Functional Safety Manual
for the Memosens transmitter Liquiline M CM42 SIL
Version:
Page:
2.0
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The measurement screen will now look like:
4.7
Using the safe sensor calibration and adjustment
Important remark!
You can also do the calibration in Classic mode (unsafe calibration/adjustment), this is
not checked for when using a SIL sensor. It is up to the user to check, if a correct "safe"
calibration is used.
4.7.1
2 point pH calibration
The two point calibration uses the following formulas to compute the slope and the zero
point of the sensor in the transmitter (the transmitter transforms the given equations
internally to reduce computational errors):
Use two buffers (only E+H buffers with pH 7.00 and pH 4.00 and in this sequence are
allowed), measure the two voltages U
1
and U
2
with their pH-values pH1 and pH2.
Then we have:
Slope from the two measured values: S
Tk
= (U
1
– U
2
) / (pH1 – pH2)
Temperature compensation (ATC) is done by using an adapted slope:
S'
25°C
= S
Tk
* ((273.15 + 25°C) / (273.15 + Tk [°C]))
Zero-Point
(x=2 is used):
pH
NP
= - (U
x
/ S
Tk
) + pH
x
Ux = voltage measured at electrode
S
Tk
= slope at temperature Tk,
S'
25°C = slope at 25°C/77°F
pHx = pH-value of the buffer solutions (x is 1 or 2) – the pH-values are taken from the E+H buffer
tables with regard to the temperature of the buffers (T1 or T2)
T1: temperature of pH-buffer 1, T2: temperature of pH-buffer 2
