Comparison of CCA and CTA
Whatever the type of anemometer, the amplifier must increase the compensation for the delay in sensor response with increasing frequency, but so does the noise of the system. In the past, constant current systems, especially systems that were not compensated, were considered superior because they had levels of noise lower than the constant temperature systems. However, this is only true at low frequencies and in any case the use of compensating amplifiers significantly reduces this advantage. It is now believed that, through the adoption of solid-state circuits, the two systems are equivalent in terms of noise level.
In addition to noise level and frequency response, other practical considerations are important such as ease of use and flexibility of the system. In this, the system at constant temperature has many advantages:
■ It keeps constant the overheating ratio of the sensor at all speeds and prevents the sensor burning when the flow speed falls abruptly.
■ It is compatible with the film sensor while the constant current system is not due to the complex frequency response of the films.
■ It allows measurements in liquids, where large changes in heat transfer occur when speed fluctuates.
■ It allows linearization of the voltage with speed.
■ It can compensate for the temperature of the fluid.
For these reasons, the constant temperature system is nowadays preferred
to the constant current system, which is used only for temperature