3.3 Multi-mode electrode (MME)
757 VA Computrace – Hardware
25
1 Install multi-mode electrode in 757 VA Computrace Stand
•
With the measuring head arm
19
tilted back, slide the empty measuring
vessel
6
into the holder
3
of the 757 VA Computrace Stand and then
lower the measuring head arm
19
.
•
Carefully insert multi-mode electrode
17
in opening
55
of the measuring
head
20
(during insertion, the tip of the capillary
88
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
30
for the inert gas supply into connection
72
of the
multi-mode electrode
17
.
•
Screw FEP tubing
38
for the inert gas supply into connection
73
of the
multi-mode electrode
17
.
•
Attach electrode cable
16
(WE) to screw connection
89
of the multi-mode
electrode
17
: push cable lug under the screw and then tighten screw
firmly.
3 Fill capillary with mercury
•
Switch on 757 VA Computrace Stand with mains switch
12
(the 757 VA
Computrace Stand must first be installed properly as described in
section
3.2
).
•
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 757 VA Computrace Stand by
clicking on
DME
. This pressurizes the multi-mode electrode
17
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
6
with 10 mL ultrapure water and add 1 drop KCl
solution (in pure water, mercury drops from the capillary only with diffi-
culty).
•
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
76
•
Turn slotted screw
75
using a suitable coin slowly in a clockwise direction
until the mercury flow stops.
•
Open slotted screw
75
slightly in an anticlockwise direction until the
mercury flow restarts.
•
Gently tap the MME with your finger and turn the slotted screw
75
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 continues to flow.)
•
Finally, turn slotted screw
75
a quarter of a turn clockwise.
