How are the CS650 and the CS655 different from the CS616?

The CS650 and CS655 are multiparameter smart sensors that send data by RS-232 serial or SDI-12 communications. The CS650 and CS655 measure temperature, period average, and signal attenuation (voltage ratio). The sensors calculate volumetric water content, permittivity, and bulk electrical conductivity. Permittivity and volumetric water content values are corrected for signal loss in conductive soil. Each CS650 or CS655 may be given a unique SDI-12 address so that many sensors can communicate with a data logger while they are connected to the same terminal. SDI-12 commands are used to poll the sensor. Both the CS650 and the CS655 are more expensive than the CS616.

The CS616 output is a square sine wave whose frequency varies with changing bulk dielectric permittivity. It requires a data logger capable of detecting the frequency or average period at which the sine wave crosses the zero volt threshold. Each CS616 requires its own analog input channel on the data logger. An enable voltage must be sent to the CS616 to supply power and make a measurement. The period average reading is converted to volumetric water content with a quadratic or power function. The CS616 makes no temperature or electrical conductivity measurement and does not compensate for signal loss in conductive soil. The CS616 is less expensive than both the CS650 and the CS655, but it does less.    

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