Metrohm 757 VA Computrace - Manual (Page 36)

3 Installation
757 VA Computrace – Hardware
32
3.3.9 Cleaning the MME
If the mercury in the multi-mode electrode is contaminated and this leads to distur-
bances, the MME must be cleaned and refilled with ultrapure mercury. Proceed as
follows:
1 Remove multi-mode electrode from 757 VA Computrace
Stand
• Unscrew FEP tubing 30 and 38 from the MME, disconnect electrode
cable 16 from MME.
• Take multi-mode electrode 17 out of measuring head 20 while gently
tapping the MME to knock off any mercury drops on the glass capillary
into the measuring vessel.
2 Remove old mercury
• Place multi-mode electrode 17 in a horizontal position in the electrode
holder 93 (see Fig. 11-3). The slotted screw 80 is now at the top.
• Unscrew slotted screw 80 using a suitable coin.
• Carefully turn MME and empty mercury through the threaded opening 79
into a waste container placed in the drip pan 92. While doing so, gently
tap the glass capillary 88 and the MME to ensure that all mercury flows
out of the MME.
3 Dismantle MME
• Unscrew retaining nut 87.
• Take glass capillary 88 out of opening 83, the sealing ring 85 and the
locking ring 86 are removed at the same time. Remove these two parts
from the glass capillary 88.
• Remove insert ring 84 from the MME.
• Unscrew slotted screw 75 with a suitable coin in an anticlockwise direc-
tion from screw thread 77.
• Screw locking ring 74 onto slotted screw 75 and pull out of the MME.
4 Dispose of old capillary
• Connect filling tubing 94 with the tubing coupling 97 to the two gas wash
bottles 96 and the vacuum pump (see Fig. 10).
• Insert glass capillary 88 (capillary end) in the filling cone 95 of the filling
tubing 94.
• Remove mercury from the capillary with the vacuum pump.
5 Clean MME
• Clean inner compartments of the MME, contact pin 81 and the screw
threads 77, 79 and 83 with a lint-free cloth.
• Thoroughly rinse all inner compartments of the MME and the unscrewed
individual parts with dist. water and then dry with N
2
.
Do not use any organic solvents.