ATI
PQ45P pH System
Part 7
– DataLogger
28
O&M Manual
Rev-B (7/15)
5.13 2-Point Calibration Explained
The 2-point calibration method involves the movement of the sensor through two known pH buffer
values. Therefore, the sensor must be removed from the application to utilize this method. Two-
point calibration adjusts both the slope and the offset of the sensor. It is the recommended
method of calibration for highest accuracy. In addition, this calibration method utilizes an
automatic buffer recognition and compensation method.
IMPORTANT:
the 2-point calibration mode MUST be performed when a new
sensor is first put into operation so that accurate calibration data is available for
possible later 1-point calibrations.
5.14 1-Point Calibration Explained
The 1-point calibration method is generally known as the "grab sample" calibration method. In
the 1-point calibration method, the sensor may be removed from the application and placed into
one buffer. It may also be left in the measurement process and calibrated by reference. 1-point
calibration adjusts only the sensor offset. Since the sensor slope degrades much slower than the
sensor offset, this method may be used as a frequent calibration method between more involved
2-point calibrations. For example, a user may choose to perform on-line 1-point calibrations
weekly and 2-point calibrations monthly.
5.2
Performing a 2-Point Calibration
The 2-point calibration method utilizes an automatic buffer recognition and compensation system.
For this system to operate properly, the user must first configure the proper buffers in the Set
Buffers screen (see Section 4.64). If the buffers are not present in this menu, the user can
override the automatic values and enter arbitrary values. However, the highest accuracy is
provided when the user selects and uses buffers from this pre-defined table list. With the pre-
defined buffers, the temperature variations in the buffer are automatically compensated for during
the calibration process. If the buffer data is manually entered, the calibration buffer sample must
be very temperature stable to achieve the same degree of accuracy.
Procedure
1.
Remove sensor from application. Rinse and clean if necessary.
2.
Allow sensor to temperature equilibrate with the buffer as best as possible. With the sensor
coming from an application solution that differs greatly in temperature from the buffer, the user
may have to wait as much as 20 minutes for this to occur.
3.
Scroll to the CAL menu section using the MENU key and press ENTER or the UP arrow key.
Cal
pH
will then be displayed.
4.
Press the ENTER key. The screen will display a flashing 1 for 1-point or a 2 for 2-point
calibration. Using the UP arrow key, set for a 2-point calibration and press ENTER.
