Campbell CR3000 Micrologger, Руководство оператора

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Section 5. Overview
72
5.2.2.2 Current Measurements — Overview
Related Topics:
• Current Measurements — Overview
(p. 72)
• Current Measurements — Details
(p. 380)
A measurement of current is accomplished through the use of external resistors to
convert current to voltage, then measure the voltage as explained in the section
Differential Measurements — Overview
(p. 71).
The voltage is measured with the
CR3000 voltage measurement circuitry. IX terminals supply precise current
excitation for use with resistive bridges.
5.2.2.3 Resistance Measurements — Overview
Related Topics:
• Resistance Measurements — Specifications
• Resistance Measurements — Overview
(p. 72)
• Resistance Measurements — Details
(p. 367)
• Measurement: RTD, PRT, PT100, PT1000
(p. 273)
Many analog sensors use some kind of variable resistor as the fundamental
sensing element. As examples, wind vanes use potentiometers, pressure
transducers use strain gages, and temperature sensors use thermistors. These
elements are placed in a Wheatstone bridge or related circuit. With the exception
of PRTs, another type of variable resistor. See Measurement: RTD, PRT, PT100,
PT1000
(p. 273).
This manual does not give instruction on how to build variable
resistors into a resistor bridge. Sensor manufacturers consider many criteria
when deciding what type of resistive bridge to use for their sensors. The CR3000
can measure most bridge circuit configurations.
5.2.2.3.1 Voltage Excitation
Bridge resistance is determined by measuring the difference between a known
voltage applied to the excitation (input) arm of a resistor bridge and the voltage
measured on the output arm. The CR3000 supplies a precise-voltage excitation
via Vx terminals . Return voltage is measured on H/L terminals configured for
single-ended or differential input. Examples of bridge-sensor wiring using
voltage excitation are illustrated in figures Half-Bridge Wiring — Wind Vane
Potentiometer
(p. 73)
and Full-Bridge Wiring — Pressure Transducer
(p. 73).