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To switch the furnace off, use both the Heater switch and the Instrument switch. If the furnace is
to be left off unattended, isolate it from the electrical supply.
3-zone Control Methods – models EHC and EVC
3.3
These models are typically designed to achieve an extended uniform temperature zone by the use
of three control zones. The end-zone length for the 3-zone models is 1 element (150mm). The
control zones are typically linked so that the end controllers follow the central controller in a
master-slave approach, in one of two ways. Alternatively independent control zones may be
ordered. There are thus three control methods (A, B & C).
Achieving temperature differences across the zones: a small temperature difference may be
achievable, but this is limited by the effect of radiated heat inside the furnace body, and in the
work tube, and depends also upon the furnace contents.
A. Back-to-Back Thermocouples
This is the most commonly supplied option.
The central zone of the work tube is controlled directly by the central temperature controller. Each
end zone thermocouple is wired in opposition to a central reference thermocouple, and the small
voltage resulting when the zones are at different temperatures is used by the end zone controller.
There are thus four thermocouples. The circuit diagram in section 7.2 (A) shows the thermocouple
arrangement.
Set the set point of the end zone controllers to zero. Alternatively, a small temperature difference
(offset) can be created by setting a non-zero value, but the sum of the main controller set-point
and the slave controller offset
"measured temperature" display shows the actual offset.
To alter the set point refer to the control manual supplied with this furnace.
Sometimes a furnace using this type of control does not cool down: the end zone controllers try to
remain at the current central temperature. Should this occur, contact Carbolite's technical
department.
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0.0
°C/F/k
Zone temperature
difference; use
access offset "set point
Figure 3-1. 2132 Slave Controller navigation
B.
Retransmission of Set point Using Broadcast Communications
When this is ordered there are three independent thermocouples connected to the three controllers.
The controllers are linked together, the central controller communicating the desired set point to the
end zone controllers.
Additional communication modules are fitted in the controllers, rather than an additional
thermocouple as in A. The communication between the controllers of the Eurotherm 3000 series is
known as Broadcast comms. The wiring connections between the controllers are shown in section
7.3 page 22.
It is possible to switch off the linked control and allow the controllers to work independently. In
level 2 of the end zone controller (see controller operating instruction), scroll to
Up Down and select NO. There is no need to alter the centre controller.
exceed the furnace maximum temperature. The
MUST NOT
Output
List
oP
°C/F/k
OP.Hi
Power
limit
setting if
/
to
present
"
MF65-1.01
Access
List
Home
°C/F/k
List
codE
For factory access to
lists and parameters not
available to the operator
L-r
E range
and use the
17
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