Elster 83 462 140, Operating Manual And Installation Instructions, Page: 88 / 126

Volume Conversion Device EK260
88 Elster GmbH
4 Applications
4.1 Rated operating conditions for the various conversion methods
In determining the actual permissible measurement range for the pressure and
temperature of the gas, apart from the technical possibilities offered by the connected
measurement sensor, the conversion method must also to be considered. The alarm limits
Tmin, Tmax, pmin and pmax can lie outside of the measurement range and differ by up to
5% (for pressure) or 1°C (for temperature) from the measurement range limits. In this w ay
testing of the device at the measurement range limits for temperature and pressure is
simplified.
On reaching or exceeding the alarm limits, an alarm is triggered and counting takes place
in the disturbance quantity counters.
The following correction methods are available for certain applications:
Fixed value K=1 (Md.K = 0, see Chapter 3.5)
This fixed value can be used when the gas shows only slight deviations (up to 0.25%) from
the ideal gas behaviour. For natural gases and their mixtures, i.e. gas mixtures, which
have a high methane content, this applies at temperatures above -10°C up to an absolute
pressure of 1.5 bar or an overpressure of 0.5 bar.
The pressure range can be extended to 2.0 bar absolute pressure or 1.0 bar overpressure
if the temperature is always higher than
- +5 °C for gases with H
o,b
< 11.5 kWh/m³
- +12 °C for gases with H
o,b
≥
11.5 kWh/m³
Wider pressure and temperature ranges can be set for the gas composition present at a
measuring point if compliance with the error limit is proven by calculations. This also
applies to other fuel gases (e.g. town gas). For the calcul ations the conditions given in the
following section apply.
Fixed value K
≠
1 (Md.K = 0, see Chapter 3.5)
Fixed values for K, which differ from 1, may be suitable for measuring points, the absolute
pressure of which always lies below 11 bar and for which the gas pressure and the gas
temperature only vary within known limits. The fixed value must be calculated using one of
the following methods:
- S-Gerg 88 after testing the reliability of the method (see below)
- AGA8-DC92 according to ISO 12213 Part 2 /1/
Through a calculation using the same method, it must be proven that the K -values only
deviate by at the most 0.25% from this fixed value in the permissible measurement range
(i.e. with compliance to the pressure and temperature limits). The principles of the
calculation and the calculated results at the limits of the measurement range must be
recorded in the operational and rating data book, page "Proof of measures implemented".
The alarm limits p
min
, p
max
, T
min
and T
max
must be set according to the measurement range
(see above).