Magnehelic Duct Pressure Sensor - The magnehelic measures duct pressure inside of ductwork. It is important, for many reasons, to know the pressure inside of duct work. This magnehelic measures the supply side pressure of the blower inside the air handler. The static pressure in this system is actually controlled by a static pressure transducer which is directly hooked up to a DDC controller that controls a variable frequency drive based on static pressure. The static pressure transducer is a solid state magnehelic and works in much the same way a magnehelic works except the transducer is digital and sends out a signal that registers the pressure it is reading. The magnehelic pictured is simply for visual display and reading the static pressure inside the air handler. It does not send out any signals. A technician can walk up to the air handler in a quick glance tell if everything is okay with the blower and duct system based on pressure. Pressure sensors with switches in them are also used to determine a air filter status. A differential pressure switch can be installed in an air handler with pressure probes on either side of the filter. A differential pressure set point is adjusted into the switch so that when the filters load up the switch trips and sends a signal to the DDC controller. This alerts the operator of the system that the filters are loaded up and need to be changes. This differential pressure switch is usually calibrated and set using a magnehelic pressure sensor.
This can also be used to find problems with the air handler and duct work system. If the pressure is too high or too low then the maintenance staff knows there is a problem that needs to be resolved. Example, dirty air filters will cause increased pressure on one side of the filter bank and low pressure on the other side. Tools like these add to the cost of the equipment but make things so much easier for the maintenance staff. They also increase reliability.
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