Time constant

The time constant of the CTA depends on the speed with which the electronic circuit, in response to the attempt to change the temperature of the wire, sends more or less current in the wire; it depends on certain factors such as the thermal properties of the sensor and the fluid, the overheating ratio, the temperature coefficient of resistance, the speed of the fluid, the gain of the amplifier, the resistance of the bridge and the bandwidth of the amplifier. However, it can be said that the time constant of the CTA is linked to that of the CCA by the ratio:

where S = gain of the amplifier. The time constant of the wire is thus reduced a few hundred times, from fractions of ms to some ms. The frequency limit is typically in the order of hundreds of kHz.