atmos:535:projects:sr50_sonic_ranging_sensor
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atmos:535:projects:sr50_sonic_ranging_sensor [2008/12/11 17:12] – rjohnson | atmos:535:projects:sr50_sonic_ranging_sensor [2020/01/29 17:25] (current) – external edit 127.0.0.1 | ||
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+ | ====== SR50 Sonic Ranging Sensor ====== | ||
+ | * Manafacturer: | ||
+ | * Model Number: SR50 | ||
+ | |||
+ | --- //[[|Randy Johnson]] 2008/12/11 11:46// | ||
+ | |||
+ | ===== Description ===== | ||
+ | |||
+ | ==== Cost ==== | ||
+ | |||
+ | ==Initial Cost:== | ||
+ | * Instrument: ~$1000 | ||
+ | * Data Logger: ~$400 | ||
+ | * Cable: ~$0.58/foot | ||
+ | |||
+ | ==Maintenance: | ||
+ | *The maintenance on the SR50 Sonic Ranging Sensor should be minimal. | ||
+ | |||
+ | *The silica gel desiccant is used insure a dry environment for the electronics and the electrostatic transducer inside the SR50 Sonic Ranging Sensor. | ||
+ | |||
+ | ==== Measurement Physics ==== | ||
+ | |||
+ | ===Purpose: | ||
+ | |||
+ | *The SR50 Sonic Ranging Sensor is a device that is used to measure distance by using ultrasonic sound waves. | ||
+ | |||
+ | ===Production of Ultrasonic Sound:=== | ||
+ | |||
+ | *An electrostatic transducer is a device that is capable of converting electrical signals into ultrasonic sound waves. | ||
+ | |||
+ | {{atmos: | ||
+ | |||
+ | *The image located above reperesents the construction of an electrostatic transducer. | ||
+ | |||
+ | *The gold foil and the aluminum plate are connected to a 50 kHz signal generator. | ||
+ | |||
+ | *The electric field that is formed between the two parallel plates causes an attractive force between these plates. | ||
+ | |||
+ | *Now that an attractive force has been established between the gold foil plate and the aluminum plate the two plates want to physically move closer to one another. | ||
+ | |||
+ | *Because the electrostatic transducer is being driven by a 50 kHz signal generator which produces a sinsusoidal signal in time, there comes a point at which no voltage is applied to either the gold foil or the aluminum plate. | ||
+ | |||
+ | *Next, the 50 kHz signal applies a positive voltage to the aluminum plate and a negative voltage to the gold foil plate. | ||
+ | |||
+ | *It is easy to see that the gold foil plate is constantly moving toward and away from the aluminum plate. | ||
+ | |||
+ | ===Detection of Ultrasonic Sound:=== | ||
+ | |||
+ | *The electrostatic transducer is also capable of detecting ultrasonic sound. | ||
+ | |||
+ | ===Measuring Distance with Sound:=== | ||
+ | |||
+ | *The electrostatic transducer can both produce sound waves and detect them. The SR50 Sonic Ranging Sensor takes advantage of that fact to use the electrostatic transducer to measure distance. | ||
+ | |||
+ | *Using this time the Sonic Ranging Sensor calculates a round trip distance by using the simple fact the distance = rate x time. The rate in this equation is simply the speed of sound in air. Dividing the round trip distance by two allows the Sonic Ranging Sensor to deliver the distance to the target. | ||
+ | |||
+ | *One important thing to note is that the speed of sound in air is dependent upon the temperature of the air. For this reason the SR50 Sonic Ranging Sensor needs an independent temperature reading. | ||
+ | |||
+ | {{atmos: | ||
+ | |||
+ | ===Measuring Snow Depth=== | ||
+ | |||
+ | *To effectively measure the snow depth two measurements must be taken. | ||
+ | |||
+ | {{atmos: | ||
+ | |||
+ | *The second distance that must be measured is the distance from the sensor to the top of the snow. Subtracting the distance to the snow from the distance to the ground yields the snow depth. | ||
+ | |||
+ | |||
+ | === Performance Characteristics ==== | ||
+ | |||
+ | {{atmos: | ||
+ | |||
+ | *The performance characteristics listed above were taken from the SR50 Sonic Ranging Sensor Instruction Manual produced by Campbell Scientific, Inc. To download the instruction manual and to find more information about the Sonic Ranging Sensor from Campbell Scientific the following website will prove helpful: http:// | ||
+ | |||
+ | ==== Field projects ==== | ||
+ | |||
+ | *The SR50 Sonic Ranging Sensor is being used or has been used at many field sites. | ||
+ | *One such field site is the Surface Transportation Weather Research Center' | ||
+ | *This field site has four SR50 Sonic Ranging Sensors. | ||
+ | *Below is data taken from three of those sensors on January 1, 2007 from 12:00:00 AM to 12:59:00 AM. | ||
+ | |||
+ | {{atmos: | ||
+ | |||
+ | *The measurements shown were taken once a minute for one hour. | ||
+ | *These data indicate that there was a large variation in the snow depth over the area of interest. | ||
+ | *The other thing to consider is that perhaps the sensors were not calibrated correctly. | ||
+ | *The table below shows the average snow depth for each sensor during this time period and the standard deviation for each sensor. | ||
+ | |||
+ | {{atmos: | ||
+ | |||
+ | *One can see that the standard deviations are all under 1 cm. This is a good sign because the accuracy of this instrument is supposed to be within 1 cm or 0.4% of the distance measured (whichever is greater). | ||
+ | *Below is an example of what the data looks like when it comes in from the SR50 and the data logger and has been transferred to an Excel file. | ||
+ | |||
+ | {{atmos: | ||
+ | |||
+ | |||
+ | ==== Documentation ==== | ||
+ | |||
+ | *SR50 Sonic Ranging Sensor Instruction Manual from Campbell Scientific, Inc. www.campbellsci.com/ | ||
+ | *Surface Transportation Weather Research Center (STWRC) Buxton Field Site Snow Depth Data for SR50 January 2007. | ||
+ | |||
+ | ==== Reference ==== | ||
+ | |||
+ | *Campbell Scientific, Inc. http:// | ||
+ | *SensComp: | ||
+ | *http:// | ||
+ | *http:// | ||
+ | *PhysicsForums: | ||
+ | *Dr. Matt Nolan, University of Alaska Fairbanks: http:// | ||
+ | *Jennifer Hershey, STWRC Field Site Manager | ||
+ | *Special Thanks: | ||
+ | *Jennifer Hershey | ||
+ | |||
+ | ===== Calibration ===== | ||
+ | |||
+ | ==== Method ==== | ||
+ | |||
+ | *The SR50 Sonic Ranging Sensor can measure distances between 0.5 meters and 10 meters. | ||
+ | |||
+ | *The SR50 Sonic Ranging Sensor also relies on an independent temperature reading. | ||
+ | |||
+ | ==== Sources of Error ==== | ||
+ | |||
+ | *There are several ways in which error can be introduced into the measurements taken by the SR50 Sonic Ranging Sensor: | ||
+ | *Error in the Independent Temperature Reading | ||
+ | *Tilted Instrument | ||
+ | *Obstructed View | ||
+ | *Uneven Target Surface | ||
+ | *Small Target | ||
+ | *Poor Sound Reflectors | ||
+ | |||
+ | ==== Calibration Checked ==== | ||
+ | |||
+ | *In order to check the calibration, | ||
+ | |||
+ | ==== Exposure Requirements ==== | ||
+ | |||
+ | *The SR50 Sonic Ranging Sensor was built to endure harsh environments. | ||
+ | *The sensor was designed to operate from -45< | ||
+ | *If one is measuring snow depth, one should take into account effects such as snow drift. | ||
+ | *Obstructive Objects must also be taken into account: | ||
+ | *Fences will gather more snow near them because of the wind. Placing a sensor near a fence will result in higher than normal snow depths. | ||
+ | *Trees will prevent the accumulation of snow from underneath their branches. | ||
+ | *The SR50 Sonic Ranging Sensor must also be supported by good, strong, stable supports. | ||
+ | |||
+ | ===== Deployment ===== | ||
+ | |||
+ | ==== Measurement Methods ==== | ||
+ | |||
+ | === Deployment Platforms ==== | ||
+ | |||
+ | *The SR50 Sonic Ranging Sensor can be deployed in many different platforms. | ||
+ | *The SR50 could be used to detect a change in water levels. | ||
+ | *The SR50 is also used to measure snow depths for surface transportation research. | ||
+ | *The SR50 is even used in the study of glaciers. | ||
+ | |||
+ | |||
+ | === Communication ==== | ||
+ | |||
+ | *Communication with the SR50 Sonic Ranging Sensor is vital. | ||
+ | *CR10(X) | ||
+ | *CR500 | ||
+ | *CR510 | ||
+ | *CR23(X) | ||
+ | *BDR320 | ||
+ | *CR200 | ||
+ | *Data loggers are responsible for retrieving the data from the Sonic Ranging Sensor and delivering the information to a personal computer. | ||
+ | |||
+ | ==== Power and Installation ==== | ||
+ | |||
+ | *Requires 9-16 volts D.C. | ||
+ | *Consumes 2mA (quiescent) or 250mA (peak). | ||
+ | *Must have a clear cone radius. | ||
+ | *The SR50 Sonic Ranging Sensor must also be properly mounted. | ||
+ | |||
+ | ==== System Automation ==== | ||
+ | |||
+ | *The SR50 can be programmed to take data automatically. | ||
+ | |||
+ | |||
+ | ===== Data ===== | ||
+ | |||
+ | ==== Quality Control ==== | ||
+ | |||
+ | *The SR50 Sonic Ranging Sensor has several quality control measures: | ||
+ | *If the distance to the target is moving by more than 4 cm/sec then the reading is rejected (another important reason to make sure the instrument is stably supported). | ||
+ | *If the SR50 fails to detect an echo then a 0 is returned for the distance. | ||
+ | |||
+ | ==== Quality Assurance ==== | ||
+ | |||
+ | *There is an option for the data to return with quality numbers. These numbers range from 162 to 600. | ||
+ | *162 - 210: Means the target was well defined. | ||
+ | *210-300: Means the target was not clearly defined. | ||
+ | *300 - 600: Means the target was of poor quality. | ||
+ | *High numbers can be caused by little sound reflection or an uneven target surface. | ||
+ | |||
+ | |||