Metrohm 797 VA Computrace - Manual (Page 36)

2 Installation
797 VA Computrace / Hardware-Manual 8.797.8001EN
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9 Connect Multi-Mode Electrode
• Screw FEP tubing 34 for the inert gas supply into connection 71 of the
Multi-Mode Electrode 21.
• Screw FEP tubing 42 for the inert gas supply into connection 72 of the
Multi-Mode Electrode.
• Attach electrode cable 20 (WE) to screw connection 88 of the Multi-Mode
Electrode push cable lug under the screw and then tighten screw firmly.
10 Pressurize the MME
• Switch on 797 VA Computrace Stand with mains switch 14 (the 797 VA
Computrace Stand must first be installed properly as described in section
2.2).
• Start the VA Computrace program and click on or MAIN WINDOW / Utility
/ Computrace control to open the COMPUTRACE CONTROL window. Then switch
on the inert gas supply to the 797 VA Computrace Stand by clicking on
DME . This pressurizes the Multi-Mode Electrode 21 and the mercury begins
to flow slowly out of the capillary.
• Gently tap the MME with your finger (to remove any air bubbles) and allow
mercury to flow out of the capillary into the empty measuring vessel for
approx. 2 min.
• Fill measuring vessel 7 with 10 mL ultra pure water and add 1 drop KCl
solution (in pure water, mercury drops from the capillary only with difficul-
ty).
• Allow mercury to flow out of the capillary for ca. 2 min while checking the
drop formation: The drop time should be ca. 3 s.
11 Adjusting the sealing needle 75
• Turn slotted screw 74 using a suitable coin slowly in a clockwise direction
until the mercury flow stops.
• Open slotted screw slightly in an anticlockwise direction until the mercury
flow restarts.
• Gently tap the MME with your finger and turn the slotted screw very slowly
clockwise until the mercury flow just stops. (The tapping action is used to
knock off the mercury drop so that it is easier to see whether mercury con-
tinues to flow).
• Finally, turn slotted screw a quarter of a turn clockwise.
12 Checking the MME for leaks
• Switch on the dropping mercury electrode by selecting
DME in the COM-
PUTRACE CONTROL window and clicking on . The mercury drops
freely out of the capillary.
• Select
HMDE and click on . A single mercury drop is formed.
Knock this off by gently tapping the MME 21 with your finger and check
that the mercury flow has really stopped. Repeat this operation several
times.
• If mercury continues to flow, turn slotted screw 74 still further in a clock-
wise direction and repeat check.
• If it is not possible to stop the mercury flow, both the glass capillary 87 and
the sealing needle 75 have to be replaced (see section 2.3.9).