SDM-SIO2R Two-Channel Serial I/O Module with Relays


The SDM-SIO2R is a digital sensor expansion module that expands the serial I/O interface via Synchronous Device for Measurement (SDM) communications on a data logger. The serial I/O functionality is identical to the SDM-SIO1A One-Channel Serial I/O Module and the SDM-SIO4A Four-Channel Serial I/O Module, except it has two channels. The SDM-SIO2R also has terminals to connect sensor power and sensor heater power, which are controllable via the SDMGeneric instruction in CRBasic. 

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Benefits and Features

  • Hot swappable in the field
  • Modular design
  • Expandable as needed
  • Removable terminals
  • Power control ability for each individual sensor


Detailed Description

The SDM-SIO2R features a connector bus system that connects multiple SDM-SIO2R modules on a DIN rail without having to wire each individual unit. C1, C2, C3, 12V, V+, and G are all bussed between multiple units, making it easy to expand sensor count. Up to eight units can be bussed together with up to 15 sensors. This is the maximum number of SDM addresses available.


Function Expands the serial I/O interface via Synchronous Device for Measurement (SDM) communications on a data logger
Number of Channels 2
Supported Data Rates 300, 1200, 2400, 4800, 9600, 19200, 38400, 57600, and 115200 bits/s
Supported Modes of Operation
  • Hardware CTS/RTS flow control is supported in RS-232 mode. The handshaking lines can also be used as general purpose I/O lines.
  • RS-232 (full duplex and receive only)
  • RS-485 (half and full duplex)
  • RS-422 (full duplex)
Supported Data Formats 8, seven-bit data size*; none, odd or even parity; one or two stops bits

*In seven-bit mode with no parity, the user must ensure that the characters received by the SDM-SIO2R have a delay of at least one bit period between them. This does not affect any other configuration and does not affect transmissions out of the SDM-SIO2R.
Auto Baud Rate Detection Not supported
PakBus Communications Use of the serial port for general PakBus communications is not currently supported.
Operating Voltage
  • Power supply +12 V connection
  • 9 V (minimum
  • 12 V (nominal)
  • 30 V (maximum)
Operating Temperature -40° to +70°C
Standard Humidity Range 0 to 95% (non-condensing)
Dimensions 133.35 x 76.2 x 19.05 mm (5.25 x 3 x 0.75 in.)
Weight 108.5 g (3.8 oz)

Buffer Sizes

-NOTE- Both transmit and receive buffers are fill and discard type. That is, after the buffers become full, no new information is accepted. All further data is discarded until space is made when the data logger requests data from the SDM-SIO2R.
Transmit Buffer Size 767 bytes (buffer from the data logger to the sensor)
Receive Buffer Size 6143 bytes (buffer from the sensor to the data logger)

Current Consumption

Standby Current (12V & V+ ON)
  • 13.22 mA (nominal)
  • 13.23 mA (maximum)
Standby Current (12V & V+ OFF)
  • 63.22 mA (nominal)
  • 64.71 mA (maximum)


Please note: The following shows notable compatibility information. It is not a comprehensive list of all compatible products.

Data Loggers

Compatible Note
CR1000 (retired)
CR200X (retired)
CR206X (retired)
CR295X (retired)
CR3000 (retired)
CR5000 (retired)
CR800 (retired)
CR850 (retired)
CR9000X (retired)

Distributed Data Acquisition

Compatible Note

Additional Compatibility Information

The SDM-SIO2R requires a desiccated, non-condensing environment; a Campbell Scientific enclosure is recommended. The SDM-SIO2R is DIN rail mountable and will not mount to a typical Campbell Scientific one-inch diamond grid pattern back panel without the use of a DIN rail, which is sold separately.

The SDM-SIO2R does NOT support auto baud rate detection nor the use of the serial port for general PakBus communications.