SDM-CVO4 4-Channel Current and Voltage Output Module
Lets Datalogger Control Voltage
Expands datalogger's current/voltage output capability
weather applications water applications energy applications gas flux & turbulence applications infrastructure applications soil applications


The SDM-CVO4 is attached to a datalogger and outputs variable voltage or current signals under datalogger program control. Typical applications include driving remote current-loop display units, retransmitting measured values to industrial control systems, sending control signals to valve controllers, and providing excitation voltages or currents to external sensors.

Read More

Benefits and Features

  • Expands datalogger current/voltage output capability
  • Provides four independent current or voltage outputs
  • Drives remote current-loop display units
  • Retransmits measured values to industrial control systems that have current or high voltage inputs
  • Sends control signals to valve controllers
  • Provides excitation voltages or currents to external sensors


Close-up of labels

Detailed Description

The SDM-CVO4 includes four output channels for connecting the external devices. It outputs variable voltage or current signals under datalogger program control. The outputs are isolated both from the datalogger and the other channels on the SDM-CVO4, thereby avoiding ground loop problems. Each output can be set to 0 to 10 Vdc or 0 to 20 mA by the datalogger program. (Current outputs can also be scaled and limited to 4 to 20 mA.)

In the current mode, the output either acts as a two-wire current controller, where the loop is powered from a remote voltage source, or generates a 0 to 20 mA current source using a voltage output derived from its own power supply.


The SDM-CVO4 includes an internal isolation barrier and components rated to provide signal isolation for transients up to 1500 Vac (rms), 2500 Vdc nominal. The isolation is between any output and the SDM-CVO4 ground connection and between individual output channels.

Protection components are built-in, which will break down in a controlled fashion at voltages close to this limit. (See the Instruction Manual, Section 4.5 Safety Considerations, for details).


Operating Temperature -25 to +50°C
Operating Voltage 12 Vdc nominal (8 to 16 V)
Minimum Voltage Drop 2.5 V (@ 20 mA current flow) across the internal current regulating circuit
Maximum Input Voltage 20 Vdc (relative to channel ground)
EMC Status Complies with EN55022-1:1998 and EN50082-1:1998.
  • 17.8 x 10.2 x 2.3 cm (7.0 x 4.0 x 0.9 in.) without mounts
  • 23.4 x 11.2 x 2.3 cm (9.2 x 4.4. x 0.9 in.) with mounts
Weight 363 g (13 oz)


Tested Isolation Each channel of each unit is tested for isolation resistance at 500 Vdc.

Pass level > 10 MΩ
Maximum Recommended Continuous Operating Voltage 240 Vac rms differential between an output and datalogger ground, providing all issues relating to local regulations for safe installation and operation are followed (Refer to Section 4.5 Safety Considerations in the Instruction Manual.)

Current Mode

Range 0 to 20,000 µA
Resolution 5 µA
Minimum Output Current (leakage) 5 µA (at +50°C)
Accuracy at +23°C ±0.02% of set current + (±5 µA)
Typical Accuracy at -25° to +50°C ±0.1% of set current + (±5 µA)
Worst Case Accuracy at -25° to +50°C ±0.15% of full scale range + (±5 µA)

Voltage Mode

Range 0 to 10,000 mV
Resolution 2.5 mV
Maximum Output Current 30 mA per channel
Minimum Load Current 5 µA if output < 200 mV
Accuracy at +23°C ±0.02% of set voltage + (±2.5 mV)
Accuracy at -25° to +50°C ±0.13% of set voltage + (±2.5 mV)

Current Drain @ 12 Vdc

Typical Active Current 27 or 54 mA, depending on operating mode (no load on output ports)

To estimate the total current, add the active current to the sum of all output currents multiplied by 1.5. For example, if each port is at 10 mA output, the total = 54 + (1.5•4•10) = 114 mA.
With All Outputs Off < 0.5 mA



The SDMCVO4 instruction controls the SDM-CVO4 operation in CRBasic; Instruction 103 controls the SDM-CVO4 operation in Edlog.

Datalogger Considerations

Compatible Contemporary Dataloggers

CR200(X) Series CR800/CR850 CR1000 CR3000 CR9000X CR6

Compatible Retired Dataloggers

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

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

†Although the CR9000X and CR9000 are compatible, the SDM-CVO4 does not support their fastest communication rates and therefore may not be practical for CR9000(X) applications.

#On the CR7X, SDMs connect to the C1, C2, and C3 terminals provided on the CR700X control module (after Sept 1996).

Power Considerations

The SDM-CVO4 power requirements are large compared to most Campbell Scientific products—especially when driving significant loads. Care must be taken to ensure the power supply can deliver this higher demand. Alkaline batteries are not recommended for long-term applications.

The SDM-CVO4 has two internal power supplies—one for channels 1 and 2 and one for channels 3 and 4. The power supply for channels 3 and 4 is only turned on if the datalogger sends an instruction that sets the output of those channels. If channels 3 and 4 are not used, the power consumption is approximately 20 mA lower than when all outputs are used.

Where supported by the datalogger, and when the application allows it, the SDM-CVO4 can be shut down to reduce its power consumption to less than 0.5 mA. In this state, all outputs are switched off.

Enclosure Considerations

The SDM-CVO4 requires a desiccated, non-condensing environment; a Campbell Scientific enclosure is recommended. A mounting bracket, grommets, and screws attach the SDM-CVO4 to the backplates of a Campbell Scientific enclosure.

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-CVO4: 5

Expand AllCollapse All

  1. The SDM-CVO4 allows most Campbell Scientific dataloggers to produce a value by whatever means measured or derived as a scaled 0 to 20 or 4 to 20 mA signal (four terminals).

    The datalogger sends an instruction to the SDM-CVO4 with the voltage or current to be transmitted to the other device. The SDM-CVO4 does not itself convert a voltage to a current. A datalogger is needed to make a measurement and instruct the SDM-CVO4 as to what the output should be. 

  2. 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.

  3. For the CR1000, to get continuous analog outputs, an SDM-AO4A (4-channels, non-isolated, voltage only) or an SDM-CVO4 (4-channels, isolated, voltage or current) is needed. Multiples of these devices can be used to get more outputs.  For single channels of output, some third-party devices can be used.

  4. To get continuous analog outputs, either the SDM-AO4A (four channels, non-isolated, voltage only) or the SDM-CVO4 (four channels, isolated, voltage or current) is needed. Multiples of those devices can be used to acquire more outputs.
  5. Yes. The CR3000 and CR5000 have two native Continuous Analog Output channels. The SDM-AO4A (voltage) or SDM-CVO4 (voltage or current) can also be used.

Case Studies

Utah: Water-Supply SCADA System
In 2010, Trenton and Amalga, two northern Utah towns separated by only a few miles, more