At MAC Instruments, we are a leading manufacturer of industrial moisture analyzers. These critical components measure the amount of moisture mixed into the air to help our customers keep their facilities in compliance with industry and environmental standards.

Air density plays a significant role in this measurement process, as discussed in our moisture measurement handbook. A popular method of moisture measurement is based on water vapor density in the air at various standard conditions of temperature and pressure (STP). Knowing these standard measures can help customers use monitoring equipment more precisely.

Density of Air at Standard Temperature and Pressure

STP—standard temperature and pressure—represents conditions that people and systems use to calculate gaseous factors. Commonly accepted STP values are 32° F (0° C or 273 K) and 1 atm pressure. However, while STP is a relatively common term, it can mean different things based on the agency applying the standard. For example, the National Institute of Standards and Technology (NIST) sets its standard at 68° F and 101.325 kPa. On the other hand, the International Standard Metric Conditions are 59° F and 101.325 kPa for natural gas.

As different industries and applications use different STP values, the best practice is to describe the standard and list out the exact conditions for each measurement. Stating the temperature and pressure conditions for every readout, inspection, and process can keep records clear.

According to the International Standard Atmosphere (ISA) values—15° C at sea level—the density of dry air is at:

  • In Metric units: 1.225 kg/m^3
  • In Imperial units: 0.0765 lb/ft^3

Although pure water vapor cannot exist at STP, these density values for dry air can be used to calculate a theoretical value for water vapor density at STP. As the density of pure water vapor is 62.19% of the density of dry air, theoretically, 100% water vapor would have a density of 0.0762 kg/m^3 or 0.048 lb/ft^3 at STP.

Uses of STP in Moisture Analyzer Applications

Knowing these measurements can help facilitate a better understanding of moisture analyzers. At MAC, we offer several high-performance moisture analyzers, including:

  • MAC 116 Moisture Analyzer controls the flow of steam in food industry applications to maintain proper moisture levels for optimal production yield and cooking time.
  • MAC 125 Moisture Analyzer can measure absolute humidity and total pressure to calculate the area’s moisture level. This continuous monitoring helps keep facilities compliant with environmental and industrial regulatory standards.
  • MAC 155 Moisture Analyzer monitors emission stack gases. The equipment can help ensure that the stack gas’s moisture or humidity levels meet regulatory requirements.

Contact MAC Instruments for Quality Moisture Analyzers

Continuous monitoring is the first step to keeping your facility compliant and safe. By using our moisture analyzers, customers benefit from:

  • MACEasier installation and operation
  • Higher sensitivity to water vapor and moisture content
  • Faster and more accurate results
  • A more user-friendly interface
  • Greater performance stability

If you are interested in learning more about our moisture analyzers, contact us at 419-621-2322 or request a quote.

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