User Guide
Landcal Blackbody Source
Type P1600B2
Page 21
9 Maintenance
9.1 Introduction
1) Before starting any maintenance/repair work, always ensure that the
furnace is disconnected from the electricity supply.
2) Before starting any maintenance/repair work, always ensure that the
furnace has been allowed to cool to room temperature.
3) Upon completion of any furnace maintenance work, check the furnace for
electrical safety before use.
9.2 Routine Servicing
The source is fully tested and evaluated before supply and should give years of
trouble-free operation. No regular servicing or maintenance is required. The
furnace outer surface can be cleaned with a damp cloth. Do not allow water
to enter the case. Do not clean with organic solvents. In the unlikely event
of a failure, return the source either to a LAND company directly, or to one
of the LAND distributors for repair. The instructions in the following sections
provide information for the customer replacement of the heating elements, the
replacement of the insulation cassette and the replacement of other consumable
items. Adjustment of the power setting may be required from time to time.
9.3 Power Adjustment
Power limit
The furnace control system incorporates electronic power limiting. Power is
supplied to the elements in bursts of about 1/3 second duration. This prevents
overheating of the elements. The ‘power limit’ is programmed into the furnace
controller and may be calculated as a percentage as follows:
power limit
= 100 x target power x ohms
volts
2
where:
target power
is the wattage given on the furnace rating label
ohms
is the overall resistance (see example)
volts
is the live-neutral voltage (e.g. 240, not 415)
example:
3 phase furnace with 2 elements of 7.4W each in series per circuit (phase),
running on 380/220V, with a target power of 7000W
ohms = 7.4 x 2/3 = 4.93
power limit = (100 x 7000 x 3)/(220 x 220) = 71%
Element ageing
Silicon carbide elements gradually increase in resistance with use, a process
known as ageing. Their heating power reduces correspondingly. To ensure
sufficient power to the furnace, it may be necessary to adjust the power limit,
and, ultimately, to replace the elements.
