AO2000-LS25
LASER ANALYZERS | OI/AO2000-LS25-EN REV. D
77
To obtain the optimal signal-to-noise ratio with one of the
optional calibration cells (accessory available from ABB), the gas
concentrations in Table
Recommended gas concentrations for
should be used for our standard monitors (contact
ABB Service for non-standard monitors).
Note
The hydrogen fluoride (HF) measurement is calibrated using a
special 0.1 to 0.15 m long PTFE cell with sapphire windows. The
PTFE cell can be supplied by ABB.
If only one sample gas with high gas concentration is available,
the sample gas must be diluted with nitrogen using a calibrated
gas mixing system. Dilution must be made up to the values
specified in the table
Recommended gas concentrations for
Significantly lower concentrations should not be used because
the measurements might be influenced by noise as well as by
adsorption and de-sorption processes in the cell and the tubes.
Recommended gas concentrations for calibration
Measured gas
Concentration range
HF
50 to 500 ppm (PTFE cell)
HCl
15 to 200 ppm
NH
3
30 to 400 ppm
H
2
O (low conc.), HCN, CH
4
50 to 500 ppm
H
2
S
300 to 2000 ppm
CO, CO
2
0.5 to 5 Vol.-%
CO, CO
2
(low conc.)
50 to 500 ppm
NO
500 to 5000 ppm
NOTICE
Impairment of calibration
Impairment of calibration due to unsuitable sample gases.
• Only use certified sample gases (e.g. in accordance with
DIN ISO 6141 or DIN ISO/IEC 17025).
Calibration instructions
• When gas is flushed through the cell, the cell pressure is
higher than the ambient pressure. The pressure difference
depends on the flow rate and the diameter and length of the
outlet tubes.
– It is therefore highly recommended to measure the gas
pressure close to the cell, using an absolute pressure
sensor in order to provide the device with correct gas
pressure during the verification and calibration
procedure.
– If only the ambient pressure is known or the pressure
sensor is located far away from the cell, one can switch
off the gas flow before calibration, wait 1 minute for the
measurement readings to stabilize and subsequently
perform calibration. In this case the gas pressure is equal
to the ambient pressure.
• Special care should be taken for reactive and “sticky” gases
such as HF, NH
3
, H
2
O, HCl and H
2
S. Because of the nature of
these gases, it is difficult to obtain the required
concentration in the calibration cell due to adsorption and
de-sorption in the connection tubes and within the cell itself.
• For H
2
O or gas mixtures with H
2
O component, a heated
measuring cell and a connection lead of at least 180 °C is
required. The heated line should be connected directly to the
gas mixing system, e.g. HOVACAL.
• Use cells made of stainless steel or PTFE for HF.
• Use connecting tubes made of PTFE.
• Use connections that are as short as possible between the
calibration gas cylinder and the calibration cell.
• Flush the cell with calibration gas with a high flow rate of
5 to 7 l/min.
• Wait until the concentration in the cell has stabilized.
• Switch off the flow and observe how fast the concentration
degrades.
– If it degrades rapidly, the cell needs to be passivated.
• Check that the measured concentration remains the same
with increasing flow rate. If it does, the concentration in the
cell most likely has reached the expected value.
