Instruction Manual
Calibration - pH and ORP
LIQ_MAN_6081-P
February 2014
Calibration - pH and ORP
31
display will return to the screen in step 6.
17. If the slope is out of range (less than 45 mV/pH or greater than 60 mV/pH) or if the offset
exceeds the value programmed in Section 8.4, an error screen appears. The display then
returns to the screen in step 6.
18. To return to the main display, press MENU then EXIT.
19. Choosing Setup in step 7 causes the Buffer Stabilize screen to appear. The transmitter will not
accept calibration data until the pH reading is stable. The default requirement is a pH change
less than 0.02 units in 10 seconds. To change the stability criteria:
19.a. Enter the desired stabilization time
19.b. Enter the minimum amount the reading is permitted to change in the time specified in
step
20. To return to the main display, press MENU then EXIT.
10.3
Procedure–Manual Two-Point Buffer
Calibration
1. Obtain two buffer solutions. Ideally, the buffer values should bracket the range of pH values to
be measured.
2. Remove the pH sensor from the process liquid. If the process and buffer temperatures are
appreciably different, place the sensor in a container of tap water at the buffer temperature. Do
not start the calibration until the sensor has reached the buffer temperature. Thirty minutes is
usually adequate. Make a note of the temperature.
3. Press MENU. The main menu appears. Choose Calibrate.
4. Choose pH.
5. Choose BufferCal.
6. Choose Manual.
7. Choose Buffer1.
8. Rinse the sensor with water and place it in buffer 1. Be sure the glass bulb and reference
junction are completely submerged. Swirl the sensor.
9. The reading in the top line is the live pH reading. Wait until the live reading is stable. Then,
use the arrow keys to change the reading in the second line to the match the pH value of the
buffer. The pH of buffer solutions is a function of temperature. Be sure to enter the pH of the
buffer at the actual temperature of the buffer.
10. Remove the sensor from buffer 1 and rinse it with water. Place it in buffer 2. Be sure the glass
bulb and the reference junction are completely submerged. Swirl the sensor. Choose Buffer2.
11. The reading in the top line is the live pH reading. Wait until the live reading is stable. Then,
use the arrow keys to change the reading in the second line to the match the pH value of the
buffer. The pH of buffer solutions is a function of temperature. Be sure to enter the pH of the
buffer at the actual temperature of the buffer.
12. The screen at left appears momentarily.
13. If the calibration was successful, the transmitter will display the offset and slope (at 25°). The
display will return to the screen in step 5.
14. If the slope is out of range (less than 45 mV/pH or greater than 60 mV/pH) or if the offset
exceeds the value programmed in Section 8.4, an error screen appears. The display then
returns to the screen in step 6.
15. To return to the main display, press MENU then EXIT.
10.4
Procedure–Standardization
1. The pH measured by the transmitter can be changed to match the reading from a second or
referee instrument. The process of making the two readings agree is called standardization.
2. During standardization, the difference between the two values is converted to the equivalent
voltage. The voltage, called the reference offset, is added to all subsequent measured cell
voltages before they are converted to pH. If after standardization the sensor is placed in a
buffer solution, the measured pH will differ from the buffer pH by an amount equivalent to the
standardization offset.
3. Install the pH sensor in the process liquid.
4. Once readings are stable, measure the pH of the liquid using a referee instrument.
5. Because the pH of the process liquid may change if the temperature changes, measure the pH
of the grab sample immediately after taking it.
6. For poorly buffered samples, it is best to determine the pH of a continuously flowing sample
