The rising cost of energy and drive for efficiency has resulted in more intelligent Heating, Ventilation and Air Conditioning (HVAC) control systems within commercial buildings and manufacturing facilities. PLCs are commonly used to measure and control HVAC distribution systems. Feedback loops and damper controls direct the flow of conditioned air to particular zones.  Filtration systems are also monitored for efficiency and maintenance purposes.

It was determined that a higher level of control was necessary for a new semi-conductor manufacturing plant.  An initiative to further improve these building control systems identified the fact that the heating and cooling generation systems could be controlled to a higher degree of efficiency. In order to implement these efficiencies, it was necessary to monitor current system flow, total flow, temperature and density. The cost of implementing discrete sensors for these measurements was prohibitive. After further evaluation, it was determined that a HART-enabled flowmeter could provide all the necessary data.  

The next step was to identify an interface to the flowmeter that would allow a full read/write dialog and provide data quickly and efficiently to the PLC.

Spectrum Controls Analog I/O with HART Protocol was selected. A series of four 1756sc-IF8H analog input modules were interfaced to Rosemount Magnetic Flowmeters and Probar Mass Flowmeters to obtain system flow, total flow, temperature and density. Through the use of simple ladder logic, the I/O modules allow the totalizer of each meter to be reset when necessary by sending a HART command from the PLC. All this was accomplished without any additional wiring and with nominal cost impact.

The result is a higher level of heating and cooling efficiency and a better window into the data used to control the overall system operation.  Analog I/O with HART Protocol simplified the task of incorporating HART data into the PLC control routines and provides a window to this data with a higher level of system control.