Campbell Scientific CR3000 Micrologger - Manual (Page 329)

Section 8. Operation
329
8.1.8 RS-232 and TTL
Read More! Serial Input / Output Instructions
(p. 512)
and Serial I/O
(p. 205).
The CR3000 can usually receive and record RS-232 and 0 – 5 Vdc logic data
from sensors designed to transmit via these protocols. Data are received through
the CS I/O port with the proper interface (see the appendix CS I/O Serial
Interfaces
(p. 569)
), the RS-232 port, or the digital I/O communication ports (C1 &
C2, C3 & C4, C5 & C6, C7 & C8). If additional serial inputs are required, serial
input expansion modules (see the appendix Serial Input Expansion Modules
) can
be connected to increase the number of serial ports. Serial data are usually
captured as text strings, which are then parsed (split up) as defined in the user
entered program.
Note Digital I/O communication ports (control ports) only transmit 0 – 5 Vdc
logic. However, they read most true RS-232 input signals. When connecting serial
sensors to an Rx control port, the sensor power consumption may increase by a
few milliamps due to voltage clamps. An external resistor may need to be added
in series to the Rx line to limit the current drain, although this is not advisable at
very high baud rates. Figure Circuit to Limit Control Port Input to 5 Volts (p.
329) shows a circuit that limits voltage input on a control port to 5 Vdc.
Figure 106: Circuit to limit control port input to 5 Vdc
8.1.9 Field Calibration
Read More! Field Calibration of Linear Sensors (FieldCal)
(p. 156)
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 CR3000
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.