Campbell Scientific CR800 and CR850 Measurement and Control Systems - 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 — 4 channels (C1 to C4) configurable for serial input, SDM, SDI-12,
state, frequency, pulses, edge counting and edge timing.
• C1 to C4 —- 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 — SDI-12 input / output
• C1 & C2, C3 & C4 — 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. 541),
Pulse /
Frequency Input Expansion Modules
(p. 538),
and Serial Input / Output Peripherals
(p. 539)
for information on available input-expansion modules.
5.1.3.2 Voltage Outputs
The CR800 has several terminals capable of supplying switched voltage to
peripherals, sensors, or control devices.
Read More! See Control Outputs
(p. 312).
• Switched Analog Output (Excitation) — two channels (VX1 to VX2) 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 — 4 channels (C1 to C4) configurable for on / off and PWM
(pulse width modulation) or PDM (pulse duration modulation) on C4.
• Switched 12 Volts dc (SW12) — 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. SW12 can source up to 900
mA. See the table Current Source and Sink Limits
(p. 84).