Metrohm 797 VA Computrace - Manual (Page 32)

2 Installation
797 VA Computrace / Hardware-Manual 8.797.8001EN
24
1 Install Multi-Mode Electrode in 797 VA Computrace Stand
• With the measuring head arm 23 tilted back, slide the empty measuring
vessel 7 into the holder 5 of the 797 VA Computrace Stand and then lower
the measuring head arm.
• Carefully insert Multi-Mode Electrode 21 in opening 58 of the measuring
head 24 (during insertion, the tip of the capillary 87 must not touch the
measuring head) and push in carefully as far as it will go. Avoid water drops
touch the tip of the capillary.
2 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.
3 Fill capillary with mercury
• 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
the 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.
4 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 drops so that it is easier to see whether mercury con-
tinues to flow).
• Finally, turn slotted screw a quarter of a turn clockwise.
5 Checking the MME for leaks
• Switch on the dropping mercury electrode by selecting
DME in the COM-