Connection and wiring

SDM‑SIO2R connections to the data logger are made via the Input connector. Strip wires 7 to 9 mm and twist. Open the clamp by inserting a small screwdriver into the small hole and prying away from the clamp. Insert the wire. Release the clamp and verify the clamp grips the wire rather than the plastic insulation. See Input connections.

Input connections

SDM‑SIO2R connections to serial devices are made via the terminals arranged along the top of the unit. The terminals are spring loaded providing an easy and reliable method of connection. Strip wires 7 to 9 mm and twist. Open the clamp by pushing the orange tab down with the tip of a small flat-blade screwdriver and insert the wire into the round hole. Release the clamp and verify the clamp grips the wire rather than the plastic insulation. See Serial and switched power connections

Serial and switched power connections

If there is a need to insert more than one wire in each terminal, if using multi-strand wire, twist the conductors together first. If using solid wires, solder or crimp multiple pairs together before insertion.

Ferrules can be used for connections.

NOTE:

The SDM‑SIO2R Input connector can handle wire sizes ranging from 14-28 AWG.
The SDM‑SIO2R 6- Pin and 4-pin sensor communication connectors can handle wire sizes ranging from 16-24 AWG.
- When using 20-24 AWG ferrules on the SDM‑SIO2R 6-pin communication connectors, longer ferrules must be used (for example, Campbell Scientific pn 40233).

If necessary, a connector can be removed from the device by unlocking the slide bar. See Connector release slide bar.

Connector release slide bar

NOTE:

The 12V power ground for the SDM‑SIO2R must be common ground with the data logger in order for the C1/C2/C3 communications to work.

NOTE:

The sensor with the highest current draw should be connected to the SDM‑SIO2R that is plugged into power and communications on the Input connector. It is recommended that this is the center SDM‑SIO2R in the system.

SDM‑SIO2R input terminal labels and functions shows all the input connections on the SDM‑SIO2R.

SDM‑SIO2R input terminal labels and functions
Power				SDM
V₊	V_-	12V	G	C1	C2	C3
1	2	3	4	5	6	7

SDM‑SIO2R communication terminal labels and functions shows all the serial communication connections on the SDM‑SIO2R. Note that there are two communication connectors. One for Sensor 1 and one for Sensor 2.

SDM‑SIO2R communication terminal labels and functions
Communication
RG	GND	RTS	Tx	CTS	Rx
1	2	3	4	5	6

SDM‑SIO2R power pass-through terminal labels and functions shows all the power pass-through connections on the SDM‑SIO2R. Note that there are two power pass-through connectors. One for Sensor 1 and one for Sensor 2.

SDM‑SIO2R power pass-through terminal labels and functions
Power pass-through
V-	V+	G	12V
1	2	3	4

SDM‑SIO2R functional description of input connections
Pin	Case text	Connection to	Description
1	V+	Power supplies	Power supply 0-30V AC or DC
2	V-		Power supply return 0-30V AC or DC
3	12V		Power supply 9-30 V DC (powers internal electronics and LEDs)
4	G		Power supply ground
5	C1	Data logger	SDM_Data
6	C2		SDM_Clock
7	C3		SDM_DataEnable

SDM‑SIO2R functional description of sensor connections
Pin	Case text (RS-232 Function)	RS-485 Function	Connection to	Description
1	RG¹		Sensors Note that all of the sensor connections are repeated on two connectors: Sensor 1 and Sensor 2	RG – RS‑485 ground. Connected to G via 100 Ω 1 W resistor.
2	GND²			GND - ground for RS-232 communications
3	RTS	TD+		RS‑232 RTS. RS‑485 half duplex non-inverting. RS‑485 full duplex outgoing.
4	Tx	TD–		RS‑232 transmit. RS‑485 half duplex inverting. RS‑485 full duplex outgoing.
5	Rx	RD+		RS‑232 receive. RS‑485 receiver non-inverting. RS‑485 full duplex incoming.
6	CTS	RD–		RS-232 CTS. RS‑485 receiver inverting. RS‑485 full duplex incoming.
1	V-			AC or DC voltage source return from power supply
2	V+			AC or DC voltage source from power supply
3	G			DC ground from power supply
4	12V			DC voltage source from power supply
¹ Connection RG has a 100 Ω resistor in series with the data logger ground connection. This connection should be used when connecting RS-485 equipment by long wire lengths. It ensures both systems have a common ground reference point. See Precautions before connecting. ² The GND can be used for the RS-232 zero volt reference or any other ground connection needed, for example, shields.

The connection of the wires to the remote serial device or sensor will vary with type of device and method of communication. It is necessary to work out the best mode of operation of the serial device, taking into consideration issues such as power consumption, cable lengths (RS-485 being better than RS-232 for long cables), synchronization of data collection, etc.

NOTE:

If possible, use screened cable for connecting the SDM‑SIO2R to remote sensors or devices. Check the manual of the device for details on where to connect the screen for maximum effectiveness.

RS-422 mode is functionally the same as RS-485 mode except the connection is limited to a point-to-point system. Connections and programming for RS-422 are otherwise identical to full-duplex RS-485.

When operating in RS-232 mode, the SDM‑SIO2R also supports hardware handshaking.

Wiring examples for connecting the SDM‑SIO2R provides examples of different connection schemes for the serial devices. Further discussion of different modes of operation is given in Operation.