Chemglass CG-1972-65 - Manual (Page 19)

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3.13 Changing Between PID and ON/OFF Operating Modes. The controller can heat in either of 2
operating modes, PID (Proportional, Integral, Derivative) or ON/OFF mode. The difference between
them is the way they supply power to the heater.
In ON/OFF mode (the simplest heating mode),
the controller is ON when it’s below the set point
and OFF when above. The disadvantage of this
mode is a large over shoot of the set point (5 -
30
o ) on initial warm up and oscillation of
temperature around the set point thereafter. The
reason for the overshoot is because the heater
turns off only after crossing the set point and
until the heater cools down the temperature
continues to rise. This method works well for
heaters that transfer heat rapidly (such as heat
lamps), it’s acceptable for heaters such as heating mantles (≈ 5 o overshoot), but it’s terrible for heaters
that transfer heat slowly (vacuum ovens, heating blocks, etc.).
In PID mode the controller monitors the shape of
the heating curve during initial warm up and
decreases power to the heater before the set
point is reached so that the solution reaches the
set point with minimal over shoot. [Notice that
the heater turns off for varying periods of time
before the set point temperature is reached]. The
second feature of PID mode is that it adjusts the
percent of time the heater is on so that the set
point is maintained precisely. The advantage of
PID mode is that it delivers stable temperature
control with any heater from heat lamps to
vacuum ovens. The disadvantage is that the controller must be properly tuned to the heater being used,
whereas ON/OFF mode requires no tuning. Since both heating modes have their advantages (simplicity
vs. accuracy), instructions to change the controller to ON/OFF mode are given below (though PID mode
will probably give better results 95% of the time). The controller can be set back to PID mode by
following the procedure in Section 3.10.
1. Press and hold in both the ▲ and ▼ keys on the front of the temperature
meter until the word “tunE” appears in the display, then let go of the
buttons.
2. Press ▲ until the word “CyC.t” appears in the display.
3. While holding in the ‘
* ’ key, press the ▼ key until the word “on.of” appears
in the display. NOTE: if the display shows the letter “A” when the ‘ * ’ keys
is held in, press the ▲ key until “on.of” is in the display, then let go of all
the keys.
4. Press the ▼ key until the word “bAnd” appears in the display. While
holding in the ‘ * ’ key, press the ▼ key until the value “0.1” appears in the
display, then let go of all the keys.
5. Press and hold in both the ▲ and ▼ keys on the front of the controller until
the temperature is displayed, then release both keys.
Procedure to change
controller to ON/OFF mode
The controller can be set
back to PID control by
following the procedure in
Section 3.10. To completely
reset the controller to
original factory settings,
follow the procedure in the
Appendix, Section II.