CS650 and CS655 Water Content Reflectometers
19
CS650. For the CS655, the upper limit for bulk EC is 3.04 dS/m,
corresponding to a solution EC of 8 dS/m. When this bulk EC condition
occurs, the soil is considered out-of-bounds and the
M3!
command reports
NAN or 9999999 for both permittivity and volumetric water content.
Voltage ratio is too high
When the voltage ratio is greater than 17, bulk electrical conductivity readings
become unstable. When this bulk EC condition occurs, the
M3!
command
reports NAN or 9999999 for both permittivity, volumetric water content, and
bulk EC.
8.2.2 Use of Multiplexers
Multiplexers such as Campbell Scientific AM16/32B can connect up to 32
CS650 sensors to a single control or
U
terminal. When using multiplexers, the
simplest configuration is for all sensors to have the same SDI-12 address.
When multiplexing CS650 sensors, use the switched 12V terminal so power to
the sensor is turned off under program control before the multiplexer switches
to the next terminal.
Failure to turn off the switched 12 Volt terminal before
clocking the multiplexer damages the multiplexer relays.
The proper sequence in the datalogger program for measuring CS650 sensors
on a multiplexer is:
1.
Set RES control port high to enable multiplexer
2.
Pulse CLK control port to advance to next multiplexer terminal
3.
Set switched 12 volt terminal high to supply power to CS650
4.
Delay for 3 seconds for sensor to warm up
5.
Send SDI-12 command(s) to CS650
6.
Set switched 12 volt terminal low to remove power from CS650
7.
Repeat steps 2 through 5 for each CS650 connected to the multiplexer
8.
Set RES control port low to disable multiplexer
Program examples in Appendix
(p. B-1)
, show the
commands used in CRBasic.
8.3 Water Content Reflectometer Method for Measuring
Volumetric Water Content
8.3.1 Description of Measurement Method
For the water content measurement, a differential emitter-coupled logic (ECL)
oscillator on the circuit board is connected to the two parallel stainless steel
CAUTION
