Today, HTP is enjoying its second generation of family leadership and is a full-fledged manufacturer on the cutting edge of energy-efficient space and water heating technology. This outlet temperature is fairly slow to react, as the solid material mass creates a large lag time: There are several parameters influencing the temperature of the outlet air other than the moisture content of the drying material. An analogy for understanding cascade control is that of delegation in a work environment. One of the benefits of cascaded flow control is that this problem becomes confined to the secondary (flow control) loop, and is effectively removed from the primary control loop. This would make the process characteristic “runaway” in nature, as any fixed amount of current will cause the platform to accelerate995. An example of cascade control applied to a real industrial process is shown here, for a dryer system where heated air is used to evaporate water from a granular solid. ICM Cascade Module for Greenstar Boilers designed to control cascade system–where several smaller boilers are connected in parallel to achieve a higher output. Water-to-Air Geothermal Heat Pump Systems, Water-to-Water Geothermal Heat Pump Systems, Product Approvals, Certifications, Recalls & Regulatory Info. Larger turndown allows for higher system efficiency. Here with servomechanisms we see how cascading not only has the effect of “shielding” certain load variables from the master controller’s view, but it also simplifies the dynamic characteristics of the process from that same point of view. Velocity, for instance, is the time-derivative of position (\(v = {dx \over dt}\)). Optional Controls for Greenstar Boilers. Instead of the position controller having to regulate an inherently “runaway” process, it now sees the process as having an “integrating” characteristic, since any constant output signal from the position controller results in the platform holding to a constant velocity (i.e. It is worth noting that the inclusion of a flow control “slave” loop to this boiler water level control system also helps to overcome a potential problem of the control valve: nonlinear behavior. Cascade Control is an advanced application of the PID that can improve control of systems that are subject to significant lag. If any of these parameters were to suddenly change, the effect would be slow to register at the outlet temperature even though there would be immediate impact at the bottom of the dryer where the heated air enters. However, much more precise control of the platform is achievable by sensing position, velocity, and motor current, and controlling each one of those variables with its own loop. ), fluid flow being one of the fastest-responding process types in existence. platform position will change at a constant rate over time, rather than at an accelerating rate). Temperature controller TC-1b is able to be a slave to controller TC-1a because the natural response time of the temperature at the dryer’s bottom is much shorter than at the dryer’s top with respect to any changes in steam valve position. A simple control system drawn in block diagram form looks like this: Information from the measuring device (e.g. Large space heating or domestic jobs can include multiple units in a “cascade system,” allowing for higher turndown ratio. Create one now. (information from Econergy | Original article: Copyright © 2020 HTP Comfort Solutions LLC. This flow of information is collectively referred to as a feedback control loop. longer-term than the completion time of the tasks given to subordinates). These include air flow, ambient air temperature, and variations in steam temperature. A common implementation of cascade control is where a flow controller receives a setpoint from some other process controller (pressure, temperature, level, analytical, etc. Please contact us via this form! This level/flow cascade control system also embodies the principle of the secondary (slave) loop being faster-responding than the primary (master) loop. If it were not for cascading, a single PID controller would have to control position by manipulating the acceleration of the platform (i.e. To phrase it simply, distorted valve response becomes “the flow controller’s problem” rather than something the level controller must manage. However, so long as the slave controller does a good job of stabilizing the air temperature entering the dryer, the master controller will never “see” the effects of those load changes. All Rights Reserved. Below are more advantages of using a cascaded system instead of a single larger boiler –, Above: three HTP Elite boiler units cascaded, (information from Econergy | Original article: http://www.econergy.ltd.uk/about/news/?artid=70&pageNum=0&blk=68 ).
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