Low pressure measurements are required in various applications such as air flow, static duct and cleanroom pressures inHVAC能源管理系统(EMS)。其他应用包括使用在医疗器械，环境污染控制，煮沸燃烧效率和各种各样的研究和开发要求。Although the focus will center mainly on air flow and pressure, the same principles apply to liquids.
Low pressure ranges are typically from 0.1" H2O (0.004 PSI) FS up to 25" H2O (0.903 P
SI) FS. The pressure transducers used to make these measurements are very sensitive and overpressure can adversely affect accuracy, or in extreme cases, damage the units. Below are four considerations to keep in mind when dealing with low pressure measurements.
1. Pressure Cautions
Low differential pressuremeasurements can be made with high line pressure, although be sure that the line pressure doesn't exceed the maximum pressure rating of the device. Pressure relief valves with adequate venting capacity should be used in any system in the supply is capable of delivering the air, gas or fluid at pressure greater than the capacity of the pressure sensor.
2. Installation Recommendations
对于高管线压力下的压差测量，建议在每条管线上安装带有阀门的压力传感器。A shunt valve across the high and low (reference) pressure ports
should also be installed (See Figure 1), which is especially helpful for liquid measurement applications. Valve C should be open and Valves A and B closed whenever the system is first being wetted or pressurized. Next, Valves A and B should be opened slowing the avoidfluid hammer.Valve C can then be closed, allowing the system to operate.
When the differential pressure is removed, open Valve C first, then close Valve A and B. Many types of pressure transducers are sensitive to vibration and the mounting position. Contact the pressure transducer manufacturer if either are an issue, since both can alter the accuracy.
3. Temperature Cautions
Temperature variations in both the ambient conditions and the media (liquid or gas) can affect the accuracy of the pressure transducer's output signal. Check the operating temperature range and thermal error specification of the pressure sensor to determine compatibility for the application.
4. Media Compatibility
Media compatibility with a pressure transducer must be insured to prevent failure or contamination of the media itself. Most manufacturers will list the materials of construction that will come in contact with the media, and provide recommendations on which to avoid.
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