Installation And Checkout Using The Power Computer Science Essay

Published Date: 02 Nov 2017

Introduction

This section is a guide to getting started with the AR200 and this manual. The AR200 has

a number of configurable parameters, but many applications can use the sensor in its

default factory configuration.

The recommended order for reading the manual is:

• Quick Start Instructions

• General Description

• Operating Guidelines

• Installation and Checkout using the Power and Interface section as a reference

This should provide the information necessary to connect the sensor and verify its

operation, either with a serial terminal program at 9600 baud, or by connecting the current

loop interface.

To understand more about the serial configuration options, read the Serial Communications

chapter. For details on the current loop, voltage, and limit switch outputs, read the chapter

titled Analog Output.

For custom configuration, the AR200 Command Set section provides information on

setting up the AR200 for specific application requirements. The remaining sections deal

with specifics of the outputs and with general performance characteristics of the sensor.

1.1. Quick Start Instructions

Mount the sensor in such a way that the case is not twisted or warped. Using three hard

points along the front and back edges or a slightly compliant mounting system are the best

methods. Do not clamp or squeeze the sensor case excessively. If the case is distorted, the

sensitivity and accuracy of the sensor may be affected.

Connect the red (+) and black (Ground) wires of the power/signal cable to a 12 to 30 volt

power supply (15 volts is suggested for best power efficiency), or plug in the power supply

if the sensor came with one.

1.1.1. Analog and Limit Switch Signals

In 4-20mA analog output mode, the orange wire is the current output, and the brown wire is

current return. These may be connected to a resistor such as 500 ohms to get a 2 to 10 volt

signal, or connected to a current meter.

In 0-10V analog output mode, the orange wire is the voltage output, and the brown wire is

current return. These may be connected to a resistor 1.3K ohms or larger to get a 0 to 10

volt signal.

In NPN limit switch output mode, the orange wire is limit switch 1 output and the brown

wire is limit switch 2 output. When the switch is active, the output will sink up to 150mA

to the black (Ground) wire. When the switch is not active, the output will be high

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impedance and no current will flow through it. These outputs may be connected through a

resistance to a voltage between the supply and ground. The resistance should be chosen

such that the outputs sink no more than 150mA.

In PNP limit switch output mode, the orange wire is limit switch 1 and the brown wire is

limit switch 2 output. When the switch is active, the output will source up to 150mA

through the red (+) wire. When the switch is not active, the output will be high impedance

and no current will flow through it. These outputs may be connected through a resistance

to a voltage between the supply and ground. The resistance should be chosen such that the

outputs source no more than 150mA.

1.1.2. Serial Data Wires

The serial data wires may be connected to a standard PC port if the serial LED indicates

RS-232 mode. The output from the sensor may be viewed with a terminal emulator such as

Windows HyperTerminal.

When power is applied the function LED on the sensor will light, and if a target surface is

placed in the measurement range of the sensor, the sensor will print distance to the target

from the start of the measurement range, in inches, 5 times per second. If there is no target

in the measurement range, the sensor will output zeros (or occasional random readings if

outside lighting is changing rapidly), and the laser will flash 10 times per second.

1.1.3. Important Configuration Considerations

There are 3 sensor configuration commands that significantly affect operation. Satisfactory

operation for specific applications will only be attained with appropriate configuration

settings. See the AR200 Command Set section for details on configuring the sensor.

Background Light Elimination On/Off When Background Light Elimination is on (the

factory default) the sensor captures 2 images, one with the laser off and one with the laser

on, and subtracts them to reduce the effects of ambient lighting. The maximum attainable

sample rate with Background Light Elimination on is 600 samples per second, vs. 1250

with it off. On brightly lit targets performance may be improved with this setting On. If the

environmental lighting is changing rapidly, the improvement may be reduced.

Set Sample Interval The sample interval is set in tenths of milliseconds: Using 8 as the

parameter will set the sample rate to 0.8 milliseconds, or 1250 samples per second. Using

10000 will set the sample rate to once per second. For fastest output, use serial binary

format at 57,600 baud or higher or the analog output. If an analog output is selected,

disable the serial output to attain 1250 samples/second.

Set Sample Priority If the light reflected from the target is low, the time needed to take a

sample may be longer than the time set with the Set Sample Interval Command. The

Sample Priority command controls whether the sensor outputs a sample at the sample

interval programmed even if there is no sample available (Zero will be output if the

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reflection from the target is low or the target is out of the measurement range). In the

default configuration (priority given to "sample rate") if the sensor is unable to collect

enough light to obtain a measurement the sensor will output zero at the specified sample

rate. Alternatively, if this command is used to give priority to "sample quality" and the

sensor is unable to take measurements, it will reduce the sample rate. If no sample is

attained in 0.1 seconds, the sensor will put out zero even if sample quality is given priority.

Note that the current loop will hold its value until another sample is available if priority is

set to "sample quality".

See the Principles of Operation Section for more information.

Note: The laser may be turned on and off with the Sampling On/Off command.

After making changes to the configuration, it may be saved by using the Write command.

The present configuration may displayed with the Show Configuration command.

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2. General Description

The AR200 is a laser diode based distance measurement sensor for ranges from 6 to 50 mm

(models are actually quarter, half, one and two inch respectively), with 12 and 100 μm

accuracy respectively. There are four different standard models. Each model has a different

standoff (center of span) distance, full scale span, and center of span accuracy. These are

listed in the table below. For more detailed specifications see the data sheet. The standoff

distance represents the distance from the face of the sensor to the center of the

measurement range. For the AR200 sensor, the standoff specification is approximated.

Model Standoff [mm]

(approximate)

Span [mm] Linearity/

Accuracy [μm]

AR200-6 21 6.35 +/- 12.7

AR200-12 24 12.7 +/- 25.4

AR200-25 34 25.4 +/- 50.8

AR200-50 42 50.8 +/- 101.6

2.1.Principles of Operation

The AR200 uses triangulation to measure distance. The laser beam is projected from the

housing and is reflected from a target surface to a collection lens. The lens focuses an

image of the spot on a linear array camera. The camera views the measurement range from

an angle that varies from 45 to 65 degrees at the center of the measurement range,

depending on the model. The position of the spot image on the pixels of the camera is then

processed to determine the distance to the target. The camera integrates the light falling on

it, so longer exposure times allow greater sensitivity to weak reflections.

The exposure time and laser power level are controlled to optimize the accuracy of the

measurements for the signal strength and environmental light level measured. If the sample

rate set allows time for internal averaging of multiple exposures before transmission that is

done. Exposure time and laser power are adjusted from sample to sample, so rapidly

changing conditions may result in momentary loss of signal or overexposure. If the sensor

cannot take another exposure before it is time to transmit a sample, a zero value will be

output.

As described in the Quick Start section, there are several operating mode options that

significantly affect the behavior of the sensor. The first of these is sample rate. Lower

sample rates allow more averaging of the range signal and lower noise levels. Higher

sample rates may be used when the reflected signal is relatively strong.

The sensor may be set to either wait (up to 0.05 seconds or 0.1 second if background light

elimination is on) until it has good data before updating the output, or to update the output

at the specified rate even if that interval does not permit acquisition of a good sample and a

zero must be sent.

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If high levels of ambient light are present, the use of the background light elimination mode

may improve measurement quality. In this mode a camera exposure is taken with the laser

off and subtracted from a subsequent exposure with the laser on. This will eliminate many

ambient light effects, unless the ambient light levels in the target area are changing rapidly.

In this case the light measured during the laser on exposure may be different from that

during the laser off exposure, reducing the benefits of this mode. The total time required for

obtaining a sample in this mode will be approximately twice what it is with background

light elimination off.

If the sensor cannot detect a distinct peak in the camera data or the measurement is just

beyond the end of the full scale span (but with the spot still on the camera near one end),

the sensor will output zero distance. If there is no target in the measurement range and

background light elimination is on, the sensor will generally put out zeros. However, if

lighting conditions are changing rapidly or if background light elimination is off, a bright

spot can be taken as the laser spot and a false range reading generated when there is no

target in range. For best rejection of spurious signals, the AR200 should be ordered with the

optical filter option.

The AR200 emits visible laser light (red, 650 nm wavelength). All models are Class II

laser products and are limited to 1 mW of power. The aperture warning label and product

identification placard shown below appear on the AR200 models.

Figure 1 Laser Aperture Warning Label and side placard

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2.2.Mechanical Dimensions

The following page shows the mechanical dimensions for the AR200. The rectangular

window on the front panel is the collection point for return light. Both of these areas

should have a clear path to the target throughout the full measurement span. The sensor has

two #4 (M3) clearance holes for mounting the sensor. One face of the sensor has output

selection pushbuttons. The top of the sensor has a "Function" button. The cable is for

power and communication (both serial and analog limit switch). Weights are shown on the

data sheet at the back of the manual. The outer case of the sensor is anodized aluminum.

The front windows and the end caps are sealed to the case, creating a dustproof, splash

proof enclosure.

Mechanical Dimensions

40°

20 mm

(.80")

64 mm

(2.53")

2.8 mm

(.11")

48.5 mm

(1.91")

2.8 mm

(.11")

21 mm

(.83")

9 mm

(.34")

69.8 mm

(2.75")

54 mm

(2.13")

Laser

Axis

Camera

Axis

O.D. 6.3 mm (.25") Cable,

8 Conductor

Laser &

Camera

Window

2 Mounting Holes

M3 (#4) through

3mm (.120") Dia

BLK

YEL

GRN

GRN

YEL

120 ohm

YEL

GRN

RS-422/RS-485 Term RS-485 RS-232

2

RED

BRN

1

ORNG

2

BRN

BLK

1

ORNG

NPN LS PNP LS

- +

ORNG

BRN

0-10 VDC

BRN

ORNG

4-20 mA

0 VDC: LASER Disabled

0 VDC: Buttons Disabled

12-30 VDC

Open: LASER Enabled

Open: Buttons Enabled

-

RED +

WHT

BLU

BLK AR-200-6

AR-200-12

AR-200-25

AR-200-50

MODEL No.

S/N:

COMPLIES WITH 21 CFR

1040.10 AND EN60825-1:2001

Acuity R E S E A R C H

Figure 2 Mechanical Dimensions of AR200

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2.3.Installation and safety

The AR200 sensor is typically installed by affixing the sensor to a machined bracket with

bolts through the two mounting holes in the sensor. These holes are 3 mm in diameter and

their location is shown in the mechanical drawing above. Laser light is emitted from the

top of the rectangular window, closest to the "Laser Radiation" placard. An illustration of

how light is emitted is shown below.

Figure 3 Direction of laser emission

This laser device should not be aimed at human eye. Installers of laser sensors should

follow precautions set forth by CFR 1040.10 or by their local safety oversight organization.

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3. Operating Guidelines

Use protective eyewear whenever there is a risk of being exposed to the output beam

of the AR 200. Use eyewear specifically designed to block laser radiation of the frequency

used by the sensor.

Do not point the sensor at any person, particularly a person’s eyes or face. Laser

radiation can damage the eyes without sensation or warning.

Do not attempt to disassemble the sensor. Improper disassembly will destroy the optical

alignment of the sensor and necessitate factory repairs.

Do not operate the sensor in areas where the sensor case is exposed to direct sunlight

for extended periods or where the air temperature is more than 50°C (122°F) or less

than -10°C (14°F).

Avoid excessive vibration and shocks. The sensor contains securely mounted but

precisely aligned optical components.

Do not scratch the windows on the front face of the sensor, particularly in the central

area. Keep the front windows clean with a damp cotton cloth. The windows are glass with

an anti-reflection coating. Avoid the use of cleaning solvents other than alcohol.

Operate only with DC supply voltages between 10 and 30 volts, unless the sensor came

with an AC to DC power supply.

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4. Installation and Checkout

4.1.Cabling

The AR 200 has a multipurpose cable with soldertail wires. If the AR200 is ordered with a

power supply, the power/signal cable will be connected to the power supply. Connection

and termination according to the instructions is essential for correct sensor operation. Read

the wire descriptions for connection information.

4.1.1. Standalone Cabling

To use the AR200 without a serial connection to a host computer, the only connections

necessary are the power, ground line, and the analog output connection to your data

display or recording equipment. See the Signal and Power Interface section for wire

connections. In its default configuration, the AR200 will begin measuring and

transmitting range data on power-up.

In 4-20mA analog output mode, the best accuracy and linearity for the current loop is

obtained with a 500-ohm load to current loop return at the measurement point.

In 0-10V analog output mode, the best accuracy and linearity for the voltage output is

obtained with a 10K-ohm load to the voltage output return at the measurement point.

4.1.2. Connection to a Host Computer

A 9-pin serial D-sub serial connector can be attached to the serial output wires to connect

the AR200 directly to an IBM-PC compatible 9-pin serial port. Connect a 15 volt power

supply to the power and ground lines of the Power/Signal cable. See the Signal and Power

Interface for wire connections. Only the power and ground need be connected for operation

with the serial interface. For testing use a terminal emulation program such as the

Windows HyperTerminal, set to 9600 baud, 8 bits, no parity, 1 stop bit.

4.2.Power On

When power is applied the function LED will flash briefly and then stay on, and a red laser

beam will be emitted from the front laser aperture window. The sensor will begin

transmitting range readings as soon as the laser comes on.

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4.3.Verifying Operation

In its default configuration, the AR200 transmits 5 samples per second at 9600 baud over

the serial line, and transmits measured distance over the current loop output (if installed)

with the same update rate. The current loop should put out 4 mA at zero range, and 20 mA

at full span. Check either, or both, signals to verify basic sensor operation.

4.4.Troubleshooting

The sensor displays simple error indications using the LED on the end cap. Trouble

shooting steps are shown below:

Symptom Possible Cause Correction

LED never turns on Power lines not

connected

Power lines reversed

polarity

Power supply voltage

too low or too high

Check wire connections

Check wire connections

Check power supply

voltage when loaded

No laser light and no

range data

Sampling is turned off

Power supply voltage is

too low

Ambient light level is

too high

Turn Sampling on

Check power supply

input voltage

Reduce the ambient

light level.

LED flashes

continuously at 1Hz

rate. Messages are

continuously transmitted

over the serial port. See

section on nonvolatile

memory for more detail

Configuration data lost

Calibration data lost

Press function button,

factory default

configuration is loaded

Call Acuity for

instructions

4.4.1. Serial Communications Check

If no information is received over the serial port, check the power supply and serial cable

connection. The sensor may in a configuration that prevents serial communication, such as

being set at the wrong baud rate. Turn the power off, press the function button on the

AR200, and turn the power on with the button held down. The LED should stay off until

the button is released, and then flash briefly. This will reset the sensor to the factory

default configuration (9600 baud, 8 bits, no parity, 1 stop bit), and should enable serial

communication with the host system.

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4.4.2. Range Output Check

If the range output is in error, check that the sensor and target are stationary and stable, that

the target is in the middle of the measurement span as an initial test range, and that the

beam is hitting the target