Campbell Scientific CR3000 Micrologger - Manual (Page 61)

Section 5. System Overview
61
as compared to pulse-count measurements. The frequency resolution of pulse-
count measurements can be improved by extending the measurement interval by
increasing the scan interval and by averaging. For information on frequency
resolution, see Frequency Resolution
.
Pulse — 4 channels (P1 to P4) configurable for counts or frequency of the
following signal types.
• High-level 5-Vdc square-wave
• Switch closures
• Low-level ac sine-wave
Digital I/O — 8 channels (C1 to C8) configurable for serial input, SDM, SDI-12,
state, frequency, pulses, edge counting and edge timing.
• C1 to C8 —- state, frequency, pulse, edge counting and edge timing
measurements
• Edge timing resolution — 136 ns
• SDM-C1, SDM-C2 and SDM-C3 — Synchronous Devices for Measurement
(SDM) input / output
• C1, C3, C5, C7 — SDI-12 input / output
• C1 & C2, C3 & C4, C5 & C6, C7 & C8 — serial communication input /
output
9-Pin RS-232 — 1 port (RS-232) configurable for serial input
Refer to the appendices Digital I/O (Control Port) Expansion
(p. 565),
Pulse /
Frequency Input Expansion Modules
(p. 562),
and Serial Input / Output Peripherals
(p. 563)
for information on available input-expansion modules.
5.1.3.2 Voltage and Current Outputs
The CR3000 has several terminals capable of supplying switched voltage and
current to peripherals, sensors, or control devices.
Read More! See Control Outputs
(p. 333).
• Switched Analog Output (Excitation) — four channels (VX1 to VX4) for
precise voltage excitation ranging from -5000 mV to +5000 mV. These
channels are regularly used with resistive bridge measurements. Each
channel will source up to 25 mA.
• Digital I/O — 8 channels (C1 to C8) configurable for on / off and PWM
(pulse width modulation) or PDM (pulse duration modulation) on C4, C5 and
C7.
• Switched 12 Volts dc (SW12V) — Two terminals control (switch on / off )
primary voltage under program control to switch external devices (such as
humidity sensors) requiring 12 Vdc on and off. SW12V can source up to 900
mA. See the table Current Source and Sink Limits
(p. 89).
• Continuous Analog Output (CAO) — two CAO terminals (CAO1 and
CAO2) capable of driving voltages from –5000 mV to 5000 mV at ±15 mA.