Campbell CR800 Series - Switched-Voltage Excitation; Current Source and Sink Limits

Section 8. Operation
389
• PLC Control Modules — Overview (p. 394)
• PLC Control Modules — Lists (p. 565)
The CR800 wiring panel is a convenient power distribution device for powering
sensors and peripherals that require a 5 Vdc, or 12 Vdc source. It has one
continuous 12 Vdc terminal (12V), one program-controlled, switched, 12 Vdc
terminal (SW12), and one continuous 5 Vdc terminal (5V). SW12, 12V, and 5V
terminals limit current internally for protection against accidental short circuits.
Voltage on the 12V and SW12 terminals can vary widely and will fluctuate with
the dc supply used to power the CR800, so be careful to match the datalogger
power supply to the requirements of the sensors. The 5V terminal is internally
regulated to within ±4%, which is good regulation as a power source, but typically
not adequate for bridge sensor excitation. TABLE: Current Sourcing Limits
(p. 389)
lists the current limits of 12V and 5V terminals. Greatly reduced output
voltages on these terminals may occur if the current limits are exceeded. See
Terminals Configured for Control
(p. 392) for more information.
Current Source and Sink Limits
Terminal
Limit
1
VX or EX (voltage excitation)
2
±25 mA maximum
SW12
3
< 900 mA @ 20°C
< 630 mA @ 50°C
< 450 mA @ 70°C
< 360 mA @ 85°C
12V + SW12 (combined)
4
< 1.85 A @ 20°C
< 1.33 A @ 50°C
< 1.00 A @ 70°C
< 0.74 A @ 85°C
5V + CS I/O (combined)
5
< 200 mA
1
Source is positive amperage (+); sink is negative amperage (–).
2
Exceeding current 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.
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
Two switched, analog-output (excitation) terminals (VX1 to VX2) operate under
program control to provide ±2500 mV dc excitation. Check the accuracy