Campbell Scientific CR3000 Micrologger - Manual (Page 39)

Section 4. Quickstart Tutorial
39
4.1.3.2.2 Current Excitation
Resistance can be determined by supplying a precise current and measuring the
return voltage. The CR3000 supplies a precise excitation current via current
excitation terminals. Return voltage is measured on analog input terminals.
Examples of bridge sensor wiring using current excitation are illustrated in figure
Current Excitation -- PRT
(p. 39).
Note When using long leads with current excitation, consult Minimizing Settling
Error
(p. 292).
Figure 7: Current excitation wiring -- PRT
4.1.3.3 Pulse Sensors
Pulse sensors are measured on CR3000 pulse-measurement channels. The output
signal generated by a pulse sensor is a series of voltage waves. The sensor
couples its output signal to the measured phenomenon by modulating wave
frequency. The CR3000 detects each wave as the wave transitions between
voltage extremes (high to low or low to high). This is termed “state transition”.
Measurements are processed and presented as counts, frequency, or timing data.
Note A period-averaging sensor has a frequency output, but it is connected to a
single-ended analog input channel and measured with the PeriodAverage()
instruction (see Period Averaging
(p. 327)
).
4.1.3.3.1 Pulses Measured
Figure Pulse Sensor Output Signal Types
(p. 40)
illustrates three pulse sensor output
signal types.