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MAC155 Humidity Probe & Humidity Transmitter For Continuous Stack Monitoring With Built in Two Point Calibration

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The MAC155 moisture/humidity analyzer enables you to augment your process safety and comply with US EPA regulations. Several high-quality components such as a humidity probe and humidity transmitter combine to make this device exceptionally user-friendly. MAC155 is used in industrial operations worldwide for 24/7 monitoring of stack emission gases. It is designed for measuring humidity in exhaust gases in temperatures ranges up to 1200°F (650°C). MAC Instruments also provides a range of special accessories to expand the usability of the humidity probe in temperatures up to 2400°F (1300°C).

A defining attribute of the MAC155 humidity transmitter is that it features an in-built calibration system. This makes daily 2-point in-situ calibration and system checks possible, and facilitates adherence to US EPA regulations and local mandates pertaining to exhaust stack installations. The humidity probe is protected from particles by a 10 micron stainless steel sintered filter element that can be easily cleaned and replaced.

The humidity probe on this unit is exceedingly sensitive to water vapor/humidity. However, it does not rely on a wet bulb, mirrors, optics, chemicals, or compressed air to provide readings. This humidity meter is highly responsive to the partial pressure of water vapor, thus displaying instantaneous readings. You can confidently depend on MAC Instrument’s patented solid state design to help you improve overall process efficiencies in the toughest industrial settings. The MAC155 humidity transmitter is available in two models for low range and high range continuous humidity monitoring.

  • MAC155 Humidity Analyzers is Available in Two Models:
    • MAC155-L covers 3% to 15% or 6% to 30% ranges (user selectable)
    • MAC155-H covers 3% to 15%, 6% to 30%, 9% to 45%, or 12 % to 60% ranges (user selectable)
  • Features of the MAC-155 Moisture/Humidity Transmitter
  • Measure % Moisture By Volume In Exhaust Gasses At Temperatures up to 1200°F
    • Optional to 2400°F
  • NEMA 4X Waterproof Design
    • Suitable for outdoor installation
  • Contains Built In Equipment Allowing Daily 2 Point Calibration Check
    • Sensor is flooded with an internally generated reference gas of specific humidity levels
  • Can Be Re-Calibrated In the Field Using Internal Calibrator
  • System Calibration
    • Sensor signal substitution can be externally initiated to generate an output signal 50% of full output.
    • From the MAC155 Controller, 3 different output signals can be generated.
    • Provides a method of checking total system including data acquisition equipment.
  • Patented Measurement Process
  • In Situ Measurement
    • Mounts directly to stacks or ducts
  • 0-20mA or 4-20mA Signal Output User selectable Self powered or loop powered (jumper selectable)
  • Filter Blow Back Option
    • Allows automatic filter cleaning (requires 10 psi clean dry air)
  • Case Heater Option
    • Extend ambient temperature rating to -40°F

The Standard For High Temperature Humidity Measurement

  • The MAC155 In Situ Moisture Analyzer is designed to continuously monitor emission stack gases.
  • It is designed to meet EPA and local regulatory requirements for stack gas moisture/humidity measurements.
  • The patented solid state design has been proven in hundreds of industrial process control applications.
  • The moisture sensor is extremely rugged and requires no chemicals, compressed air, optics or mirrors.
  • The % moisture by volume is measured using a proprietary high temperature capacitive sensor that responds to water vapor pressure in the presence of other gasses.
  • The MAC155 Moisture Analyzer used as Humidity Transmitter is provided with automatic two point calibration check at user selectable humidity levels. The on board calibration system can challenge the sensor with a controlled water vapor sample. An internal tank holds enough water to generate vapor samples for one year of daily calibration checks.


  • Measurement Range
    • (MAC155-L)
      • 3% to 15% or 6% to 30% water vapor by volume (user selectable)
    • (MAC155-H)
      • 3% to 32%, 6% to 30%, 9% to 45%, or 12% to 60% water vapor by volume (user selectable)
  • Maximum Stack Gas Temperature
    • 1200°F (optional to 2400°F)
  • Ambient Temperature Range
    • 30°F to 140°F (-40°F with case heater option)
  • Altitude Range
    • sea level to 6000 feet
  • Accuracy
    • ±1% of full scale
  • Linearity
    • +/-1% of full scale
  • Response Time
    • 60 seconds or less to reach 90% of final value
  • Analog Output
    • 0-20mA or 4-20mA. Internal powered
  • Power Requirements
    • 120V 60HZ @ 3A max

Calibration System

  • Calibration Check Points
    • (MAC155-L)
      • 6% and 12% or 12% and 24%
    • (MAC155-H)
      • 6% and 12% or 12% and 24% 0r 18% and 36% or 2[4% and 48%
  • Calibration Point Accuracy
    • +/-1% of full scale
  • Distilled Water Tank Capacity
    • 26 oz. (22 oz. usable)
  • Water Usage
    • 20 oz. per year