18
12. Return the sensor to the process.
13. Depress and hold both push buttons to scroll
through the menu items to “
HoId
”, then release
both push buttons to remove the transmitter
from hold status. The hold flag will disappear
and the display will stop flashing “
HoId
”.
NOTE
To observe the calculated slope value, follow
the instructions in
Section 5.5
.
NOTE ON BUFFERS
The pH of buffer solutions changes with
temperature. This is very important to know
if you are calibrating in a very hot or cold
environment and you need good accuracy.
Rosemount Analytical recommends use of
the following NIST (National Institute of
Standards and Technology - formerly NBS)
buffers:
5.4 pH STANDARDIZATION.
After a buffer calibration, the system should be stan-
dardized on line by taking a grab sample. Standard-
ization will not calculate the electrode slope, but will
improve system accuracy.
1.
Take a grab sample which is as close to the
sensor as possible. Note the transmitter pH
reading at this time.
2.
Using a calibrated pH instrument, determine
the pH of the process or grab sample. The
reading must be temperature compensated to
25°C (77°F) if the sample is not at 25°C. Note
this value.
3.
Calculate the difference by subtracting the pH
value noted in Step 1 from the pH value found
in step 2.
4.
Depress and hold both push buttons to scroll
through the menu items to “
Std
”, then release
both push buttons. The display will show the
present pH value with the last digit flashing.
5.
Correct the pH standardize value for time lag by
adding the difference calculated in step 3 to the
amount displayed on the transmitter.
Example:
If pH in step 1 is 2.3 and pH in step
2 is 2.8, the difference noted in step 3 would be
+.5 pH. The present transmitter pH value would
be increased by .5 pH.
6.
Depress and hold push button #1 (scroll) and
#2 (shift) as needed to display the pH value cal-
culated in step 5.
7.
Enter the value into memory by depressing both
push buttons briefly. The transmitter will return
to displaying the present pH value.
5.5 pH GLASS SLOPE.
The slope (efficiency) of the pH glass electrode can
be entered directly if known (slope limits: 47.3 to
59.9 mV/pH). As the electrode ages the slope will
decrease.
1.
Depress and hold both push buttons to scroll
through the menu items to “
SLP
”, then release
both buttons. The display will show the present
slope with the last digit flashing.
2.
Depress and hold push button #1 (scroll) and
#2 (shift) as needed to manually enter a slope
value, if desired.
3.
Enter the value into memory by depressing both
push buttons briefly. The transmitter will return
to displaying the present pH value.
°C
°F
pH
pH
pH
5
41
4.00
6.95
9.39
10
50
4.00
6.92
9.33
15
59
4.00
6.90
9.28
20
68
4.00
6.88
9.22
25
77
4.01
6.86
9.18
30
86
4.01
6.85
9.14
35
95
4.02
6.84
9.10
40
104
4.03
6.84
9.07
45
113
4.04
6.83
9.04
50
122
4.06
6.83
9.01
MODEL 2081 pH
SECTION 5.0
START-UP AND CALIBRATION
Содержание 2081 pH
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