D-FL 100 DS is a MPPT (multipoint pitot tube), which uses the impact pressure measurement method.
The method is very accurate however at low flow rates, the measurable pressure difference is very small. As a result, the measured threshold is determined by the uncertainty of the differential pressure transmitter.
Basis of D-FL 100 is a specially designed probe with two measuring chambers, each equipped with several bores.
The measuring chambers are pneumatically separated from each other.
The measuring chambers are connected to a differential pressure transmitter.
The probe generates a differential pressure in flowing sample gas dependant on:
DURAG offers a precise differential pressure transmitter as an option to the probe. The selected transmitter has a basic range of 0-10 hPa and can be set to a minimum output range of 0 to 0.5 hPa corresponding to 4-20mA output .
Ex works the transmitter is configured to:
The zero suppression can be parametrized different or disabled.For special applications DURAG configurates the zero suppression to 3% (= 0.001 hPa).
As a result of this supression function of the dP transmitter those measuring gas flows, which produce a differential pressure signal, which is smaller than the threshold are indicated as 0 m/s (= 4mA).
Consequently the setpoint of the threshold determines the minimum detection limit of D-FL 100.
The detection limit of a D-FL 100 typically is a function of the measured gas temperature as follows:
values valid for 6% (3%) threshold of zero suppression
These detection limits depend on the principle but are no special property of D-FL 100!
Measured values higher than the listed detection limit are precise, because the measurable difference pressure of the probe is increasing quadratic with gas velocity.
Last update on 16. April 2012 by Axel Kumm.