CE4 4-Channel Current-Excitation Module
Multiply Capability
Provides excitation current for up to 4 model 229 soil-water sensors
weather applications water applications energy applications gas flux and turbulence applications infrastructure applications soil applications


The CE4 is a current-excitation module that applies a constant current to the heating element of up to four 229 Heat Dissipation Water Matric Potential Sensors. A current-excitation module is required when you use 229 sensors to measure soil water matric potential.

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Benefits and Features

  • Provides excitation current for up to four 229 sensors
  • Allows up to four AM16/32-series multiplexers to be connected, which significantly expands the system's capacity
  • Compatible with most Campbell Scientific data loggers


Detailed Description

A CE4 current excitation module can provide a constant current to the heating element of the 229. The CE4 sources current for up to four 229s. The module requires a 12 Vdc power source. The number of 229 sensors measured by one data logger can be increased by connecting a CE4 to one or more AM16/32-series multiplexers. Up to four multiplexers can be connected to the CE4.

Note: The CE4 module switches currents that are greater than 30 mA, which degrades the contact surfaces of the mechanical relays. Therefore, the multiplexer channels to which the CE4 have been connected may become unsuitable for other applications. (Refer to the multiplexer manual for more information.)


Output 50 mA ±0.25 mA (regulated)
Output Channels 4
Power 12 Vdc source required
Active Current Drain 25 mA + (50 mA) x (number of 229s connected to the CE4)
Dimensions 11.5 x 5.4 x 2.7 cm (4.5 x 2.1 x 1.1 in.)
Weight 131 g (4.6 oz)


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)
CR9000 (retired)
CR9000X (retired)

Mounting Equipment

Product Compatible Note

Additional Compatibility Information

Data Logger Considerations

The CABLE3CBL can be used to connect the CE4 to the data logger (see Ordering Info).

Power Considerations

The CE4 requires 12 Vdc power. A data logger control port is typically used to activate the module. When the control signal is received, all 4 channels output a 50 mA source current to the connected loads (typically 229 probes). When the control signal is dropped to 0 Vdc, output from the module ceases.

When active, the current required from the 12 V supply is approximately the following:

25 mA + (50 mA)(the number of 229 sensors connected to the CE4 outputs).


The CE4 can source current for four probes directly. In applications that require more sensors, the output(s) of the CE4 can be connected to as many as four AM16/32B multiplexers, greatly expanding system capacity.

When using multiplexers, the user should be aware that switching currents of greater than 30 mA will degrade the contact surfaces of the mechanical relays. This will adversely affect the suitability of these relays to multiplex low voltage signals. Although a relay used in this manner no longer qualifies for low voltage measurements, it continues to be useful for switching currents in excess of 30 mA. Therefore the user is advised to record which multiplexer channels are used to multiplex the 50 mA excitation for the 229-L probes in order to avoid using those channels for low voltage measurements in future applications.

Enclosure Considerations

The CE4 requires a desiccated, non-condensing environment; a Campbell Scientific enclosure is recommended. The CE4's case has mounting flanges for attachment to the 1"-on-center hole grid of Campbell Scientific enclosures. Grommets and screws are provided to attach the flanges to the backplate of our enclosures.

Frequently Asked Questions

Number of FAQs related to CE4: 7

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  1. No. Typically a PRT will experience self-heating if more than 1 mA of current excitation is applied, while the CE4 or CE8 output is 50 mA.
  2. The CE4 and CE8 have CMOS circuitry controlled by a 0 to 5 Vdc analog signal provided by a data logger control port.

  3. The active current drain can be calculated using the following equation:
    Current drain = 25 mA + (50mA) x (number of 229-L sensors connected to the CE4 or CE8)

    For example, the current drain of a CE4 with 3 sensors is calculated like this:
    Current drain = 25 mA + (50 mA) x (3 sensors) = 25 mA + 150 mA = 175 mA.

    • The current drain for a CE4 ranges from 75 mA to 225 mA.
    • The current drain for a CE8 ranges from 75 mA to 425 mA.
  4. While this could be done for a maximum resistance of 50 ohms in the ±2500 mV range and 100 ohms in the ±5000 mV range, it is not the best way to determine resistance. The preferred method for measuring an unknown resistance is to use data logger excitation channels. Current excitation channels can be used with a CR3000. Analog excitation channels with half-bridge or full-bridge circuitry can be used for other data loggers. See the specific data logger’s manual for further details

  5. The CE4 and CE8 are constant current devices designed to produce 50 mA of current on each channel.  The voltage output will vary with the resistance of the connected load following Ohm’s law:  

    Vout = 0.05 A/RL where Vout is produced in volts and RL is the resistance of the load in ohms.

  6. Campbell Scientific recommends using the CABLE3CBL-L, a 22 AWG cable with three conductors and a drain wire. However, any type of copper wire between 18 AWG and 22 AWG could be used to control the CE4/CE8.

  7. The CE4 and CE8 are constant current devices designed to produce a constant current to the 229-L Water Matric Potential Sensor. See the 229-L product page for more information. 

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