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 using 229 probes to measure soil water matric potential.
The CE4 is typically activated via a datalogger control port. When the CE4 receives the datalogger's control signal, all four of the CE4's channels output a 50 mA source current to the connected loads. When the control signal is dropped to 0 Vdc, output from the module ceases.
The CABLE3CBL can be used to connect the CE4 to the datalogger (see Ordering Info).
The CE4 requires 12 Vdc power. A datalogger 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.
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.
Number of FAQs related to CE4: 7
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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.
The CE4 and CE8 have CMOS circuitry controlled by a 0 to 5 Vdc analog signal provided by a datalogger control port.
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.
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.
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 datalogger 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 dataloggers. See the specific datalogger’s manual for further details
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.