Campbell CR800 Series, Operator'S Manual

Page: 391 / 598

Section 8. Operation
391
8.2.4 Switched-Unregulated Voltage (SW12 Terminal)
The SW12 terminal is often used to power devices such as sensors that require 12
Vdc during measurement. Current sourcing must be limited to 900 mA or less at
20 °C. Voltage on a SW12 terminal will change with CR800 supply voltage.
CRBasic instruction
SW12()
controls the
SW12
terminal. Configure
SW12()
as
a measurement or processing task in the instruction. Use it as a processing task
when controlling power to SDI-12 and serial sensors that use SDI12Recorder()
or SerialIn() instructions respectively. CRBasic programming using IF THEN
constructs to control
SW12
, such as when used for cell phone control, should also
use the SW12() instruction. See Execution and Task Priority
(p. 150).
A 12 Vdc switching circuit designed to be driven by a C terminal is available
from Campbell Scientific. It is listed in
Relay Drivers — List
(p. 566).
8.3 PLC Control — Details
Related Topics:
• PLC Control — Overview
(p. 87)
•
PLC Control Modules — Overview
(p. 394)
•
PLC Control Modules — Lists
(p. 565)
• Switched Voltage Output — Specifications
• Switched Voltage Output — Overview
(p. 59)
•
Switched Voltage Output — Details
(p. 388)
•
Current Source and Sink Limits
(p. 389)
The CR800 can control instruments and devices such as the following:
• Wireless cellular modem to conserve power.
•
GPS receiver to conserve power.
•
Trigger a water sampler to collect a sample.
• Trigger a camera to take a picture.
•
Activate an audio or visual alarm.
•
Move a head gate to regulate water flows in a canal system.
• Control pH dosing and aeration for water quality purposes.
•
Control a gas analyzer to stop operation when temperature is too low.
•
Control irrigation scheduling.
Controlled devices can be physically connected to C terminals, usually through an
external relay driver, or the SW12V
(p. 391)
terminal. C terminals can be set low (0
Vdc) or high (5 Vdc) using PortSet() or WriteIO() instructions. Control modules
are available to expand and augment CR800 control capacity. On / off and
proportional control modules are available. See appendix PLC Control Modules
— List
(p. 565).