Digital Temperature Controller Reference Manual
Digital Temperature Controller Reference Manual
Digital Temperature Controller Reference Manual
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TECHNICAL DESCRIPTION<br />
A maximum of six zones can have paddle control on the paddle thermocouples. The control<br />
is differential, integral (D.I) on the paddle, which is cascaded on the spike thermocouple. In<br />
this type of control, there are 6 control blocks with 6 unique parameters. For each parameter,<br />
there are 5 distinct temperature ranges in steps of 300 oC.<br />
A block diagram of the control loop is shown in Figure 2-3.<br />
2.4.1 Spike Control<br />
The inputs for the spike P.I.D. control are the spike thermocouple reading, spike setpoint<br />
and spike P.I.D. parameters. The spike setpoint is calculated from the profile table. If the<br />
setpoint is not given in the table, the value can be obtained by interpolation.<br />
2.4.1.1 Spike derivative block<br />
The derivative control is used to make immediate changes, whenever the thermocouples<br />
readings change. The output of the block is proportional to the slope of the temperature and<br />
the derivative parameter. Hence, an increase in the derivative parameter will increase the<br />
effect of the derivative function.<br />
The input to this block is the thermocouple reading and not, as in most systems, the<br />
deviation between the setpoint and the reading. It is, also, switched off before the P.I. control<br />
blocks. The effect of these two actions on the ramping is shown in Figure 2-2. As can be<br />
seen the overshoot is greatly reduced. The deviation between setpoint and temperature<br />
during ramping is equal to the Derivative Output (DO = slope x parameter).<br />
The inputs to this block are the current spike thermocouple reading and the derivative<br />
parameter in seconds. The spike derivative value is an average of different spike<br />
thermocouple readings taken over a period of time. This gives a slope or trend to the<br />
movement of temperature in units/s.<br />
The spike derivative output is the derivative value multiplied by the spike derivative<br />
parameter in units of degrees. This value added to the setpoint deviation (setpoint reading)<br />
gives the P.D. output. The P.D. output is limited to plus or minus the proportional band<br />
output.<br />
Figure 2-2 Ramping comparisons<br />
DIGITAL TEMPERATURE CONTROLLER REFERENCE MANUAL 2-5
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