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Acuity laser sensors are precision measuring devices manufactured by Schmitt Measuring Systems, Inc. Acuity products include CMOS detector laser displacement sensor models for accurate measuring and a laser rangefinder for long-distance sensing. Our laser measurement tools are made in the United States and are used by worldwide customers in forest products, metal working, medical and heavy industrial applications.

Acuity laser measurement sensors include over twelve varieties of laser triangulation sensors, three long-range laser rangefinders and a versatile laser line scanner.

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The AR200 Laser Measurement Sensor

The AR200 laser measurement sensor is Acuity's most compact product to employ a CMOS detector. Four metric models satisfy precision measuring requirements from 6 mm to 50 mm with up to 12 micron accuracy.

Applications:

• wafer fabrication
• steel strip mill

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Acuity laser displacement sensor

The AR600 Laser Displacement Sensors are a series of high accuracy measuring devices for industrial application. Models vary in measuring range and can achieve resolutions better than 1.0 micron. The AccuRange 600 models are often used in metal working and forest products industries.

Applications:

• metals industry
• lumber
• road profiling
• thickness measurement
• concrete block profile

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Acuity AR4000 Series

Acuity AR4000 series of laser rangefinders can accurately measure distances up to 54 feet (16.5m). These unique devices employ time-of-flight measurement principles with concentric emitters and collectors. When designated with the optional high power laser and band pass filter, the AR4000-LIR is used outdoors in bright sun light.

Applications:

• hoist
• sawmill automation
• bridge height clearance
• cattle industry

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The AccuRange Line Scanner

The AccuRange Line Scanner is precise spinning mirror assembly that when coupled with Acuity's laser rangefinder, creates a laser scanner. The laser scanner sweeps a laser spot through a 360° rotation for the measuring of profiles and scenes. The AccuRange line scanner is often further integrated to creat 3D laser scanners.

Applications:

• sawmill optimization and bucking
• 3D laser scanners
• 3D images
• scanning logging trucks
• truck trailer profiling
• coke drum inspections
• energy research

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All sensors require some laser light to return to them from the target surface in order to function. The amount of light needed is a measure of the sensitivity of the device. In general, the most sensitive devices are the most costly, and accurate measurements at high sample rates require stronger reflection than for lower sample rates.

For diffuse targets, the higher the reflectance of the target, the better a sensor's performance will be. Light materials such as wood, paper, or white paint are uncooperative targets that work well at all distances. The darkest coal-black materials 50 feet from a rangefinder may return only one ten-millionth of the light that reaches them to a rangefinder. Maximum range and depth of field may be limited to as little as 1/5 of what is possible with ordinary, light-colored surfaces.

In addition to the amount of light a surface reflects, the way in which light is reflected can affect an optical sensor's performance. Many surfaces are partially specular and partially diffuse. These can be difficult to measure, and the amount of light or returned to a sensor may vary greatly with the angle of the target surface.

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Quantifying Sensor Performance
The accuracy of a sensor is a measurement of the difference that can be expected between a sensor's reading and the actual distance measured. The resolution is the smallest change in distance that a sensor can detect, and is typically a smaller value than the accuracy error. Accuracy may be affected by temperature, target reflectance or ambient light, which generally will not affect the resolution. The AR4000 laser rangefinder has a basic resolution limit of .012 inch (0.3 mm) for a single sample, with accuracy of 0.1 inch (2.5 mm). For many applications, resolution is more important than absolute accuracy. The AR600 and AR200 laser displacement sensors have accuracies which are +/- 0.1% and +/- 0.2% of their measuring spans, respectively. In general, laser sensor manufacturers may interchangably use the terms Accuracy and Linearity although, linearity is a term most often associated with analog measuring devices.

Repeatability is a measure of sensor stability over time. Typically, sample to sample repeatability will be lower for very fast sample rates, since less time is used to average the measurement. As the sample rate is lowered, repeatability will improve, but this does not continue indefinitely. Beyond some slower sample rate, repeatability will start to worsen as long term drift in the components and temperature changes cause changes in the sensor's output.

Laser Spot Size And Impact On Performance
Other specifications which may be important are the laser spot size and the divergence of the beam. Some applications require a small spot for high-resolution measurement while others require a larger diameter spot for averaging rough surfaces or for eye safety concerns. A small, focussed laser spot will help to resolve tiny features on a target's surface. A large spot will reflect off larger areas which may contain features at several different heights. The reported distance would be the average of those individual heights or simply the spot that returns the most light to the detector (usually the highest peak).

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The AR4000 laser rangefinder has a spot size of 0.1 inches (2.5 mm) at the sensor's face. Over the measurement range, the laser diverges and the spot gets larger. The divergence is 0.5 milliradians. As an example, the spot size at 54 feet (the sensor's maximum calibrate range) would be: 0.1 inch + 648 inches X 0.0005 = 0.424 inches [calculator should be in radian mode]

The AR600 and AR200 triangulation laser sensors use a different optics scheme than the AR4000 rangefinder. The laser spot is smallest when focussed at the standoff distance. The standoff distance is the distance from the face of the sensor to the middle of the span. The laser beam diverges on both directions from the standoff. When reading any laser sensor specification, note the laser spot size at the standoff and the ends of the span.

For more information visit the Acuity Website.