BA-40100-02-V17 | 21
Operating instructions
IMPORTANT!
Store buffer solutions in a cool and dark place. Con-
sider their useful life. Make sure that the buffer solu-
tion is not contaminated. For this reason single-rod
measuring cells should not be moved directly from
one buffer solution to another.
5.2.4 1-point calibration
Single-point calibration may also be used for pH calibration with a sin-
gle-rod measuring cell (see section “19.1.4 Menu 1.2: Calibration” on
page 31).
Submerge the pH combination electrode in a buffer solution which is
equivalent or close to the zero point of the electrode. The ideal electrode
zero-point (0 mV) is at a pH of 7.00. However, the real zero-point shows
minimum variations as against this minimum value. For the zero point
calibration a buffer solution of pH 6.80 (TOPAX DX default setting) is
available from the manufacturer.
When immersing the pH single-rod measuring cell in this solution, a
voltage of 12 mV can be displayed on the TOPAX DX theoretically. The
measured physical value however always differs from the theoretical
one.
When the physical value on the display becomes stable you can save the
reference value with "OK".
Now enter the transconductance of the single-rod measuring cell.
IMPORTANT!
If the actual measured voltage differs significantly
from the theoretical zero-point of the measuring cell,
there is a zero-point drift on the measuring cell. Ze-
ro-point drift should not exceed the specifications of
the DIN 19265 (±40 mV).
5.2.5 Offset compensation
In accordance with DIN 19643, the pH value should be checked via an
electro-metric pH value measurement.
External influences can cause the pH value of the electro-metric meas-
urement, measured by hand with the photometer, to deviate by a con-
stant value. The menu "offset alignment" offers the posibility to eliminate
the difference.
ATTENTION!
The offset value is set to "0" after each new cali-
bration.
5.3 Measurement output Redox potential
5.3.1 Technical data
Power output
Values
Input
Voltage signal of a Redox single-rod measuring cell
(0-1000 mV)
Input resistance
10
9
ohm
Measuring accuracy 1 % (after calibration)
The Redox potential is measured with the help of the Redox single-rod
measuring cell. It measures the voltage which exists in the water due to
oxidizing and reducing ions.
5.3.2 Calibration
Calibrate the single-rod measuring cell during startup. For calibration of
the Redox single-rod measuring cell only one reference value must be
set. The physical measurement on the measuring cell (mV) is shown on
the display during calibration.
For calibration a buffer solution is required in order to measure a defined
voltage in connection with the Redox combination electrode. (given val-
ue: 468 mV). This value can be changed when using other buffer solu-
tions or when using single-rod measuring cells with other electrolytes.
To change, use the buttons in the operating cross. The actual voltage
measured is shown on the display during calibration. This reading differs
slightly from the fixed buffer solution value. The deviation should not
exceed 10% approximately.
The plausibility of the transconductance measurement is monitored
throughout the process.
After a reaction time (approx. 1 minute) the physical value does not
change anymore.
The reference value can be now adjusted and saved by pressing OK .
IMPORTANT!
With older single-rod measuring cells the response
time can increase or the reading differ significantly
from the buffer solution value. This indicates that the
single-rod measuring cell must be checked and re-
placed if necessary.
The single-rod measuring cell is directly connected to the input termi-
nals of the circuit board of the input module 5-fold (see section “4.3
Structure of the device” on page 8).
IMPORTANT!
The measuring signal of the Redox combination
electrode can be also configured for controlling the
disinfection.
