The SEMTECH FEM provides accurate, real time fuel economy measurements using the carbon balance method. An NDIR analyzer measures CO, CO2, and HC as hexane.

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Fuel Economy Meter

SEMTECH FEM: Fuel Economy Meter

The SEMTECH FEM is a fuel economy meter with unsurpassed accuracy and ease of use. This patent pending design combines our high speed, high performance, exhaust flow meter with a CO/CO2 gas analyzer, packaged into an integrated system, providing accurate, real-time fuel economy measurements using the carbon balance method. Sample handling is integrated into the system, with an internal sample probe, heated filter, water trap, and Nafion dryer. The system accomodates standard flow tube sizes from 1" through 6" diameters, and is also scalable, enabling custom sizes upon request.

  • Features
  • Specifications
  • Accessories
  • Options
  • 1065 Compliant: The SEMTECH FEM meets the US EPA 1065 compliance requirements for in-use testing.
  • High Speed Sampling: The SEMTECH FEM internally samples the differential pressure channels at up to 5 kHz, accounting for every pressure pulse from an engine, from idle to maximum rpm. Standard output rate is 1 Hz.
  • Sample Handling: Sample probe, heated filter, water trap, and Nafion dryer are integrated into the tube electronics. An additional Nafion dryer is included in the control module.
  • Embedded Calibration: Calibration coefficients embedded in the flow tube electronics are automatically recognized on connection. Therefore, tubes of varying sizes can be interchanged with one control module.
  • Multiple Tube Sizes: Eight flow tube sizes accommodate engines from less than 0.8L displacement up to 24L. Available tube sizes are 1", 1.5", 2", 2.5", 3", 4", 5", and 6".
  • Back Purge: A software controlled back purge pump is included in the flow tube assembly, along with solenoids that route high pressure air backward through the pitot tube, purging contaminants and any condensation in the pressure lines. No dismantling is required.
  • Auto Zero: With a single software command, internal solenoids open the pressure sensors to ambient air, allowing fast and easy zeroing while the engine is still operating.
  • Graphical Panel Display: A full color, graphic touch screen displays live data, and enables system setup and basic functions, such as zero and span.
  • Power Supply Monitoring: Power can be either 12 VDC, 110 VAC, or 220 VAC, with both current and voltage monitoring.
  • Rugged Construction: The unit can be used in harsh environments, including, for example, off-highway testing.
  • Shock Resistance: The mechanical design has been optimized for resistance to shock and vibration, ensuring data in the most rugged of in-use environments.
  • Design Details: Over a decade of experience in in-use emissions testing has gone into the design details of the SEMTECH ECOSTAR system, including:
    • EMI protection, including gaskets, filters and capped connectors
    • Stress relief for pneumatic connections
    • Channels for cable management
    • Standard Swagelok™ bulkhead connectors
    • Rugged Deutsch connectors for power and auxiliary connectors
    • Handles that lock to other SEMTECH ECOSTAR modules for stable system integration

Flow Tube Specifications

Exhaust Temperature Range -5 to 700°C
Exhaust Temperature Accuracy ±1% of reading or ± 2°C, whichever is greater
Flow Measurement Linearity |xmin x (a1 - 1) + a0 | ≤ 1% of max
Slope a1 between 0.99 and 1.01
Standard Error of Estimates (SEE) ≤ 1% of max
Coefficient of Determination r2 ≥ 0.990
Flow Measurement Accuracy ±2% of reading or ±0.5% of full scale, whichever is greater
Warm-Up Time 60 minutes to meet specifications
System Response Time T0-90 ≤ 2.5 seconds; synchronized to match
rise time of gaseous analyzers
Data Rate 5 Hz
Resolution 0.1 kg/hr
Power Input 12 VDC; using power supply from FEM module
Communications RS 232
Control Module Dimensions
(L x D x W)
36.0 x 18.0 x 10.0cm
14.2 x 7.0 x 4.0 in
Control Module Weight 4 kg
9 lb


Flow Tube Outer Diameter
Flow Tube Length

FEM Module Specifications

Gas CO CO2
Max Range
(Full Scale) (1)
8% vol.
18% vol.
Resolution 10 ppm
0.01% vol. CO2
|xmin x (a1 - 1) + a0 | ≤ 0.5% of span
Slope a1 between 0.99 and 1.01
Standard Error of Estimates (SEE) ≤ 1% of span
Coefficient of Determination r2 ≥ 0.998
Accuracy ≤ ±2% of reading or ≤ ±0.3% of full scale, whichever is greater
As low as ±50 ppm
As low as ±0.1% vol. CO2
Repeatability ≤ 2% of point or ≤ ±1% of point (span) whichever is greater
Precision ≤ 1% of span
Noise ≤ 2% of span
Zero Drift (Over 1 hour) ≤ ±50 ppm
±0.1% vol.
Span Drift (Over 8 hours) ≤ ±2% of span value or
≤ ±20 ppm, which ever is greater
±0.1% vol., whichever is greater
Rise Time (T10-90) ≤ 2.5 seconds
System Response Time (T0-90)

≤ 10 seconds

Data Rate 5 Hz
Sample Flow Rate (nominal) 1.5 l/min

Physical Specifications
Power 12 VDC Nominal (10.5 - 14.5 VDC)
110 VAC or 240 VAC
Warm-Up Time 60 minutes to meet specifications
Storage Temperature
Dry -10 to 60°C ambient
Operating Environment -10 to 45°C ambient
Dimensions (W x D x H) 43.6 x 31.1 x 9.1 cm
17.2 x 12.3 x 3.6 in.
Weight 10.0 kg
22.0 lbs.
Data Transmission USB
Electromagnetic Interference and Susceptibility CE Standards: IEC 61326: 2002-2

Gas Requirements & Consumption
Gas Use Description Consumption
Maximum span gases for vehicle exhaust CO 8% vol. 1.5 l/min
CO2 18% vol.
O2 25% vol.
Zero Gas Purified N2 or Purified Synthetic Air

NOTE: Specifications are subject to change without notice. While due caution has been exercised in the production of this document, possible errors and omissions can occur.

  • Connecting Harness: The pneumatic lines, power and communications cables are packaged in a flexible sheath, connecting the flow tube assembly to the electronics module. The harness is available in 6', 12' and 18' lengths.
  • Heated Sampling Tube Kit: Each heated sampling tube assembly comes with a Marman flange clamp and flow tube extension in the selected diameter.
  • Dust Filter: A standard Briggs & Stratton air filter is fitted into the filter box on the rear of the unit.
  • Cyclone Mounting Kit: The cyclone on the heated tube assembly can be mounted either parallel or perpendicular to the tube assembly, depending on the orietation of the tube mounting. This kit provides the parts required to re-orient the cyclone.


  • GPS - The GPS/Weather Probe uses a GPS receiver to track the route taken by the vehicle.
  • Paramagnetic O2 Sensor: Robust analyzer measures the O2 component of exhaust. This option is offered in lieu of the standard electrochemical O2 sensor.
  • Vehicle Interface: Vehicle network data is obtained through the vehicle interface, recording important vehicle parameters along with the emissions data.
  • Shock Mount Plate: This custom designed shock mount plate protects your equipment by absorbing the inevitable vibrations that come with in-use testing.