Campbell Scientific CR1000 Measurement and Control System - 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 — 2 channels (P1 to P2) 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 — 540 ns
• C1, C2 and 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. 563),
Pulse /
Frequency Input Expansion Modules
(p. 560),
and Serial Input / Output Peripherals
(p. 561)
for information on available input-expansion modules.
5.1.3.2 Voltage Outputs
The CR1000 has several terminals capable of supplying switched voltage to
peripherals, sensors, or control devices.
Read More! See Control Outputs
(p. 327).
• Switched Analog Output (Excitation) — three channels (VX1 to VX3) for
precise voltage excitation ranging from -2500 mV to +2500 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 (SW-12) — One terminal controls (switch on / off )
primary voltage under program control to switch external devices (such as
humidity sensors) requiring 12 Vdc on and off. SW-12 can source up to 900
mA. See the table Current Source and Sink Limits
(p. 84).