Figure 4. Dependence of the frequency of generations on the concentration
of gas
Figure 5. Dependence of sensitivity on gas concentration
Thus, the scheme of the frequency transducer of gas concentrations with an active
inductive element is shown in Figure 6. Bipolar transistors VT1, VT2 and VT3 realize
the electric oscillation generator in which the oscillatory circuit is formed by the
capacitive component of the impedance at the collector-collector electrodes of the
bipolar transistors VT1 and VT2 and the inductive component of the impedance at the
electrodes of the emitter-collector of the bipolar transistor VT3. Thus, such a transducer
circuit is fully realized in the form of an integrated circuit. The main parameters of the
frequency transducer are the function of the conversion, that is, the dependence of the
generation frequency on the change in the gas concentration and the equation of
sensitivity.
In Figure 7 the theoretical and experimental dependence of the active component
on the supply voltage at different values of the control voltage is given. An increase in
the supply voltage of more than 9 V (
2
U
= 3.5V) leads to a lower dependence of the
active resistance from U
1
, and in the area from 9 V to 11 V has almost linear
dependence.
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