CN-0371 Software User Guide
Overview
CN-0371 is a complete linear variable differential transformer (LVDT) signal conditioning circuit that can accurately measure linear position or linear displacement from a mechanical reference. Synchronous demodulation in the analog domain is used to extract the position information and provides immunity to external noise. A 24-bit sigma-delta ADC digitizes the position output for high accuracy.
LVDTs utilize electromagnetic coupling between the movable core and the coil assembly. This contactless (and therefore frictionless) operation is a primary reason why they are widely used in aerospace, process controls, robotics, nuclear, chemical plants, hydraulics, power turbines, and other applications where operating environments can be hostile and long life and high reliability are required.
The entire circuit, including the LVDT excitation signal, consumes only 10 mW of power. The circuit excitation frequency and output data rates are SPI programmable. The system has a programmable bandwidth versus dynamic range trade-off. It supports bandwidths of over 1 kHz, and at a bandwidth of 20 Hz, the circuit has a dynamic range of 100 dB, making it ideal for precision industrial position and gauging applications.
This circuit note discusses the design steps needed to optimize the circuit shown in Figure 1 for a specific bandwidth including noise analysis and component selection considerations.
This user guide will discuss how to use the evaluation software to collect data from the EVAL-CN0371-SDPZ Evaluation Board (CN-0371 Board)
Required Equipment
General Setup
Installing the Software
Extract the file
CN0371 Eval Software.zip and open the file
setup.exe.
NOTE: It is recommended that you install the CN-0371 Evaluation Software to the default directory path C:\Program Files\Analog Devices\CN0371\ and all National Instruments products to C:\Program Files\National Instruments\
Click
Next to view the installation review page
Click
Next to start the installation
Upon completion of the installation of the
CN-0371 Evaluation Software, the installer for the
ADI SDP Drivers will execute.
NOTE: It is recommended that you close all other applications before clicking “Next”. This will make it possible to update relevant system files without having to reboot your computer.

Press
“Next” to set the installation location for the
SDP Drivers.
It is recommended that you install the drivers to the default directory path
C:\Program Files\Analog Devices\SDP\Drivers
Press “Next” to install the SDP Drivers and complete the installation of all software. Click “Finish” when done.
Connecting the Hardware
Connect the
EVAL-CFTL-LVDT (LVDT) to
J3 of the
EVAL-CN0371-SDPZ (CN-0371 Board) as depicted below.
NOTE: If a different LVDT is used other than the E-100 LVDT from Measurement Specialties, Inc the wiring schematic will be different!
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Using the Evaluation Software
Linearity and Calibration Tabs

Displacement Display
The upper left hand corner shows the current measurement displacement in terms of voltage (
V) and distance in millimeters (MM). In order to get accurate measurements, the system should be calibrated as described below.
Calibration Tab
The system can be calibrated using a two point calibration.
The core should be placed at the maximum displacement. The displacement should then be entered in the Distance field. Then the Set new MAX button should be clicked.
The core should next be placed at the minimum displacement. The displacement should then be entered in the Distance field. Then the Set new MIN button should be clicked.
This completes the calibration.
Linearity Table
The table can be filled out, and linearity automatically calculated as follows:
The core should be set to a known position. That position should be entered in the Distance (MM) field. The Get new data point button should be clicked. This creates a new entry in the Linearity table. The linearity is calculated and the data point is added to the Linearity plot.
Additional data points can be added in a similar manner. The data points do not need to be linearly spaced or taken in a particular order.
Error Calculation
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Live Measurement and Noise Data Tabs

Live Measurement Chart
Noise Data Tab
Noise Data in volts (RMS), volts (p-p), ENOBs (RMS) and ENOBs (p-p) are displayed. The volts are calculated based on the 3.3V ADC reference. ENOB measurements are based on full-scale voltage in the settings tab.
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Live Measurement and Settings Tabs

Settings Tab
Full-Scale Range entry enables users to scale the voltage used for the ENOBs calculations in the Noise Data tab.
Measure I/Q buttons allow selecting either the Phase 0 or Phase 90 setting on the ADA2200
Data Rate Divider sets the AD7192 output data rate. This value can be set from 1 to 1023.
Output Data rate is the calculated ADC data rate. It is equal to 4800/(Data Rate Divider).
Registration
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