Campbell Scientific CR3000 CR3000 Micrologger - Page 60

Section 5. System Overview A library of sensor manuals and application notes are available at www.campbellsci.com to assist in measuring many sensor types. Consult with a Campbell Scientific applications engineer for assistance in measuring unfamiliar sensors. 5.1.3 CR3000 Wiring Panel The wiring panel of the CR3000 is the interface to many CR3000 functions. These functions are best introduced by reviewing features of the CR3000 wiring panel. The figure Wiring Panel (p. 35) illustrates the wiring panel and some CR3000 functions accessed through it. Read More! Expansion accessories increase the input / output capabilities of the wiring panel. Read Measurement and Control Peripherals (p. 332) for more information. 5.1.3.1 Measurement Inputs Hard-wired measurements require the physical connection of a sensor to an input channel and CRBasic programming to instruct the CR3000 how to make, process, and store the measurement. The CR3000 wiring panel has the following input channels: Analog Voltage - 28 channels (Diff 1 to 14 / SE 1 to 28) configurable as 14 differential or 28 single-ended inputs. • Input voltage range: -5000 mV to 5000 mV. • Measurement resolution: 0.67 µV to 1333 µV Period Average - 28 channels (SE 1 to 28) • Input voltage range: -2500 mV to 2500 mV. • Maximum frequency: 200 kHz • Resolution: 68 ns Note Both pulse-count and period-average measurements are used to measure frequency output sensors. Yet pulse-count and period-average measurement methods are different. Pulse-count measurements use dedicated hardware - pulse count accumulators, which are always monitoring the input signal, even when the CR3000 is between program scans. In contrast, period-average measurement instructions only monitor the input signal during a program scan. Consequently, pulse-count scans can usually be much less frequent than period-average scans. Pulse counters may be more susceptible to low-frequency noise because they are always "listening", whereas period averaging may filter the noise by reason of being "asleep" most of the time. Pulse-count measurements are not appropriate for sensors that are powered off between scans, whereas period-average measurements work well since they can be placed in the scan to execute only when the sensor is powered and transmitting the signal. Period-average measurements utilize a high-frequency digital clock to measure time differences between signal transitions, whereas pulse-count measurements simply accumulate the number of counts. As a result, period-average measurements offer much better frequency resolution per measurement interval, 60