Campbell SR50A Series User manual

INSTRUCTION MANUAL
SR50A and SR50AT
Sonic Ranging Sensors
'FCSVBSZ 2016
Copyright © 20 16
Campbell Scientific (Canada) Corp.

SR50A Sonic Ranging Sensor
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Warning!
Always disconnect the sensor before opening.
Avertissement!
Toujours débrancher le capteur avant de l'ouvrir.
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.

WARRANTY ANDASSISTANCE
This equipment is warranted by CAMPBELL SCIENTIFIC (CANADA) CORP. ("CSC") to
be free from defects in materials and workmanship under normal use and service for
twenty-four (24) months from date of shipment unless specified otherwise. *****
Batteries are not warranted. ***** CSC's obligation under this warranty is limited to
repairing or replacing (at CSC's option) defective products. The customer shall assume
all costs of
removing, reinstalling, and shipping defective products to CSC. CSC will
return such products by surface carrier prepaid. This warranty shall not apply to any
CSC products which have been subjected to modification, misuse, neglect, accidents of
nature, or shipping damage. This warranty is in lieu of all other warranties, expressed or
implied, including warranties of merchantability or fitness for a particular purpose. CSC
is not
liable for special, indirect, incidental, or consequential damages.
Products may not be returned without prior authorization. To obtain a Return
Merchandise Authorization (RMA), contact CAMPBELL SCIENTIFIC (CANADA) CORP.,
at [phone]. An RMA number will be issued in order to facilitate Repair Personnel
in identifying an instrument upon arrival. Please write this number clearly on the outside
of the shipping container. Include description of symptoms and all pertinent details.
CAMPBELL SCIENTIFIC (CANADA) CORP. does not accept collect calls.
Non-warranty products returned for repair should be accompanied by a purchase order to
cover repair costs.

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TABLE OF CONTENTS
1Specifications.................................................................................................................... 4
2Introduction....................................................................................................................... 6
3Operation .......................................................................................................................... 7
3.1 Quality Numbers........................................................................................................ 7
3.2 Temperature Compensation for SR50A version........................................................ 8
3.3 Temperature Compensation for SR50AT version...................................................... 9
3.4 SDI-12 Operation..................................................................................................... 10
3.4.1 SDI-12 Wiring .................................................................................................. 10
3.4.2 SDI-12 Addresses ............................................................................................. 11
3.4.3 SDI-12 Commands............................................................................................ 11
3.5 RS-232 Operation..................................................................................................... 14
3.5.1 RS-232 Wiring.................................................................................................. 14
3.6 RS-485 Operation..................................................................................................... 15
3.6.1 RS-485 Wiring.................................................................................................. 15
3.7 RS-232 and RS-485 Settings.................................................................................... 16
3.7.1 BAUD Rate Setting........................................................................................... 18
3.7.2 Address ............................................................................................................. 19
3.7.3 Operational Mode Setting................................................................................. 19
3.7.3.1 Measure in Poll Mode................................................................................ 19
3.7.3.2 Auto Measure Auto Output Mode............................................................. 20
3.7.3.3 Auto Measure Polled Output Mode........................................................... 20
3.7.4 Distance to Target or Depth.............................................................................. 20
3.7.5 Distance to Ground ........................................................................................... 21
3.7.6 Measurement Interval Units.............................................................................. 21
3.7.7 Measurement Interval Value............................................................................. 21
3.7.8 Output Unit ....................................................................................................... 22
3.7.9 Quality Output .................................................................................................. 22
3.7.10 Temperature Output.......................................................................................... 22
3.7.11 Diagnostics Output............................................................................................ 22
3.8 Serial Commands ..................................................................................................... 22
3.8.1 Setup command................................................................................................. 22
3.8.2 Poll command ................................................................................................... 23
3.8.3 Information command....................................................................................... 23
3.8.4 Temperature Input command............................................................................ 23
3.9 RS-232/RS-485 Data Output Format....................................................................... 24
3.9.1 Measurement Output......................................................................................... 24
3.9.2 Information Message Output ............................................................................ 26
4Sensor Mounting and Installation................................................................................... 28
4.1 Beam Angle.............................................................................................................. 28
4.2 Mounting Height ...................................................................................................... 28
4.2.1 Reference point................................................................................................. 29
4.3 Mounting Options .................................................................................................... 29

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5Maintenance.................................................................................................................... 32
6Disassembly/Assembly Procedures................................................................................ 33
7Jumper Settings............................................................................................................... 37
8SR50A Firmware Updates.............................................................................................. 38
9Data Interpretation & Filtering ....................................................................................... 40
9.1 Data Interpretation.................................................................................................... 40
9.2 Data Filtering............................................................................................................ 40
10 Datalogger Program examples........................................................................................ 43
10.1 Programming Example 1...................................................................................... 43
SR50A SDI-12 “M1!” CR10X Datalogger......................................................................... 43
10.2 Programming Example 2...................................................................................... 45
SR50AT SDI-12 “M3!” CR10X Datalogger ...................................................................... 45
10.3 Programming Example 3...................................................................................... 46
SR50A SDI-12 “M1!” CR1000 Datalogger ....................................................................... 46
10.4 Programming Example 4...................................................................................... 47
SR50AT SDI-12 “M4!” Snow Depth Output CR1000....................................................... 47
10.5 Programming Example 5...................................................................................... 49
SR50A RS-232 Mode CR1000........................................................................................... 49
10.6 Programming Example 6...................................................................................... 51
SR50AT RS-232 Mode CR1000 ........................................................................................ 51
11 Warnings/Cautions.......................................................................................................... 53
12 APPENDIX A: SR50AH Heater Option ........................................................................ 54
12.1 Heater Introduction............................................................................................... 54
12.2 Specifications........................................................................................................ 54
12.2.1 Heating Cable Requirements ............................................................................ 54
12.3 Maintenance.......................................................................................................... 55
13 APPENDIX B: Optional Open Faced Transducer for Harsh Environments.................. 60
13.1 General.................................................................................................................. 60
14 APPENDIX C: SR50A-316SS and SR50AT-316SS Options........................................ 61
14.1 Introduction .......................................................................................................... 61
TABLE OF FIGURES
Figure 1 SR50AT-CBL............................................................................................................ 9
Figure 2 SR50A to MD485 wiring ......................................................................................... 16
Figure 3 Beam Angle Clearances .......................................................................................... 28
Figure 4 Distance from edge of transducer housing to grill ................................................... 29
Figure 5 SR50A Mount - mounted parallel to pipe ................................................................ 30
Figure 6 SR50A Mount - mounted perpendicular to pipe ...................................................... 30
Figure 7 SR50A - mounted using Nurail and C2151 mounting stem..................................... 31
Figure 8 Disconnect cable from sensor................................................................................... 33
Figure 9 Remove 6 screws from the transducer housing........................................................ 34
Figure 10 Remove transducer housing and disconnect wires................................................. 35
Figure 11 Location of Desiccant in transducer housing assembly ......................................... 35
Figure 12 Remove and Replace Desiccant ............................................................................. 36
Figure 13 Remove the 2 flat philips screws to expose the PCB............................................ 36

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1 Specifications
Power Requirements: 9-18 VOLTS D.C.
Power Consumption: Quiescent
SDI-12 Mode < 1.0mA
RS-232/RS485 Mode < 2.25mANote1
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 BAUD)
RS-485 (1200 to 38400 BAUD)
Measurement Range: 0.5 to 10 meters
Accuracy: ±1 cm or 0.4% of distance to target
(whichever is greater)
Excludes temperature compensation errors.
An external temperature compensation is
required for the SR50A..
Resolution: 0.25mm
Required Beam Angle Clearance: 30°
Operating Temperature: -45°C to +50°C
Maximum Cable Length: SDI-12: 60 m
RS-232: 60 m (default 9600 BAUD or less),
30 m (384000 BAUD)
RS-485: 300 m Note2
Cable Type: 4 conductor, 2-twisted pair, 22 AWG,
Santoprene jacket
Chassis Types: Aluminum, or 316 stainless steel
Dimensions: Length 10.1 cm
Diameter 7.6 cm

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Weight:
Aluminum chassis: 375g (13.2oz)
Stainless steel chassis: 795g (28oz)
Cable (SR50A) 15 feet: 0.25kg (0.55lbs)
Temperature
Measurement (SR50AT): 0°C to +50°C ±0.2°C
-45°C to 0°C ±0.75°C
IP Rating
Electrical Housing IP67
Transducer IP64
Note 1: The quiescent current draw is less than 1.25mA if the BAUD rate is 9600 BAUD or
less.
Note 2: Power supply must not drop below 11.0 Volts or heavier gauge wire is required

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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. The time from transmissions to return of an
echo is the basis for obtaining the distance measurement.
Since the speed of sound in air varies with temperature, an
independent temperature measurement is required to
compensate the distance reading for the SR50A. A simple
calculation is applied to initial readings for this purpose.
The SR50AT version of sensor comes with a temperature
probe that will allow the SR50AT to output temperature
compensated values.
The SR50A is capable of picking up small targets or targets
that are highly absorptive to sound, such as low density snow.
The SR50A makes use of a unique echo processing algorithm
to help ensure measurement reliability. If desired, the SR50A
can also output a data value indicative of measurement quality.
The SR50A was designed to meet the stringent requirements of
snow depth measurement which makes it well suited for a
variety of other applications. The rugged aluminium housing is
built to withstand harsh environments and offers several
mounting options.

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3 Operation
The SR50A has several output formats: SDI-12, RS-232 and
RS-485. The SR50A is shipped from the factory configured as
an SDI-12 sensor (address 0). By moving a set of three
jumpers inside the SR50A the output type can be optionally set
from SDI-12 to RS-232 or RS-485. Refer to Section 6 for
details on opening the SR50A and Figure 7 for the optional
jumper settings.
The SR50A performs multiple echo processing regardless of
output formats. The SR50A bases every measurement on
several readings and applies an algorithm to improve
measurement reliability.
The distance to target readings that are obtained from the
sensor are referenced from the metal mesh on the face of the
transducer. The SR50A projects an ultrasonic beam that can
pick up objects in its field of view that is 30° or less. The
closest object to the sensor will be detected if it is within this
field of view. Unwanted objects must be outside the field of
view. If a target is in motion, the SR50A may reject a reading
if the target distance changes at a rate of 4 centimetres per
second or more.
The SR50A will complete a measurement and output the data
typically in 1 second. In RS-232 and RS-485 Serial modes the
output data transmission is completed within one second for
BAUD rates of 9600 and above. The total time for an SDI-12
Measurements can exceed 1 second due to the long
communications times associated with the 1200 BAUD data
rate.
If the SR50A rejects a reading or does not detect a target, zero
will be output for distance to target or –999 for depth values.
3.1 Quality Numbers
Measurement signal quality numbers are also available with
output data; these give an indication of the measurement
certainty. The quality numbers have no units of measure and
can vary from 152 to 600. Numbers lower than 210 are
considered to be of good quality. A value of zero however,

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indicates a reading was not obtained. Numbers greater than
300 indicate that there is a degree of uncertainty in the
measurement. Causes of high numbers include:
xsensor is not perpendicular to the target surface
xtarget is small and reflects little sound
xtarget surface is rough or uneven
xtarget surface is a poor reflector of sound (extremely low
density snow)
Quality number range
Quality range description
0
Not able to read distance
152-210
Good signal strength
210-300
Reduced echo signal strength
300 to 600
Poor signal strength
It is not necessary to make use of the quality numbers but they
can provide additional information such as an indication of
surface density in snow monitoring applications. The quality
numbers will increase during snowfall events consisting of
low-density snow.
3.2 Temperature Compensation for SR50A version
The SR50A version of the sensor does not include a
temperature sensor to compensate the speed of sound for
variations in air temperature. Temperature corrections for the
speed of sound will need to be applied to the readings in either
post processing or by the measurement/monitoring device.
Campbell Scientific recommends the Model 107 air
temperature probe for this purpose. A radiation shield is also
recommended. Temperature compensation must be applied to
the sensor output using the following formula:
273.15
KELVINT
READING
=DISTANCE
SR50A
q
FORMULA 1. Temperature Compensation
The SR50A calculates a distance reading using the speed of
sound at 0°C (331.4 m/s). If the temperature compensation

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formula is not applied, the distance values will not be accurate
for temperatures other than 0°C.
3.3 Temperature Compensation for SR50AT version
The SR50AT version of the sensor includes a temperature
sensor to compensate the speed of sound for variations in air
temperature. The temperature sensor is incorporated into the
SR50AT Cable as shown in Figure 1 SR50AT-CBL
Figure 1 SR50AT-CBL
By default the temperature correction will be on for RS-232
and RS-485 modes. For the SDI-12 output mode the
datalogger must include a measurement command that has
temperature in the output. Otherwise the internal temperature
correction will not be applied. The following “M” commands
automatically apply the temperature compensation to the
readings from the SR50AT:
M2, M3, M4, M7 and M8
(see section 3..4.3 for the complete list of SDI-12 commands).
Command M9 is used to obtain a temperature measurement
without a distance reading. The M9 command makes it

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possible for the SR50AT to function as an SDI-12 temperature
sensor.
If the internal SR50AT temperature correction needs to be
bypassed, the temperature output setting will need to be turned
off for RS-232 and RS-485 modes. Using measurement
commands M, M1, M5 and M6 in SDI-12 mode will not use
the SR50AT probe to compensate for the speed of sound. The
compensation will then need to be done externally as for the
SR50A version.
A radiation shield is required for the SR50AT temperature
probe. Without a radiation shield the heating of the sensor
from the sun’s radiation can cause large errors in the
temperature reading and this will be reflected in the distance
measurement.
3.4 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.
3.4.1 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.
Color
Function
Connection
Black
Power Ground
Power Ground
Red
+12VDC Power
Power Source
Green
SDI-12 I/O
Recorder/Reader SDI-12 Com port or control port
White
Not Used
Ground
Clear
Shield
Shield/Earth Ground

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3.4.2 SDI-12 Addresses
The SR50A can be set to one of ten addresses (0 to 9) which
allows up to ten sensors to be connected to a single digital I/O
channel (control port) of an SDI-12 datalogger.
The SR50A is shipped from the factory with the address set to
0. The address on the SR50A can be changed by sending an
SDI-12 change address command. The change address
command can be issued from most SDI-12 recorders. For
some Campbell Scientific dataloggers the SDI-12 transparent
mode will need to be entered to change the address.
When it is necessary to measure more than one SR50A, it is
easiest to use a different control port for each SR50A instead of
changing the address. If additional control ports are not
available, then the address will need to be changed.
To change the address of a sensor that has the default address
of 0 to the address of 1 the following command can be sent:
“0A1!”
Only one sensor of the same address should be connected when
using the change address command.
3.4.3 SDI-12 Commands
The SDI-12 protocol has the ability to support various
measurement commands. The SR50A supports the commands
that are listed in the following table.
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
or temperature values (SR50AT version only outputs valid
temperature values).
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.
In order to obtain the Snow Depth values (aM4! or aM8!) the
user must properly set the Distance to Ground value in the
SR50AT sensor. This can be done by sending an extended

SR50A Sonic Ranging Sensor
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command in SDI-12 mode or by using the setup menu in RS-
232 or RS-485 modes.

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SDI-12
Command
Command Function/Description
Values Returned
aM!
Distance-Meters
D
aM1!
Distance-Meters, Quality Number
D, Q
aM2!
Distance-Meters, Temperature °C
D, TNote1
aM3!
Distance-Meters, Quality Number, Temperature °C
D, Q, TNote1
aM4!
Snow Depth Meters, Quality Number, Temperature
SD, Q, T
aM5!
Distance-Inches
D
aM6!
Distance-Inches, Quality Number
D, Q
aM7!
Distance-Inches, Quality Number, Temperature °C
D, Q, TNote1
aM8 !
Snow Depth Inches, Quality Number, Temperature
SD, Q, TNote1
AM9 !
Temperature °C
TNote1
aMC!
aMCn!
Measurement Commands with Checksum
See aM and aM1
- aM8
Output is the same as
aM, aM1
-aM9
Checksum is added
aC!
Concurrent Measurement Command
Distance-Meters
D
aCn!
Concurrent Measurements
Same as M1 –M8
Output is the
Same as M1 –M8
aCC!
aCCn!
Concurrent Measurement Commands with Checksum. See aM
and aM1
- aM8
Output is the same as
aM, aM1
-aM8
Checksum is added
aD0!
Send Data
Dependent upon command Sent
aV!
Verification command
S1,S2,V,WD
S1 = Firmware Signature
S2 = BootRom Signature
V = Supply Voltage
Note1
WD = Watch Dog Errors
aI!
Send Identification
013CAMPBELLSR50A 2.0SN
SN = Serial number (5 digits)
?!
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.
a
Address is returned
aXT;CC.CC!
Extended
command
Provide the SR50A with a temperature value to perform on board
temperature compensation. The temperature must be in degrees
Celsius with a maximum of 7 characters including sign and
decimal.
a
Address is returned
aR0!
Returns the Distance to Ground Setting in the SR50A. The units
returned are in Meters
DG
aR1!
Returns the Distance to Ground Setting in the SR50A. The units
returned are in Inches
DG
aR2!
Returns the temperature sent to the SR50A for Internal
Temperature compensation. This value remains the same unless
power is cycled or a new temperature values is
sent.
T
Where a = address of SDI-12 device.
Where n = numbers 1 to 9
NOTE 1: (SR50AT version only)

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3.5 RS-232 Operation
The SR50A sensor comes from the factory with the internal
jumpers set to SDI-12 mode. To use the SR50A in the RS-232
mode of operation the jumpers will need to be set as outlined in
Section 7.
3.5.1 RS-232 Wiring
The following table/diagram illustrates the wiring for the
SR50A in RS-232 mode.
Color
Function
Connection
Black
Power Ground
System Ground and/or RS-232 Receiver Ground
(Pin 5 of a computer (DTE) DB-9 connector)
Red
+12VDC Power
Power Source
Green
RS-232 (SR50A Output)
Recorder/Reader RS-232 Input
(Pin 2 of a computer (DTE) DB-9 connector)
White
RS-232 (SR50A Input)
Recorder/Reader RS-232 Output
(Pin 3 of a computer (DTE) DB-9 connector)
Clear
Shield
Shield/Earth Ground
The following is an illustration of an SR50A using a DB9M-
TERM to provide a DB-9 connection for interfacing to a PC.
Figure 1 SR50A using a DB9M-TERM

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3.6 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. For this
reason the Auto Measure Auto Output is not recommended for RS-485
communications. It is much better to have a master initiate the
communications by making use of the Measure On Poll or the Auto
Measure Polled Output modes.
Campbell Scientific’s MD485 interface can be used to connect one or
More SR50A sensors in RS-485 mode to an RS-232 device. This can
be useful for sensors that require lead lengths that exceed the limits of
either RS-232 or SDI-12 communications.
3.6.1 RS-485 Wiring
The following table/diagram illustrates the wiring for the
SR50A in RS-485 mode.
Color
Function
Connection
Black
Power Ground
System Ground and/or RS-232 Receiver Ground
(Pin 5 of a computer (DTE) DB-9 connector)
Red
+12VDC Power
Power Source
Green
RS-485 A
To RS-485 A terminal
White
RS-485 B
To RS-485 B terminal
Clear
Shield
Shield/Earth Ground

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Figure 2 SR50A to MD485 wiring
3.7 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 Current SR50A SettingNote
Data Bits 8
Parity None
Stop Bits 1
Flow Control None
Note The factory default BAUD rate is 9600 BAUD. Once
the BAUD rate is changed the new BAUD rate must be used
for further communications to the SR50A. It is important to
keep track of the BAUD rate setting on the SR50A. If the
BAUD rate setting is unknown, we recommend trying the
default value of 9600 BAUD. If that does not work, start at
BAUD rate 1200 and go through all the BAUD rate settings
until the correct one is found.

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When the hyperterminal session is started the command
“SETUP” needs to be entered. Hitting the Enter will transmit
the CR LF characters which are required after the text
“SETUP”. The text “SETUP” is not case sensitive so any
combination of upper and lower case letters will work.
The Initial menu will look as follows:

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The following is a summary of settings that can be changed on
the SR50A RS-232 or RS-485 operating modes.
Setting Description
Options
Default Value
BAUD Rate
1200
4800
9600
19200
38400
9600 BAUD
Address RS-232/RS-485
Any 2 Alphanumeric
Characters
33
Serial Operational Mode
Measure on Poll
Auto Measure Auto Output
Auto Measure Polled Output
Auto Measure Auto Output
Distance to Target or
Depth output
Distance to Target
Depth
Distance to Target
Distance to Ground
Decimal Value in Meters
0.0
Measurement Interval
Units
Seconds
Minutes
Hours
Seconds
Measurement Interval
Value
Integer 1-255
60
Output Unit
Meters
Centimeters
Millimeters
Feet
Inches
Meters
Quality Output
On
Off
Off
Temperature Output
On
Off
Off
Output valid only for SR50AT
Diagnostics Output
On
Off
Off
3.7.1 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. Higher BAUD rates (19200 or 38400)
may be used where faster communications are required.