This product is no longer available and has been replaced by: SDM-AO4A. Some accessories, replacement parts, or services may still be available.
SDM-AO4 Analog Output Module


The SDM-AO4 is a synchronous device for measurement (SDM) that provides four analog outputs. Values in the datalogger are transferred to the SDM-AO4 as digital values. The SDM-AO4 then performs a digital-to-analog conversion and outputs an analog voltage signal.

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Benefits and Features

  • Expands datalogger current/voltage output capability
  • Supports proportional control or strip charts


Detailed Description

The SDM-AO4 provides four independent, continuous, analog outputs for proportional control or driving strip charts. Measured or processed values in the datalogger are scaled to millivolts and transferred to the SDM-AO4 as digital values. The SDM-AO4 then performs a digital to analog conversion and outputs an analog voltage signal. The output voltage level is maintained until updated by the datalogger.

SDM Operation

The datalogger enables individual modules through an addressing scheme; multiple SDMs (in any combination) can be connected to one datalogger. After a module is enabled, it operates independently of the datalogger until additional commands are received or results are transmitted.


Analog Output Range ±5000 mV
Analog Output Resolution 2.5 mV
Output Resistance 200 ohm
Accuracy ±(0.5% of l Vout l +5 mV) for loads 75 kohm or greater
Operating Voltage 9.6 to 16 Vdc
Typical Current Drain 10.5 mA
Output Current < 0.125 mA
Minimum Load 75000 ohm


Datalogger Considerations

Up to 16 SDM devices can be connected to a single datalogger.


The SDMAO4 Instruction controls the SDM-AO4 operation in CRBasic; Instruction 103 controls the SDM-AO4 operation in Edlog.

Compatible Contemporary Dataloggers

CR200(X) Series CR800/CR850 CR1000 CR3000 CR9000X

*For the CR3000 and CR5000, SDMs are connected to the ports labeled SDM-C1, SDM-C2, and SDM-C3.

Compatible Retired Dataloggers

CR500 CR510 CR10 CR10X 21X CR23X CR9000 CR5000 CR7X
* **

**The CR7X requires a CR700X module ordered after 1 Sept 1996 or upgraded to include a CR700X CPU module.

Power Supply

It is often convenient to power the SDM-AO4 from the datalogger power supply, but when doing so consideration must be given to the SDM-AO4’s 10.5 mA continuous current drain. The alkaline supply available with the datalogger has 7.5 Ahr and will power one SDM-AO4 for less than one month. This supply is not recommended for continuous long-term operation. The datalogger’s sealed rechargeable power supply, float charged by an ac supply or solar panel, may be used for long-term operation.

The SDM-AO4 may also be powered from an external 12 V supply, independent from the datalogger supply. The low side of an external 12 V supply should be connected to datalogger ground and not directly to earth grounded.

Enclosure Considerations

The SDM-AO4 requires a desiccated, non-condensing environment; a Campbell Scientific enclosure is recommended. SDM-AO4 serial numbers 2145 or higher have built-in keyhole flanges for mounting to the backplates of Campbell Scientific enclosures; the first unit to use these flanges was shipped in 18 September 1997. Grommets and screws are provided to attach the flanges/bracket to the backplate of our enclosures. Older SDM-AO4s required our 6279 SDM-AO4 Mounting Bracket (now retired) for this purpose.

Compatible Enclosures

ENC10/12 ENC10/12R ENC12/14 ENC14/16 ENC16/18

Case Studies

Northern California: Hydro-SCADA
The Yuba County Water Agency (YCWA) needed to upgrade an unsupportable hydrologic supervisory, control, more

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