MBRAUN MB 120B-G, Operating Instructions Manual

Page: 89 / 105

Equipment needed for calibration:
• Calibration flow cell: a small (approx. 50 ml) cylindrical metal chamber with a DN 40 KF - flange on
one side to fit the sensor KF-40 flange; a gas inlet and a gas outlet
,
preferably mounted on the side of
the cylinder and not directly perpendicular to each other to avoid laminar flow in-side the chamber. All
tubing and the chamber material must be stainless steel and with smooth surface.
• Regulated power supply 24 VDC +- 0,1 VDC, 500 mA
• Calibrated voltmeter 0 to 10 VDC
• Sensor cable to fit the power supply and the voltmeter (see user manual of the probe!)
• Pure argon gas of better 99.9999 grade
• Calibration gas argon (better 99.9999 grade) with a mixture of 10 ppmv +- 2 ppmv moisture (vapor of
water) with analysis certificate
Procedure
Caution!
This procedure describes a recalibration only; original first calibration includes more parameters!
Please observe: 1 ppmv of moisture corresponds to 20 mV output voltage of the probe.
1. The MB MO-SE-1 is fixed in a gas-calibration assembly and the calibration chamber is flushed with pure
argon for at least 5 minutes at 20 to 50 liters/hour flowrate.
2. The sensor is connected to the power-supply and voltmeter; power is applied.
3. Pure argon is applied at a flowrate of 20 to 50 liters/hour for at least five hours or over night
4. The reading of the probe is recorded, it should be less 0.2 ppmv (i.e. 4 mV output voltage); if more, the
offset pot is adjusted so that the reading is less 0.2 ppmv.
5. Calibration argon with a moisture content of about 10 ppmv is applied at a flowrate of 20 to 50 liters/hour for
1 hour. Then the spanpot is adjusted so that the reading is equivalent to the (certified) moisture content of
the calibration argon (e.g. 9.9 ppmv should give a reading of 198 mV).
6. Pure argon is applied and the zero reading is recorded after 2 hours, it has to be less
than
0.5 ppmv; otherwise
repeat from step 4.
Other gas concentrations can be used, but the concentration should be less
than
40 ppmv due to the worse linearity
of the sensors over 50 ppmv. Also
,
“zero-gas” of a moisture concentration of some ppmv is acceptable when it
is far away from the concentration of the calibration gas.
The calibration cycle depends on the demand for accuracy as well as on the conditions of the gas to be mea-
sured (purity, spurious gases etc.). We recommend a maintenance (cleaning) procedure (see maintenance
document for MB-OX-SE1) every 3 months, as the calibration parameters of a clean MB MO-SE-1 are very
stable over years.
!
Chapter 14
Analyzers
90