Paired Products

DirectShear – Capacitive | Control Unit


The CSU-1001 AC/DC Capacitive Sensor Unit (CSU) is a fully integrated analog synchronous modulation/demodulation system that provides the ability to measure mean and fluctuating quantities of interest, e.g., wall shear stress or pressure, using a capacitive sensor. The CSU provides low-noise power to the sensor head and conditions the analog voltage signal received from the sensor head for output to a data acquisition system. Capacitive sensing at DC is achieved by shifting the sensor baseband frequencies to a modulated signal and demodulating the returned signal from the sensor, enabling simultaneous real-time measurement of both mean and dynamic components.

SKU: CSU-1001 Categories: ,
Weight 5 lbs
Dimensions 18 × 18 × 12 in
Form Factor


The DirectShear™ sensor heads are micromachined, floating element devices that enable time-resolved, one-dimensional, direct mean and fluctuating wall shear stress measurements.


  • Micromachined floating element shear stress sensor that enables time-resolved, one-dimensional, direct shear stress measurements
  • Compact, robust sensor package for flush mounting
  • Optimized Sensor Control Unit (SCU) for high dynamic range and bandwidth
  • Suite of sensor models for different applications
  • Originally developed for NASA
  • Ability to measure mean and fluctuating quantities using a variety of capacitive devices
  • Integrated rechargeable lithium-ion battery system minimizes power line noise
  • Multi-pin shielded sensor connector provides supply voltages and carrier signals
  • System status and battery voltage LED indicators


  • Instrumentation-grade skin friction sensing
  • Aerodynamic drag research
  • Detection of flow separation
  • Wind tunnel instrumentation


  • Direct measurement of shear stress — no heat transfer calibration
  • Non-intrusive — minimal flow disturbance
  • Simultaneous mean and fluctuating shear stress measurements
  • High resolution, dynamic range and bandwidth
  • Highly accurate, quantitative measurements

Sensor Head Housing Details

  • Non-intrusive — backside contacts for minimal flow disturbance
  • Standard stainless steel cylindrical housings available with or without shoulder and key alignment and detachable cable
  • Multiple sensor head form factors, materials and finishes available to meet installation requirements.
  • Custom housings/materials available
  • Suite of 6 sensor models available for different applications (see Specifications table)
  • Also available in multi-sensor 1x4 array package
ModelShear Stress (Pa)Bandwidth (kHz)Sensitivity (mV/Pa)Resolution (mPa)Element Size
CS-0510100.751000.12mm x 0.5mm
CS-0110501.5400.12mm x 0.4mm
CS-06101002.51012mm x 0.4mm
CS-02103005111mm x 0.2mm
CS-03101000100.350.5mm x 0.15mm
CS-04105000200.08100.5mm x 0.15mm

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-Capacitive Sensors?

DirectShear-Capacitive Sensors are typically used in low-speed wind tunnel testing applications.

What is the operating temperature range for DirectShear-Capacitive Sensors?
Capacitive models are specified for 0-50°C
What is the difference between the H2U and PXI control units?
The H2U version is a standalone unit that runs on its own battery powered system and provides location flexibility, but is the larger and more expensive of the two options. The PXI model was developed to provide our customers a minimized overall footprint of the control unit, but does not utilize advanced PXI features at this time.
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 - Capactive Sensors ITAR or export controlled?
These sensors are not ITAR items. They are also not subject to the EAR.

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