Metrohm Multi-Mode Electrode pro - Manual (Page 50)

5.2 Large maintenance
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6.1246.120 Multi-Mode-Electrode pro
5.2.10 Adjusting the needle valve
Adjusting the needle valve
Before you can adjust the needle valve, the following requirements must
be fulfilled:
￭ The MME pro is mounted onto the measuring head of the instrument
and the inert gas supply is connected.
￭ An empty measuring vessel is placed beneath the MME pro.
￭ The instrument is connected to a PC on which the 797 VA Computrace
software is installed and running.
Note
If you use another software than 797 VA Computrace, then follow the
instructions on adjusting the needle valve in the manual of your instru-
ment.
For adjusting the needle valve you need the wrench (6.1247.220) or a
coin which will fit the slot of the screw.
1 Preparation
￭ Place an empty measuring vessel.
￭ Set the inert gas supply to 1.0 to 1.2 bar, in order to pressurize
the electrode.
￭ In the 797 VA Computrace software, open the dialog Compu-
trace Control with Utility
▶ Computrace Control and select
the electrode type HMDE.
￭ As soon as a drop of mercury appears at the tip of the capillary,
fill approximately 20 mL of water and a few drops of KCl-solution
into the measuring vessel.
2 Rough adjustment
￭ With the wrench, rotate the screw of the needle holder (1-1)
clockwise until the mercury stops dropping.
Check: After each half rotation of the screw, knock off the drop
and check if a new drop is forming.
3 Fine adjustment
￭ Rotate the screw slowly counterclockwise until a new drop is
forming.
￭ Reseal the capillary with a small rotation in clockwise direction
(ca. 10°).