Analog Devices ADA4571 Manual de usuario

ADA4571R-EBZ User Guide

UG-739

One Technology Way •P. O . Box 9106 •Norwood, MA 02062-9106, U.S.A. •Tel: 781.329.4700 •Fax: 781.461.3113 •www.analog.com

ADA4571 End of Shaft Evaluation Board

FEATURES

USB 2.0 interface

Jumper for temperature compensation mode enable

Jumper for power down mode enable

Measurement test points and coaxial connectors

EVALUATION KIT CONTENTS

ADA4571 magnetic stimulus:

Dipole magnet

Brushed or brushless dc motor with integrated control

electronics

Evaluation software CD-ROM (Windows® 7 32-bit and 64-bit

compatible GUI)

ADDITIONAL EQUIPMENT NEEDED

Customer supplied 6 V to 12 V bench supply

SDP interface board

USB cable (supplied with SDP interface board)

GENERAL DESCRIPTION

The end of shaft evaluation system is composed of a Windows

LabVIEW® GUI software, an ADA4571 motherboard, a

magnetic stimulus mounted on top of a brushless dc motor, a

daughter board with ADA4571 in its SOIC package, and a USB

interface and controller board, the SDP-S.

The motherboard features an on-board 5 V regulator, a

2-channel simultaneous sampling ADC and jumpers for

enabling the temperature compensation and power-down

modes within the ADA4571. The motherboard also features

test points and unpopulated coaxial connectors for the three

outputs of the device.

The daughter board features the ADA4571 mounted above the

magnetic stimulus as well as test points for the three outputs of

the device.

The SDP board is used to control the ADC on the motherboard

and interface with the GUI.

EVALUATION BOARD CONNECTION DIAGRAM

USB

PC GUI INTERFACE

SDP CONTROL

CARD

EVALUATION

SYSTEM

WITH MAGNETIC

STIMULUS

POWER

SUPPLY

6V TO 12V

SUPPLY

12526-001

Figure 1. ADA4571 End of Shaft Evaluation System

PLEASE SEE THE LAST PAGE FOR AN IMPORTANT

WARNING AND LEGAL TERMS AND CONDITIONS.Rev. 0 | Page 1 of 13

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UG-739 ADA4571R-EBZ User Guide

TABLE OF CONTENTS

Features .............................................................................................. 1

Evaluation Kit Contents................................................................... 1

Additional Equipment Needed....................................................... 1

General Description ......................................................................... 1

Evaluation Board Connection Diagram........................................ 1

Revision History ............................................................................... 2

Getting Started .................................................................................. 3

Software Installation Procedures................................................ 3

Evaluation Board Hardware.............................................................4

Jumper Configuration ..................................................................4

DUT Outputs .................................................................................4

How to Use the Software ..................................................................5

Starting Up the Evaluation GUI..................................................5

Overview of the Main GUI Window..........................................6

Evaluation Board Schematics and Artwork................................ 12

Related Links................................................................................... 13

REVISION HISTORY

10/14—Revision 0: Initial Version

Rev. 0 | Page 2 of 13

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ADA4571R-EBZ User Guide UG-739

GETTING STARTED

SOFTWARE INSTALLATION PROCEDURES

There are two pieces of software to install: the Windows GUI

and the SDP drivers.

Windows GUI Installation

Use the following steps to install the GUI.

1. Before connecting the USB cable or powering the board,

insert the ADA4571-EBZsetup CD and from the installer

directory, run the installer Setup.exe.

2. When the Destination Directory screen appears (see

Figure 2), click Next. Optionally, you may change the

destination folder by clicking Browse, selecting a different

destination folder, and clicking Next.

Figure 2. Choose Destination Location

3. When the Start Installation window appears click Next to

continue with the installation (see Figure 3).

Figure 3. Review Installation

4. Click Next to complete installation of the Windows

LabVIEW GUI.

SDP Installation

Next, install the Analog Devices, Inc., SDP driver. This driver

allows the SDP control board to interface with the LabVIEW

GUI.

1. When the SDP drivers setup wizard appears, click Next

(see Figure 4).

Figure 4. SDP Driver Installation

2. When the Choose Install Location screen appears (see

Figure 5), click Next. Optionally, you may change the

destination folder by clicking Browse, selecting a different

destination folder, and clicking Next.

Figure 5. Choose Install Location

3. Click Finish to complete the installation of the SDP

drivers.

4. Connect the SDP control card to the motherboard and

plug the SDP control card into the PC with the supplied

USB cable. The computer now recognizes the SDP control

board and the LabVIEW GUI may be opened to continue.

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UG-739 ADA4571R-EBZ User Guide

EVALUATION BOARD HARDWARE

The ADA4571 end of shaft demo evaluation system comprises

of two boards (ADA4571 motherboard and ADA4571 daughter

board) and a brushless dc motor.

The ADA4571 evaluation system can be powered directly

from the host PC USB or from an external bench supply. For

maximum performance, it is recommended that an external

bench power supply be used.

When supplied directly from the host PC USB, the applied

voltage is approximately 5 V. However, due to errors in the

regulated USB voltage this value will vary and introduce extra

errors into the system.

To power the motherboard by an external bench supply, apply

6 V to 12 V to P7, the red terminal. When supplied by an

external bench supply, the applied voltage is regulated to 5 V

on the motherboard resulting in a better performance than

powering directly from the host PC USB. If the bench supply

features current-limiting, it is recommended to set the current

limit to 100 mA, as a precaution.

To power the motor by an external bench supply, 3 V to 9 V can

be applied to P6, the blue terminal. The ground is shared with

the ground of the motherboard. The speed of the brushless dc

motor providing the magnetic stimulus to the ADA4571 is

proportional to the voltage applied at this terminal. The

attached motor provides a more constant rotational speed at

lower applied voltages. Due to the LabVIEW GUI measuring

the linearity of the outputs from the device, a more constant

rotational speed is necessary to see the true performance of the

ADA4571. See the Angular Error (Linearity) section for more

information on motor performance.

JUMPER CONFIGURATION

Refer to the ADA4571 motherboard schematic (see Figure 15)

or the configuration panel to understand the purpose of each

jumper.

Configure the motherboard default jumper as follows (see

Figure 15):

•Install the P9 and P10 jumpers in the standard position to

connect the motor and board power to the external supply

terminals.

•Install the P3 jumper connecting GC to VDD. This enables

the gain control mode of the part. When P3 connects GC

to GND, gain control mode is disabled.

•Install the P2 jumper connecting PD to GND. This disables

the power-down mode of the part. When P2 connects PD

to VDD, power-down mode is enabled and the ADA4571

outputs are put into a high impedance state.

DUT OUTPUTS

The outputs of the ADA4571 may be monitored at the test

points located on the daughter board or the motherboard. The

VSIN, VCOS, and VTEMP pins are all accessible on both of the

boards.

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ADA4571R-EBZ User Guide UG-739

HOW TO USE THE SOFTWARE

STARTING UP THE EVALUATION GUI

For maximum performance when the evaluation board is first

powered up, control both the motor and the board using an

external bench power supply. The jumper settings for P9 and

P10 should be set for Ext Motor and Ext +5V as indicated on

the board.

Plug the positive supply for the board into the red terminal, P7,

on the motherboard. This terminal requires 6 V to 12 V which

is then regulated to 5 V on the motherboard using the on-board

ADP3336. This supply powers both the on-board ADC, AD7866,

as well as the daughter board containing the ADA4571.

Plug the positive supply for the motor into the blue terminal,

P6, on the motherboard. Due to mechanical nonlinearities of

the dc motor, such as cogging during coil commuting, extra

errors are introduced to the system at higher rotational

velocities. For best performance, apply 3 V to Ext Motor

terminal. If the motor supplied is a brushless dc motor; 3 V

results in rotational speeds of approximately 2,000 RPM. Speeds

up to 10,000 RPM are possible with a supply voltage of 12 V

applied to this terminal. If the motor supplied is a brushed dc

motor, 3 V results in rotational speeds of approximately

200 RPM.

The nonidealities of the motor result in a higher reported

nonlinearity of the device. This is an artifact of the motor

and not the ADA4571. With an ideal magnetic stimulus, the

ADA4571 has the same angular error performance regardless

of rotational velocity.

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UG-739 ADA4571R-EBZ User Guide

OVERVIEW OF THE MAIN GUI WINDOW

Figure 6 shows the main GUI window, as it appears, after

launching the GUI.

When the program is first launched the SDP controller board

must be recognized by the GUI before proceeding. Pressing

Connect SDP reads the EEPROM ID of the motherboard to

ensure the correct program is being used. If the SDP controller

board is not connected or if the drivers are not installed

correctly an error message will be shown. Ensure that the

drivers are installed correctly if this occurs.

After the SDP control board is properly connected and the

program recognizes the motherboard, the Instructions tab

appears. Click the Read tab to begin.

Initially all of the figures will be blank. To begin press Run (see

Figure 6). The various output graphs are explained in detail in

the following sections.

There are two different categories of output waveforms as

indicated by the GUI. The waveforms on the top of each tab,

indicated as Uncorrected Plots,are without any post processing

to correct for output offset before calculations are done on the

raw data. In the case of the bottom waveforms, indicated as

Offset Corrected Plots, the offset of each channel is subtracted

from the raw data before completing any further calculations.

These differences are discussed in further detail for each

waveform in the Raw Waveforms section.

Figure 6. ADA4571 Main Window

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ADA4571R-EBZ User Guide UG-739

Raw Waveforms

The first figure is labeled Raw Waveforms (see Figure 11).

This figure shows the sampled ADC raw data as the motor is

spinning. The amplitude is shown in 12-bit code. The dual

channel AD7866 simultaneously samples the sine and cosine

channels at 100,000 samples per second. The internal 2.5 V

reference of the AD7866 has been subtracted in hardware as

the readout of the ADC is in twos complement. Therefore, the

two signals are centered around zero in the raw waveform plot.

The magnetic stimulus is sampled over many rotations and

then cropped to three mechanical revolutions or six electrical

revolutions. It is important that these two channels are

simultaneously sampled or extra errors will be introduced

from the phase delay between the sampling of the individual

channels.

Figure 7. Raw Sine and Cosine Waveform

There are two different figures shown depicting these sine and

cosine waveforms. The uncorrected figure has not had any post

processing applied and shows the absolute raw data from the

sensor. For the offset corrected figure, the full three mechanical

revolutions are averaged independently for both the sine and

cosine channels giving the offset for the channel. These offset

values are then subtracted from their respective channel to give

the end waveform centered perfectly about zero.

Note that when powering the board through a USB instead of

by an external power supply there will be some variation in the

supply voltage of the ADA4571. Due to the readout of the

AD7866 being in twos complement form with respect to the

internal 2.5 V reference, the offset of these waveforms will

be higher than the inherent offset of the ADA4571.

Arc Tangent2 (Magnetic Angle)

The second set of figures are labeled ArcTangent (Magnetic

Angle)(see Figure 8). These figures depict the calculated

electrical angle of the ADA4571. This calculation is performed

by the following equation:

Angle = ArcTangent2(VSIN/VCOS)

Because the two AMR bridges are deposited at a 45° relative

angle, the sine and cosine outputs are 90° out of phase. This

constant 90° phase difference results in the calculated angle

over a constant rotary speed as a straight line.

Normally the ArcTangent function will have a range of (−90°

to +90°). However, if quadrant information is kept and cor-

rected for after the calculation the second and third quadrant

can be distinguished from the first and fourth. The function

ArcTangent2 has this quadrant information and therefore the

range is extended to (−180° to +180°). The program then zeros

this waveform and therefore shows the angle between (0° and

360°).

Figure 8. ArcTangent Calculation Plot

The electrical angle period will repeat for every sinusoidal

period of the sine and cosine outputs from the ADA4571. Just

like the raw waveform data, three mechanical revolutions or six

electrical revolutions are used for calculations. This results in

six periods of angle information shown.

The Uncorrected ArcTangent (Magnetic Angle) plot will

have a slight bowed shape to it due to the sensor offset in the

raw waveform. The Offset Corrected ArcTangent (Magnetic

Angle) plot shows the angle information after the offset is

nulled from each individual channel. This offset correction to

the raw waveforms before the ArcTangent calculation results

in a much more linear output plot.

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UG-739 ADA4571R-EBZ User Guide

Angular Error (Linearity)

There are two different motors that may be supplied with your

demo board: a brushless dc motor or a brushed dc motor. The

brushed dc motor will introduce extra errors into the system

due to cogging of the motor during rotation. To fully evaluate

the performance of the sensor, an externally applied magnetic

stimulus that has a smoother rotational velocity should be used

with the supplied LabVIEW GUI.

The third set of figures are labeled Angular Error (Degrees)

(see Figure 6). This figure shows the linearity of the ArcTangent

plot discussed in the Arc Tangent2 (Magnetic Angle) section.

There is no encoder attached to the magnetic stimulus on the

board and therefore the program cannot compare the calculated

angle to the actual position of the magnet. Therefore, this plot is

calculating the linearity of both the ADA4571 and the brushless

dc motor providing the magnetic stimulus.

Due to the nonidealities of the brushless dc motor providing

the magnetic stimulus, the reported angular error will always

be higher than the actual error of the ADA4571. The motor

provides a more constant rate of speed at lower rotational

velocities and therefore the reported linearity will be lower

at slower speeds. These extra errors are not indicative of the

bandwidth of the ADA4571 as the part can handle motor

rotational speeds as high as 50,000 RPM.

Figure 9 shows the Uncorrected Angular Error (Degrees) plot.

When powered by the host PC USB supply this waveform

reports higher error than when powered by an external supply.

This increased error is because the internal 2.5 V reference is

subtracted in hardware from each ADC channel resulting in a

higher inherent offset of the sensor if the supply voltage is not

exactly 5 V. When powered by an external power source the

ADA4571 supply is regulated to 5 V and, therefore, the ADC

introduces no extra offset or errors to the system.

Figure 9. Uncorrected Linearity Error Plot

Figure 10 shows the Offset Corrected Error (Degrees) plot.

Large spikes appear in this plot due to the nonidealities of the

magnetic stimulus. When the motor commutes, there is a kick

from the excitation coils resulting in a higher reported linearity

error at these points. The sensor measures the position of the

magnetic stimulus and so these kicks during commuting will

show up as an error from an ideal linear plot. This nonideality

from the magnetic stimulus is more prevalent at higher speeds

but is not a result of the sensor. The included motor is very

smooth at lower speeds and, therefore, these spikes will not

appear in the error plot.

Figure 10. Offset Corrected Linearity Error Plot

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ADA4571R-EBZ User Guide UG-739

Fourier Transform

The fourth set of figures are labeled Fourier Transform. These

figures show the spectral analysis of the two independent

output signals. The fundamental frequency corresponds to the

motor speed. Harmonics from the sensor are also depicted in

this plot. The y-axis of this plot shows the magnitude of the

frequency components. This value is the root mean squared

(RMS), magnitude in 12-bit code of that specific frequency.

The x-axis is shown in hertz. The fundamental frequency

shown depicts the electrical frequency. This will be two times

the mechanical frequency. An example calculation for motor

speed in RPM from a 100 Hz fundamental electrical frequency

is shown as,

100 Hz × (1 electrical cycle)/(2 mechanical cycles) ×

(60 seconds)/(1 minute) = 3,000 RPM

Figure 11. Spectral Output for Sine and Cosine Channels

Due to the layout of the AMR bridge odd harmonics which are

usually present in the output of sensors, such as third and fifth,

are suppressed.

Spectral analysis of the sensor can be useful for debuging

purposes. Even harmonics appear in this plot when there is

gross misalignment between the center of the AMR sensor

and the magnetic stimulus.

Radius Plot

The fifth set of figures are labeled Radius Check (see

Figure 12). This figure plots the sine channel on the y-axis and

the cosine channel on the x-axis. Both axes are shown in 12-bit

codes. Due to the sinusoidal nature of the two channels and the

90° phase delay between the sine and cosine channels the plot is

circular in nature.

The radius of this plot is constant throughout the entire rotation

of the magnetic stimulus. The exact radius of this plot is

inversely proportional to the temperature of the ADA4571. At

lower device temperatures, the radius increases while at higher

device temperatures the radius decreases; when held at a

constant temperature the radius will also be constant.

Figure 12. Radius Plot of Output Waveforms

The temperature dependent variation in output amplitude of

the AMR bridge is due to the reduced change in resistance of

the AMR film at higher temperatures. The ADA4571 provides

an internal regulated voltage to the AMR bridge supply. By

enabling the temperature compensation mode of the ADA4571,

this regulated supply voltage varies with temperature. At higher

temperatures, the regulator provides a higher bridge supply

voltage, thus increasing the output amplitude of the device.

Using this mode, the output amplitude and, therefore, radius

in this plot will be more consistent over the wide temperature

range of −40°C to 150°C.

This mode is enabled by default by an internal pull-up resistor

on the GC pin. Moving Jumper P3 to the correct position as

outlined in Figure 14 and Figure 15 will disable the temper-

ature compensation mode of the device. There is an internal

temperature sensor on the ADA4571 that is used to adjust the

bridge supply voltage. The internal temperature sensor voltage

is available to the end user and can be monitored on the

daughter board or the motherboard as outlined in Figure 14

and Figure 15.

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UG-739 ADA4571R-EBZ User Guide

Figure 13. ADA4571 Part DiagnosticsTab

Rev. 0 | Page 10 of 13

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