MF47-3.05
5
3.0
O
PERATION
The instructions for operating the temperature controller are given in a separate manual If the
furnace is fitted with a time switch, see also the supplementary manual MS03. If cascade control is
fitted, see the supplementary manual MS07.
3.1
Operating Cycle
The furnace is fitted with an instrument switch. The switch cuts off power to the controllers and
contactor.
Connect the furnace to the electrical supply. The cooling fans will operate.
Operate the instrument switch to activate the temperature controller. The controller becomes
illuminated and goes through a short test cycle.
Close the furnace door and adjust the temperature controller – see the controller manual.
Set the overtemperature controller to a temperature a little (say 15°C) above the maximum setpoint
or program temperature.
Unless a time switch is fitted and is off, the furnace starts to heat up. The Heat light glows brightly
at first, more dimly as the furnace temperature approaches a program setpoint.
If the overtemperature trip operates then an indicator or message in the overtemperature controller
flashes, and the heating elements are isolated. Find and correct the cause before resetting the
overtemperature controller according to the instructions supplied.
To switch the furnace off, set the Instrument switch to off. The case cooling fans remain on and the
chamber can be unloaded.
Do not disconnect the furnace from the electrical supply until it cools to below 300°C; ensure that
the cooling fans are still running if the furnace is above that temperature.
If the furnace is to be left off unattended and has cooled down, isolate it from the electrical supply.
3.2
Operator Safety - Electrical
The furnace incorporates a safety switch which interrupts the heating element circuit when the
door is opened. This prevents the user touching a live heating element, but also prevents the
furnace from heating up if the door is left open.
The operation of this switch should be checked periodically – see section 4.1.2.
3.3
Operator Safety - Heat
Furnace surfaces
The case surface gets hot; even though this is within permitted limits, operators should at all times
take care. The chimney gets especially hot – do not touch it.
Opening the furnace door
Wear heat-resistant clothing, including appropriate hand and face protection (see also the warning
about eye protection in section 5.8). Opening the door when hot could damage clothing, or even set
it alight, because of high levels of radiated heat. Do not keep any inflammable objects near the
furnace, nor objects which could be damaged by radiated heat.
See also section 3.5.
3.4
Loading the Furnace
When heating large objects, in particular poor conductors, avoid shielding the thermocouple from
the heating elements. Also ensure that nothing is within 15mm of the elements.
The thermocouple is intended to sense the temperature near the heating element, but if a large
object is placed in the chamber it may record the average temperature of the object and the
elements, which can lead to overheating of the elements. Allow large objects to gain heat at a
lower temperature and then reset the controller to a temperature close to the desired maximum.
