Section 7. Installation
145
•
Connect grounds associated with
12V
and
SW12V
terminals and
U
and
C
terminals configured for continuous excitation and control to
G
terminals.
•
Connect excitation grounds to the nearest
terminal on the same
terminal block.
•
Connect the low side of single-ended sensors to the nearest terminal
on the same terminal block.
•
Connect shield wires to the
terminal nearest the terminals to which
the sensor signal wires are connected.
Note
Several ground wires can be connected to the same ground
terminal.
If offset problems occur because of shield or ground leads with large current flow,
tie the problem leads directly to the ground lug.
7.3.3 Ground Potential Differences
Because a single-ended measurement is referenced to CR6 ground, any difference
in ground potential between the sensor and the CR6 will result in a measurement
error. Differential measurements MUST be used when the input ground is
known to be at a different ground potential from CR6 ground. See the section
Single-Ended Measurements — Details
(p. 422)
for more information.
Ground potential differences are a common problem when measuring full-bridge
sensors (strain gages, pressure transducers, etc), and when measuring
thermocouples in soil.
7.3.3.1 Soil Temperature Thermocouple
If the measuring junction of a thermocouple is not insulated when in soil or water,
and the potential of earth ground is, for example, 1 mV greater at the sensor than
at the point where the CR6 is grounded, the measured voltage is 1 mV greater
than the thermocouple output. With a copper-constantan thermocouple, 1 mV
equates to approximately 25 °C measurement error.
7.3.3.2 External Signal Conditioner
External instruments with integrated signal conditioners, such as an infrared gas
analyzer (IRGA), are frequently used to make measurements and send analog
information to the CR6. These instruments are often powered by the same
Vac-line source as the CR6. Despite being tied to the same ground, differences
in current drain and lead resistance result in different ground potentials at the two
instruments. For this reason, a differential measurement should be made on the
analog output from the external signal conditioner.
Summary of Contents for CR6 Series
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Page 76: ...Section 5 Overview 76 FIGURE 20 Half Bridge Wiring Example Wind Vane Potentiometer ...
Page 80: ...Section 5 Overview 80 FIGURE 23 Pulse Input Wiring Example Anemometer ...
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Page 454: ...Section 8 Operation 454 FIGURE 104 Narrow Sweep High Noise ...
Page 459: ...Section 8 Operation 459 FIGURE 106 Vibrating Wire Sensor Calibration Report ...
Page 535: ...Section 8 Operation 535 8 11 2 Data Display FIGURE 121 CR1000KD Displaying Data ...
Page 537: ...Section 8 Operation 537 FIGURE 123 CR1000KD Real Time Custom ...
Page 538: ...Section 8 Operation 538 8 11 2 3 Final Storage Data FIGURE 124 CR1000KD Final Storage Data ...
Page 539: ...Section 8 Operation 539 8 11 3 Run Stop Program FIGURE 125 CR1000KD Run Stop Program ...
Page 541: ...Section 8 Operation 541 FIGURE 127 CR1000KD File Edit ...
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Page 610: ...Section 11 Glossary 610 FIGURE 137 Relationships of Accuracy Precision and Resolution ...
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