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Technical Data for the Acuity distance meter
Specifications for long-range distance measurement

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Acuity's rangfinders are very unique distance measuring devices. They employ a modified time-of-flight measurement principle that leads to very fast and accurate measuring speeds.Measurement principle of AR4000

The AR4000 differs from other long-distance rangefinders in that the laser emitter and return signal collection lens are concentric. The illustration below reveals the major functionality of the rangefinder. A collimated beam of laser light is emitted from a diode in the center of the fresnel collection lens. Light hits a target and is diffusely reflected, collected by the lens and focussed on an avalance photdiode. The AR4000 distance measuring technology is patented (US patent 5,309,212 ).

Non-contact measurement is made simple with the three models within the AR4000 rangefinder series. All models are compact and durable, residing in a NEMA-4 enclosure for challenging industrial environments.

The AR4000-LIR laser rangefinder has a working range to 54 feet (16.45 m) on light surfaces (85% diffuse reflectance, such as paper or light paint) or 35 feet on a 30% reflectance target with an accuracy of 0.1 inches (2.5 mm). It uses an infrared 780 nm 8 milliwatt laser. This is the sensor of choice for best accuracy in most applications. An optional 20 mW laser upgrades is also available for the AR4000-LIR sensor with an accuracy of 0.2 inches, for extended range to darker surfaces (54 feet on 30% reflectance) and in sunlight.
The AR4000-LV rangefinder has a working range of zero to 40 feet on 85% diffuse reflectance surfaces or 30 feet on a 30% reflectance target with an accuracy of 0.3 inches. It uses a visible 670 nm 5 milliwatt laser. This is the sensor of choice where a visible beam spot is required or your application must remain under and FDA Class IIIb laser category.
The AR4000-RET distance measuring rangefinder is used with reflective tape supplied with the sensor. It is a low-power, Class I eye-safe device, with an accuracy of 0.1 inches (2.5 mm) with a range of 2 to 54 feet (16.5 m). This is the sensor of choice where it is possible to apply the adhesive-backed retroreflective tape (3M brand) to the target surface, since this provides a strong return signal for optimum operation. We suggest using either the 3M™ Scotchlite™ High Gain Reflective Sheeting 7610 or the 3M™ Scotchlite™ Photoelectric Grade Smooth Surface Sheeting 7590 (for weather-resistant applications).

AccuRange™ 4000 rangefinder data sheet
This four-page specification brochure shares all of the technical details about the sensor includeing electrical, mechanical, software and physical specifications. The data sheet details the cabling and outputs for the sensor and gives a list of sensor input commands for configuration. The data sheet provides explanations for beam divergence and accuracy.

> Access the AccuRange 4000 laser rangefinder Data Sheet Adobe PDF file size 600 KB

Acuity's AR4000 User's Manual
This user's manual is a multi-page document which explains how to operate and install the sensor hardware. Output formats are described and sensor commands are explained at length.

> Access the AccuRange 4000 device User's Manual Adobe PDF file size 1.7 MB

Output interfaces
Acuity offers the following standard and optional outputs for the AR4000 laser rangefinder devices:

> Standard RS-232 Serial Output
> Optional RS-422 Serial Output
> Optional Current Loop Output
> Standard Voltage Signals for Signal Strength, etc.
> Optional Pulse Width Output for high speed sampling

Standard RS-232 Serial Output
All sensors come with an RS-232 serial output on a 6 foot, 9 pin cable that connects directly to PC style serial ports. Serial output can be configured for one of several data formats. ASCII may be used for visual reading with a terminal device or emulation program, or a binary format can be used with application software. The data may include calibrated distance output only, uncalibrated range and other sample data only, or both. The other sample data includes reflected optical signal strength, background light level, and internal sensor temperature. These values are also available as voltage levels on the sensor's power/signal cable. They may be used for external calibration if the sample rate is too high for each sample to be calibrated internally. When the binary format calibrated distance output only is selected, the maximum sample rate is 700 samples per second. Baud rate is selectable from 300 to 34,800 baud.

Optional RS-422 Serial Output
For long distance communications (more than 20 to 30 feet, depending on the baud rate), the RS-232 serial output may be replaced with an RS-422 serial output. The available sample rates, formats and software configuration commands are all the same as for the RS-232. The sensor can also be ordered with RS-485 (half duplex version of 422), but the AR4000 does not presently support any standard 485 network protocols.

Optional Current Loop Output
A 4-20 milliamp current output may be ordered as an option. If the AR4000 is ordered with this output it uses the same output line as the pulse width output on the power/signal cable, so 4-20 output is not available on sensors configured for the High Speed Interface. Serial I/O is still available. The zero and span for the current loop output may be set at any location, with a minimum span of 9 inches. The span point (20 mA) may be made closer than the zero point if desired. Either calibrated or uncalibrated range may be selected. If serial output is turned off, calibrated output on the current loop allows sample rates of 1000 samples per second, and uncalibrated range output allows update rates up to 3,000 samples per second. The 4-20 mA output has a maximum voltage capability of 10 volts, and it is suggested that a 400 to 500 ohm load be used at the reading instrumentation for best accuracy.

Standard Voltage Signals for Signal Strength, etc.
The AR4000 has 3 lines which transmit 0 to 5 volt analog signals representing reflected optical signal strength, ambient light in the target area, and internal sensor temperature. These may be used to monitor signal quality, and they are sampled by the High Speed Interface for high speed data acquisition. The same information is available through the serial interface; these lines provide an alternate, higher-bandwidth data path.

Optional Pulse Width Output (Standard with High Speed Interface)
All AR4000 sensors shipped with a High Speed Interface also have an uncalibrated pulse width output. The duration of the low portion of the pulse changes linearly with the uncalibrated sensor reading, and the period of the signal is controlled by the sample rate for which the sensor is configured. This output is typically used with the High-Speed Interface or application-specific hardware at sample rates beyond the 700 sample/second limit of the serial interface. Calibration may be performed externally using the signal strength and other voltage outputs in conjunction with the pulse width output.

Laser rangefinder : AR4000 equipment overview