Hach NT3100sc User Manual page 16

Option Description
Factor Enters a slope factor to adjust the standard calibration.
Options: from 0.8 to 1.2 (default: 1)
Note: Use grab samples with known values or standard solutions to determine the slope
factor.
Standard Start calibration—Starts a one-point calibration.
calibration
Standard value—Selects the value for the calibration standard.
Note: The Standard calibration option is not available if matrix calibration is active.
Calibration Sets the calibration interval. Options: off (default), 1 week, 4 weeks, 3 months or 6 months.
interval Note: Not available if matrix calibration is active.
5.3.2 Matrix calibration
The matrix calibration is only available for the NT3200sc probe and can have one, two or three
calibration points. The matrix calibration adapts the calculation for nitrate and nitrite to the conditions
in the medium. A matrix calibration is based on a laboratory comparison measurement. Start the
matrix calibration after the probe is in the medium and has adapted to the environment. Wait a
minimum of 15 minutes with the default configuration settings to let the probe adjust to the
temperature, complete some wiping cycles to clean the measurement gap and remove air bubbles.
The matrix calibration is necessary to adjust the measurements to the background environment. If a
single calibration point is used, it is recommended to select the calibration point at the lower limit of
the operating range of the application. For two calibration points, select the calibration points at the
lower and upper limit of the operating range. If a third calibration point is used, set the third
calibration point in the middle of the operating range.
The limit of the operating range depends on the application:
• If the nitrate concentration changes and nitrite is almost constant, set the limit to the lowest and
highest NO concentration.
3
• If the nitrite concentration changes and nitrate is almost constant, set the limit to the lowest and
highest NO concentration.
2
• If the nitrate and nitrite concentrations change, set the limit to the lowest and highest NO
concentration.
If one more calibration point is added, the probe knows automatically which of the three calibration
points needs to be rewritten.
Each calibration point is shown in Matrix calibration > Information and can be deleted manually.
If one of the events that follows occurs, delete all of the existing calibration points and record new
calibration points:
• The probe is moved to a different environment
• The matrix changes significantly
• The matrix changes seasonal
• The process changes
• Comparison measurements with laboratory values are not matching
• An error message shows that a matrix calibration is necessary
Note: Doing or erasing a matrix calibration does not have an effect on the factory calibration.
Make sure that the steps are followed for each calibration procedure:
• The probe is in the medium and has adapted to the environment.
• Collect the grab sample, then immediately validate on the controller that the grab sample was
collected.
• Collect the sample as near as possible to the sensor.
• Start the matrix calibration only when the concentrations are stable.
• To measure the grab sample, refer to
16 English
Instructions for laboratory measurements
3
on page 26.