17 D6F-series MEMS Flaw Sensor User’s Manual (A286)
6.4.5 Output changes in various gases
By the measurement principle of flow sensors, the output characteristics are affected by the
physical properties of the medium involved in the heat conduction. For example, constant
pressure specific heat, thermal conductivity, density and viscosity coefficient will affect the
sensitivity of the sensor. This means that the output characteristics depend on the type of
gases. Application media to be measured are specified for respective models. When
performing the measurement of gas flow that is not stated in the specifications, the output
characteristics are different from the output characteristics in the specifications. Please be
careful to check the output characteristics in use.
Fig.21 shows a comparison of the output
characteristics of the D6F-01A1-110 for He and Air.
Fig .21 Output characteristics measured value of Air and He in D6F-01A1-110
(Left graph : 0 to 1 L/min range , Right graph : 0 to 40L/min range)
6.4.6 The behavior in over flow rate range
OMRON’s flow sensors define the assumed flow rate range (wind speed range in air flow
sensor) in each type. Even if the flow rate is below the minimum or the flow rate is over the
maximum, there is little adverse effect on the sensor itself. If the flow rate exceeds the upper
limit of the specified flow range, the output is gradually increased beyond the upper limit of
the output signal, and then saturated at a constant output voltage. Similarly in the case
where the flow rate is below the lower limit of the flow rate range, the output signal is
reduced beyond the lower limit, and then saturated at a constant output voltage. Output
characteristics that exceed the defined flow rate range are not covered under warranty.
6.4.7 The influence of humidity
Humidity of the fluid can have an adverse effect on the measurement accuracy in mass
flow sensors. Please use dry gas taking into account that the mass increases if the humidity
is high.
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