Hach Ultrapure pH/ORP Module Manuel D'utilisation page 10

Option
TEMP
COMPENSATION
SET ISO POINT
LOG SETUP
RESET DEFAULTS
Calibrate the sensor
About sensor calibration
The sensor characteristics slowly shift over time and cause the sensor to lose accuracy. The sensor
must be calibrated regularly to maintain accuracy. The calibration frequency varies with the
application and is best determined by experience.
Calibration adjusts the sensor reading to match the value of one or more reference solutions. For pH
sensors a temperature element is used to provide pH readings that are automatically adjusted to
25 °C for temperature changes that affect the active and reference electrode. This adjustment can be
manually set by the customer if the process temperature is constant.
Calibration slope and offset limits
A calibration will fail if the new slope value is < -20% or > 10% of the original slope value, or if the
new offset value is ± 3 pH of the original offset value.
If the new slope and offset values are within these limits the calibration will pass. However, if the new
slope value is < -10% or > 5% of the original slope value, or if the new offset value is ± 2 pH of the
original offset value, a warning will be generated and a warning icon displayed on the measurement
screen. To remove the warning icon from the display, push the enter key, select the sensor and
acknowledge the warning.
pH calibration procedure
Sensors can be calibrated with 1 or 2 reference solutions. Standard buffers are automatically
recognized. Make sure that the correct buffer set is used (refer to
on page 14).
10 English
Description
For pH sensors only—adds a temperature-dependent correction to the measured
value:
• NERNST—Linear compensation (0.1984 mV/°C)
• ULTRA PURE WATER—Compensation according to the ultrapure water curve
• MATRIX 1—Compensation according to the sulphate curve (4.48 mg/L sulphate
corresponds to a pH of 4.0 at 25 °C)
• MATRIX 2—Compensation according to the ammoniac/hydrazine curve
(0.272 mg/L ammoniac + 20 μg/L hydrazine corresponds to a pH of 9.0 at 25 °C)
• MATRIX 3—Compensation according to the ammoniac/morpholine/hydrazine
curve (1.832 mg/L ammoniac + 10 mg/L morpholine + 50 μg/L hydrazine
corresponds to a pH of 9.0 at 25 °C)
• MATRIX 4—Compensation according to the phosphate curve (3 mg/L phosphates
+ 0.3 mg/L ammoniac)
• USER DEFINED—Set the value of the linear slope
Note: The above standards are only valid up to a maximum temperature of 50 °C.
For user defined sensors only. Most sensors have an isopotential point of 7.00 pH
(default), however sensors for special applications may have a different isopotential
value. Set the slope, pH and isopotential values for the user defined sensor.
The measurement board is limited to measurements of ± 1000 mV. If the
combination of slope, pH and isopotential values entered cause measurements to
go outside this limit, the measurement value on screen will display a string of "+" or
"-" characters to indicate a measurement above or below the limit.
Sets the time interval for data storage in the data log—5, 30 seconds, 1, 2, 5, 10,
15 (default), 30, 60 minutes.
Sets the configuration menu to the default settings. All sensor information is lost.
N O T I C E
Change calibration options