Campbell Scientific CR200/CR200X-series Dataloggers - Manual (Page 62)

Section 5. Measurement and Control Peripherals
Figure 33: Control Port Current Sourcing
5.1.1.2 Switched 12 V Control
The SW Battery port can be set low (0 V) or high (12 V) using the SWBatt ()
instruction. The port is often used to control low power devices such as sensors
that require 12 V during measurement. Current sourcing must be limited to 900
mA or less at 20°C. See TABLE. Current Sourcing Limits (p. 38).
A 12V switching circuit, driven by a digital I/O port, is also available from
Campbell Scientific.
Note The SW Battery supply is unregulated and can supply up to 900 mA at
20°C. See TABLE. Current Sourcing Limits (p. 38). A resettable polymeric
fuse protects against over-current. Reset is accomplished by removing the load
or turning off the SW Battery for several seconds.
5.1.1.3 Relays and Relay Drivers
Compatible, inexpensive and reliable single-channel relay drivers for a wide
range of loads are available from various electronic vendors such as Crydom,
Newark, Mouser, etc.
5.1.1.4 Component Built Relays
FIGURE. Relay Driver Circuit with Relay (p. 51) shows a typical relay driver
circuit in conjunction with a coil driven relay which may be used to switch
external power to some device. In this example, when the control port is set
high, 12 V from the datalogger passes through the relay coil, closing the relay
which completes the power circuit and turns on the fan.
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