This product is no longer available and has been replaced by: SDM-CD16ACA.
SDM-CD16AC 16-Channel AC/DC Relay Controller
Services Available
Repair Yes
Calibration Yes
Free Support Yes


With an SDM-CD16AC, 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.

Read More

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 16 SDM-CD16ACs, allowing up to 256 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


Detailed Description

The SDM-CD16AC 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-CD16AC is a synchronously addressed data logger peripheral. Data logger 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 16 SDM-CD16ACs 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 (@ 125 Vac)
  • 5 A (@ 250 Vac)
Normally Closed Rating
  • 1 A (@ 30 Vdc)
  • 3 A (@ 125 Vac)
  • 2 A (@ 250 Vac)

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.

Data Loggers

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-CD16AC 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-CD16AC 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 16 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-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 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-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 data logger's ground.

Campbell Scientific does not recommended using the data logger’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.


SDM-CD16AC Program Examples v.1 (3 KB) 04-11-2022

There are three example programs for the CDM-CD16AC. The first program demonstrates using two SDM-CD16AC modules to control pumps and heaters based on water level and temperature thresholds. The remaining two programs are designed to control the temperature in five greenhouses. The temperature will be maintained between 23 and 28 °C in each greenhouse. In each greenhouse, the SDM-CS16AC controls a heating unit, a refrigerating unit, and an air-mixing fan according to these conditions.  

Heating unit: Activate when temperature < 23.5 °C. Deactivate when temperature > 25.5 °C

Cooling unit: Activate when temperature > 27.5 °C. Deactivate when temperature < 24.5 °C

Mixing fan: Activate whenever the heating or cooling units are activated. Activate for 5 minutes out of every 15 minutes.

The difference between program 2 and program 3 is the method used to control outputs. Program 2 uses an array to set the SDM-CD16AC outputs. Program 3 uses a Long integer, with each bit in the variable controlling one of the outputs.

Frequently Asked Questions

Number of FAQs related to SDM-CD16AC: 1

  1. 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.

Case Studies

New Mexico: SCADA System
In April of 2015, Sandia National Laboratories (SNL) contracted with Montrose Air Quality Services (MAQS) more
Flemish Coast: Pile Monitoring
Cofely Fabricom NV/SA (GDFSuez) has utilized Campbell Scientific equipment on numerous projects in both more
New Jersey: Trout Hatchery
Moving clean, cold water through a trout-rearing facility is essential to its success. A more
Australia: Examining the Impacts of Carbon Dioxide and Climate Change
An experimental facility (OzFace) has been established in Townsville, Australia to examine the impacts more
California: Monitoring Water Quality at a Recirculating Aquaculture Facility
In August 1996, Stolt Sea Farm ( installed a Campbell Scientific monitoring and control system more
Mississippi: Dissolved Oxygen Monitoring and Control
Successful aquaculture ultimately hinges on concentrations of dissolved oxygen. Measurement of DO is the more

This Product Replaced

Privacy Policy Update

We've updated our privacy policy.  Learn More

Cookie Consent

Update your cookie preferences.  Update Cookie Preferences