Campbell CR3000 Micrologger, Руководство оператора

Страница: 425 / 644

Section 8. Operation
425
Current Source and Sink Limits
Terminal
Limit
1
4
Polyfuse protected. See footnote 3.
5
Current is limited by a current limiting circuit, which holds the current at the maximum by
dropping the voltage when the load is too great.
8.2.1 Switched-Voltage Excitation
Four switched, analog-output (excitation) terminals (VX1 to VX4) operate under
program control to provide ±5000 mV dc excitation. Check the accuracy
specification of terminals configured for exctitation in Specifications
(p. 95)
to
understand their limitations. Specifications are applicable only for loads not
exceeding ±25 mA.
CRBasic instructions that control voltage excitation include the following:
•
BrFull()
•
BrFull6W()
•
BrHalf()
•
BrHalf3W()
•
BrHalf4W()
•
ExciteV()
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 (IX Terminals)
Three switched, current-output terminals (IX1, IX2, and IX3), each used in
conjunction with a common return (IXR) terminal, operate under program control
to provide –2500 µA to +2500 µA for making resistance measurements. Check
the accuracy specification of these terminals in Specifications
(p. 95)
to understand
their limitations. CRBasic instructions that control current excitation include the
following:
•
ExciteI()
•
Resistance()
See Current Excitation Cabling
(p. 421)
for precautions when measuring resistances
> 1000 Ω or sensors with leads > 50 feet.