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 hence 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

EVAL-SDP-CB1Z Controller Board (SDP-B Board)
EVAL-CN0371-SDPZ Evaluation Board (CN-0371 Board)
EVAL-CFTL-LVDT Linear Variable Differential Transformer (Measurement Specialties, Inc. E-100 Economy Series LVDT)
CN-0371 Evaluation Software
PC with the following Minimum Requirements
- Windows XP Service Pack 2 (32-bit)
- USB type A Port
- Processor rated at 1GHz or faster
- 512 MB RAM and 500 MB available hard disk space
USB type A to USB type mini-B cable

General Setup

The EVAL-CN0371-SDPZ (CN-0371 Board) connects to the EVAL-SDP-CB1Z (SDP-B Board) via the 120-Pin connector
The EVAL-CFTL-6V-PWRZ (+6V DC Power Supply) powers the EVAL-CN0371-SDPZ (CN-0371 Board) via the DC barrel jack
The EVAL-CFTL-LVDT (LVDT) connects to the EVAL-CN0371-SDPZ (CN-0371 Board) via the 6-pin header at J3.

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!
Connect P3 of the EVAL-CN0371-SDPZ (CN-0371 Board) to CON A of the EVAL-SDP-CB1Z (SDP-B Board)
Connect the USB cable to J1 of the EVAL-SDP-CB1Z (SDP-B Board)

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
- The linearity error is calculated based on the distance from an ideal straight line between the two calibration points taken.

—-

Live Measurement and Noise Data Tabs

Live Measurement Chart
- The Live measurement chart shows the last 200 ADC readings taken. The data shown is displayed in volts (left side vertical axis) and millimeters (right side vertical axis) based on the most recent calibration.
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.

—-

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).

Wiki