controller outside the
hood away from corrosive gases.
17
