Carbolite VMF Series - Manual (Page 6)

AAF, GSM, VMF
6 MF06 – 3.32
Any metal object used to probe into the furnace chamber while the furnace is
connected to the supply must be earthed (grounded). This applies in particular to
metal sheathed thermocouples, where the sheaths must be earthed. The refractory
material of the chamber lining becomes partly conducting at high temperatures, and
the electric potential inside the chamber can be at any value between zero and the
supply voltage. Unearthed probes can cause serious electric shock.
3.4 Atmospheres
When an optional gas inlet is fitted there is a label near the inlet saying "INERT GAS ONLY". In
practice inert or oxidising gases may be used, but not combustible or toxic gases. Chamber
furnaces are not gas tight, so it should be understood that gas usage may be high, and that the
chamber is likely always to contain some air. Residual oxygen levels of 1% may be expected.
3.5 Operator Safety
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.
Avoid burns: furnace surfaces can be hot. Before you remove a hot object from the furnace make
sure you have a safe place to put it down.
3.6 Power Adjustment
The furnace control system incorporates electronic power limiting, which is used in some models
to compensate for voltage to achieve the same power over a range of voltage supplies. In other
models the power limit is set to 100% over all common voltages. The power limit parameter
OP.Hi
may be accessible to the operator, but should not generally be altered.
See section 8.2 for details of power limit settings. DO NOT adjust the power to a level higher that
the design level stated: this may cause fuse to blow, and could damage the heating elements.
The power limit may be set to a lower limit if the furnace is to be used at a low temperature only:
this may give better control stability. It may set to zero to permit demonstration of the controls
without the heating elements taking power; to resume heating reset it to its standard value.