LTI 20/20 TruSpeed User manual

User’s Manual

LTI 20/20 TruSpeed
User’s Manual
Part Number 0144805
Copyright Notice:
Information in this document is subject to change without notice and does not
represent a commitment on the part of Laser Technology Inc. No part of this
manual may be reproduced in any form or by any means, electronic or mechanical,
including photocopying, recording, or information storage and retrieval systems, for
any purpose other than the purchaser’s personal use, without the express written
consent of Laser Technology, Inc.
Copyright © Laser Technology, Inc., 2007. All rights reserved.
Printed in the United States of America
First Edition— First Release: July 2007
First Edition— Second Release: September 2007
Trademarks:
TruSpeed is trademark of Laser Technology, Inc.
All other trademarks are the property of their respective owner.
Patents:
This product is covered by pending patent applications and/or
one or more of the following issued patents: 5,359,404
5,521,696
5,715,045
LTI Contact Information:
Laser Technology, Inc.
7070 S. Tucson Way
Centennial, CO 80112 USA
Phone: [phone]
Fax: [phone]
Web Site: www.lasertech.com

LTI 20/20 TruSpeed User’s Manual Table of Contents
Page 1
LTI 20/20 TruSpeed
User’s Manual Table of Contents
Section #1 - Getting Started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Unpacking Your TruSpeed . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . .. . . . 3
TruSpeed Basic Package . . . . .. . . . . . . . . .. . . . . . . . . .. . . . . . . . 3
Available Accessories . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . .. . . . 3
Important Safety Information . . . . . . . . . . . . . . . . . .. . . . . . . . . . . .. . . . 3
About the TruSpeed . . . . .. . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . .. . . . 4
Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
LCD Screen . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . .. . . . . . . . . . . . 5
Test Port . .. . . . . . . . . . . .. . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . 5
Sighting Scope . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . .. . . . . . . . . . 5
Buttons on the Keypad . . .. . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . 6
Optional Shoulder Stock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Attaching the Shoulder Stock . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Removing the Shoulder Stock . . . . . . . . . . . . . . . . . .. . . . . . . . 7
Installing / Removing the Batteries . . . .. . . . . . . . . .. . . . . . . . . . . . 8
Removing the Battery Tube from the Handle . . . . . . . . . .. . . . 8
Inserting the Batteries in Battery Tube . . . . . . . . . . . . . . . . . . . 8
Re-inserting the Battery Tube into the Handle . . . . . . . . . . . . . . 8
Battery Voltage Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Powering ON the TruSpeed . . . . . . .. . . . . . . . . .. . . . . . . . . . . .. . 10
Powering OFF the TruSpeed . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . 10
Understanding the Display Indicators . . . . . . . . . . . . . . . .. . . . . . . . 11
Miscellaneous Display Features . . . . . . . . . . . . . .. . . . . . . . . . 12
Adjusting the Aiming Reticle's Intensity . . . . . . . . . . . .. . . . . . . . . . 13
Restoring Factory Default Settings . . . . . . . . . . . . . . . .. . . . . . . . . . 13
Listening to the TruSpeed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Understanding Error Conditions . .. . . . . . . . . .. . . . . . . . . .. . . . . . 14
Error Codes . . . . . .. . . . . . . . . .. . . . . . . . . .. . . . . . . . . . . .. . 15
RFI Considerations . . . . . . . . . .. . . . . . . . . .. . . . . . . . . . . .. . 15

Laser Technology, Inc. LTI 20/20 TruSpeed User’s Manual
Page 2
Section #2 - Speed Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Taking a Sample Measurement . . . . . . . . . . . . . . . . . .. . . . . . . . . . . .. . 17
Choosing a Roadside Location . . . . . . . . . .. . . . . . . .. . . . . . . . . .. . . . 17
Line of Sight . . . . . . . . . . . . .. . . . . . . . . .. . . . . . . . . . . .. . . . . . . . 18
The Cosine Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Measuring a Moving Vehicle . . . . . . . . . . . . . . . .. . . . . . . . . .. . . . . . . . 20
Using the Weather Mode . . . . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . 21
Using the Continuous Mode . . . . . . . . . . . .. . . . . . . . . .. . . . . . . .. . . . 22
Laser Jammer Detection . . . . . . . . . . . . .. . . . . . . . . .. . . . . . . . . . . .. . 23
Section #3 - Test Mode and Instrument Tests . . . . . . . . . . . . . . . . . . 24
Display Integrity Test . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . .. . . . . . . . 24
Scope Alignment Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Instrument Confidence Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Fixed Distance Test .. . . . . . . . . . . .. . . . . . . . . .. . . . . . . . . . . .. . 27
Delta Distance Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Self Test . . . . . . . . . . . .. . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . .. . . . . . 30
Model and Firmware Version Number Display . . . .. . . . . . . . . .. . . . . . 30
Serial Number Display . . . . . . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . 30
Section #4 - Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Section #5 - Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Section #6 - Troubleshooting Tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Section #7 - Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Section #1 - Getting Started
Page 3
Section #1 - Getting Started
Unpacking Your TruSpeed
When you receive your TruSpeed, check to make sure that you have received
everything that you ordered, and that it all arrived undamaged.
TruSpeed Basic Package
FTruSpeed instrument with polarizing filter
FTwo C cell batteries
FUser's manual
Available Accessories
You may have also ordered one or more of these optional accessories:
FTruSpeed Battery Eliminator
FCarrying Case
FShoulder Stock
FTruSpeed Yoke (includes adapter for monopod/tripod mounting)
FMonopod
FTripod
Important Safety Information
Avoid staring directly at the laser beam for prolonged periods .
• The TruSpeed is designed to meet FDA eye safety requirements and is
classified as eye-safe to Class 1 limits, which means that virtually no
hazard is associated with directly viewing the laser output under normal
conditions. As with any laser device, reasonable precautions should be
taken in its operation. It is recommended that you avoid staring into the
transmit lens while firing the laser. The use of optical instruments with
this product may increase eye hazard.
Never attempt to view the sun through the scope.
• Looking at sun through the scope may permanently damage your eyes.
Never point the instrument directly at the sun.
• Exposing the lens system to direct sunlight, even for a brief period, may
permanently damage the laser transmitter.
Do not operate the instrument in extreme temperatures.
• TruSpeed components are rated for a temperature range of
-22° F to +140° F. Do not operate the instrument in
temperatures outside that range.

Laser Technology, Inc. LTI 20/20 TruSpeed User’s Manual
Page 4
About the TruSpeed
Laser Technology's LTI 20/20 TruSpeed is part of the Laser Technology family of
handheld laser speed and ranging devices. Compared to our other
laser speed measurement products, the TruSpeed includes:
• Simplified menus and options.
• Built-in Weather Mode that is an alternate speed measurement mode. It
is a simplified gating option. This factory-defined gate ensures that
targets are beyond the range where rain and snow can affect the laser's
ability to capture a speed reading.
• Continuous Mode that is an alternate speed measurement mode. It
displays one speed reading after another until you release the TRIGGER.
• Liquid Crystal Display (LCD) screen for instant access to measurements
and options.
• Sighting scope with in-scope aiming reticle and in-scope
speed measurement display.
• Seven-button keypad that provides quick and easy access to the
instrument functions.
• Sounds and visual indicators that ensure confidence of positive target
acquisition.
• Test port for verifying reference timing.
Figure 1 shows the TruSpeed's front and rear panels.
1. Sighting Scope
2. Transmit Lens
3. Receive Lens
4. Battery Release
5. Shoulder Stock
Release
6. Battery Tube
7. Handle / Battery
Compartment
8. TRIGGER
9. Shoulder Stock
Attachment
Point
10. Test Port
11. Speaker
12. Keypad
13. LCD Screen
Figure #1

Section #1 - Getting Started
Page 5
Sensors
The TruSpeed has two lenses on the front panel. The top lens transmits the
infrared laser signals. The bottom lens receives signals back from the target and
feeds signal information to the internal circuitry.
The internal circuitry consists of a laser range sensor and timing, analysis,
computation, and display circuits. The TruSpeed determines distance through its
laser range sensor, by measuring the time of flight of short pulses of infrared light.
The TruSpeed has a broad spectrum of sensitivity, and can work with both
reflective and non-reflective targets. The maximum measurement distance varies
with target and environmental conditions. The absolute maximum is about 2,000
feet.
LCD Screen
The LCD Screen displays menu items, option indicators, error codes, and speed
measurement results.
Test Port
Your TruSpeed includes a Test Port located on the rear panel. The Test Port allows
you to connect the instrument to a remote computer for laboratory testing
purposes only.
Sighting Scope
Mounted on top of the TruSpeed is a single-power sighting scope. The scope
features:
• The polarizing light filter is adjustable to
optimize viewing contrast. Figure #2 shows
the polarizing light filter's adjustment ring.
• In-scope speed measurement display.
• The in-scope aiming reticle helps you aim
accurately to the target. Figure #3 shows
reticle. This reticle represents the size of the
laser beam.
LYou can vary the intensity of the aiming
reticle to account for different lighting
conditions. For more information, see page 13.
Figure #2
Figure #3

Laser Technology, Inc. LTI 20/20 TruSpeed User’s Manual
Page 6
Buttons on the Keypad
The TruSpeed has a 7-button keypad located on the rear panel of the instrument.
The buttons provide easy access to the instrument functions. The table below
lists the buttons and the functions of each.
Button Name Function
Speed
Mode Activates the instrument’s speed measurement mode.
Weather
Mode Activates the instrument’s alternate speed measurement mode: simplified gating
option. Targets must be at a distance
greater than 200 feet.
Continuous
Mode Activates the instrument’s alternate speed measurement mode: displays one speed
reading after another until you release the
trigger.
Backlight Toggles the display backlight
ON/OFF
Test
Mode Activates the instrument’s Test Mode, which allows you to verify the TruSpeed’s
mechanics.
Brightness
Control Varies the intensity of the in-scope aiming reticle.
Power ON/
OFF Press and release to power ON the instrument.
Press-and-Hold for approximately 3 seconds
to power OFF the instrument.

Section #1 - Getting Started
Page 7
Optional Shoulder Stock
The Shoulder Stock is available for purchase as an accessory item. The Shoulder
Stock helps stabilize the TruSpeed while capturing speed measurements and is
designed for either left-handed or right-handed use.
Attaching the Shoulder Stock
1. Flip the Shoulder Stock Release toward the front of the TruSpeed.
2. Align the pronged-end of the Shoulder Stock with the Shoulder Stock
Attachment Point as shown in Figure #4.
3. Slide the Shoulder Stock straight into the two holes.
4. Flip the Shoulder Stock
Release toward the rear
of the TruSpeed to
secure the Shoulder
Stock.
Removing the Shoulder Stock
1. Turn the Shoulder Stock Release toward the front of the TruSpeed.
Continue to hold the Shoulder Stock Release in this position.
2. Pull the Shoulder Stock straight toward you.
Figure #4
(Enlarged to
show step #1)
Figure #5
(Enlarged to
show step #1)

Laser Technology, Inc. LTI 20/20 TruSpeed User’s Manual
Page 8
Installing / Removing the Batteries
Two C cell batteries are required to power the TruSpeed. The batteries are
located in the Battery Tube inside the Handle.
Removing the Battery Tube from the Handle
1. Hold the TruSpeed with one hand and
hold the bottom of the Handle with
your other hand.
2. Press the Battery Release, the black
button on either side, just behind the
TRIGGER.
3. Slide the Battery Tube out of the
Battery Compartment.
Inserting the Batteries in Battery Tube
1. With the positive end pointing toward the bottom of the Battery Tube,
align the battery with the opening of the Battery Tube as shown in
Figure #7A and B.
2. Insert the battery into the Battery Tube and slide the battery to the top
of the tube.
3. Position the second battery as described in step #1 and insert the
battery into the tube as shown in Figure #7C.
Re-inserting the Battery Tube into the Handle
The Battery Compartment is designed to the Battery Tube only fits one way.
1. Align the notched edges of the Battery Tube with those of the Battery
Compartment.
2. Slide the tube into the compartment until it locks into place.
LTo remove the batteries from the Battery Tube, just reverse the above
instructions.
Figure #6
Figure #7

Section #1 - Getting Started
Page 9
Battery Voltage Level
The TruSpeed continuously monitors its power source. LTI has defined an
acceptable battery voltage range to ensure that the instrument has sufficient
battery voltage to guarantee correct operation.
Appearance
of the
Battery Icon Explanation
3 segments are lit and the display is steady. The
estimated battery life is between 67% and 100%.
2 segments are lit and the display is steady. The
estimated battery life is between 34% and 66%.
1 segment is lit and the display is flashing. The
estimated battery life is between 33% and 11%.
Only the outline is lit, no segments are lit and the
display is steady. The estimated battery life
approximately 10%, and the instrument is still
operating normally.You should replace the batteries
as soon as possible.
Only the outline is lit, no segments are lit and the
display is flashing. “bAtt” appears in the upper
display and “CHAng” appears in the lower display.
All system operation will be locked out and the only
button that will work is the Button, which you
can use to power oFF the TruSpeed.

Laser Technology, Inc. LTI 20/20 TruSpeed User’s Manual
Page 10
Powering ON the TruSpeed
1. Press the TRIGGER or the
button. Briefly, the instrument’s
microcontroller will perform the Self
Test.
• If all tests prove positive, “PASS” appears briefly in the upper display
and “SELF” appears in the lower display as Figure #8 shows. Then the
Speed Mode will be active and the Speed Measurement Screen (page 16)
will be displayed.
•
If all tests do not prove positive, the appropriate error code will appear
in the upper display (page 15).
Powering OFF the TruSpeed
1. Press and hold the button for approximately 3 seconds.
LIf the instrument fails the Self Test:
1. Press the button to power OFF the TruSpeed.
2. Press the button to once again power ON the
TruSpeed and repeat the Self Test.
¶If the error repeats and you need assistance, contact LTI.
See the inside front cover for LTI contact information.
LTo help save its batteries, the TruSpeed has a factory-defined power
OFF interval. The instrument will automatically power OFF if there is no
activity for a period of 15 minutes. Instrument activity includes any
button presses.
Figure #8

Section #1 - Getting Started
Page 11
Understanding the Display Indicators
Figure #9 shows the LCD Screen.The table
below lists the display indicators and the
function of each. These are presented in
order of location on the screen, from left to
right starting in the upper left corner.
Display
Indicator Function Explanation
Display
Backlight
Visible: The LED backlight is ON.
Not Visible: The LED backlight is OFF.
Upper
Display Provides access to speed measurements and messages.
Speed
Units MPH: Miles per Hour. km/h: Kilometers per Hour.
Test
Mode The instrument’s Test Mode is active (page 24).
Continuous
Mode The instrument’s Continuous Mode is active (page 22).
Weather
Mode The instrument’s Weather Mode is active (page 21).
Lower
Display Provides access to range measurements and messages.
Range
Units
F: Feet.
m: Meters.
Laser
Fire The instrument’s laser is firing.
Battery Identifies the approximate current
battery voltage. The indicator shown
here represents 100%-67% battery
life (page 9).
Figure #9

Laser Technology, Inc. LTI 20/20 TruSpeed User’s Manual
Page 12
Miscellaneous Display Features
The table below lists the miscellaneous display features.
Display
Feature Explanation Refer to Pages
bAtt
CHAng You must replace the batteries. Appears in the upper and lower displays. 9
br xx The in-scope aiming reticle’s intensity
setting. Appears in the upper display. 13
-d1- Delta Distance Test - Distance #1. Appears
in the upper display. 29
-d2- Delta Distance Test - Distance #2. Appears
in the upper display. 29
dEF
CLEAr The factory default settings have been restored. Appears in the upper and lower
displays.
13
E xx Error Code. An error condition has occurred
during a speed measurement attempt or in
the system hardware. Appears in the upper
display.
15
PASS Successful completion of the instrument
Self Test. Appears in the upper display. 30
SELF The instrument is performing (or has
performed) the instrument Self Test.
Appears in the lower display.
30
SN Serial Number. “SN” appears in the upper
display. The serial number associated with
the unit appears in the lower display.
30
tt The instrument’s test tone is active. Used
during the Scope Alignment Test. Appears
in the upper display.
25

Section #1 - Getting Started
Page 13
Adjusting the Aiming Reticle's Intensity
The in-scope aiming reticle has eight intensity settings from DIM (01) to
BRIGHT (08).
1. Press the button. The display
should look similar to Figure #10.
The factory default setting is
"br 05" as shown in the figure.
2. Press the button until the
desired setting is achieved. It's
easy to get the desired setting if
you look through the scope while
making the adjustment.
¶Each time you press the button, the "br xx" value
increases by 1.
¶If you press the button while "br 08" is displayed,
you will see "br 01" next.
3. Press the TRIGGER to return to the measurement mode that was most
recently active.
Restoring Factory Default Settings
1. Verify that the TruSpeed is powered ON.
2. Simultaneously, press and hold the
button and the button until
“dEF CLEAr” appears on the screen.
The display should look like Figure #11.
3. Release both buttons. The Speed Mode
will be active and the Speed
Measurement Screen will be displayed.
L• Powering OFF the instrument does not change this setting. The
next time the instrument is powered ON, the setting will be the
same.
Figure #10
Figure #11

Laser Technology, Inc. LTI 20/20 TruSpeed User’s Manual
Page 14
Listening to the TruSpeed
The TruSpeed emits a variety of beeps and tones during use. The sounds vary
and depend on what the instrument is doing. The table below lists and explains
each of the sounds.
Understanding Error Conditions
Although it’s rare, error conditions can occur during a measurement attempt or in
the system hardware. To make sure that you never get an erroneous speed
reading, the TruSpeed monitors both the system hardware and the measurement.
When the instrument detects an error condition, it displays an error code instead
of a measurement.
Figure #11 shows an example of an error
code, “E 03” Measurement error - unstable
targeting.
Sound Explanation
3 Low-Pitched and
1 High-Pitched Beeps At Power ON.
Low-Pitched Growl The instrument is attempting to lock onto a
target.
1 Low-Pitched and
2 High-Pitched Beeps The instrument was not able to complete the intended speed measurement due to an error.
An error code will be displayed to the indicate
the nature of the error (page 15).
High-Pitched
Double Beep The instrument successfully completed the intended speed measurement.
High-Pitched
Triple Beep The laser’s return sensor detected interference from a light source such as a xenon headlight
or laser jammer device. The speed reading is
valid.
High-Pitched
Oscillating Ring Jam tone. The instrument’s laser return sensor is being overwhelmed by interference from a
light source such as a headlight or laser jammer
device.
Low-Pitched
Single Beep At Power OFF.
Figure #11

Section #1 - Getting Started
Page 15
Error Codes
The table below lists and explains each of the possible error codes.
**See inside front cover for LTI contact information.
RFI Considerations
The TruSpeed does not display a specific error message indicating the presence of
radio frequency interference (RFI). The instrument's electronics have been
designed for optimum RFI immunity. If RFI is present, the instrument displays an
error code. The exact code depends on the level and nature of the RFI.
Code Explanation
E 01 Measurement Error - the target was out of range or was too
close.
E 02 Measurement Error - insufficient data. The unit does not have
enough data to measure speed.
Possible Cause: early release of the TRIGGER or time-out.
E 03 Measurement Error - unstable targeting. Data is not stable
enough to measure speed.
Possible Causes: poor aiming or panning off the target.
Measurement Error - low level of interference from a light
source such as a xenon headlight.
E 07 Jam Detect - high level of interference from a light source
such as a xenon headlight.
E 52 Temperature too cold. Stop operation.
E 53 Temperature too hot. Stop operation.
E 55 E57
E 56 E58 Calibration Errors. Please turn OFF unit and try again. If the same error is continuously repeated, please contact
LTI.
**
E 60 Memory failure. Please turn OFF unit and try again. If the
same error is continuously repeated, please contact LTI. **
E 62 Receiver Failure. Please turn OFF unit and try again. If the
same error is continuously repeated, please contact LTI.
**
E 99 General System Failure. Please contact LTI. **

Laser Technology, Inc. LTI 20/20 TruSpeed User’s Manual
Page 16
Section #2 - Speed Measurements
When you power ON the TruSpeed the instrument will perform the Self Test.
Figure #12 shows successful completion of the Self Test. See page 30 for more
information about the Self Test.
The next screen is automatically displayed and should look similar to Figure #13.
• The dashes that appear in the upper display indicate where the
speed measurement will appear.
• “MPH” means the speed will be measured in miles per hour.
• The dashes that appear in the lower display indicates where the distance
to the target vehicle will appear.
• "F" means the distance will be measured in feet.
• The Battery Icon indicates the approximate battery voltage
level (page 9).
Figure #12
Figure #13

Section #2 - Speed Measurements
Page 17
Taking a Sample Measurement
1. Ensure that the TruSpeed is powered ON and that the Speed Mode is
active.
2. Use the sighting scope and aiming reticle to aim the instrument to a
convenient target - an interior wall will do.
3. To fire the laser:
¶Press and hold the TRIGGER. The laser will fire after a short delay
(about one-half of a second).
-or-
¶Press the TRIGGER twice.
The 1st press turns on the in-scope aiming reticle.
The 2nd press takes the measurement.
4. Continue to press the TRIGGER and keep the instrument sighted on the
target:
¶A low-pitched growl means that the instrument is attempting to lock
onto the target.
¶1 Low-Pitched and 2 High-Pitched Beeps mean that a measurement
error occurred. An error code will be displayed (page 15).
¶2 high-pitched beeps mean that a speed was captured. The
measured speed will be displayed on the LCD screen and will be
projected in the scope, just below the aiming reticle.
After you release the
TRIGGER, the instrument will
display the most recent speed
reading and the distance at
which it was captured. The
display screen will look similar
to Figure #14. If you did not
capture a speed, an error code
will be displayed (page 15).
Choosing a Roadside Location
When choosing a spot on the side of the road for measuring moving vehicles, you
will need to consider:
• Is the location safe?
• Do you have a clear line of sight?
• What is the approximate angle between the instrument's position and
the target vehicle's direction of travel?
• What is the approximate distance to the target vehicles?
• How is the weather? Will you need to use the Weather Mode?
Figure #14

Laser Technology, Inc. LTI 20/20 TruSpeed User’s Manual
Page 18
Line of Sight
Ideally, you should have a clear line of sight to the target vehicle.
•
If there is a momentary break in the beam, the instrument will
accumulate data and may be able to capture the target vehicle's speed.
The instrument will display an error code if it cannot capture the target
vehicle's speed.
•
If there is an extended break in the beam, the instrument will display an
error code.
The Cosine Effect
If the target vehicle is moving directly toward or away from you, the speed
measured by the TruSpeed is identical to the vehicle's true speed. However, the
instrument is usually set up on the side of the road for safety. This results in an
angle between the instrument's position and the target vehicle's direction of
travel. When the angle is significant, the measured speed is less than the target's
true speed. The phenomenon is known as the cosine effect. Cosine is the
trigonometric function that relates to this phenomenon.
The difference between the measured speed and the true speed depends upon
the angle between the instrument's ideal position- the position where targets
would be moving in direct line with the instrument- and its actual position.
Measured Speed by Angle: The Cosine Effect:
L• The larger the angle, the lower the measured speed.
• The effect always works to the motorist’s advantage.
• Loosely speaking, the cosine effect is not significant as long as the
angle remains small. The table below shows this effect.
Angle
(degrees) True Speed
30 MPH 40 MPH 50 MPH 60 MPH 70 MPH
Measured Speed (MPH)
0 30.00 40.00 50.00 60.00 70.00
1 29.99 39.99 49.99 59.99 69.99
3 29.96 39.94 49.93 59.92 69.90
5 29.89 39.85 49.81 59.77 69.73
10 29.54 39.39 49.24 59.09 68.94
15 28.98 38.64 48.30 57.94 67.61
20 28.19 37.59 46.99 56.38 65.78
45 21.21 28.28 35.36 42.43 49.50
90 00.00 00.00 00.00 00.00 00.00