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For example, if the free chlorine concentration is 0.88 ppm as measured by the colorimeter, the temperature is 25 °C as measured by
the Chlorine DataStick, and the pH is 6.73 as measured by the pH DataStick, then the hypochlorous acid concentration value in ppm
that must be written to the Chlorine DataStick will be
7.3 PLC Programming Guidelines
This section provides some guidelines for the PLC programmer.
Assume that the following floating-point registers are allocated within the PLC:
Register
Variable
[
F8:1
HOCl
F8:2
T
as read from the Chlorine DataStick
F8:3
pH
F8:4
[
HOCl
[
F8:5
HOCl
[
F8:6
HOCl
[
]
HOCl
The PLC reads
pH
from the pH DataStick and stores the value in F8:3.
7.3.1 Measurement
The PLC calculates [HOCl] + [OCl
The free chlorine concentration value in F8:4 can then be displayed to the user.
7.3.2 Calibration
At calibration time, the user enters a free chlorine value that the PLC stores in F8:5. The PLC then calculates
equation (5) and stores the value in F8:6:
The hypochlorous acid concentration value in F8:6 can then be written to the Chlorine DataStick to calibrate it.
Thermo Scientific AquaSensors™ DataStick™ Measurement System User Guide
[
]
=
HOCl
. 0
056714
+
1
]
as read from the Chlorine DataStick
as read from the pH DataStick
[
]
]
−
+ OCl
for displaying to the user
[
]
]
−
+ OCl
entered by user at calibration time
]
to be written to the Chlorine DataStick at calibration time
T
and
from the Chlorine DataStick and stores the values in F8:1 and F8:2, respectively, and it reads
−
] and stores the value in F8:4 using equation (4):
(
) (
=
F
8
4 :
F
(
F
8
6 :
. 0
88
−
×
×
+
×
8
10
25
. 1
476
10
−
. 6
73
10
⎧
×
. 0
056714
10
)
×
+
8
1 :
1
⎨
⎩
(
F
)
=
−
×
×
8
. 0
056714
10
+
1
10
=
. 0
76
−
8
(
)
−
×
+
×
8
F
8
2 :
. 1
476
10
(
)
−
F
8
3 :
10
[
]
HOCl
)
8
5 :
(
)
−
+
×
8
F
8
2 :
. 1
476
10
(
)
−
F
8
3 :
⎫
−
8
⎬
(6)
⎭
using
(7)
108
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Troubleshooting
