4.0
3508 Dual Loop Cascade Control (if fitted)
4.1
Principle of Cascade Control
When cascade control is fitted, the Load Loop 3508 senses the temperature of the
workload, and the Element Loop 3508 senses the element temperature. Depending on
the oven or furnace model, the Load Thermocouple may be in a fixed position, or may
be movable. The Element Thermocouple is fixed in a predetermined position near the
heating elements. The Load Thermocouple should be placed as near as possible to the
work to be heated.
The Load Loop communicates with the Element Loop, calling for heat according to the
load temperature and the current program or set point. The Element Loop regulates
the heat according to element temperature and the requests from the Load Loop.
The element temperature could, in principle, vary between the furnace or oven
maximum and minimum, regardless of the working temperature of the load. In
practice, the cascade control system is configured to limit the element temperature to a
band around the load temperature, typically of ±10% of the set-point temperature.
The set point of the load loop, shown at the top of the display, can be adjusted by the
operator. The Element Loop, shown at the bottom of the display, should not be
adjusted by the operator & will automatically regulate the element temperature to
achieve the Load set temperature.
In a three-zone furnace for which the “three zone cascade” option has been ordered
the centre zone is a 3508 Dual Loop & separate end zone controls are fitted. The
operator sets the Load loop set point on the 3508 centre zone. The end zone controllers
work automatically & need no adjustment by the operator.
4.2
Operation of Cascade Control
The operator may ignore all the complications of the system, and program the Load
Loop according to the standard instructions for that controller. The home display shows
the load loop at the top of the display and the Element loop at the bottom. By pressing
the page key, separate views of load and element loops will be shown.
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4.0 3508 Dual Loop Cascade
