Campbell Scientific CR1000KD CR1000 Measurement and Control System - Page 327
Analog-Input Expansion Modules, 2.2 Pulse-Input Expansion Modules, 2.3 Serial-Input Expansion
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Section 8. Operation over a proprietary, three-wire serial communications link utilizing channels C1, C2 and C3. Read More! For complete information on available measurement and control peripherals, go to the appendix Sensors and Peripherals, www.campbellsci.com, or contact a Campbell Scientific applications engineer. 8.2.1 Analog-Input Expansion Modules Mechanical relay and solid-state relay multiplexers are available to expand the number of analog sensor inputs. Multiplexers are designed for single-ended, differential, bridge-resistance, or thermocouple inputs. 8.2.2 Pulse-Input Expansion Modules Pulse-input expansion modules are available for switch-closure, state, pulse-count and frequency measurements, and interval timing. 8.2.3 Serial-Input Expansion Modules Capturing input from intelligent serial-output devices can be challenging. Several Campbell Scientific serial I/O modules are designed to facilitate reading and parsing serial data. Campbell Scientific recommends consulting with an applications engineer when deciding which serial-input module is suited to a particular application. 8.2.4 Control Outputs Controlling power to an external device is a common function of the CR1000. On-board control terminals and peripheral devices are available for binary (on / off) or analog (variable) control. A switched, 12-Vdc channel is also available. See Switched Unregulated (Nominal 12 Volt) (p. 86). 8.2.4.1 Digital I/O Ports Each of eight digital I/O ports (C1 - C8) can be configured as an output port and set low (0 Vdc) or high (5 Vdc) using the PortSet() or WriteIO() instructions. Ports C4, C5, and C7 can be configured for pulse width modulation with maximum periods of 36.4 s, 9.1 s, and 2.27 s, respectively. A digital-I/O port is normally used to operate an external relay-driver circuit because the port itself has limited drive capacity. Drive capacity is determined by the 5-Vdc supply and a 330-ohm output resistance. It is expressed as: Vo = 4.9 V ‐ (330 Ohms) * Io Where Vo is the drive limit, and Io is the current required by the external device. Figure Control Port Current Sourcing (p. 328) plots the relationship. 327
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