Cascade Control is the technical name for a multi-loop control system where the air temperature set point (Inner Loop) is determined by deviation of the part temperature (Outer Loop) from its set point.
The controller is configured at the factory to allow the Air Temperature to deviate no more than +15°C or –15°C from the Part Temperature set point. This means if the set point is 85°C, the Air Temperature could go as high as 100°C if the Part Temperature lagged sufficiently during a heat up condition. In the example shown here, the Air Temperature went as high as 90.7°C when the Product Temperature achieved 83.0°C. Conversely, the Air Temperature went as low as 18.6°C when the Product Temperature achieved 23.4°C in order to reach a 23.0°C set point. In both instances, The Air Temperature then began to approach the Part Temperature as the part began to stabilize, until the two temperatures were ultimately nearly identical.
The graph shown here represents Air Temperature vs. Part Temperature when Cascade Control is used. The Air Temperature is allowed to overshoot or under shoot in a controlled manner as required to achieve the desired Part Temperature while minimizing lag time.
Air vs. Part Temperature with Cascade Control
The F4T with Cascade Control can be easily switched from Part Temperature Control Mode to Air Temperature Control Mode by pressing the Air Control key on the display
Without Cascade Control the Part Temperature will take longer to stabilize due to its thermal mass as shown in the graphs below.
Air vs. Part Temperature without Cascade Control
Part Temperature with and without Cascade Control
Without Cascade Control, the DUT never quite reaches the temperature setting. Longer test time if you actually wait for the DUT to reach Set Point.
With Cascade Control, the air temperature is biased higher/lower in a precise manner for the fastest response at the DUT.
The Cascade Control Option is available for TestEquity Temperature Chambers. It is ordered as model number F4T-T-CASCADE. It is not availble for Temperature/Humidity Chambers.
Note that Cascade Control and Cascade Refrigeration are two completely unrelated terms. Cascade Refrigeration systems uses two interdependent compressors to achieve very low temperatures. Cascade Control is available for both Single-Stage and Cascade Refrigeration systems.