Grundfos Oxiperm Pro OCD-162 - Dosing Coefficient (KD); Measurement; Measuring Cell; Calibrating the Measuring Cell

English (GB)
25
5.6.13 Dosing coefficient (KD)
Internal value used to calculate the actuating variable for
proportional control:
y
out
= K
D
x Q
WM
5.7 Measurement
5.7.1 Measuring cell
Depending on the measuring cell, the ClO
2
concentration,
temperature and pH or ORP value of the sample water can be
measured. ClO
2
measurement is required for dosing with setpoint
control or with combined control.
5.7.2 Calibrating the measuring cell
A constant ClO
2
value is necessary for the calibration.
ClO
2
value
To calibrate the measured ClO
2
value, a reference measurement
must be taken (single-point calibration). This can be done with a
photometer and the appropriate reagents. For details, please see
the installation and operating instructions of the photometer.
The unit of the slope is µA/ppm.
pH value
Two different buffer solutions have to be used to calibrate the
measured pH value (two-point calibration). For details, please
see the installation and operating instructions of the measuring
cell.
The unit of the slope is mV/pH. The unit of the offset is mV.
ORP value
The ORP value indicates the voltage of all ions in the water. ORP
calibration is done with single buffer solution. For details, please
see the installation and operating instructions of the measuring
cell.
The unit of the offset is mV.
5.7.3 Calibration data
In the calibration logbook, the last 10 calibration data records are
listed in chronological order. Example: pH calibration logbook.
5.7.4 Monitoring the cleaning motor
The cleaning motor is monitored indirectly by regularly checking
the current ClO
2
value.
Fig. 16 Process of monitoring the cleaning motor
If the ClO
2
value drops to less than 50 % within a period of 8
seconds, an alarm is triggered. This check is only performed, if
the value which was 8 seconds ago was higher than 4 % of the
measurement range.
5.7.5 Temperature compensation of the ClO
2
value
The influence of temperature on the measured ClO
2
value can be
compensated by measuring the temperature separately with a
Pt100 sensor.
K
D
=
A
ClO2
Q
DPmax
xS
DP
xC
ClO2
A
ClO2
added quantity [mg/l]
Q
DPmax
max. dosing flow [l/h]
S
DP
stroke length [%]
C
ClO2
ClO
2
concentration in batch tank [g/l]
K
D
dosing coefficient [h/m
3
]
Q
WM
flow rate at water meter [m
3
/h]
Measuring
cell
ClO
2
Temperature
pH or
ORP
cleaning motor
monitoring
AQC-D11 ●● ● ●
AQC-D6 ● -- -
number . . . . . . . . . . . . 1/10
date 2008-09-23
time 09:01
slope -54.2
asym. 11.31
buffer 1 4.01
buffer 2 7.00
cal. temp. 25.0
TM06 1065 1514
t
0
the current time
t
0
-8 the time 8 seconds before the current time
V (t
0
) the current ClO
2
value
V (t
0
-8) the ClO
2
value 8 seconds before
Store the measured ClO
2
value in V(t
0
)
Is V(t
0
-8) > 4 % of
measuring range?
Is V(t
0
) < 50 % of
V(t
0
-8)?
Alarm "fault of cleaning
motor"
yes
no
yes
no