Paired Products

DirectShear – Optical | Control Unit


The OSU-1001-H2U AC/DC Differential Optical Sensor Unit is an integrated fiber optic and electronic system that provides the ability to measure mean and fluctuating quantities of interest using a differential optical sensor, e.g., wall shear stress or pressure. The OSU provides a stable light source and fiber optics to transmit light to and from the sensor head as well as optoelectronics to convert the light reflected from the sensor head to a single analog voltage signal for output to a data acquisition system.

Two integrated rechargeable lithium ion batteries minimize noise due to EMI and provide up to 20 hours of continuous operation. The control unit makes use of transimpedance amplifiers and an instrumentation amplifier to enable measurement of both mean and dynamic components.

SKU: OSU-1001-H2U Categories: ,
Control Unit Form Factor


Key Features

  • Mean and fluctuating optical sensor measurements compatible with all DirectShear CS Series models
  • Selectable low-noise AC or rechargeable Li-ion battery power source
  • Optimized high dynamic range and bandwidth
  • System status and battery voltage LED indicators
  • Rugged, industrial LC Duplex fiber connection
  • Removable shielded sensor cable


  • Time-resolved, direct mean and fluctuating wall shear stress measurements
  • Differential optical shear stress sensors for subsonic and transonic applications
  • Instrumentation-grade skin friction sensing
  • Aerodynamic drag research
  • Detection of flow separation
  • Wind tunnel instrumentation


    • Direct measurement of shear stress
    • Harsh environment capable
    • Non-intrusive - minimal flow disturbance
    • High resolution, dynamic range and bandwidth
    • Immune to EMI
ModelShear Stress (Pa)Bandwidth (kHz)Sensitivity (mV/Pa)Resolution (mPa)Element Size
OS-0510100.81900.11.5mm x 0.7mm
OS-0110501.8400.51mm x 0.7mm
OS-06101002.52011mm x 1mm
OS-02103005520.4mm x 0.4mm
OS-03101000101.3500.3mm x 0.3mm
OS-04105000200.3500.3mm x 0.3mm

The following additional components and specifications are recommended for AC and DC testing/calibration with the capacitive sensor control unit:

  • RG58 coaxial cable with BNC connectors
  • Data acquisition system (DAQ) – AC/DC measurement
    • Sensing Range: ±1, ±5, ±10V – sensor dependent (see datasheet)
    • Resolution: 18+ bits
    • Sampling frequency:
      • Sensor dependent w/ analog filter between sensor output and analog-to-digital converter (ADC)
      • 100+ kS/s w/o analog filter
  • Digital multimeter – DC measurement only
    • 6.5 digits with power line cycle (PLC) integration
    • DAQ or PC connection (e.g., GPIB)

Related Publications

Related Research Projects

Frequently Asked Questions

What is the typical application for DirectShear - Optical Sensors?
DirectShear Sensors are typically used in wind tunnel testing applications. Optical models are designed specifically for high-temperature and harsh environments.
What are the operating temperature ranges for DirectShear - Optical sensors?
Optical models are designed for more extreme environments and can withstand temperatures from 0-400°C.
How do acceleration forces affect the sensor?

The sensor can survive large accelerations; more than 200g. The floating element’s small size and mass limit any significant inertial loads. However, accelerations will affect the output of the sensor. To account for acceleration, an additional accelerometer should be placed near the DirectShear sensor and subtract the coherent power between the DirectShear sensor and the accelerometer. IC2 provides the acceleration sensitivity data in the calibration packet included with each sensor purchase. IC2 is currently working on a future generation of the sensor that will compensate for acceleration automatically. Please contact IC2 for additional information regarding acceleration compensation.

Does each sensor need its own control unit?
Yes. Each sensor requires a dedicated control unit and each unit supports a single sensor at a time; however, multiple sensors can be paired with a single control unit in cases where spares or different sensor types are desired. Engineering services are available for customers who desire custom configurations of control units to support multiple sensors.
Are DirectShear Sensors NIST traceable?
IC2 currently dynamically calibrates its sensors in an acoustic plane wave tube and is working on a new Mean Shear Facility for improved calibration capabilities. DirectShear sensor calibrations are not NIST traceable because no standard yet exists. Our DirectShear sensor is the first of its kind on the market that makes this measurement. It is in our purview and we have had discussions with NIST about creating a standard.
How is the sensor typically mounted to the wall of a test section?
The sensor head should be aligned such that the deflection of the sensing element corresponds to the direction of flow (long axis of the sensing element is in the streamwise direction). While angular misalignment during installation can decrease the overall sensitivity, the reduction in sensitivity is minor at small angles (less than 15°). Installation of the sensor head with the alignment key on the upstream side ensures that the sensor is properly oriented. The sensor head should be inserted until the surface of the sensor head is flush with the facility wall. Proper design of the sensor installation port will provide repeatable installation depths and alignment via use of the shoulder and alignment key on the sensor head. Please contact IC2 for support with sensor installation.
How cautious should I be when handling the sensor?
The sensing element (the front face) is extremely fragile. Any physical contact with the exposed sensing element can cause damage to the sensor. A protective cap is provided for handling purposes and should remain covered at all times when not in use. Proper sensor cleaning procedures are outlined in the provided User Manual.
Are DirectShear - Optical Sensors ITAR controlled?
These sensors are not ITAR items, but may be subject to the EAR in certain configurations.

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