Campbell Scientific CR3000 Micrologger - Manual (Page 90)

Section 7. Installation
90
Table 6. Current Source and Sink Limits
Terminal Limit
1
5V + CS I/O (combined)
5 < 200 mA
1
"Source" is positive amperage; "sink" is negative amperage (-).
2 Exceeding current limits limits will cause voltage output to become unstable. Voltage should
stabilize once current is again reduced to within stated limits.
3
A polyfuse is used to limit power. Result of overload is a voltage drop. To reset, disconnect and
allow circuit to cool. Operating at the current limit is OK so long a a little fluctuation can be
tolerated.
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.
7.4.5.1 Switched Voltage Excitation
Four switched, analog-output (excitation) terminals (VX1 - VX4) operate under
program control to provide -5000 mVdc to +5000 mVdc excitation. Check the
accuracy specification of these channels in CR3000 Specifications
to understand
their limitations. Specifications are only applicable for loads not exceeding ±25
mA.
Note Table Current Source and Sink Limits
(p. 89)
has more information on
excitation load capacity.
CRBasic instructions that control excitation channels include:
• BrFull()
• BrFull6W()
• BrHalf()
• BrHalf3W()
• BrHalf4W()
• ExciteV()
Note Excitation channels can be configured to provide a square-wave ac
excitation for use with polarizing bridge sensors through the
RevEx parameter of
the previously listed bridge instructions.
7.4.5.2 Switched Current Excitation
Three switched, current-output terminals (IX1, IX2, and IX3), each used in
conjuction 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 channels in CR3000 Specifications
to
understand their limitations. CRBasic instructions that control excitation channels
include:
• ExciteI()
• Resistance()