Table of Contents
Advertisement
OPM223/253
5.5
Use the CAL key to access the calibration function group.
Use this function group to calibrate the sensor. The calibration can take place in a number of
ways:
• By measuring in two calibration solutions with known pH value.
• By entering data for the slope and zero point
• In the case of ORP measurement, by entering the mV value or two different % values
!
Note!
• During commissioning, calibration is absolutely essential so that the measuring system can
return precise measurement data.
• If the calibration is aborted by simultaneously pressing the PLUS and MINUS keys (return to
C19, C25 or C36), or if the calibration is faulty, the original calibration data are used again.
A calibration error is indicated by "ERR" and the sensor symbol flashes on the display.
Repeat calibration!
• For each calibration, the device automatically switches to Hold (factory setting).
• Any offset set is automatically deleted after the calibration is accepted.
• If the slope or zero point are outside the ranges given in C16 and C17, error 32 becomes
active for slope or error 33 becomes active for zero point. The electrode must then be
checked and replaced if necessary.
Things to note elements when calibrating ISFET sensors
Switch-on behaviour
A control circuit is created when the measuring system is switched on. During this time
(approx. 5 ... 8 minutes), the measured value adjusts to the real value. This settling behaviour
occurs every time the liquid film between the pH-sensitive semi-conductor and the reference
lead is interrupted (e.g. caused by dry storage or intensive cleaning with compressed air). The
settling time depends on the length of the interruption.
Sensitivity to light
Like all semi-conductor elements, the ISFET chip is sensitive to light (measured value
fluctuations). However, this only affects the measured value if the sensor is directly exposed
to sunlight. For this reason, avoid direct sunlight when calibrating. Normal ambient light does
not have any effect on the measurement.
Calibration
Operation
59
Advertisement
Table of Contents
