Measures: Exhaust Flow Rate


Sensors offers exhaust flow meters for the measurement of total raw exhaust mass flow from either compression or spark ignition engines and vehicles. All of our EFMs operate under Bernoulli’s principle using averaging pitot tubes, and employing 5 high performance, dual-stage, differential pressure transducers, allowing for operation over extremely wide dynamic ranges.



SEMTECH® EFM4 combines a single flow tube integrated with the electronics; a simplified system for those requiring only a single tube size.



SEMTECH® EFM5 utilizes the same electronics and transducers as the EFM4 but employs interchangeable tube sizes providing a versatile solution for those measuring a range of engine sizes. Multiple flow tubes can be used with a single, separate electronics module.

SEMTECH® EFM4 / EFM5 can be attached directly to SEMTECH® SCS or electrically and pneumatically connected via harness and heated line, respectively if the SEMTECH® DS+ unit is installed inside the vehicle. Eight flow tube diameters: 1”, 1.5”, 2”, 2.5”, 3”, 4”, 5”, and 6”, are available to accommodate various engine sizes depending upon exhaust flow.

Available Tube Sizes and Flow Rates
SEMTECH EFM4/5 Tube Sizes and Flow Rates Chart

The SEMTECH® EFM4 / EFM5 is the first generation of EFM where all measurement components are completely self-contained in a single module mounted directly on the flow tube, eliminating the need for transport lines, and continues to offer the following benefits:

  • High Speed Sampling: The EFM 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.
  • Back Purge: A software-controlled back purge pump is included in the heated sampling 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.
  • Autozero: 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.
  • Sampling tube assemblies come with two elbow extensions to facilitate installations.

Each heated tube assembly includes the following accessory kit (unique to each size):

  • Marmon Flange Clamps (2)
  • 90° Flow Tube Extension Inlet (1)
  • 90° Flow Tube Extension Outlet (1)
  • Gaskets (2)
  • Extension Cable (POE)
  • Hard Case for Flow Tube and Harness
  • Pneumatic Capacitor (for 1.0”,1.25”, 1.5”, 2.0” gasoline vehicles only)
Flow Tube OD (cm / in) 2.5 / 1.0 3.8 / 1.5 5.1 / 2.0 6.4 / 2.5 7.6 / 3.0 10.1 / 4.0 12.7 / 5.0 12.7 / 6.0
Flow Tube Length (cm / in) 50.8 / 20 50.8 / 20 50.8 / 20 64.0 / 25 64.0 / 25 64.0 / 25 76.2 / 30 91.4 / 36
Exhaust Temperature Range -5°C 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
Resolution Resolution 0.1 kg/hr