We claim that the ALICAT mass flow controller has the fastest control response speed in the world. However, how can we prove ourselves in the face of many peers who also call our devices' fast '? Rapid control response not only ensures that the device quickly reaches the set value, but also maintains a stable flow rate to avoid being affected by pressure fluctuations. Undoubtedly, the response speed of a device plays a crucial role in measuring accuracy and stable flow control. Let's witness together whether ALICAT is truly the fastest in the world.
Physical time constant (Tau)
The physical time constant, represented by the Greek letter Tau, is one of the few standards used today to describe response time. It is defined as the time required for the controller to reach a certain percentage of the set value, which is 1-1/e, where e is an irrational number as the base of the natural logarithm, with a value of 2.72, so 1-1/e is 63.2% of the set value. Although this definition is a physical standard, it may not explain much, as the remaining 36.8% of the set point may take more or less time than the previous 63.2%. From the screenshot of the oscilloscope below, it can be seen that ALICAT? The mass flow controller reached 63.2% of the set value in just 7.4 milliseconds.
Any specified percentage change range for setting values
Many technical parameters of mass flow controllers use changes within a certain percentage range of the set value to define the device response speed, such as the time required to reach 90% from 10% of the set value. Due to the maximum variation in the initial and final 10% control response curves, the resulting control response speed may not be equivalent to the actual control performance. As shown in the following figure, ALICAT? The mass flow controller took 11.4 milliseconds to reach the set value, and it can be clearly observed from the oscilloscope waveform that the span at 50% is the largest, while the spans below 10% and above 90% are much smaller. For this graph, if the device response speed is defined based on the time it takes to reach 90% from the set value of 10%, then the conclusion is 6-7 milliseconds.
Stable time
Due to the possibility of overshoot of the controller after reaching the set value, the time required for manufacturers to reach the set value and stabilize is usually used as the equipment response speed, and an allowable range is given to the waveform oscillation amplitude. For example, a tolerance range of 2% indicates that the flow fluctuation is stable within 2% of the set value. The accuracy of general mass flow controllers is between 0.5% and 2%, but some manufacturers have expanded the stability tolerance range to 10%. At ALICAT?, We believe that if the user wants to control the flow at the expected set value, then its stable allowable range must also fall within the equipment accuracy range. As shown in the screenshot of the oscilloscope below, the controller reached a stable allowable range equivalent to the device accuracy (1% of full scale) at 27.6 milliseconds