Honeywell 4909 CPVC - Manual (Page 27)

Platinization and Platinum Black
7/99 4909 CPVC Conductivity Cell Insertion/Removal Assembly– Operations Manual 19
5. Platinization and Platinum Black
Only the electrodes having constants from 5 to 50 must be replatinized if the velvety-black deposit has been
rubbed off the electrodes in service or in cleaning, or if platinized electrodes are recommended and this
black deposit is not present when the cell is received. Always replatinize if a brush was used in cleaning the
electrodes. The indication of a need for replatinization of the electrodes is a long term drift of the
measuring instrument caused by an apparent increase in cell constant as the platinum black coating is
depleted from the electrode surfaces. The electrodes of the high constant cells are not visible since they are
located near the middle of the flow channels. Therefore the need for platinization is only indicated by the
effect on the measuring instrument. Do not platinize cells intended for measuring high purity water.
Before platinizing, clean the cell with detergent and brush as described in Section 4.1.
Support the cell in a cylindrical vessel with the end of the cell raised from the bottom. It is not necessary to
remove the cell from the fittings for platinizing. However, the guard tube must be removed from the low
constant cells. Pour in platinizing solution (p/n 31103011) to a level above the cross-channel.
To platinize the 5, 10, 20, 25 and 50 constant cells, immerse an auxiliary platinum electrode* in the solution
to a point about midway between the cross-channel or tube hole and the open end of the cell. Both
electrodes of the cell are platinized simultaneously by connecting the negative terminal of the battery (see
Table 4.2 for voltage) to both leadwires of the cell.
ATTENTION
* This third electrode should be chemically pure platinum. Its shape is unimportant. It may be one of the
electrodes in another conductivity cell or a platinum strip, sheet, rod, wire, etc.
Connect the positive terminal of the battery to the auxiliary platinum electrode. Note the time in seconds
listed in Table 4.2. During the platinizing operation, move the cell up and down gently to keep the solution
stirred. Then disconnect the battery and remove the cell. Rinse the cell thoroughly in tap water and then
rinse in distilled water.
Pour the platinizing solution back into its container as it may be used a number of times.