Ideal for difficult sensing applications, the Non-Contact DVRT® is designed to measure the displacement and proximity of a metal target without physical contact. The measurement is unaffected by interposed nonmetallic, non-conductive materials, such as polymers and biomaterials. The stainless shell of the device houses two coils; one for sensing and the other for temperature compensation. The coils and Teflon® cable are mounted on a stable PEEK substrate. This assembly is potted into the stainless housing using high-grade, vacuum-pumped epoxy and includes integral strain relief. This packaging allows the sensor to be used in applications requiring long-term immersion in water and saline solutions.

Datasheet

High Performance

  • Sub-micron resolution with large stroke/size ratio
  • High dynamic range for difficult measurements

Ease of Use

  • Non-contact position measurement
  • Plug and play usability
  • Easily customized to suit specific requirements
  • Signal conditioning options for any application

Electrical Specifications (Obtained using DEMOD-DVRT® and DVRT® with 800 Hz low pass filter at constant temperature)

Measurement range
NC-DVRT-1.0
NC-DVRT-1.5
NC-DVRT-2.5
NC-DVRT-5.0
1.0 mm
1.5 mm
2.5 mm
5.0mm (not compatible with DEMOD-DC®)
Accuracy ±0.2 to ±1% with polynomial calibration
Sensitivity DEMOD output/sensor range
Signal to noise standard - 1000 to 1with filter 3dB down at 800 Hz
Resolution dependent upon displacement area
Frequency response 800 Hz standard, 20 KHz optional
Temperature coefficient offset 0.0039%/°C (typical)
span 0.016%/°C (typical)
dependent on target material
Hysteresis ±2 microns (typical)
Repeatability ±2 µm (typical) at constant temperature

Mechanical Specifications

Size

NC-DVRT®-1.0
NC-DVRT®-1.5
NC-DVRT®-2.5
NC-DVRT®-5.0
diameter x length (thread)

4.83 mm x 19.0 mm (10-32 UNF-2A )
6.35 mm x 19.0 mm (¼-28 UNF-2A)
12.70 mm x 19.0 mm (½-20 UNF 2A)
19.1 mm x 32.0 mm (smooth body)
Housing material 300 series stainless steel
Attachment method threaded stainless nuts (excluding NC-DVRT-5.0)
Leadouts 45 cm, shielded, teflon insulated, stainless wire reinforced, multistrand conductors
Connector keyed 4-pin Lemo, polyolefin relief
Operating
temperature
-55 to 175 °C
Cable diameter 0.036 “ to 0.070 “

Contact us for information on custom designs suitable for immersion, corrosive and high pressure environments.

 

As an example. here is the Quick Start Guide for the M-DVRT-9: http://files.microstrain.com/Micro_Sub_DVRT_Quick_Start_Guide.pdf

Page 7 refers to the Slope and Offset that you will need to enter into the Smart Motherboard software.

In the Smart Motherboard software, click Tools.

Click Configuration and the Configuration screen appears.

Select the appropriate channel (remember that each channel, i.e., each DVRT and DEMOD –DVRT signal conditioner card in the Smart Motherboard is calibrated separately) by checking the Channel check box.

Select the Linear Radio Button.

Enter the Slope and Offset in the number scroll boxes.

Select None in the Peak Detect drop-down.

Change the Units from Volts to mm (for millimeters) by wiping through with your mouse.

Click File.

Click Save As Default.

Click File.

Click Return and you are ready to sample in millimeters.

Yes, as a courtesy, LORD MicroStrain® will provide an appropriate drill bit and tap to match the DVRT's thread size at a nominal charge.

In most cases, MicroStrain calibrates every DVRT with its accompanying electronics and provides a detailed calibration certificate. The certificate provides 3 methods of calibration and all the particulars including formulas to resolve voltage into engineering units.

  • Standard Least Squares Linear Fit provides a simple mathematical method to convert sensor output to displacement and delivers reasonable accuracy.
  • Polynomial Fit provides a more mathematically intensive method to convert sensor output to displacement and in turn delivers a high degree of accuracy. A possible drawback to some users of this method may be that it can not accurately report measurements beyond its stroke length (i.e., over-stroking).
  • Multi-Segment Linear Fit provides the most mathematically intensive method to convert sensor output to displacement, delivers a high degree of accuracy and is not subject to the drawback of over-stroking.
  • Body length to stroke ratios for DVRTs are typically 2.5 to 1 as compared to 6 to 1 for LVDTs.
  • Microminiature DVRTs are available in body diameters of only 1.5 mm (.060") and with core diameters of only 0.5 mm (.020"); this makes them the World's smallest commercially available linear displacement transducers.
  • DVRTs maintain their temperature stability due to the use of two coils arranged differentially.
  • Each DVRT is capable of submersion as a standard feature.
  • Each DVRT can be hermetically sealed as an option.
  • Microminiature DVRTs are available with super-elastic, nickel titanium cores.
  • DVRTs have a standard operating temperature range up to 175 degrees C; LVDTs typically only operate up to 85 degrees C.
  • DVRTs have been operated successfully in liquid nitrogen; LVDTs typically only operate to -20 degrees C.

DVRT (Differential Variable Reluctance Transducer) and LVDT (Linear Variable Differential Transformer) combined with their signal conditioners convert a linear displacement into a linear variable electrical output signal. The displacement is detected by the movement of a core within the coils inside of the sensor. The difference between the sensors is in their coil format.

DVRT: The coil shown below is energized using an AC excitation through the center tap. The coil is usually arranged in a Wheatstone bridge with the Center Tap being the bridge excitation (forming a "half bridge"). With the core in the central location (null) the signals Va and Vb are equal. When the core moves, Va and Vb vary proportionally. Since this design is less complicated we are able to produce considerably smaller sensors than LVDT manufacturers.

LVDT: The primary coil is excited with an AC waveform. When the core is in the central location, the coupling between the secondary coils (Va & Vb) and the primary coil Ve) is equal. When the core moves, Va changes proportionally to Vb in both magnitude and phase.

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