Pico-pH-SUB
| Manual
© PyroScience GmbH
21
detector (indicated by an enabled ERROR Bit2 in R
0
), which will lead to an invalid pH
measurement. As a rule of thumb, the sum of
signalIntensity
and
ambientLight
should be
kept below ca. 2000 mV (the optical detector saturates around 2500 mV).
The output parameter
ambientLight
is a measure how much ambient infrared light is
entering the pH sensor. In principle, such ambient light is not influencing the pH
measurement. However, excess ambient light might lead to a saturation of the optical
detector (indicated by an enabled ERROR Bit2 in
R
0
), which will lead to an invalid pH
measurement. As a rule of thumb, the sum of
signalIntensity
and
ambientLight
should be
kept below ca. 2000 mV (the optical detector saturates around 2500 mV).
Example Communication:
Command
MEA
˽1˽3
↵
Response
MEA
˽1˽3˽
0
˽30120˽0˽0˽0˽
20135
˽0˽
87016
˽
11788
˽0˽0˽123022˽0˽0˽
7105
˽0˽0˽0
↵
This example command triggers the measurement of the sample temperature (typ.
external Pt100) and of the optical pH sensor. The highlighted output parameters of the
shown example response are interpreted as follows:
R
0
= 0
→
No error or warning occurred; the measurement is valid!
tempSample
= 20.135 °C
signalIntensity
= 87.016 mV
ambientLight
= 11.788 mV
pH
= 7.105
5.4.3
CPH
–
Calibrate pH Sensor
This command is used for calibrating the pH sensor at up to 3 different calibration
points. The sensor must be calibrated at 2 points and a pH offset adjustment is possible
for advanced users. In contrast to electrochemical pH sensors, optical pH sensors are
calibrated outside of the dynamic range where the pH indicator is either fully
protonated or fully deprotonated. The first calibration point is called "low pH calibration"
and is performed using a highly acidic buffer (pH 2, item no.
PHCAL2
). As second
calibration point, "high pH calibration" is performed using a highly basic buffer (pH 11,
item no.
PHCAL11
). After these two calibration points, the sensor is ready to use.
"Offset calibration point" adds an offset to the pH output. This offset has to be
determined using a well-known buffer at the pH value of the pKa of the sensor (e.g. a
buffer with pH 8 must be used for -PK8 sensors). It is
highly advised to read the pH
sensor manual
for more details on the calibration (equilibration time, salinity, which
buffers must not be used, etc.…).
Command:
CPH
˽
C
˽
N
˽
P
˽
T
˽
S
↵
Response:
CPH
˽
C
˽
N
˽
P
˽
T
˽
S
↵
