Campbell CR6 Series, Руководство оператора

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Section 8. Operation
474
Note Square-wave ac excitation for use with polarizing bridge sensors is
configured with the RevEx parameter of the bridge instructions.
8.2.2 Switched-Current Excitation
U
terminals can be configured as current-output terminals. These are used under
program control for making resistance measurements. Check the accuracy
specification of these terminals in Specifications
(p. 101)
to understand the
limitations. Use the terminal adjacent to the current source terminal as the
current return. CRBasic instructions that control current excitation include the
following:
•
ExciteI()
•
Resistance()
See Current Excitation Cabling
(p. 470)
for precautions when measuring resistances
> 1000 Ω or sensors with leads > 50 feet.
8.2.3 Continuous-Unregulated Voltage (12V Terminal)
Use 12V terminals to continuously power devices that require 12 Vdc. Voltage
on the 12V terminals will change with CR6 supply voltage.
Caution Voltage levels at the 12V and switched SW12 terminals, and pin
8 on the CS I/O port, are tied closely to the voltage levels of the main
power supply. For example, if the power received at the BAT terminals is
16 Vdc, the
12V
and
SW12
terminals, and pin 8 on the
CS I/O
port, will
supply 15.7 Vdc (0.3 V less than main supply) to a connected peripheral.
If the connected peripheral or sensor is not designed for that voltage level,
it may be damaged.
8.2.4 Switched-Unregulated Voltage (SW12 Terminal)
The SW12 terminals are often used to power devices such as sensors that require
12 Vdc during measurement. Voltage on a SW12 terminal will change with CR6
supply voltage. CRBasic instruction
SW12()
controls the
SW12
terminals.
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. 210).
A 12 Vdc switching circuit designed to be driven by a U or C terminal is available
from Campbell Scientific. It is listed in Relay Drivers — List
(p. 656).