Beko METPOINT OCV, Installation And Operation Manual, Page: 18 / 76

System and functional description
18 METPOINT ® OCV
7 System and functional description
The METPOINT
®
OCV was developed for the detection of vaporous and gaseous hydrocarbons in compressed air free
from aggressive, caustic, toxic, flammable and fire-accelerating constituents.
When the stipulated installation requirements are met, aerosols should not exist at the inlet into the METPOINT
®
OCV
device. Irrespective of this, oil components in the form of aerosols with a concentration of max. 5 mg/m
3
are detected
and indicated. However, isokinetic sampling does not take place (identical velocity at the place of withdrawal and in the
measuring device), as this is not a constituent part of DIN ISO 8573 for oil vapour. The aerosol content would therefore
be determined underkinetically with the result that a higher measured value than the actual one is indicated. As far as
aerosols are concerned though, there is a danger that the measuring device will be contaminated very strongly at high
concentrations and that, as a result, no usable data can be acquired. This condition is identified by the sensor
electronics and indicated as a failure on the display. Simultaneously, information about necessary measures is provided
to the customer, e.g. cleaning measures or purging with zero air.
The METPOINT
®
OCV consists of two major components, the sensor unit with sampling probe and the evaluation unit
with user interface (display). Via a signalling cable with a length of 5 m, the sensor unit is connected with the evaluation
unit. The sampling probe is installed centrically from the top in the rising main, so that the probe takes compressed air
in the centre of the compressed-air flow to be monitored.
The sensor of the METPOINT
®
OCV functions according to the proven and reliable principle of photoionisation.
The measuring principle of a photoionisation detector PID is based on the ionisation of the gas molecules through UV
radiation and registration of the resulting ion current. The normal components of the compressed air (oxygen, nitrogen,
carbon dioxide, argon, water etc.) are not ionised by the UV lamp. In contrast, hydrocarbons are reliably ionised. The
strength of the ion current is directly proportional to the concentration of the ionised molecules. The electrical signal is
measured, electronically amplified, and shown on the display as the total of the measured substances.
For corresponding operational reliability, the performance of the sensing technology is continuously monitored during
the measurements. In the event that a defined safety limit value has not been reached, an alarm is activated which
informs the user that the device needs to be checked by BEKO. A clear text will appear which is highlighted in red.
The PID sensor shows the overall concentration of all photoionisable compounds contained in the sample and does not
differentiate between individual components/substances. Even hydrocarbon compounds with less than six carbon
atoms (<C
6
) can be detected, e.g. isobutene. However, this requires these molecules to be ionised by the UV lamp.