Calibration will be required during system start up or when a variation in conductivity readings exists between the displayed conductivity and the conductivity value determined from a reliable source (such as a hand held tester). The conductivity probe should be cleaned prior to calibration (see 7.0 MAINTENANCE for probe cleaning instructions).
The ‘SYSTEM RUN’ or ‘CONDUCTIVITY reading ’ screen is used to calibrate the controller. Press the ‘ENTER’ key from this main menu screen to access the calibration mode. The ‘CALIBRATION’ screen will display the word CAL and then the current conductivity reading. Place the probe in the conductivity standard. Allow the conductivity reading to stabilize. Use the ‘UP’ or ‘DOWN’ keys to enter the correct conductivity reading, and then press enter. This will save the reading value and re-calibrate the controller based on this value.
If the probe reading is off by more than 50%, then the controller will indicate an error by displaying ‘CAL LIM uS‘. This means that the probe has failed or needs cleaning.
Alternately, a sample of cooling tower water may be analyzed by a precalibrated conductivity monitor, and the DC4500 controller calibrated to match that reading using the sample as a standard solution.
The DC4500 Controller provides a circuit board test-switch to aid in troubleshooting the unit and system. The switch is located under the access cover on the lower section of the controller (see Figure 5).
The conductivity test-switch allows the user to determine if the conductivity circuit is operating correctly. When placed in the test position, this switch switches the conductivity probe and wiring out of the circuit and places an internal precision resistor. This resistor has a known conductivity reading of 3000 uS +/- 5%. If the unit has been calibrated then this reading could be displayed as + or – 50% of this 3000 µS value (+4500 µS, -1500 µS).
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