4.0 Operation
thermocouples are wired in opposition to the centre zone reference thermocouple. If
the temperatures of the centre and end zones are the same then 0°C will be displayed
on the end zone controllers. If the end zone temperatures are either higher or lower
than the centre zone, the end zone controller will display the difference in temperature
(higher = positive value, lower = negative value).
It is best practice to set the setpoint of the two end zone controllers to zero.
Alternatively, a small temperature difference (offset) can be created by setting a non-
zero value, for example to compensate for heat losses at the end or where using a gas
flow. However, the sum of the centre zone controller setpoint and the end zone
controller offset MUST NOT exceed the furnace maximum temperature.
To alter the setpoint with the display showing the Home screen, press Down
or Up
once to display the setpoint and then press again or hold down to
adjust it. The display returns to the measured temperature when no key is
pressed for a short period of time.
Sometimes a furnace using this type of control does not cool down because the end
zones lose heat first and therefore the end zone controllers try to compensate for this
by switching on the end zone elements, preventing the furnace from cooling.
B. Retransmission of Setpoint
Three independent thermocouples are connected to three controllers. The three
controllers are linked together and the centre zone controller communicates the desired
setpoint to the end zone controllers. If the centre zone controller is set to a setpoint or is
running a program, the end zone controllers will automatically follow.
For products with the CC-T1 controller, please refer to the separate CC-T1 controller
manual for details on enabling and disabling setpoint retransmission.
For other products, additional communication modules are fitted in the controllers. The
communication between the controllers of the Eurotherm 3000 series is known as
Broadcast communications. It is possible to switch off the linked control and allow the
controllers to work independently. In the level 2 menu of the end zone controllers (see
controller operating instruction), scroll to L-r. Where the end zone controller is a 3216
use the
up
down buttons and select NO. Where the end zone controller is a 3508
use the
up
down buttons to select SP1, (SP1 = Local, and SP2 = Remote). There
is no need to alter the centre zone controller.
It is possible to set an offset (local trim) between the centre and end zone controllers.
This can be either a positive or negative difference from the centre zone temperature.
Once entered, this offset will always be added to, or subtracted from, the retransmitted
setpoint temperature.
For products with the CC-T1 controller, please refer to the separate CC-T1 controller
manual for details on how to set an offset trim.
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