The SR50A is a rugged acoustic sensor for measuring the distance from the sensor to a target. It is typically used to measure snow or water depth, but it is well-suited for other uses.

Because the speed of sound in air varies with temperature, an independent temperature measurement is required to compensate the distance reading. A simple calculation is applied to initial readings for this purpose.

Note: This sensor may not be suitable for marine environments.

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Benefits and Features

  • Wide operating temperature range
  • User-selectable options for output
  • Compatible with most Campbell Scientific dataloggers

The "-L" on a product model indicates that the cable length is specified at the time of order.


Detailed Description

The SR50A was designed to meet the stringent requirements of measuring depths and uses a multiple echo processing algorithm to help ensure measurement reliability.

SDI-12, RS-232, and RS-485 output options are available for measuring the SR50A. 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.

The SR50A replaced the SR50 in March 2007. The newer SR50A is smaller and has different output options than its predecessor.



Measurement Time < 1.0 s
Output Options SDI-12 version 1.3, RS-232, RS-485 (output options selected by configuring internal jumpers)
Baud Rates 1200 to 38400 bps (RS-232, RS-485 modes)
Power Requirements 9 to 18 Vdc (typically powered by datalogger’s 12 Vdc power supply)
Measurement Range 0.5 to 10 m (1.6 to 32.8 ft)
Beam Acceptance ~30°
Resolution 0.25 mm (0.01 in.)
Accuracy ±1 cm (0.4 in.) or 0.4% of distance to target (whichever is greatest). Requires external temperature compensation.
Operating Temperature Range -45° to +50°C
Length 10.1 cm (4.0 in.)
Diameter 7.5 cm (3 in.)
Weight 375 g (13.2 oz) without cable
Cable Weight 250 g (8.2 oz) for a 4.57-m (15-ft) cable

Maximum Cable Length

SDI-12 60 m (200 ft)
RS-232 60 m (200 ft) Baud rates ≤ 9600 bps
RS-485 300 m (984 ft)
Cable lengths greater than 60 m require a heavier gage wire if the power supply drops below 11 Vdc.

Power Consumption

Typical Active 250 mA
Quiescent SDI-12 Mode < 1.0 mA
Quiescent RS-232/RS-485 Modes
  • < 1.25 mA (≤ 9600 bps)
  • < 2.0 mA (> 9600 bps)



To achieve an unobstructed view for the SR50A's beam, the SR50A is typically mounted to a tripod mast, tower leg, or user-supplied pole via the CM206 6-ft crossarm. The 19517 mounting kit attaches directly to the crossarm. The 19484 mounting stem attaches to the crossarm via the 17953 NU-RAIL fitting or CM220 right-angle mount. If the surface is at an angle, the CM230 Adjustable Inclination Mount should be used instead of the NU-RAIL fitting or CM220 mount.

Datalogger Considerations

Compatible Contemporary Dataloggers

CR200(X) Series CR800/CR850 CR1000 CR3000 CR9000X

Compatible Retired Dataloggers

CR500 CR510 CR10 CR10X 21X CR23X CR9000 CR5000 CR7X


SR50A/AT OS v.1.3 (52 KB) 08-22-2007

Current SR50A / AT firmware. View Update History

Frequently Asked Questions

Number of FAQs related to SR50A-L: 17

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  1. Yes, but more routine maintenance of the sensor is needed in marine environments.

  2. Yes. The accuracy of the sensor is 1 cm or 0.4% of distance to water (whichever is greater). As long as the water level is deeper than this, the water height can be confidently determined.

  3. Approximately 800 feet. This is a function of the limitations of the SDI-12 signal.

  4. Because the speed of sound changes with temperature, Campbell Scientific recommends using the SR50A-L in tandem with a temperature sensor for the most accurate measurements.

  5. This sensor requires regular maintenance in a marine environment. The SR50A-L functions properly if care is taken to keep the vent free of salt accumulation and the interior free of moisture by replacing the desiccant as needed. It may also be necessary to carefully clean the face of the sensor to remove salt deposits.

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