SR50 Sonic Ranging Sensor Revision: 1/07 C o p y r i g h t © 1 9 9 5 - 2 0 0 7 C a m p b e l l S c i e n t i f i c , I n c .
Warranty and Assistance The SR50 SONIC RANGING SENSOR is warranted by CAMPBELL SCIENTIFIC, INC. to be free from defects in materials and workmanship under normal use and service for twelve (12) months from date of shipment unless specified otherwise. Batteries have no warranty. CAMPBELL SCIENTIFIC, INC.'s obligation under this warranty is limited to repairing or replacing (at CAMPBELL SCIENTIFIC, INC.'s option) defective products.
SR50 Sonic Ranging Sensor Table of Contents PDF viewers note: These page numbers refer to the printed version of this document. Use the Adobe Acrobat® bookmarks tab for links to specific sections. 1. SR50 Specifications ....................................................1 2. Introduction..................................................................2 3. Operation (General) .....................................................3 3.1 3.2 3.3 3.4 3.5 SDI-12 Operation.......................................
SR50 Sonic Ranging Sensor Table of Contents Tables 1. SR50 SDI-12 Command List ..................................................................... 9 2. Address Jumper Settings for Pulse Train and ASCII Outputs.................. 19 Appendices A. Making Concurrent Measurements with the SR50 ......
CAUTIONARY NOTES 1. The order in which the connections are made is critical. Always connect Ground first, followed by +12V and then the remaining SDI-12/Data Bus, Sensor Enable Line and Shield. When disconnecting the sensor, the reverse order should be followed. 2. Before disassembling the transducer assembly, refer to “Assembly/Disassembly Procedures” on page 24 of the manual. 3.
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SR50 Sonic Ranging Sensor 1. SR50 Specifications Power Requirements: 9-16 VOLTS D.C. Power Consumption: 2 mA (Quiescent) 250 mA (Measurement Peak) Measurement Time: 0.6 seconds typical 3.0 seconds max. Output: SDI-12 (version 1.
SR50 Sonic Ranging Sensor Measurement Range: 0.5 to 10 meters Accuracy: ±1 cm or 0.4% of distance to target (whichever is greater) requires external temperature compensation Resolution: 0.1mm Beam Acceptance Angle: Approximately 22° Operating Temperature: -45°C to +50°C Maximum Cable Length: 60 meters (SDI-12 & ASCII) 300 meters (Pulse train) Cable Type: Part number L9720, 4 conductor, 2-twisted pair, 22 AWG, Santoprene Dimensions: Length 31 cm Diameter 7.5 cm Weight: 1.3 kg 2.
SR50 Sonic Ranging Sensor 3. Operation The SR50 has several output formats: SDI-12, Pulse Train, and serial ASCII output. A group of four jumpers inside the SR50 allow setting an address for SDI-12 operation or as an option setting for Pulse Train and ASCII outputs. The SR50 performs multiple echo processing regardless of output formats. The SR50 bases every measurement on several readings and applies an algorithm to improve measurement reliability.
SR50 Sonic Ranging Sensor DISTANCE = READINGSR50 T°KELVIN 273.15 FORMULA 1. Temperature Compensation The SR50 calculates a distance reading using the speed of sound at 0°C (331.4 m/s). If the temperature compensation formula is not applied, the distance values will not be accurate for temperatures other than 0°C. A temperature compensated distance is obtained by multiplying the SR50 reading by the square root of the air temperature in degrees Kelvin divided by 273.15.
SR50 Sonic Ranging Sensor 3.1.1 SDI-12 Wiring Color Black Function Ground Datalogger Connection Ground (G) Red +12V +12V Green SDI-12 Bus Control Port White Ground Ground (G) Clear Shield Ground (G) FIGURE 1. SDI-12 Wiring CAUTION The order in which the connections are made is critical. Always connect Ground first, followed by +12V and then the remaining SDI-12/Data Bus, Sensor Enable Line and Shield. When disconnecting the sensor, the reverse order should be followed.
SR50 Sonic Ranging Sensor values that are arranged in order from closest to the furthest. If no targets were detected, the SR50 outputs three zeroes. The "10" command requests the sensor to perform a self check. This will verify the CPU operation and generate a ROM signature value to verify the software version that is in the sensor. SR50’s with software version 1.1 have Concurrent Measurement capability.
SR50 Sonic Ranging Sensor Probe is used and that the SR50 SDI-12/DATA Bus is wired to control port 1 (see Figure 2). This program is similar to that used on a CR23X. ;{CR10X} ; *Table 1 Program 01: 60 Execution Interval (seconds) ; Measure the 107 temperature probe. 1: Temp (107) (P11) 1: 1 Reps 2: 1 SE Channel 3: 1 Excite all reps w/E1 4: 1 Loc [ T_KELVIN ] 5: 1 Mult 6: 273.15 Offset ; S.E. Chan #1 used for this example ; Excite Chan #1 used for this example ; This converts the value to degrees Kelvin.
SR50 Sonic Ranging Sensor 6: Z=X*Y (P36) 1: 2 2: 5 3: 2 X Loc [[ DEPTH ] Y Loc [ MULT ] Z Loc [[ DEPTH ] 7: Z=X+F (P34) 1: 2 2: 2.0 3: 2 X Loc [ DEPTH F Z Loc [ DEPTH ] ] ; <<<<<<<<<< Insert the distance from sensor to bare ground ; This is actual snow depth. ; Hourly data output… 8: If time is (P92) ; Output data at the interval you require for your data analysis.
SR50 Sonic Ranging Sensor TABLE 1.
SR50 Sonic Ranging Sensor 3.3 Pulse Train Output This option is most commonly used with 21X or CR10s without SDI-12. The SR50 sensor can also output a pulse train to represent the distance to target value. The pulse train option outputs a series of 5 Volt pulses on the SDI12/Data Bus with each pulse representing a distance to target unit. Several options are available in the type of pulse train that is output. The pulse frequency can be selected as either 1000 Hz or 100 Hz. Selectable units are 2.
SR50 Sonic Ranging Sensor 3.3.1 Pulse Training Wiring Color Black Function Ground Datalogger Connection Ground (G) Red +12V +12V Green Data Bus Pulse Channel White Sensor Enable Control Port Clear Shield Ground (G) FIGURE 3. Pulse Train Wiring CAUTION The order in which the connections are made is critical. Always connect ground first, followed by +12V and then the remaining SDI-12/Data Bus, Sensor Enable Line and Shield. In disconnecting the sensor the reverse order should be followed.
SR50 Sonic Ranging Sensor 3.4 Two 21X Program Examples for Pulse Train Output 1 H L 2 H L 3 H L 4 H L 5 H L 6 H L 7 H L 8 H L S N 10800 6145, 6146, 6147 EXCITATION 1 2 3 4 CAO 1 2 CONTROL 1 2 3 4 5 6 PULSE INPUTS 1 2 3 4 +12 SERIAL I O I.D. DATA 21X MICROLOGGER 1 2 3 A 4 5 6 B 7 8 9 C * 0 # D MADE IN USA Green White Clear Red Black FIGURE 4.
SR50 Sonic Ranging Sensor The following instructions set the sensor enable line high long enough for the SR50 to detect it, then set it low. 1: Set Port (P20) 1: 1 2: 1 Set High Port Number 2: Excitation with Delay (P22) 1: 1 Ex Chan 2: 1 Delay w/Ex (units = 0.01 sec) 3: 0000 Delay After Ex (units = 0.01 sec) 4: 0.0 mV Excitation 3: Set Port (P20) 1: 0 2: 1 Set Low Port Number The P3 instruction counts the pulse train being transmitted from the SR50. Distance-to-surface will automatically be reset to 0.
SR50 Sonic Ranging Sensor 8: Z=SQRT(X) (P39) 1: 24 X Loc [ ATempComp ] 2: 24 Z Loc [ ATempComp ] 9: Z=X*Y (P36) 1: 21 2: 24 3: 21 X Loc [ Dis2Surf ] Y Loc [ ATempComp ] Z Loc [ Dis2Surf ] Add distance-to-ground to distance-to-snow (which is negative) to calculate snow depth. In the following instruction, Parameter 2 is a constant. You enter the distanceto-ground at your site. 10: Z=X+F (P34) 1: 21 X Loc [ Dis2Surf ] 2: 2.00 F 3: 10 Z Loc [ SnowDepth ] An hourly output example, yours may vary.
SR50 Sonic Ranging Sensor 3.4.2 Pulse Train Programming Example 2 Example 2 will measure every execution interval. This program will measure the SR50 when Flag 1 is set high, which can be done manually and/or at a specified interval. All instructions above those that define the Output Interval must remain together. Note that in this example the datalogger program executes every 10 seconds, but the SR50 measures and processes only every 15 minutes.
SR50 Sonic Ranging Sensor If Flag 2 is high, compute the air temperature compensation factor and correct the distance-to-surface measurement for air temperature (see Formula 1). 3: If Flag/Port (P91) 1: 12 Do if Flag 2 is High 2: 30 Then Do 4: Z=F (P30) 1: 273.
SR50 Sonic Ranging Sensor Parameter 2 of P92 determines how often to measure. 12: If time is (P92) 1: 0 Minutes into a 2: 15 Minute Interval 3: 11 Set Flag 1 High 13: If Flag/Port (P91) 1: 11 Do if Flag 1 is High 2: 30 Then Do Enable the sensor by pulsing Control Port 1. 14: Set Port (P20) 1: 1 Set High 2: 1 Port Number 15: Excitation with Delay (P22) 1: 1 Ex Chan 2: 1 Delay w/Ex (units = 0.01 sec) 3: 0000 Delay After Ex (units = 0.01 sec) 4: 0.
SR50 Sonic Ranging Sensor -Input Locations10 SnowDepth 21 Dis2Surf 22 T_Kelvin 23 273_15 24 ATempComp 25 Temporary 3.5 ASCII Output The SR50 sensor is also capable of outputting data in printable ASCII format. With the ASCII output option, serial ASCII data (0 and 5 volt levels only) is output on the SDI-12/Data Bus. Several options define the type of ASCII data output. The baud rates of 300 and 1200 can be selected as either TTL or RS232 logic levels. The baud rate of 9600 can only be selected as RS-232.
SR50 Sonic Ranging Sensor TABLE 2. Address Jumper Settings for Pulse Train and ASCII Outputs ADDRESS OUTPUT FORMAT 0 Pulse Train 1000 Hz 2.5mm/Pulse 1 Pulse Train 100 Hz 2.5mm/Pulse 2 Pulse Train 1000 Hz 1cm/Pulse 3 Pulse Train 100 Hz 1cm/Pulse 4 Pulse Train 1000 Hz 0.1 inch/Pulse 5 Pulse Train 100 Hz 0.
SR50 Sonic Ranging Sensor HEIGHT 22 Deg. RADIUS FIGURE 5. SR50 Cone Angle The SR50’s mounting stem (1.25” outside diameter) enables various installation options. A 3/4” x 1” pipe crossover (model L1049, 1.25” x 1” inside diameter) enables the SR50 to mount to any 3/4” pipe (1” outside diameter). The SR50’s mounting stem also has 1” pipe thread to accommodate other threaded installation options.
SR50 Sonic Ranging Sensor Clamp 120 L1049 2.3 Meter 1-1/4 Inch Pipe FIGURE 6b. SR50 Tower Mount The SR50 should be mounted perpendicular to the target surface. If the sensor is mounted at an angle, it will reduce the sensor’s ability to detect the target surface. Figure 7 demonstrates the difference between an SR50 that is mounted properly and one that is not. Perpendicular mounting and maintaining an unobstructed path are both demonstrated.
SR50 Sonic Ranging Sensor Unobstructed Path 22 Deg. 22 Deg. Perpendicular to Surface 22 Deg. 22 Deg. FIGURE 7. SR50 Mounting Considerations 5. Data Interpretation The SR50 makes use of an effective algorithm to help prevent false readings and to improve the sensor accuracy. Retries and sensitivity adjustments are also part of the echo detection algorithm. It is important to remember that under certain circumstances the SR50 may not be able to obtain a reading.
SR50 Sonic Ranging Sensor If multiple targets are requested, the distance values will be reported from closest target to furthest. When using multiple target detection, it is also possible for a sound wave to travel out to the target and back twice which results in the second or third distance to target being approximately twice that of the first target distance (multiples). Target quality numbers can also be recorded when using the SDI-12 or ASCII output option.
SR50 Sonic Ranging Sensor 7. Assembly/Disassembly Procedures It is important to follow these instructions to disassemble the SR50. Disassembly is required to change the Address/Option jumpers and to inspect or replace the desiccant. There are two small packages of desiccant inside the transducer housing as well as desiccant inside the electronics enclosure (Refer to Figure 8). IMPORTANT NOTES Before proceeding with any maintenance on a data acquisition system, always retrieve the data first.
SR50 Sonic Ranging Sensor 1. If the sensor is in operation, always disconnect the SR50 from the datalogger before disassembling. 2. To remove the transducer housing, undo the four Phillips screws which are located at the bottom end of the sensor (These are the screws which are countersunk most into the housing identified by the arrows below). 3. The transducer and mount should now fall out. This will expose the desiccant that is in the transducer housing.
SR50 Sonic Ranging Sensor .0033 F P7 F IM 1% IM 1% 100 S7 T7 Y3 N13 013 P13 013 1.8K R13 T10 .047 F X11 IN4001 20 1/2W V13 T13 1M 1% 10K 1% 10K 1% 402K 1% 40.2K 2% 210K 1% 620K 1% 40.2K 1 4.7K 620K 1% 0.01 F F13 W13 V10 2N6034 220K G12 0.1 F LT1086-5 Y12 R10 F IRFD113 S10 1.8K LM2901N Y8 1.5KE20CA T11 10K P10 220K K10 68HC71103 IN4148 G10 1000pf IN4148 R11 1 TI578A F 5% D10 1000pf X3 1 S11 N12 3300pF 0.
Appendix A. Making Concurrent Measurements with the SR50 Concurrent Measurement ability allows the datalogging system to initiate measurements in SDI-12 devices and continue processing its program without waiting for a reading from the SDI-12 device. When the sensor has a valid measurement it will send this to the datalogger the next time it is polled. This allows for faster execution of the datalogger program. Concurrent measurement ability is available with SR50’s with OS version 1.1 or higher.
Appendix A. Making Concurrent Measurements with the SR50 Place measurement in Loc X. If measurement is > -1000 then use measurement Else Add 1 to a counter If the counter = 3 (means there were 3 bad readings in a row) then do: Use bad reading for measurement. Reset counter. Example Program: In this example, an SR50 is mounted 2 meters above the ground. Snow depth and measurement quality numbers are the desired output.
Appendix A. Modifying the Non-Volatile Memory 4: If (X<=>F) (P89) 1: 3 X Loc [ Raw_Dist ] 2: 3 >= 3: -1000 F 4: 30 Then Do 5: Z=X (P31) 1: 3 2: 8 X Loc [ Raw_Dist ] Z Loc [ DEPTH ] 6: Z=X (P31) 1: 4 2: 9 X Loc [ Raw_Qual ] Z Loc [ QUALITY ] 7: Z=F x 10^n (P30) 1: 0.0 F 2: 00 n, Exponent of 10 3: 5 Z Loc [ FAILCOUNT ] 8: Else (P94) ; If the measurement was not valid, increment the failure counter.
Appendix A. Making Concurrent Measurements with the SR50 14: End (P95) 15: End (P95) ; Apply air temperature correction to the reading... 16: Z=F (P30) 1: 273.15 F 2: 0 Exponent of 10 3: 6 Z Loc [ REF_TEMP ] 17: Z=X/Y (P38) 1: 2 X Loc [ T_KELVIN ] 2: 6 Y Loc [ REF_TEMP ] 3: 7 Z Loc [ MULT ] 18: Z=SQRT(X) (P39) 1: 7 X Loc [ MULT 2: 7 Z Loc [ MULT ] ] 19: Z=X*Y (P36) 1: 8 X Loc [ DEPTH 2: 7 Y Loc [ MULT 3: 8 Z Loc [ DEPTH ] ] ] 20: Z=X+F (P34) 1: 8 X Loc [ DEPTH 2: 2.
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