Campbell CR3000 Micrologger, Руководство оператора

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Section 8. Operation
426
8.2.3 Continuous-Regulated (5V Terminal)
The 5V terminal is regulated and remains near 5 Vdc (
±
4%) so long as the
CR3000 supply voltage remains above 9.6 Vdc. It is intended for power sensors
or devices requiring a 5 Vdc power supply. It is not intended as an excitation
source for bridge measurements. However, measurement of the 5V terminal
output, by means of jumpering to an analog input on the same CR3000), will
facilitate an accurate bridge measurement if 5V must be used.
Note Table Current Source and Sink Limits
(p. 424)
has more information
on excitation load capacity.
8.2.4 Continuous-Analog Out (CAO Terminal)
Continuous analog out (CAO) terminals are regulated and remain near the set
voltage (
±
4%) so long as the CR3000 supply voltage remains above 10 Vdc.
Measurement of the output from CAO (by means of jumpering to an analog input
on the same CR3000) enables an accurate bridge measurement if a CAO terminal
must be used for excitation.
The CAO sample capacitor is a good example of capacitor dielectric absorption, a
phenomenon wherein a capacitor charge / discharge time is greatly increased
because of a small percentage of dielectric molecules being quite slow to respond.
The CR3000 CAO circuitry uses polypropylene capacitors for the sampling
capacitor, which have the lowest dielectric absorption of commonly available
capacitors, yet the effect is still noticeable for large step changes in the CAO
output voltage. Hence a default 2.6 ms charge time is employed in the CAO
instruction to minimize dielectric absorption errors following CAO voltage step
changes. Using fast update (see FastUpdate parameter in ExciteCAO()
instruction) following a large step change can result in a fairly large (5% or so)
CAO setting error for the first scan, with the error being reduced upon subsequent
scans after the step change.
8.2.5 Continuous-Unregulated Voltage (12V Terminal)
Use 12V terminals to continuously power devices that require 12 Vdc. Voltage
on the 12V terminals will change with CR3000 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 POWER IN 12V
and G terminals is 16 Vdc, the 12V and SW12 terminals, and pin 8 on
the CS I/O port, will supply 16 Vdc to a connected peripheral. If the
connected peripheral or sensor is not designed for that voltage level, it
may be damaged.
8.2.6 Switched-Unregulated Voltage (SW12 Terminal)
The SW12 terminals are often used to power devices such as sensors that require
12 Vdc during measurement. Current sourcing must be limited to 900 mA or less