Sensyflow iG: measuring principle
42/14-39 EN
Sensyflow iG, Version 1.00
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Sensyflow iG: measuring principle
For many years, thermal gas-mass flow meters with analog design have been established as complete
process measuring devices in the chemical industry.The digital Sensyflow iG represents a logical step in
the consequent development of this well-proven technology.
9.1 Physical basics of the measurement
Thermal flow metering procedures utilize the flow-dependant cooling of a heated resistor as measuring
signal. In a hot-film anenometer, the heated platinum resistor is maintained at a constant overtemperature
in relation to an unheated platinum sensor inside the gas flow. The heating power required for maintaining
the overtemperature depends directly on the flow rate and the material properties of the gas. With a
known (and constant) gas composition the mass-flow can be determined by electronically evaluating the
heater current/mass-flow curve without additional pressure and temperature compensation. Together
with the standard density of the gas this results directly in the standard volume flow. Considering the high
measuring range dynamics of 1:150, an accuracy better than 1% of the measuring value is achieved.
9.2 The digital Sensyflow method
For the innovative digital Sensyflow method (patent pending) there are now four signals available to the
evaluation electronics. These contain, besides the heating power, the temperatures of the medium and
the heated sensor, which can thus be used to compensate the temperature dependency on gas charac-
teristics. By storing the gas data in the measuring system it is possible to calculate and perform an opti-
mum adaptation at any operating time.
9.3 Advantages of the digital concept
• By providing several primary and secondary signals these signals can be output in parallel at the field
bus connection. This makes a gas temperature measurement unnecessary.
• Through the implementation of complete digital signal processing it is possible to adapt the sensor con-
trol and signal processing to the process. This means that it is possible to achieve optimum measuring
dynamics at all times, even under changing operating conditions.
• The digital Sensyflow method is capable of providing a further enhanced measuring range.
• While controlling the heater power at the same time, the temperature measurement of the heating re-
sistor allows limiting this temperature. If errors occur in the system resulting in gas temperatures
beyond the specification, the heating power is switched off and the device sends a substitution value
with an additional warning signal. Both measures result in a significant prolongation of the service life
for high-temperature operation and enhanced equipment safety for the user.
Fig. 9-1 Measuring principle of the Sensyflow in digital technology
Legend:
q
m
=
gas mass-flow
T
G
=
gas temperature
R
MG
=
measuring resistor
gas temperature
R
H
=
heating resistor
R
MH
=
measuring resistor for
the heater temperature
P
H
=
heating power
q
m
T
G
q
m
P
H
R
H
R
MH
R
MG
Alarme,
Diagnose
CPU
&
Signal-
Verarbeitung
U
T
T
U
I
Heizer-Sollwert
Gas-Istwert
Heizer-Istwert
Heizer-Istwert
Heizer-Istwert
