Introduction
1
gas-lab
Q1
Page 3
The connection between sensor system and evaluation computer is
implemented via interface cable, RS422/optical fibre-converter and fibre-optics
cable, as illustrated above.
The sensor system contains two infrared sensors for measuring the absorption
of the hydrocarbons and carbon dioxide contained in the natural gas. Another
sensor additionally determines the thermal conductivity of the natural gas and
thus also measures gas components such as nitrogen, for instance, which
cannot absorb infrared light. Afterwards the evaluation computer evaluates all
three measurements. As a result, these measurements supply the gross calorific
value, standard density and CO
2
content of the natural gas. These variables are
sufficient to establish with a flow computer the compressibility ratio k (real gas
dependence) according to SGERG and the energy content of the natural gas.
Besides, other variables such as the Wobbe and methane numbers are also
determined. Other than that mentioned, the system provides also a non-
calibratable sample analysis of the natural gas. The underlying algorithm is
based on the systematic of the composition of natural gases. In case of non-
typical gases a major deviation in the measured value of a single component
can occur.
The device measures continually and determines new measurements every
second. It can therefore also be used for fast closed-loop control tasks.
The manufacturer calibrates the
gas-lab
Q1 before delivery, i.e. he performs a
zero point adjustment with nitrogen and afterwards a 3-point calibration with
ultra-pure methane and two calibration gases. The correction values are saved
in the sensor unit. This basic calibration is usually repeated during the
commissioning and on the occasion of a recalibration.
The evaluation computer automatically performs a 1-point calibration with ultra-
pure methane after a mains failure and after each switching on of the measuring
sensor technology.
Moreover, the
gas-net
Q1 offers a wealth of additional functions for monitoring
tasks and data communications. The
gas-net
Q1 also always includes a data
logging function that logs important measurements at defined intervals and
when errors occur. See Chapter 5.2 for a detailed description of the archive
structure.