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We have a Yokogawa EXA SC202G Conductivity Analyzer installed at outlet of Weak Base Anion Exchanger on water service. When the exchanger resin is to be regenerated by Caustic, this analyzer is manually isolated by closing the valve of the sample point, since conductivity at that time exceeds its range. After regeneration when it is again taken into service it displays either nothing or negative value, however conductivity at that time must be a positive value. When this analyzer is turned Off and again turned On, the problem resolves. What could be the possible cause of such a behaviour.

Conductivity during normal operation= 80 to 100 uS/cm
Max. Conductivity= 700 to 900 uS/cm
Min. Conductivity= 0 to 1 uS/cm
Service= Water
Anion Resin= RELITE A-329
Regenerant= NaOH sol.

A couple of possibilities, but first, the obligatory commercial for vendor service departments.

Vendors maintain service departments for just such questions as these. Have you contacted Yokogawa? If not, you should.

One of the potential problems may be that the conductivity cell is dry when it is closed off. This may cause the analyzer's input to become saturated, which is cleared by cycling the analyzer's power. You might want to try interlocking the analyzer's AC power supply with the isolation, so that when the analyzer is isolated, the power shuts off, and when the analyzer is no longer isolated, it waits a few seconds to make sure the sample is flowing properly and then turns itself on.

Walt Boyes
Editor in Chief
Control and Controlglobal.com
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