5. Maintenance

6.Use an Allen key (2.5 mm) to unscrew the upper of the two screws securing the lamp holder and the lamp. Note carefully the positions of the insulation sleeve and washer.

7.Disconnect the lamp from the PC-board.

8.Bend the upper part of the lamp holder slightly (2-3 mm) upwards and withdraw the mercury lamp from it by gently pulling the metal socket.

9.Insert the new mercury lamp and connect it to the PC-board.

10.Remount the upper lamp holder screw, ensuring that the insulations are correctly mounted, reinstall the cell holder and perform the maximum light adjustment described in Section 5.8.

5.9Mercury lamp-maximum light adjustment

Warning: During this adjustment stray light may escape from the

UV source and protective glasses must be worn.

1.Connect the optical unit to the control unit and plug into the mains supply.

2.Switch on the instrument and allow to warm up for about 10 minutes.

3.Insert a filter and the corresponding converter or aperture.

4.Connect the control unit to a recorder with a full scale response of 50 mV.

5. Set the range selector to SHORT and zero the recorder.

6.Set AU/ %T to % T and turn the baseline adjust fully clockwise.

7.Select a range giving a pen deflection of approx. 50 % and then rotate the lamp around its longitudinal axis until maximum pen deflection occurs.

8.Set the range selector to SHORT and adjust the recorder zero to bring the pen to the centre of the chart. Mark this pen position.

9.Set the range selector to 2 and set AU/ % T to AU.

10.Adjust the baseline control to its mid-position,five full turns from either end of its range, by means of a tool, ie. an adjustable spanner.

11.If necessary, adjust the lamp by turning it slightly to bring the pen back to the position marked in step 8.

12.Reassemble the optical unit.

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