229-L

Current Excitation Modules

Either a CE4 or CE8 current excitation module is required to provide a constant current to the heating element of the 229. The CE4 and CE8 differ only in the number of 229 sensors to which they source current. The CE4 sources current for up to four 229s, and the CE8 sources current for up to eight. Both modules require a 12 Vdc power source.

Multiplexers

In applications that require more sensors, the output(s) of the CE4 or CE8 can be connected to as many AM16/32-series multiplexers as there are outputs, greatly expanding system capacity. If using multiplexers, the user should be aware that switching currents of greater than 30 mA will degrade the contact surfaces of the mechanical relays. Therefore the datalogger should be programmed to turn off the current excitation module before switching multiplexer channels in order to protect the multiplexer relays.

Datalogger Considerations

One differential channel and one current excitation channel per probe are required. Each CE4 or CE8 current excitation module requires one datalogger control port.

Programming

The 229 is measured by a sequence of datalogger instructions where the thermocouple is measured at 0 s, 1 s, and 30 s, while a 50 mA current is applied to the heating element. This current is supplied by the CE4 or CE8 current excitation module. The rise in temperature during heating is related to the soil water matric potential.

Compatible Contemporary Dataloggers

CR200(X) Series	CR800/CR850	CR1000	CR3000	CR5000	CR7X	CR9000X

Compatible Retired Dataloggers

CR500	CR510	CR10	CR10X	21X	CR23X	CR9000

Reference Temperature Measurement

A reference temperature measurement is required. Options for measuring the reference temperature include:

• Thermistor built into the CR800, CR850, CR1000, CR3000, or CR5000 wiring panel
• PRT built into the wiring panel of the CR9050 or
• CR9051E input module for the CR9000X Measurement and Control Datalogger
• PRT built into the wiring panel of the CR723T input card for the CR7 Measurement and Control Datalogger
• CR10XTCR thermistor that connects to the CR10X wiring panel