SDM-CD8S 8-Channel Solid-State DC Controller
Expands Datalogger Control Capacity
For dc devices with moderate current loads
weather applications water applications energy applications gas flux & turbulence applications infrastructure applications soil applications


With an SDM-CD8S, your datalogger can control dc devices that have a moderate current load, such as solenoids, solenoid valves, dc motors, stepper motors, lights, horns, heaters, and fans. The SDM-CD8S is ideal for applications requiring only a few control ports, where a larger, high-powered relay module (such as the SDM-CD16S) is not necessary.

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Benefits and Features

  • Provides a manual override
  • Enables multiple SDM-CD8S devices to be wired to one datalogger, increasing the number of devices that can be controlled
  • Includes LEDs that provide a visual indicator of active outputs


Detailed Description

The SDM-CD8S has eight dc-voltage outputs and returns that can be switched on and off manually or under datalogger control. When the manual control switch is in the ON position, outputs are controlled by the position of the individual rocker switches. In the OFF position the state of the relays is controlled by the SDM commands from the datalogger.

The voltage range for this device is 8 to 26 Vdc. It can deliver up to 1 A per channel with a maximum of 6 A total for all channels. The power Input (8 to 26 Vdc) powers both the outputs and the SDM-CD8S logic.

SDM Operation

The SDM-CD8S is a synchronously addressed datalogger peripheral. Datalogger control ports 1, 2, and 3 are used to address the SDM-CD8S, then clock out the desired state of each of the eight control ports. Up to 15 SDM-CD8S Controllers may be addressed, making it possible to control a maximum of 120 ports from the first three datalogger control ports.



Supply Voltage 8 to 26 Vdc
Logic Current Drain (@ 12 Vdc)
  • 15 mA (quiescent)
  • 2.5 mA per active LED (manual or auto)
Toggle Switch
  • Individual dip switches for manual
Maximum Current
  • 1 A (per channel)
  • 6 A (all channels total)
Actuation/Release Times 8 μs/200 μs
Operating Temperature -40° to +70°C
Dimensions 11.1 x 8.6 x 2.4 cm (4.4 x 3.4 x 0.9 in.)


Datalogger Considerations

Up to 15 SDM devices can be connected to a single datalogger. To communicate with connected SDM devices, the CR3000 and CR5000 use the SDM-C1, SDM-C2, and SDM-C3 ports. The other dataloggers use ports labeled C1, C2, and C3. The 21X also requires channel 1H.

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:
*Although the CR9000X and CR9000 are compatible, the SDM-CD8S does not support their fastest communication rates and therefore is not practical for most of their applications.

**For the CR7, SDMs connect to the C1, C2, and C3 terminals provided on the CR700X control module (after September 1996).

Power Considerations

The SDM-CD8S power requirements may be large compared to most Campbell Scientific products. For most applications, an external power supply is recommended to power the SDM-CD8S.

For some applications, it may be convenient to use the datalogger’s sealed-rechargeable battery. If the datalogger’s rechargeable batteries are used, the batteries need to be float charged via a wall charger or solar panel. The current available from the wall charger limits the SDM continuous output current. Campbell Scientific does not recommend using the datalogger’s alkaline power supply.

Enclosure Considerations

The SDM-CD8S requires a desiccated, non-condensing environment; a Campbell Scientific enclosure is recommended. Grommets and screws are provided to attach the flanges/bracket to the backplate of our enclosures.

Compatible Enclosures

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

Frequently Asked Questions

Number of FAQs related to SDM-CD8S: 5

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  1. The SDM-CD8S and SDM-CD16S were specifically designed to switch solenoids (inductive loads), similar to those found on valves. The diode, to protect against voltage kickback, is built into the device. The SDM-CD16AC, however, does not have this diode.

  2. No. The SDM-CD8S was designed to switch dc loads (12 Vdc nominal; 1 A maximum per channel, total current on all channels not to exceed 6 A). The SDM-CD8S switches the - outputs, rather than the + output. This is called a low-side switch. The + output is the same voltage as the PWR used to power the SDM-CD8S to ground.

    To switch an ac load, consider using an SDM-CD16AC.

  3. Yes. Each of the channels on the SDM-CD8S and the SDM-CD16S has a manual control switch. Place the SDM-CD8S or SDM-CD16S into manual control by switching the Manual Control switch to the On position. Now each channel can be turned on or off using its respective switch.

  4. The following relay devices can be used with the CR800 and the CR850:

    • 7321
    • A6REL-12*
    • A21REL-12
    • LR4
    • SDM-CD8S
    • SDM-CD16AC
    • SDM-CD16S

    The CR800 and the CR850 can also be used with a wide variety of third-party relay devices.

    *Because the CR800 and the CR850 only have four digital ports, they do not have the ability to switch all six of the relays on the A6REL-12.

  5. Yes. SDM devices are addressable. Multiple SDM devices can be connected to a datalogger, as long as they all have a unique SDM address. Valid addresses are 0 through 15. Address 16 is reserved for SDM devices that support the Group Trigger Command. The address is set using the rotary switch on the face of the SDM-CD8S or SDM-CD16S.

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