SDM-CD16ACA 16-Channel AC/DC Relay Controller
RoHS-Compliant Controller
Use multiple modules for up to 256 control ports
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With an SDM-CD16ACA, your Campbell Scientific data logger 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 data logger’s program or controlled manually with an override toggle switch.

The SDM-CD16ACA is a RoHS-compliant version of the SDM-CD16AC.

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Benefits and Features

  • Allows the data logger to automatically turn devices on or off when a threshold (for example, temperature or water depth) has been reached
  • Addresses up to 15 SDM-CD16ACAs, allowing up to 240 ports to be controlled by one data logger
  • Includes LEDs that indicate when a port is active
  • Provides a manual override for each port
  • UL/CUL approved product; RoHS compliant


Detailed Description

The SDM-CD16ACA has a toggle switch that provides three positions: ON and OFF for manual override, and AUTO for data logger 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 data logger’s control ports or SDM terminal.

SDM Operation

The SDM-CD16ACA is a synchronously addressed data logger peripheral. Data logger control ports 1, 2, and 3 are used to address the SDM-CD16ACA, then clock out the desired state of each of the 16 control ports. Up to 15 SDM-CD16ACAs may be addressed, making it possible to control a maximum of 256 ports from the first three data logger control ports.


Function Allows a data logger to automatically activate external ac or dc devices such as motors, pumps, heaters, valves, and fans.
Number of Channels 16
Operating Temperature -40° to +55°C
Humidity Non-condensing
Contact Operation Single pole double throw (break before make)
Contact Material Gold-clad silver
Coil Voltage 11 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 data logger control
Operating Voltage 12 Vdc nominal (11 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

Normally Open Rating
  • 5 A (@ 30 Vdc)
  • 5 A (@ 250 Vac, GP)
  • 1 A (@ 240 Vac, Pilot Duty)
  • 3 A (@ 120 Vac, Pilot Duty)
  • 5 A (@ 240 Vac, Resistive)
Normally Closed Rating
  • 1 A (@ 30 Vdc)
  • 2 A (@ 277 Vac, GP)
  • 3 A (@ 125 Vac, GP)
  • 2 A (@ 120 Vac, Pilot Duty)
  • 3 A (@ 240 Vac, Resistive)

Current Drain @ 12 Vdc

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


Note: The following shows notable compatibility information. It is not a comprehensive list of all compatible or incompatible products.


Product Compatible Note
21X (retired)
CR10 (retired)
CR1000 (retired)
CR10X (retired)
CR200X (retired)
CR206X (retired)
CR211X (retired)
CR216X (retired)
CR23X (retired)
CR295X (retired)
CR3000 (retired)
CR500 (retired)
CR5000 (retired)
CR510 (retired)
CR800 (retired)
CR850 (retired)
CR9000 (retired) Although the CR9000 is compatible, the SDM-CD16ACA does not support its fastest communication rates and therefore is not practical for most of its applications.
CR9000X (retired) Although the CR9000X is compatible, the SDM-CD16ACA does not support its fastest communication rates and therefore is not practical for most of its applications.

Mounting Equipment

Product Compatible Note

Distributed Data Acquisition

Product Compatible Note
Granite 10
Granite 6
Granite 9

Additional Compatibility Information

Data Logger Considerations

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


The SDMCD16AC Instruction controls SDM-CD16ACA operation in CRBasic. Edlog Instruction 29 controls SDM-CD16ACA operation in the CR7, and Edlog Instruction 104 controls SDM-CD16ACA operation in the CR10(X), CR23X, and 21X data loggers.

Power Considerations

The data logger's rechargeable power supply, connected to our newer 1.2 A wall charger, is sufficient for powering the SDM-CD16ACA. The SDM-CD16ACA'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-CD16ACA will be used, a deep-discharge external battery may be necessary. This external battery should share a common grounding point with the data logger's ground.

Campbell Scientific does not recommended using the data logger’s alkaline batteries to power the SDM-CD16ACA for long-term applications.

Enclosure Considerations

The SDM-CD16ACA 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.

Frequently Asked Questions

Number of FAQs related to SDM-CD16ACA: 4

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  1. Yes. Up to 15 SDM devices can be attached to a data logger 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-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-CD16ACA.

  3. 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-CD16ACA.

  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-CD16ACA
    • 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.