The MAC155L & MAC155H Moisture Analyzer is an instrument designed for continuously monitoring water vapor levels in a stack or duct. It consists of two main parts: a probe that mounts to an instrumentation port on the stack or duct, and a controller typically located in a control room. The system offers multiple user-selectable ranges, with accuracy specified at ±1% of full scale over 20% to 100% of the full scale range, though accuracy may be reduced below 20% of full scale.
Function Description:
The MAC155 Probe utilizes a proprietary high-temperature capacitive sensor to measure the partial pressure of water vapor in the monitored atmosphere. An absolute pressure sensor simultaneously measures the total pressure at the moisture sensor. The internal processor then calculates the percent of water vapor by volume using the equation: % water vapor by volume = (water vapor partial pressure / total pressure) X 100. This calculation accounts for factors like altitude, barometric pressure fluctuations, and changes in equipment operating conditions.
The system includes a built-in sensor calibrator for daily two-point calibration checks. This calibrator generates a reference gas by mixing water vapor from an internal reservoir with air. The probe is then flooded with this calibration gas to immerse the sensor. Calibration points are set at 40% and 80% of the selected full scale. The internal water reservoir holds approximately 17 ounces (500mL) of distilled water, sufficient for over a year of normal operation. A "Low Water" alarm is triggered when the water level is low.
The controller displays the moisture level and provides a 4-20mA or 0-20mA analog output signal, where 4mA or 0mA represents 0% moisture by volume (MBV) and 20mA represents 100% MBV. The analog output can be forced to 0%, 25%, 50%, 75%, and 100% of full scale for testing data logging equipment.
Important Technical Specifications:
- Power: Probe: Nominal 120 VAC, 50/60 HZ @3A max. (240V 50/60Hz @1.5A option available). Controller: Supplies AC and DC power to the probe.
- Communication: Isolated RS485 serial port between probe and controller.
- Analog Output: 4-20mA or 0-20mA, user selectable.
- Accuracy: ±1% of full scale over 20% to 100% of full scale range.
- Water Reservoir Capacity: Approximately 17 ounces (500mL) of distilled water.
- Operating Temperature (Probe): Maximum ambient air temperature of 130ºF (without radiation or direct sunlight). Case cool option recommended for hotter environments.
- Probe Mounting: Horizontal position (-0°, +15°).
- Enclosure Rating: Waterproof (NEMA 4 – IP 65) connectors for electrical connections.
- Compressed Air Input (for options): 10 psi (69kPa) clean, dry, and oil-free air.
- Filter: 10 micron filter element.
- DC Power Conductor Size: Varies with length (e.g., #12 AWG for 150 feet, #4 AWG for 1000 feet).
- PLC Interface Outputs: Dry contact closure rated at 5A 120VAC.
- PLC Interface Inputs: 18VDC to 56VDC signal (nominal 24VDC).
- Modbus RTU: Slave address and baud rate configurable (default 9600 baud, slave 01).
Usage Features:
- User-Selectable Ranges: Multiple moisture by volume (MBV) ranges are available, requiring a calibration sequence if changed.
- Automatic Calibration Check: Can be scheduled to perform a daily calibration check at a user-defined time. A time setting of 0:00 disables this feature.
- Manual Calibration/Calibration Check: Allows for manual initiation of calibration or calibration check modes.
- Forced Output Signal: The analog output signal can be manually forced to specific percentages of full scale (0%, 25%, 50%, 75%, 100%) for testing external data logging equipment.
- Maintenance Mode Contact: A relay contact opens when the unit is in maintenance mode, providing an interface for data acquisition systems to record "IN-Maintenance" events.
- Local Alarm Contacts: A solid-state relay provides contact closure during an alarm event.
- RS485 Communications: For Modbus RTU communication with external devices or an optional PLC Interface.
- Ethernet Controller Option: Allows monitoring of the MAC155's status, initiation of modes, and configuration changes from a networked computer via a web page interface. Includes alarm email setup for notifications to various devices.
- Display Brightness Selection: Four levels of VFD brightness (100%, 75%, 50%, 25%).
Maintenance Features:
- Water Tank Draining and Refilling: Recommended at least once per year using distilled water (not deionized). A funnel and drip prevention tube are supplied for this purpose.
- Filter Cleaning/Replacement: The 10-micron filter element can be cleaned by blowing out dry particles with compressed air or soaking in water for water-soluble compounds. Replacement filters are available. The extension tube should also be cleaned.
- Filter Blow Back Option: Automatically cleans the filter by blowing compressed air in reverse direction during calibration checks. Requires a clean, dry, oil-free air supply.
- Peristaltic Pump Tubing Replacement: Tubing in the sampling and calibration pumps can wear out and needs replacement. Instructions for disassembly and reassembly are provided.
- Pump Testing: Procedures are outlined to test the vacuum production of both the sampling and calibration pumps using a vacuum gauge to ensure proper operation.
- Electrical Troubleshooting: LED status indicators on the main board help diagnose issues. Fuses for AC and DC power are located on the controller. Test points are available for measuring power supply voltages.
- Case Heater Option: Protects the water from freezing in cold environments (down to -40°F/-40°C).
- Case Cool Option: Uses compressed air to cool the probe in hot ambient conditions or direct sunlight, maintaining internal temperature.
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