SDM-SW8A 8-Channel Switch Closure Input Module
Expands Datalogger Input Channels
For switch closure or voltage pulse sensors
weather applications water applications energy applications gas flux & turbulence applications infrastructure applications soil applications


Your datalogger can measure more switch closures or voltage pulses with an SDM-SW8A. Sensors that output a switch closure or voltage pulse signal include tipping bucket rain gages, flow meters, and anemometers.

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Benefits and Features

  • Well suited for use in energy management studies
  • Provides eight individually configured channels
  • Measures a variety of signals: reed switches, dry contacts, or slow voltage pulses
  • Allows up to four SDM-SW8As to be connected to a single datalogger


Detailed Description

The SDM-SW8A provides eight channels for connecting the sensors. Each channel is individually configured for single-pole double-throw (SPDT), single-pole single-throw (SPST), or voltage pulse measurements. Output options include counts, duty cycle, and state.

SDM Operation

The datalogger enables individual modules through an addressing scheme; multiple SDMs (in any combination) can be connected to one datalogger. We recommend a maximum of four SDM-SW8As be connected to a single datalogger. After a module is enabled, it operates independently of the datalogger until additional commands are received or results are transmitted.


Measurement Types Switch closure (SPDT, SPST), dc voltage pulse
Input Voltage Threshold From below 0.9 to above 4.0 Vdc (±20 Vdc maximum)
Maximum Input Frequency 100 Hz (50% duty cycle)
Minimum Input Pulse Width 5 ms high, 5 ms low
Maximum Bounce Time 3 ms open without counting
Output Options State, duty cycle, counts
Maximum Count/Port 65535
Internal Sampling Frequency 500 Hz
Watchdog Reset Yes
Operating Voltage 9.6 to 16 V
Typical Current Drain
  • 3 mA quiescent
  • 6 mA active (maximum)
Operating Temperature -25° to +55°C
Relative Humidity 0 to 90% RH (non-condensing)
Maximum Cable Length 6 m (20 ft) total to all SDM devices
Consult Campbell Scientific if longer lengths are necessary.
Dimensions 15.7 x 6.9 x 2.3 cm (6.2 x 2.7 x 0.9 in.)
Weight 0.23 kg (0.5 lb)


Datalogger Considerations


In the CRBasic dataloggers, the SDM-SW8A operation is controlled by the SDMSW8A instruction. Instruction 102 controls the SDM-SW8A operation for Edlog dataloggers that were shipped after October 1988 (consult Campbell Scientific for equipment shipped prior to this date).

Compatible Contemporary Dataloggers

CR200(X) Series CR800/CR850 CR1000 CR3000 CR9000X CR6

Compatible Retired Dataloggers

CR500 CR510 CR10 CR10X 21X CR23X CR5000 CR7X CR9000
* **

Datalogger Notes:
*For the CR3000 and CR5000, SDMs are connected to the ports labeled SDM-C1, SDM-C2, and SDM-C3.

**For the CR7X, SDMs connect to the C1, C2, and C3 terminals provided on the CR700X control module (after Sept 1996).

Power Supply

Due to the 3 mA continuous and 6 mA active current drain, an auxiliary 12 Vdc power supply is recommended for powering the SDM-SW8A in remote, long term applications.

For some applications, it may be convenient to use the datalogger power supply. You can do this where ac power is available, or where a solar panel can be used for recharging the datalogger's sealed rechargeable battery.

Enclosure Considerations

The SDM-SW8A requires a desiccated, non-condensing environment; a Campbell Scientific enclosure is recommended. Grommets and screws are provided to attach the SDM-SW8A to the backplate of our enclosures.

Compatible Enclosures

ENC10/12 ENC10/12R ENC12/14 ENC14/16 ENC16/18 ENC24/30 ENC24/30S

Case Studies

Flemish Pile Monitoring
Cofely Fabricom NV/SA (GDFSuez) has utilized Campbell Scientific equipment on numerous projects in both more