SDM-CD16AC 16-Channel AC/DC Relay Controller
Greatly Expands Control Capacity
Use multiple modules for up to 256 control ports
weather applications water applications energy applications gas flux & turbulence applications infrastructure applications soil applications


With an SDM-CD16AC, your Campbell Scientific datalogger can automatically activate external ac or dc devices such as motors, pumps, heaters, valves, and fans. This ac/dc relay controller has 16 ports for connecting your ac or dc devices. Each port can be controlled automatically by the datalogger’s program or controlled manually with an override toggle switch.

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Benefits and Features

  • Allows the datalogger to automatically turn devices on or off when a threshold (for example, temperature, water depth) has been reached
  • Addresses up to 15 SDM-CD16ACs, allowing up to 240 ports to be controlled by one datalogger
  • Includes LEDs that indicate when a port is active
  • Provides a manual override for each port
  • UL/CUL approved product


Detailed Description

The SDM-CD16AC has a toggle switch that provides three positions: ON and OFF for manual override, and AUTO for datalogger control. In the ON position, the common (COM) and normally open (NO) contacts are closed. In the OFF position, the normally open contact is open. In the AUTO position, the state of the relay is controlled by the SDM command issued through the datalogger’s control ports or SDM terminal.

SDM Operation

The SDM-CD16AC is a synchronously addressed datalogger peripheral. Datalogger control ports 1, 2, and 3 are used to address the SDM-CD16AC, then clock out the desired state of each of the 16 control ports. Up to 15 SDM-CD16ACs may be addressed, making it possible to control a maximum of 240 ports from the first three datalogger control ports.


Operating Temperature -25° to +50°C
Humidity Non-condensing
Contact Operation Single pole double throw (break before make)
Contact Material Gold-clad silver
Coil Voltage 9 to 18 Vdc
Coil Resistance 360 Ω ±10%
Expected Life (contact closures) Mechanical 107
Actuation/Release Time ~4 ms
Toggle Switch
  • ON/OFF manual override
  • AUTO for datalogger control
Operating Voltage 12 Vdc nominal (9 to 18 Vdc)
Standards Underwriters Laboratories (UL) listed product (E162021)
Dimensions 24.6 x 5.1 x 8.6 cm (9.7. x 2.0 x 3.4 in.)
Weight 0.8 kg (1.8 lb)

Individual Contact Ratings

For DC Devices
  • 5 A (@ 30 Vdc)
  • 0.3 A (@ 110 Vdc)
For AC Devices
  • 5 A (1/10 hp) @ 125 Vac
  • 5 A (1/6 HP) @ 277 Vac

Current Drain @ 12 Vdc

Quiescent 6 mA
Per Active LED 45 mA (switch on or auto active)


Datalogger Considerations

Up to 15 SDMs can be connected to our dataloggers. 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.


The SDMCD16AC Instruction controls SDM-CD16AC operation in CRBasic. Edlog Instruction 29 controls SDM-CD16AC operation in the CR7, and Edlog Instruction 104 controls SDM-CD16AC operation in the CR10(X), CR23X, and 21X dataloggers.

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-CD16AC 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 Sept 1996).

Power Considerations

The datalogger's rechargeable power supply, connected to our newer 1.2 A wall charger, is sufficient for powering the SDM-CD16AC. The SDM-CD16AC's LEDs consume 45 mA each when active. If all 16 LEDs are active at once, a current drain of over 720 mA should be expected. If more than one SDM-CD16AC will be used, a deep-discharge external battery may be necessary. This external battery should share a common grounding point with the datalogger's ground.

Campbell Scientific does not recommended using the datalogger’s alkaline batteries to power the SDM-CD16AC for long-term applications.

Enclosure Considerations

The SDM-CD16AC 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-CD16AC: 4

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  1. Yes. Up to 15 SDM devices can be attached to a datalogger because they are addressable with a hex number of 0 to F.  Some of those devices may require more power, which would need to be considered when adding devices.

  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. No. The SDM-CD16S was designed to switch dc loads (7 to 48 Vdc; 2 A maximum per channel). The load power is isolated from the logic power (12 Vdc).

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

  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.

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