2216 Controller
MC11 – 1.05
5
3
A
LTERING THE
P
OWER
L
IMIT
3.1
Overview
Depending on the furnace or oven model the power limit parameter
OP.Hi
(Output High) may be
accessible or hidden.
For silicon carbide heated furnaces the parameter is accessible to allow for compensation for
element ageing (see the appropriate section in the furnace manual). In wire-heated chamber or
tube furnaces, reducing the power limit is a convenient method of improving control at low
temperatures, as outlined below.
The power limit may be set to zero to permit demonstration of the controls without heating.
In many models the power limit setting depends on the supply voltage; usually the furnace or
oven manual contains details: if in doubt, contact Carbolite Gero for advice.
The power limit parameter does not apply to the overtemperature controller, if present.
3.2
Altering the value
Press Page
until
oP
(output list) is displayed. Press Scroll
until
OP.Hi
(Output High) is
displayed. Press Down
or Up
once to display the value of
OP.Hi
and write down the value.
To alter the value, use Down
or Up
. Note that setting the value to zero prevents the furnace
or oven from heating.
Caution:
Do not increase the power limit value to a value above the design level for the oven or
furnace model, or to a value above that correctly calculated for Silicon Carbide elements. The
heating elements could burn out, or other damage could be caused.
3.3
Control at Low Temperatures
If a product is to be used at temperatures much lower than its design maximum, control stability
can often be improved by reducing the power limit. Remember to make a record of the original
setting before altering the power limit.
Example: It is desired to run a 1200°C furnace at 300°C. The normal control settings can be
expected to cause excessive overshoot as the furnace reaches temperature. If the power limit
OP.Hi
is normally set to 100%, try a setting of 40%. This should greatly reduce the overshoot.
(There is no firm calculation rule to get this example setting of 40% – experiment may be
required to achieve a good result. Avoid power limits below about 30% – control accuracy falls
off at such levels.)
