Landcal Blackbody Source
Type P1600B2
User Guide
Page 22
If the furnace does not reach temperature, or is slow, measure the element
resistances and calculate the required power limit using the method given
above. If it exceeds 100%, the elements have too high a resistance and need
replacing. The method of ascertaining and adjusting the power limit on the
controller is given below.
Always record the actual setting when first making an adjustment. If new
elements are fitted, return to the original setting, or, better, measure the new
element resistances and recalculate.
9.4 Replacing the Furnace Elements
If an element breaks and you need to replace it, follow the procedure outlined
in Section 5.2. After replacing the element, check that the connections are as
shown in Fig. 11. It is advisable to replace all six elements, even if only one or
two fail, because new elements have a lower resistance than used ones. The
elements are serial connected and the lower voltage drop across a new element
will tend to cause premature failure of the remaining older elements. Used
elements can be saved and used for future element replacements.
9.5 Replacing the Insulation Cassette
Removing the old insulation cassette
1) On the rear of the furnace, loosen the two screws on the Measuring
Thermocouple Alignment Tab and withdraw the thermocouple sheath.
2) Remove the back panel by unscrewing the 5 small screws. This is a double
panel, outer and inner. Detach the earth lead from the inner panel.
3) Make a note of the wiring sequence for the elements. Remove the element
braids and carefully withdraw the elements. Store safely until required.
4) Make a note of the wiring sequence for the control thermocouples.
Disconnect the thermocouples and carefully withdraw them. Store safely
until required.
5) Make a note of the wiring positions and wiring sequence of the element
supply terminal blocks. Disconnect the wires from the terminal blocks on
the rear of the insulation cassette.
6) Remove the cassette retainer at the rear base of the cassette.
7) On the front of the furnace, remove the central stainless steel disc.
8) Carefully withdraw the front plug containing the sighting tube by
unscrewing the 4 screws around the flange.
9) If installed, carefully withdraw the cavity from the insulation cassette.
This is a reverse of the procedure described in section 5.2 of the operating
instructions.
10) Push the cassette to the back of the case and withdraw. Care is required
as the cassette is heavy.
11) Remove the plug spacer and airflow separator from the front of the old
cassette outer case and fit to the new one.
