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MRF 16/22
5 Controllers, lights and indicators
5.1
Control panel [See Fig 5.1]
Introduction
On the control panel the green light and switch is illuminated whenever the electrical supply to
the furnace is connected, also the case cooling fan will be on. The switch cuts off power to the
controllers and contactor. Turn on the switch to activate the controllers. The controllers light up
and go through a short test cycle.
If the Setpoint temperature is greater than the measured temperature, the controller will switch
the heating elements on. Refer to section 4.5 for further notes on thermocouples at low
temperatures.
To switch off the furnace turn off the green switch. To keep the case cooling fan running, do
not disconnect the furnace from the electrical supply until the measured temperature has
cooled down below 300°C.
If the furnace is to be left unattended and has cooled down, isolate it from the electrical supply.
The heating elements and microwave power are independently controlled, either manually or
by a program. The microwave power can additionally be set to pulse on/off during its 'on' time.
When an over temperature condition occurs, the controller cuts the power to a contactor, which
in turn cuts power to the heating elements and microwave. Power is not restored until the
controller is "reset". [See section 10].
Temperature control [See section 6]
The 3508 can be used as a simple temperature controller.
PID (Proportional Integral Derivative) temperature control uses a complex mathematical
control system to adjust the power being sent to the elements and hold the furnace at the
desired temperature.
The 3508 does not contain a real-time calendar.
Over temperature controller [See section 10]
The 2132 over temperature controller is configured for immediate use. It is a digital instrument
with a latching alarm, requiring no additional panel controls. The 2132 normally displays the
over temperature Setpoint.
Set the over temperature controller to a temperature, for example 15°C, above the maximum
Setpoint or process temperature.
Microwave control [See section 7]
The microwave power is controlled independently from the furnace temperature. The
microwave power level is set as a percentage. It can be set on continuously or pulsed on/off
for preset time intervals. It can be controlled manually [sect 7] or by a program [sect 8], in
which power levels can be set for each segment.
Program editing [See section 8]
Programs can be run once or set to repeat many times. In multi program units, programs can
be run individually or linked by a call parameter as sub programs or to form single long
programs.
Both temperature and MW power can be controlled by programs. All programs are written on
the second page of the controller screen. New programs can be written while another is
MF 55-GB 1.21
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