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Technical Notes

Advanced PID
A PID (Proportional Integral Derivative) controller is usually used to control variable speed drives (VSD) in HVAC systems. This controller can be part of the Building Management System, part of an OEM device such as an Air Handling Unit or Pump Controller, or part of the frequency converter (VSD). The PID controller monitors the system by examining signals, called Feedback signals, that are transmitted from sensors placed in the system and comparing them with their expected value or Setpoint. The PID controller then adjusts the speed of the variable speed drive until the Feedback signal equals the Setpoint.  

While many VSDs contain a PI or PID controller, they are often too complicated to set up and do not have the capability needed for HVAC applications. As a result, an external PID controller may be needed. This increases the cost and complexity of the installation. The PID controller in the VLT 6000 has been specifically designed for HVAC applications to provide full functionality and simple programming. The terminology used in connection to the PID controller is well known within the HVAC industry. Feedback and setpoint settings can directly be done in the most common units such as Pa, PSI, m/h, CFM, C, F etc.

Two Zone control, for example, is an important feature for HVAC applications which is not required for most industrial applications. In HVAC systems, it is frequently necessary to monitor two feedback signals. The VLT 6000 is capable of handling the traditional single feedback with a single setpoint as well as two feedbacks with a single setpoint, and  
two feedbacks with two setpoints.





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