Electrolysis Device SGM5EL Functional description
10
4.2.2 Gas flow quantity
For exact measurements a flow rate between 5 and 10 l/h of the measuring
gases must be ensured (see also chap. 8.1.2)
Contamination effects of the gas tubes (leaks, permeability, desorption) may
cause falsified measuring result if the flow rate is too low.
Asymmetric cooling of the sensor electrodes may cause falsified measuring
results if the flow rate is too high.
4.2.3 Accuracy of the measurement
The SGM5-EL can be used as an electrolysis device
and
as an oxygen
measuring device. For the measuring of oxygen the manufacturer
guarantees a measuring error of less than 3% (relative error) only at oxygen
concentrations within a range of 20.64*10
4
... 10 ppm
1
. For measurements at
oxygen concentrations of 10 ... 0.5 ppm the relative error is less than 5% if
the gas inlet tube has no leakages or permeability.
During the electrolysis the limit values can only be reached if the measuring
gas is tuned to the measuring problem (e.g. It is not possible to get oxygen
concentrations in the “per-cent-area” from pure nitrogen).
For measurements of oxygen concentrations less than 10 ppm the following
aspects must be taken into account during evaluation:
•
composition of the measuring gas (e.g. presence of burning
gases);
•
specific characteristics of the production process (e.g. material
used);
•
temperature of the measuring gas.
To reduce the measuring error in low oxygen concentrations, the following
conditions must be provided:
•
All gas inlet and outlet pipes must be free of leakages.
•
For measurements of oxygen concentrations of less than 100 ppm,
the use of steel pipes is necessary.
•
If the measuring gas contains reducing components (e.g. alcohol), the
concentration of free oxygen cannot be determined correctly as
chemical reactions occur at the electrode. In such cases the measuring
gas should be filtered by an active carbon filter before entering the
SGM5-EL. (see Appendix)
1
Throughout the manual the measuring unit "ppm" is defined as "vol.-ppm".
NOTE
NOTE