Metrohm 757 VA Computrace - Manual (Page 35)

3.3 Multi-mode electrode (MME)
757 VA Computrace – Hardware
31
3.3.8 Changing the capillary
Contamination of the glass capillary can necessitate its replacement. In such a
case, 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.
• Place multi-mode electrode 17 in a horizontal position in the electrode
holder 93 (see Fig. 11-3).
2 Unscrew slotted screw 75
• Using a suitable coin, unscrew slotted screw 75 out of screw thread 77
until the contact surface of the black O-ring at the Plexiglas wall (thin,
black stripe) is just visible below the metal thread 77.
3 Dismantle old capillary
• Position multi-mode electrode 17 vertically in the electrode holder 93 (see
Fig. 11-1).
• Undo retaining nut 87 completely by turning anticlockwise and lift up until
the lower part of the glass capillary 88 with the wide opening is visible.
• Gently tap the glass capillary 88 to knock off any residual mercury in the
wide opening into the MME.
• Press the retaining nut 87 downward with one hand and with your other
hand take glass capillary 88 completely out of the mount.
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 capillary with the vacuum pump.
5 Replenish mercury if necessary
Proceed as described in section 3.3.2.
6 Mount new capillary
Proceed as described in section 3.3.3.
7 Fill capillary
Proceed as described in section 3.3.4 or section 3.3.5.