3.11
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 Procedure 1 in Section 3.9.
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 Procedure
1 in Section 3.9. To
completely reset the
controller to original
factory settings, follow
the procedure in the
Appendix, Section II.
3.12
Fusing. The controller is protected by a fast acting fuse designed specifically to protect solid state
relays. If this fuse is replaced IT MUST BE REPLACED BY AN EXACT EQUIVALENT, a Tron
KAA-15 or Bussman KAX-15. One of these fuses, or an exact equivalent, must be used or a significant
safety hazard will be created and will void the warranty.
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