Campbell Scientific CR3000 CR3000 Micrologger - Page 39

Section 4. Quickstart Tutorial 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. 39