Campbell Scientific CR1000KD CR800 and CR850 Measurement and Control Systems - Page 309

Field Calibration, 1.10 Cabling Effects

Page 309 highlights

Section 8. Operation Figure 98: Circuit to limit control port input to 5 Vdc 8.1.9 Field Calibration Read More! Field Calibration of Linear Sensors (FieldCal) (p. 151) has complete information. Calibration increases accuracy of a measurement device by adjusting its output, or the measurement of its output, to match independently verified quantities. Adjusting a sensor output directly is preferred, but not always possible or practical. By adding FieldCal() or FieldCalStrain() instructions to the CR800 program, a user can easily adjust the measured output of a linear sensors by modifying multipliers and offsets. 8.1.10 Cabling Effects Sensor cabling can have significant effects on sensor response and accuracy. This is usually only a concern with sensors acquired from manufacturers other than Campbell Scientific. Campbell Scientific sensors are engineered for optimal performance with factory-installed cables. 8.1.10.1 Analog Sensor Cables Cable length in analog sensors is most likely to affect the signal settling time. For more information, see Signal Settling Time (p. 282). 8.1.10.2 Pulse Sensors Because of the long interval between switch closures in tipping bucket rain gages, appreciable capacitance can build up between wires in long cables. A built-up charge can cause arcing when the switch closes, shortening switch life. As shown in figure Current Limiting Resistor in a Rain Gage Circuit (p. 309), a 100-ohm resistor is connected in series at the switch to prevent arcing. This resistor is installed on all rain gages currently sold by Campbell Scientific. Figure 99: Current limiting resistor in a rain gage circuit 309

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Section 8.
Operation
309
Figure 98: Circuit to limit control port input to 5 Vdc
8.1.9 Field Calibration
Read More!
Field Calibration of Linear Sensors (FieldCal)
(p. 151)
has complete
information.
Calibration increases accuracy of a measurement device by adjusting its output, or
the measurement of its output, to match independently verified quantities.
Adjusting a sensor output directly is preferred, but not always possible or
practical. By adding
FieldCal()
or
FieldCalStrain()
instructions to the CR800
program, a user can easily adjust the measured output of a linear sensors by
modifying multipliers and offsets.
8.1.10 Cabling Effects
Sensor cabling can have significant effects on sensor response and accuracy. This
is usually only a concern with sensors acquired from manufacturers other than
Campbell Scientific. Campbell Scientific sensors are engineered for optimal
performance with factory-installed cables.
8.1.10.1 Analog Sensor Cables
Cable length in analog sensors is most likely to affect the signal settling time. For
more information, see
Signal Settling Time
(p. 282).
8.1.10.2 Pulse Sensors
Because of the long interval between switch closures in tipping bucket rain gages,
appreciable capacitance can build up between wires in long cables. A built-up
charge can cause arcing when the switch closes, shortening switch life. As shown
in figure
Current Limiting Resistor in a Rain Gage Circuit
(p. 309),
a 100-ohm
resistor is connected in series at the switch to prevent arcing. This resistor is
installed on all rain gages currently sold by Campbell Scientific.
Figure 99: Current limiting resistor in a rain gage circuit