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12.4 Calibration of ORP
The controller reads ORP in millivolts. To control free bromine or free chlorine pH and temperature must
be maintained. 1 ppm of free chlorine at 7.5 pH and 25 C is equal to approximately 550-750 mV. This
varies with different water quality.
When calibrating ORP keep in mind that it can be affected by several factors:
pH
Water quality
Temperature
A single point calibration is sufficient for most applications using the controller. A two point calibration
can be performed if necessary.
If the ORP has been calibrated incorrectly you may restore the default values by initializing ORP
calibration.
.
Single point Calibration
We recommend that the ORP calibrations only be performed with the ORP sensor mounted as it will be
used in the system.
It is necessary to have an accurate reading of the process water to properly calibrate the controller. A
hand-held ORP meter that tests the sample is best. Once you have obtained a reading, immediately
enter the value into the controller. In the process screen, press CAL. Select ZERO. Use the number
keys to enter the value, and then press ENT. When the number is accepted, you will see the
CALIBRATION COMPLETE screen before the LCD display switches back to the original PROCESS
screen. Then take a second sample with a hand-held ORP meter and confirm the reading on the
display.
Two Point Calibration
The controller is capable of performing a two point calibration using both the ZERO and SPAN
calibrations. To perform a good two-point calibration, buffers are used with the ZERO calibration buffer
at least 200 mV lower than the SPAN calibration buffer.
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