Page 12 of 24 M6493 Issue 10.3
7.3.3. Proportional, Integral and Derivative Control.
A proportional controller continuously adjusts the power, so the heat input to
the process is approximately in balance with the process heat requirements
in order to maintain a stable temperature. The range of temperature over
which power is adjusted is from 0% to 100%. This temperature range is
called the ‘Proportional Band’. The proportional band is adjustable for
differing process conditions (zero proportional band returns the controller to
basic on / off control).
The temperature difference between the stabilised temperature and the set
point is called the ‘Offset’. The offset can be reduced by adjusting the integral
term of the PID controller. This is achieved using the integrative action time
and integrative action reset.
A derivative function can be combined with the proportional controller to
provide the controller with the ability to shift the proportional band either up to
or down to compensate for rapidly changing temperature (i.e. when an oven
door is opened or cooler fluid is introduced into a controlled vessel). The
derivative function increases the controller gain during temperature changes,
and can help to reduce overshoot on start-up.
Hence, a three-mode PID controller combines the proportional, integral and
derivative actions, to allow the set point temperature to be approached
relatively smoothly with minimal overshoot.
7.4. Front Panel Controls
The MC810B controller has four front panel keys as described below.
7.4.1. The
key is used to increase the value of the parameter shown on
the display or to scroll through the parameter menu.
7.4.2. The
key is used to decrease the value of the parameter shown on
the display or to scroll through the parameter menu.
7.4.3. The
key is a dual function key. It is used to display and store the
value of the selected parameter when in ‘Programming’ mode. When used with
the
it is used to display the ‘Setpoint’ value.
7.4.4. The
is an ‘Exit / Stand-by button. Press of 3 seconds to turn unit on
or off.
7.5. Operating Modes.
7.5.1. The MB810B has two modes of operation: Function mode and Programming
mode. The unit enters Function mode immediately following power up in auto
test phase. In Function mode the display shows the temperature measured by
the temperature sensing probe. The output power will also be switched on or off
as appropriate. If the output power is on, the amber neon indicator on the front
panel will be illuminated. The only parameter which can be altered in the
function mode is the set-point. See 7.7.1
7.5.2. In Programming mode, all the other parameters apart from set-point can be
altered. To gain access to the programming mode from Function mode, press
the keys
and
. Keep them pressed for five seconds. The
output power is always off when in programming mode. If approximately 25
seconds elapse while in programming mode with out a key being pressed the
