Instruction manual

SECTION 2. STATION INSTALLATION
2-6
TABLE 2.6-1. CA27 and KH20 Sensor Lead
Color Assignments
Sensor Color
CA27 Wind + Green
CA27 Wind - Black
CA27 Shield Clear
CA27 Temperature + White
CA27 Temperature - Black (same as Wind-)
CA27 +12 V Red
CA27 Power Gnd Black of Red and Black
KH20 Water Vapor + White
KH20 Water Vapor - Black
KH20 Shield Clear
KH20 +12 V Red
KH20 Power Gnd Black of Red and Black
Tables 2.6-2 and 2.7-1 list the connections to
the 21X for the example program in Section 3.
The following sensors are measured in the
example:
• CA27 (vertical wind speed and temperature
fluctuations)
• KH20 (water vapor density fluctuations)
• Q7 (net radiation)
• HFT3 (soil heat flux)
• TCAV (soil temperature)
• HMP35C (ambient air temperature and
relative humidity)
• 03001 (wind speed and direction)
• CS615 (soil moisture)
TABLE 2.6-2. 21X/Sensor Connections for
Example Program
Channel Sensor
Color
1H CA27 + (wind) Green
1L CA27 - (wind/temp) Black
GND Shield Clear
2H CA27 + (temp) White
2L jumper to 1L
GND
3H KH20 + (vapor) White
3L KH20 - (vapor) Black
GND Shield Clear
4H TCAV + (soil temp) Purple
4L TCAV - (soil temp) Red
GND
5H HMP35C (air temp) Orange
5L HMP35C (humidity) Green
GND Ground/Shield White/Clear
6H HTF1 #1 (soil heat flux) Black
6L HTF1 #2 (soil heat flux) Black
GND Ground/Shield White/Clear
Ground/Shield White/Clear
7H Not used
7L 03001 (wind direction) Red
GND 03001 Ground/Shield White/Clear
8H Q7 + (net radiation) Red
8L Q7 - (net radiation) Black
GND Shield Clear
1EX HMP35C (temp) Black
2EX 03001 (wind direction) Black
1C HMP35C (turn unit on) Yellow
GND HMP35C (power ground) Purple
2C CS615 (turn unit on) Orange
1P 03001 (wind speed) Black
GND Ground/Shield White/Clear
2P CS615 (soil water content) Green
GND Ground/Shield Black/Clear
+12 HMP35C Red
+12 CS615 Red
GND To the common earth ground
2.7 POWER
The CA27 and KH20 are powered by an
external battery. A user-supplied 70 Ahr deep
cycle RV battery will run the system for
approximately two months. The CA27 and
KH20 power cables are connected directly to
the battery terminals. Disconnect the power
cables when the system is not collecting data,
e.g. during a rain shower.
Power the 21X from the external battery. Table
2.7-1 summarizes the power connections.
NOTE: If the 21X is powered by an
external battery, it must have a blocking
diode in the supply line from its internal
batteries to prevent reverse charging of the
alkaline cells by the external battery. This
diode has been standard on all 21Xs
shipped since January 19, 1987. If an
earlier 21X is being used, either add the
diode (contact Campbell Scientific for
details) or turn off the 21X power switch
while the external battery is connected.