Xylem PC320 Process Controller - Manual (Page 13)

Global Water
800-876-1172
• globalw.com
- 13 -
First select whether the sensor will be calibrated using a 2 or 3 point method.
Generally; sensors are calibrated at 2 points as close to the ends of the sensor’s
measurement range as possible. For example: A 15 foot water level sensor would be
calibrated using a 2-point method and be set at zero feet and as close to 15 feet as
practically possible. However; a pH sensor with a range of 0-14 may be typically
calibrated at a pH of 4 and 10 due to the hazards of using very strong acids and bases.
Calibrating a sensor at points other than the full range of the sensor will not stop the
PC320 from measuring the full sensor range, but may slightly decrease the overall
accuracy. A ph sensor might also be calibrated using a 3-point method at pH values of
4, 7 and 10. Using a 3-point calibration will increase the accuracy of sensors that have
small amounts of nonlinearity.
After selecting the number of calibration points, press SAVE and MENU. Using the
arrow buttons, set the High Value to the upper calibration point, first setting the +/-
sign, then separately each digit. If you are calibrating a 15 foot water level sensor but
only have an 8.5 foot column of water, set the High Value to +8.50000. If you are
using a pH 10 buffer solution to calibrate a 0-14 pH sensor, set it to +10.0000. Use the
UP and Down buttons to change the sign to + or -. Use LEFT and RIGHT to select
each digit, then UP and Down to change it in the range of 0-9 or decimal point. Press
SAVE when done and then MENU to move forward. Next place the sensor in a
condition that corresponds to the High Value previously set, or use a loop or process
calibrator. Press SAVE to store the High Raw data number, then MENU. For 3-point
calibration, the next menu will allow you to set the middle calibration point; then the
Low point. A 2-point calibration will skip the middle point and jump to the Low point.
Set each of these Middle and Low calibration points in the same way as the High.
Polynomial Mode:
The calibration process previously discussed can be further modified. This is best
described with an example that will use a water level sensor and from this level data,
calculate the water flow rate in a flume.
Calibrate a water level sensor as previously described. When selecting the sensor type,
you can use the Custom Sensor and Units selection; the sensor name and units
displayed don’t actually have anything to do with calculations, they are just used as