Table of Contents
Advertisement
11 Technical information and measuring principle
Mass flow rate
Most of the conventional flow meters determine volumetric flow rates. In this case, it is necessary to cor-
rect the density of the mass flow through additional measurement of pressure and temperature. These
corrective measures make measurements more expensive and they reduce the ultimate accuracy of the
measuring system. FMT200-ECO2 (Sensyflow eco2) measuring systems provide the mass flow rate di-
rectly, i.e. without further measurement or correction.
Example:
If 10 m
will change to 2 m³, although the amount of substance and the mass are still the same (14 kg). In this
case, a volume flow meter will only indicate 20 % of the original volume flow.
As a result, a volume flow measurement for gases without a correction of pressure and temperature is
without any meaning. The mass flow meter directly determines the mass per unit of time of a flowing me-
dium; a measured value in kg/h is displayed.
Parameters such as volumetric flow rate (referred to the standard state) can be calculated directly from
the standard density of the medium:
q
q
ρ
Measuring principle
26
Thermal Mass Flowmeter FMT200-ECO2
3
V = 10 m
p = 1 bar
ρ
3
= 1,4 kg/m
m = 14 kg
3
of oxygen is compressed from 1 to 5 bar at a constant temperature, the volume or volume flow
q
= q
/ρ
in e.g.. m³/h – q
n
m
n
= volume flow rate as a function of the normal flow rate (e.g. 0 °C and 1013 hPa)
n
= mass flow rate
m
= density as a function of the normal status (e.g.. 0 °C and 1013 hPa)
n
R
h
R
T
I
h
m
Technical information and measuring principle
ρ
ρ ⋅
= m/V
m =
V
with
n
FMT200-ECO2 (Sensyflow eco2) operates according to the
principle of the hot-film anemometer. This method of mea-
surement is based on the abstraction of heat from a heated
body by an enveloping gas flow. The "flow-dependent" cool-
ing impact is used as the measuring impact.
The gas stream flows past two temperature-sensitive resis-
tors R
and R
which are part of an electrical bridge circuit.
h
T
Due to the chosen resistance ratio R
the current I
, and R
h
gas. The current I
h
to produce a constant temperature difference between the
heated resistor R
h
The electrical power generated with resistor R
pensates its loss of heat to the gas flow. As this loss of heat
is dependent on the number of particles which collide with
the surface of resistor R
flow rate.
3
V = 2 m
p = 5 bar
ρ
3
= 7,0 kg/m
m = 14 kg
<< R
, R
h
T
adopts the same temperature as the
T
is preset by the electronic control circuit
and the temperature of the gas.
, I
represents a measure of mass
h
h
is heated by
h
exactly com-
h
42/14-41 EN
Advertisement
Table of Contents
