Air Duct & HVAC Air Flow Meters

Eldridge Products, Inc.’s patented* Flow Averaging Tubes (FAT™) were designed to provide accurate flow measurement in large pipes and ducts without the expense and complexity of traditional multipoint systems by offering a cost-effective solution for Heating, Ventilation, and Air Conditioning (HVAC) and Variable Air Volume (VAV) applications. Because they also provide accurate, repeatable readings in applications with very limited upstream straight run this list has been expanded by our customers over the years to now include almost any gas measurement requirement, with particular emphasis on natural gas usage and submetering.

The Master-Touch™ FAT™ probes utilize a flow averaging tube to give a stable flow signal in applications where the flow profile is less than ideal, such as downstream of a bend, valve, tee or obstruction. The flow averaging tube has a number of large diameter (0.125”) inlet ports along the length of the upstream impact surface. The impact pressure at each inlet port is averaged inside the tube to create the axial flow through the tube and across our flow sensor. The gas flow then passes back into the main flow stream through the gas return ports located near the flow sensing elements.

Flow Meter Flow Averaging Tube

Anomalies in the actual flow profile or installations in non-circular ducts may require a C-Factor adjustment for the best accuracy. The velocity impact pressure follows a square root function. Therefore, the average velocity pressure in the FAT™ probe may vary slightly from the average of the velocities at each inlet port. The Master-Touch™ electronics easily accommodate the C-Factor adjustment.

The FAT technology is available in the same range of physical configurations as the other Eldridge Products' instruments. Inline style averaging tubes are available for pipe sizes 2" and greater with flanged ends; insertion style FAT probes can be as small as 2" or as large as necessary (90+" to date!). Integral and remote electronics with approvals for hazardous or non-hazardous locations allow the FATs to meet most installation requirements.

The Master-Touch™ MP Series Flow Averaging Tubes are approved by CSA/CUS, ATEX, IECEx and KOSHA for use in hazardous area locations.

The Master-Touch™ MPNH Series Flow Averaging Tubes are approved by CSA/CUS for use in general purpose (Ordinary) area locations.

MPNH Series Flow Averaging Tubes
MPNH Series FATs Flow Meter

*U. S. Patent No. 6,883,389 Other U.S. & foreign patents pending

Linear signal output Flow: 0–5 VDC & 4–20 mA
Temperature: 0–5 VDC & 4–20 mA
Relay Output Two 1-amp @ 30 VDC, user-selectable alarm functions
Signal Interface LCD (flow rate, flow total, gas temperature)
RS232 & RS485 Modbus RTU
Optional HART or Profibus DP
Accuracy including linearity (Ref.: 21°C): ±(1.0% of Reading + 0.5% of Full Scale + GTC)
Repeatability ± 0.2% of Full Scale
Sensor response time 1 second to 63% of final value
Turn down ratio 100:1 @ 15,000 SFPM/76 NMPS minimum FS
Ambient electronics temperature range -40° to 120°F (-40° to 50°C)
Gas temperature range 40° to 150°F (5° to 65°C)
Gas temperature coefficient (GTC) 0.05% Full Scale/°C @ 40° to 100°F (5° to 40°C)
0.10% Full Scale/°C @ 100° to 150°F (40° to 65°C)
Gas pressure effect Negligible over ±20% of absolute calibration pressure
Pressure rating maximum:  
Inline flowmeters 500 PSI Std., >500 special
Insertion flowmeters  
.500” OD 125 PSI Std., >125 special
.750” OD 55 PSI Std., >55 special
1.000” OD 30 PSI Std., >30 special
Transmitter power requirements 5 Watts or less
Input power requirement 24VDC @ 250mA
  115 VAC 50/60 Hz optional
  230 VAC 50/60 Hz optional
RAM Back-up Lithium Battery, 2.5–3.5v, >10 years
Wetted materials: 316SS, including sensor
Standard temperature & pressure (STP) 70°F & 29.92" Hg
(Air .075 lb/cubic foot)  
NIST traceable calibration Standard

Specifications subject to change without notice.

MP Series Flow Transmitter — For use in hazardous area locations
CUS Flow Meter  ATEX  IEC Ex   KOSHA

MP Series Remote Enclosure —

For use in Ordinary(Non-Hazardous) area locations:
Type 4X, IP66

Optional ACEX/DCEX
Remote Enclosure —

For use in hazardous area locations

MPNH Series —

For use in Ordinary(Non-Hazardous) area locations:
Type 4X, IP66

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