The parametrical study shows that, in the linear zone (Fig. 4),
the sensor sensitivity S decreases strongly when the heating
duration t
increases (Fig. 5). From 0.4 s to 1.2 s heating durations,
the sensitivity S is divided by 2 (between 30 and 300 Pa). The best
sensitivity S of 12.8 mHz/Pa is obtained in the pressure range of
30e300 Pa for the experiment with the lowest heating duration
t
h
h
¼ 0.4 s. It is noticed that the heating duration must be less than
the time constant of the micro-thermocouple. If not, the temperature
would be compensated. The micro-thermocouple presents a
time constant of 30 ms corresponding to a cut-off frequency of
5 Hz at atmospheric pressure [12]. In an experimental study with
Pirani sensors, Jitshin showed that the time constant of the resistive
wire decreases when the vacuum increases [9]. We demonstrated
the same result with a micro-thermocouple [14]. So, the
time constant of our vacuum gauge is lower than 30 ms in vacuum
conditions.