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Non-Contact DVRT®

Non-Contact Displacement Sensor

Differential Variable Reluctance Transducer

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.

Non-Contact Displacement Sensor

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.

 

#1483: How do I enter the Slope and Offset calibration into Smart Motherboard software?

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.

 

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#1362: Where can I acquire plastic shim stock for field calibrating the Non-Contact DVRT?

Plastic shims and shim stock can be acquired from industrial supply houses.

McMaster-Carr offers assortments as shown below.

These may be found at: www.mcmaster.com

Part Number: 9513K42
Type Shim Stock
Material Plastic
Material Type PETG and Polyester
Length x Width 5" x 20"
Specifications Met Not Rated
Assortments Standard Shim Stock
Assortments
Assortment Type Plastic Assortment - 15 Piece
Assortment Contents 1 each of these thicknesses:
.0005", .00075", .001",
.0015", .002", .003", .004",
.005", .0075",
.010" (±10%); .0125",
.015" (±.001"); .020",
.025", .030" (±5%).

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#1342: How do I repair or return a LORD MicroStrain® product?

In order to return any LORD MicroStrain® product either for repair or return, you must contact us for a Return Merchandise Authorization number (RMA). If you purchased directly from LORD MicroStrain® in the United States, please contact your Sales or Support Engineer to obtain an RMA.  If you purchased directly from a LORD MicroStrain® distributor, please contact your distributor to obtain an RMA.

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#1340: Where do I purchase LORD MicroStrain® products?

If you are located in the United States, LORD MicroStrain® supplies you directly.  If you are in located in another country, LORD MicroStrain® products are available exclusively from LORD MicroStrain® distributors.  Please use this locator to determine your distributor: http://www.microstrain.com/support/international

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#1339: Does LORD MicroStrain® provide a trial period for its products?

To enable customers to try our standard products risk free, LORD MicroStrain® offers a 30 day return on the purchase of a starter kit. In order to take advantage of this offer, a purchase order or payment for the starter kit is required when the order is placed. 30 day trial details may be found at: http://www.microstrain.com/support/warranty

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#1338: How do I get support for my LORD MicroStrain® products?

LORD MicroStrain® Support Engineers are always available to support you in any way we can by phone, email, SKYPE or Live Chat from our home page.  Contact details may be found at: http://www.microstrain.com/support/contact-support

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#1337: What is the shipping policy for LORD MicroStrain® products?

LORD MicroStrain® insures all products shipments to their full value unless the customer specifically states a different method.

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#1336: What is the warranty for LORD MicroStrain® products?

LORD MicroStrain® warrants its standard products to be free from defective material and workmanship for a period of one (1) year from the original date of purchase.  Warranty details may be found at: http://www.microstrain.com/support/warranty

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#1065: What is the maximum cable length between a DVRT and its DEMOD signal conditioner?

If you are using the standard cable type supplied with the DVRT sensors, 20 feet is the maximum for M-DVRT and MG-DVRT, and 60 feet is the maximum for S-DVRT, SG-DVRT and NC-DVRT. If you require longer cable lengths, LORD MicroStrain® can provide custom cables of lower resistance.

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#1064: Does carbon fiber affect the analog output from the DVRT?

No, carbon fiber has not been shown to pose a problem.

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#1063: Can we provide a drill bit and tap for threaded body DVRTs?

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.

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#1062: How do I use the calibration documents provided with each DVRT?

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.
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#1061: What are the major benefits of a DVRT over an LVDT?

  • 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.
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#1060: What's the output from the DVRT?

The output is an analog DC voltage proportional to linear displacement.  The full scale voltage is optionally +/-5 volts or 0-10 volts.  The analog voltage is easily read using a multi-meter or DAQ.  The voltage can also be read in the digital domain by using LORD MicroStrain® Smart Motherboards.  These Smart Motherboards provide a data gateway to PC-based software or to user-programmable LCD displays on the motherboard itself.

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#1059: Are DVRTs submersible?

Yes. DVRTs can be used in wet environments.  One of our customers uses the DVRT to measure mussel growth on the ocean floor.  An automotive customer uses the DVRT in a hot oil environment for under-the-hood testing.  Our orthopaedic customers use the DVRT for soft and hard tissue testing (in vivo and ex vivo) in cadaver and animal studies.

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#1056: Is there a comparison chart for the DVRT line?

Yes.  A comparison chart may be found at: http://files.microstrain.com/Displacement-Sensors-Comparison.pdf

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#1055: How much pressure can DVRTs withstand and still be functional?

Sandard DVRTs can operate up to 100 PSI.  However, custom-designed sensors have been used in applications up to 10,000 PSI.  Please contact your sales or support engineer for more info.

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#1054: Are DVRTs calibrated?

Typically, every DVRT is calibrated at the factory with its accompanying DEMOD signal conditioner.  The calibration is made over the entire system (DVRT and DEMOD) to insure the highest accuracy.  DVRTs and DEMODS are color-coded to insure that they stay together as a pair when in use.

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#1053: Where would I find scientific papers describing the use of DVRTs?

LORD MicroStrain® posts links to a number of published scientific papers at: http://www.microstrain.com/company/scientific-papers

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#1049: What is a ‘Motherboard’ and what is the difference between a standard Motherboard and a Smart Motherboard?

The term ‘Motherboard’ refers to the LORD MicroStrain® DEMOD-DVRT or DEMOD-DVRT-TC signal conditioner mounting chassis.  The standard Motherboard provides a mounting slot and power to the individual DEMODs.  The Smart Motherboard provides a mounting slot, power and digital communications (RS-232) to the individual DEMODs.  Both Motherboard and Smart Motherboard provide analog ouput to a DAQ.  In addition, Smart Motherboard provides digital output to a computer.  Motherboards and Smart motherboards can accommodate 1 to 8 DEMOD cards.

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#1048: What attachment options are available for DVRTs?

DVRT Type Threaded Core Threaded Body Core Clamps Body Clamps SM-Block Core/Body Magnetic Mount Core/Body
Subminiature X X     X X
Subminiature Gauging X X        
Microminiature X X X X    
Microminiature Gauging X X   X    
Non-Contact   X**        

** Non-Contact comes standard with threaded body except for 5.0.

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#1047: Can an LVDT use the DEMOD signal conditioning electronics?

In a word, no. The design of an LVDT’s coil forms a Wheatstone full bridge and the design of LORD's DVRT coil forms a Wheatstone half-bridge. LORD MicroStrain® signal conditioning electronics are designed for the half-bridge.  Likewise, a DVRT can not use a LVDT's signal conditioning electronics.

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#1046: What is the difference between a DVRT and an LVDT?

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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How To Order

To discuss configuration for your specific system requirements, please use our contact sales page.

For large quantity orders or OEM discussions, please contact Michael_Robinson@LORD.COM.

If you are outside the US, please contact one of our distributors.

Highlighted Documents

Applications

  • Process Control for Production-Line Monitoring
  • Miniature Position Control Elements
  • Linear & Angular Motion Control
  • Measuring Strain and Deflection in Materials and Structures
  • Dimensional Gauging for Quality Control

Related Products

  • DEMOD-DCDEMOD-DC® - Carrier Amplifier-Oscillator/Demodulator for DVRTs®; Inductive, Capacitive and Resistive Bridge Circuits.
  • DVRTM-DVRT® - The World's Smallest Linear Displacement Sensor! Differential Variable Reluctance Transducer
  • MG-DVRTMG- DVRT® - The World's Smallest Linear Gauge! Differential Variable Reluctance Transducer (or "half bridge LVDT")