The CE8 is a current-excitation module that applies a constant current to the heating element of up to eight 229 Heat Dissipation Water Matric Potential Sensors. A current-excitation module is required when you use 229 sensors to measure soil water matric potential.Read More
A CE8 current excitation module can provide a constant current to the heating element of the 229. The CE8 sources current for up to eight 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 CE8 to one or more AM16/32-series multiplexers. Up to eight multiplexers can be connected to the CE8.
Note: The CE8 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 CE8 have been connected may become unsuitable for other applications. (Refer to the multiplexer manual for more information.)
|Output||50 mA ±0.25 mA (regulated)|
|Power||12 Vdc source required|
|Active Current Drain||25 mA + (50 mA) x (number of 229s connected to the CE8)|
|Dimensions||16.5 x 5.4 x 2.7 cm (6.5 x 2.1 x 1.1 in.)|
|Weight||184 g (6.5 oz)|
Note: The following shows notable compatibility information. It is not a comprehensive list of all compatible or incompatible products.
The CABLE3CBL can be used to connect the CE8 to the data logger. (See the Ordering information.)
The CE8 requires 12 Vdc power. A data logger control port is typically used to activate the module. When the control signal is received, all 8 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 CE8 outputs).
The CE8 can source current for eight probes directly. In applications that require more sensors, the output(s) of the CE8 can be connected to as many as eight 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 CE8 requires a desiccated, non-condensing environment; a Campbell Scientific enclosure is recommended. The CE8'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 CE8: 7
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The CE4 and CE8 have CMOS circuitry controlled by a 0 to 5 Vdc analog signal provided by a data logger control port.
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 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
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.
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 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.