SR50A Sonic Ranging Sensor Revision: 1/11 C o p y r i g h t © 2 0 0 7 - 2 0 1 1 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 SR50A 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.
SR50A 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. Specifications ..............................................................1 2. Introduction..................................................................2 3. Operation......................................................................2 3.1 Quality Numbers..................................................................
SR50A Table of Contents 4. Sensor Mounting and Installation ............................16 4.1 Beam Angle ........................................................................................... 16 4.2 Mounting Height.................................................................................... 17 4.2.1 Reference Point ............................................................................ 17 4.3 Mounting Options ................................................................................
Warning! Always disconnect the sensor before opening. This Device complies with Part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) This device may not cause harmful interference, and (2) This device must accept any interference received, including interference that may cause undesirable operation.
SR50A Sonic Ranging Sensor 1. Specifications Power Requirements: 9 to 18 Vdc Power Consumption: Quiescent SDI-12 Mode < 1.0 mA RS-232/RS485 Mode < 2.25 mANote1 Peak Measurement Current 250 mA typical Measurement Time: Less than 1.0 second Selectable Outputs: SDI-12 (version 1.3) RS-232 (1200 to 38400 bps) RS-485 (1200 to 38400 bps) Measurement Range: 1.6 to 32.8 ft (0.5 to 10 m) Accuracy: ±0.4 in (±1 cm) or 0.4% of distance to target, whichever is greater.
SR50A Sonic Ranging Sensor 2. Introduction The SR50A Sonic Ranging Sensor measures the distance from the sensor to a target. The most common applications are measuring snow depths and water levels. The sensor is based on a 50 kHz (Ultrasonic) electrostatic transducer. The SR50A determines the distance to a target by sending out ultrasonic pulses and listening for the returning echoes that are reflected from the target.
SR50A Sonic Ranging Sensor 3.1 Quality Numbers Measurement quality numbers are also available with output data; these give an indication of the measurement certainty. The quality numbers have no units of measure but can vary from 152 to 600. When the Quality numbers are lower than 210, the measurements are considered to be of good quality. A value of zero however, indicates a reading was not obtained. Numbers greater than 300 indicate that there is a degree of uncertainty in the measurement.
SR50A Sonic Ranging Sensor 3.3 SDI-12 Operation SDI-12 is a Serial Digital Interface standard that is used for communication between data recorders and sensors. Most Campbell Scientific dataloggers are SDI-12 compatible. 3.3.1 SDI-12 Wiring It is recommended to power down your system before wiring the SR50A. Never operate the sensor with the shield wire disconnected. The shield wire plays an important role in noise emissions and susceptibility as well as transient protection.
SR50A Sonic Ranging Sensor The different commands are entered as options in the SDI-12 recorder instruction. The major difference between the various measurement commands are the data values that are returned. The user has the option to output the distance to target in either meters or feet, or to include the measurement quality numbers. If the SR50A is unable to detect a proper echo for a measurement, the sensor will return a zero value for the distance to target value.
SR50A Sonic Ranging Sensor SDI-12 Command Command Function/Description Values Returned ?! Address Query a aAb! Change Address command b is the new address aXM;D.DDD! Extended command Set the distance to ground parameter in the SR50A. The distance must be in meters with no more than 3 decimal places. A Address is returned aXI;DDD.DD! Extended command Set the distance to ground parameter in the SR50A. The distance must be in Inches with no more than 2 decimal places.
SR50A Sonic Ranging Sensor 3.5 RS-485 Operation The SR50A sensor comes from the factory with the internal jumpers set to SDI-12 mode. To use the SR50A in the RS-485 mode of operation the jumpers will need to be set as outlined in Section 7. The RS-485 on the SR50A supports half-duplex communications. This means that the SR50A can receive and transmit but both cannot occur simultaneously. Normally there is a master-slave relationship in most systems to avoid collisions between transmissions.
SR50A Sonic Ranging Sensor FIGURE 1. SR50A to MD485 Wiring 3.6 RS-232 and RS-485 Settings Once the jumpers are set for RS-232 operation a terminal program such as Hyperterminal can be used to change factory default or existing settings. The following settings apply to Hyperterminal or any other program that is used for communications. BAUD Rate Data Bits Parity Stop Bits Flow Control NOTE Current SR50A SettingNote 8 None 1 None The factory default BAUD rate is 9600 BAUD.
SR50A Sonic Ranging Sensor The Initial menu will look as follows: The following is a summary of settings that can be changed on the SR50A RS232 or RS-485 operating modes.
SR50A Sonic Ranging Sensor Setting Description Options Default Value Quality Output On Off Off Temperature Output On Off Off Output valid only for the SR50AT (available on special order only) Diagnostics Output On Off Off 3.6.1 BAUD Rate Setting The factory Default BAUD Rate Setting of 9600 BAUD is suitable for most applications. Lower BAUD rates (1200 or 4800) may improve communication reliability or allow for longer cable lengths.
SR50A Sonic Ranging Sensor 3.6.3.2 Auto Measure Auto Output Mode In this mode the SR50A will automatically exit its low power mode, initiate a measurement and output the data. The frequency by which the SR50A will perform this is set by adjusting the Measurement Interval Units and the Measurement Interval Value parameters. • No command is required from an external device to obtain a measurement. • The data recorder or equipment simply needs to read the incoming serial data from the SR50A. 3.6.3.
SR50A Sonic Ranging Sensor 3.6.6 Measurement Interval Units This setting is only applicable if either the Auto Measure Polled Output or the Auto Measure Auto Output Modes are used. The options for the Measurement Interval Units are: Seconds Minutes Hours Once a unit type is selected the number of units for the interval is set by changing the Measurement Interval Value parameter. A 60 second interval can be set by setting the units to seconds and the Measurement Interval Value to 60.
SR50A Sonic Ranging Sensor 3.7 Serial Commands 3.7.1 Setup Command The setup command places the SR50A in the serial setup mode. This command should only be sent to customize a sensor’s settings. Upper and lower case letters are accepted and a carriage return character must also terminate the string (Enter key for Hyperterminal). “setup” 3.7.2 Poll Command The poll command is used to obtain the sensor’s output values.
SR50A Sonic Ranging Sensor 3.8 RS-232/RS-485 Data Output Format 3.8.1 Measurement Output The measurement output string for the SR50A is as follows: aa;D.DDD;QQQ;TT.TT;VVVVV;CC is the hex character &h02 (2 in decimal) aa These two characters are the serial address of the sensor. The default is 33. Note this is two ASCII characters of &h33 in Hexidecimal or 51 in decimal. D.DDD This is the distance to target reading. The units depend on the Output Units setting.
SR50A Sonic Ranging Sensor VXVVV If X is a 1, then no watchdog errors have occurred. VVXXX The 3 digits XXX are for factory use and should always read 111. CC This is a 2 character checksum of the data packet. The checksum is the two’s complement of the data packet sum including control characters. The Least significant byte is used resulting in a 2 character checksum.
SR50A Sonic Ranging Sensor BBBBB This is the checksum of the boot code. WWWWW This is the checksum of the firmware. CC This is a 2 character checksum of the data packet. The checksum is the two’s complement of the data packet sum including control characters. The least significant byte is used resulting in a 2 character checksum.
SR50A Sonic Ranging Sensor FIGURE 2. Beam Angle Clearance 4.2 Mounting Height Any target to the SR50A should be at least 19.7 in (50 cm) or more from the face of the transducer. An attempt should also be made to not mount the sensor too far from the target surface. The further the sensor is from the target the more the absolute error increases. If your application is measuring snow depth in an area that will likely not exceed 4.1 ft (1.25 m) of snow then a good height to mount the sensor would be 5.
SR50A Sonic Ranging Sensor 4.3 Mounting Options There are two standard mounting options available for the SR50A sensor. The first is the SR50A Mounting Kit, part number 19517. This bracket is used to mount the SR50A to a CM206 crossarm or a pipe with a 1 in. to 1.75 in. OD. Figures 4 and 5 show a couple of angles of the SR50A mounted to a crossarm. A u-bolt attaches the bracket to the crossarm and two screws attach the SR50A to the bracket.
SR50A Sonic Ranging Sensor FIGURE 6. SR50A - Mounted using a NU-RAIL Fitting and 19484 Mounting Stem SR50A with 6-plate gill radiation shield – the picture below shows the SR50A stem attachment 5. Maintenance The SR50A’s electrostatic transducer requires equal pressure on both sides. Vent holes in the transducer housing are used to equalize pressure. Desiccant is placed inside the transducer housing to prevent the possibility of condensing humidity.
SR50A Sonic Ranging Sensor It is recommended that the transducer housing assembly (part number 19486 – Transducer Maintenance Kit) be replaced every 3 years. If the SR50A is used in an environment with high humidity, it is recommended that the transducer housing assembly be replaced every year. 6. Disassembly/Assembly Procedures It is important to follow these instructions to disassemble the SR50A.
SR50A Sonic Ranging Sensor FIGURE 8. Remove 6 Screws from the Transducer Housing FIGURE 9.
SR50A Sonic Ranging Sensor FIGURE 10. Location of Desiccant in Transducer Housing Assembly FIGURE 11.
SR50A Sonic Ranging Sensor FIGURE 12. Remove the 2 Flat Philips Screws to Expose the PCB Carefully reassemble in reverse order. 7. Jumper Settings The following diagram illustrates how the Jumpers are located on the SR50A sensor. FIGURE 13.
SR50A Sonic Ranging Sensor The SR50A can be configured with either SDI-12, RS-232 or RS-485 communications. Shunt jumpers can be located on any of the 3 sets of communication selection headers. All 3 jumpers should be placed only on one group at a time. Never install more than 3 jumpers and never mix the jumpers amongst the SDI-12, RS-232 or RS-485 locations. The other jumper located on the SR50A places the sensor in either the normal operation mode or in the Program update mode.
SR50A Sonic Ranging Sensor • Power can now be applied to the SR50A by connecting the connector and applying power to the sensor. The Green LED should remain on when powered up properly. • Setup Hyperterminal or the communications program that you are using as follows: o BAUD rate: 38400 o Data Bits: 8 o Parity: None o Stop Bits: 1 o Flow control: o 25ms line delay (under ASCII setup) XON/XOFF • From the Hyperterminal menu select Transfer -> Send Text File.
SR50A Sonic Ranging Sensor 10. Datalogger Program Examples In the following datalogger program examples only the CR1000 and the CR10X dataloggers are used. The programming of CR800, CR850 and the CR3000 dataloggers are effectively the same as the CR1000. Also for a CR23X datalogger refer to the CR10X programming examples. 10.1 SR50A Examples 10.1.1 CR1000 Example (SDI-12 “M1!”) 'CR1000 Series Datalogger 'In this example, the SR50A is mounted 2.5 meters above the ground.
SR50A Sonic Ranging Sensor 10.1.2 CR1000 Example (RS-232 Mode) 'CR1000 Series Datalogger 'In this example, the SR50A is mounted 2.5 meters above the ground. 'The SR50A is used in RS-232 mode (internal jumpers are set). 'The CR1000 sends a serial string to the SR50A, which is in "Measure on Poll Mode", 'and then receives a serial string in return which is parsed into different values.
SR50A Sonic Ranging Sensor 'Measure the 107 temperature sensor: Therm107 (Air_Temp,1,1,Vx1,0,250,1.0,0) 'Use Air_Temp to calculate corrected distance: Temp_Corr_Distance=Raw_Distance*(SQR((Air_Temp+273.15)/273.15)) 'Subtract the corrected distance from the initial distance of the SR50A to the ground: Snow_Depth=Initial_Distance - Temp_Corr_Distance 'Call Data Table and Store Data: CallTable (Table1) NextScan EndProg 10.1.3 CR10X Example (SDI-12 “M1!”) ;{CR10X} ; ;In this example, the SR50A is mounted 2.
SR50A Sonic Ranging Sensor 5: Z=SQRT(X) (P39) 1: 6 X Loc [ Mult1 2: 6 Z Loc [ Mult1 ] ] ;Distance to the Snow Surface is obtained by multiplying the temperature correction ;to the Raw Distance value 6: Z=X*Y (P36) 1: 3 X Loc [ Raw_Dist ] 2: 6 Y Loc [ Mult1 ] 3: 7 Z Loc [ DistToSnw ] ;Set the initial distance from the SR50A to the ground in meters: 7: Z=F x 10^n (P30) 1: 2.
SR50A Sonic Ranging Sensor 10.2 SR50AT Examples 10.2.1 CR1000 Example (SDI-12 “M4!”) 'CR1000 Series Datalogger 'The following sample program obtains the Snow depth output 'directly from an SR50AT sensor. 'This program is written for the SR50AT version only.
SR50A Sonic Ranging Sensor 'Main Program BeginProg Scan (60,Sec,0,0) PanelTemp (PTemp,250) Battery (Batt_volt) 'Once installed enter the actual distance from the SR50AT to the Ground with 'no snow present. If in doubt it is better to use a slightly larger value 'than a smaller value. Errors in the value will show up as an offset error 'in the snow depth values 'If a new value for the variable NewDistanceToGround is entered (non zero) 'The following code will send that value to the SR50AT.
SR50A Sonic Ranging Sensor 10.2.2 CR1000 Example (RS-232 Mode) 'CR1000 Series Datalogger 'In this example, the SR50AT is mounted 2.5 meters above the ground. 'The SR50AT is used in RS-232 mode (internal jumpers are set). 'The CR1000 sends a serial string to the SR50AT, which is in "Measure on Poll Mode", 'and then receives a serial string in return which is parsed into different values.
SR50A Sonic Ranging Sensor 'Subtract the corrected distance from the initial distance of the SR50A to the ground: Snow_Depth=Initial_Distance - Dist_To_Snow 'Call Data Table and Store Data: CallTable (Table1) NextScan EndProg 10.2.3 CR10X Example (SDI-12 “M3!”) ;{CR10X} ; ;In this example, the SR50AT is mounted 2.5 meters above the ground. ; ;The CR10X sends an SDI-12 command to the SR50AT, which outputs the ;temperature compensated distance value (Meters), ;the signal quality value and the temperature.
SR50A Sonic Ranging Sensor 6: Real Time (P77)^30811 1: 1220 Year,Day,Hour/Minute (midnight = 2400) 7: Sample (P70)^20443 1: 1 Reps 2: 6 Loc [ SnowDepth ] ;Store the Signal quality value 8: Sample (P70)^23223 1: 1 Reps 2: 4 Loc [ Sig_Qual ] ;Store the Temperature reading from the SR50AT 9: Sample (P70)^1224 1: 1 Reps 2: 5 Loc [ SR50AT_T ] *Table 2 Program 02: 0.0000 Execution Interval (seconds) *Table 3 Subroutines End Program 11.
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