Campbell CR6 Series, Руководство оператора

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Section 5. Overview
72
Analog sensors output a continuous voltage or current signal that varies with the
phenomena measured. Sensors compatible with the CR6 output a voltage. The
CR6 can also measure analog current output when the current is converted to
voltage by using a resistive shunt.
Sensor connection is to U terminals configured for differential or single-ended
inputs. For example, differential channel U1 is comprised of terminals
U1
and
U2
,
with
U1
as high and
U2
as low.
5.2.2.1 Voltage Measurements — Overview
Related Topics:
• Voltage Measurements — Specifications
(p. 102)
•
Voltage Measurements — Overview
(p. 72)
•
Voltage Measurements — Details
(p. 415)
• Maximum input voltage range: ± 5000 mV
• Measurement resolution range: 0.05 µV to 30 µV RMS
Single-ended and differential connections are illustrated in the figures Analog
Sensor Wired to Single-Ended Channel #1
(p. 73)
and
Analog Sensor Wired to
Differential Channel #1
(p. 73).
Table CR6 Terminal Definitions
(p. 62)
lists the
available analog input configurations.
Conceptually, analog voltage sensors output two signals: high and low. For
example, a sensor that outputs 1000 mV on the high lead and 0 mV on the low has
an overall output of 1000 mV. A sensor that outputs 2000 mV on the high lead
and 1000 mV on the low also has an overall output of 1000 mV. Sometimes, the
low signal is simply sensor ground (0 mV). A single-ended measurement
measures the high signal with reference to ground, with the low signal tied to
ground. A differential measurement measures the high signal with reference to
the low signal. Each configuration has a purpose, but the differential
configuration is usually preferred.
A differential configuration may significantly improve the voltage measurement.
Following are conditions that often indicate that a differential measurement
should be used:
•
Ground currents cause voltage drop between the sensor and the
signal-ground terminal. Currents >5 mA are usually considered
undesirable. These currents may result from resistive-bridge sensors
using voltage excitation, but these currents only flow when the voltage
excitation is applied. Return currents associated with voltage excitation
cannot influence other single-ended measurements of small voltage
unless the same voltage-excitation terminal is enabled during the
unrelated measurements.
•
Measured voltage is less than 200 mV.