Campbell CR800 Series, Operator'S Manual

Page: 394 / 598

Section 8. Operation
394
8.4.2 Analog Output Modules
Read More For more information see appendix
Continuous Analog
Output (CAO) Modules — List
(p. 565).
The CR800 can scale measured or processed values and transfer these values in
digital form to an analog output device. The analog output device performs a
digital-to-analog conversion to output an analog voltage or current. The output
level is maintained until updated by the CR800.
8.4.3 PLC Control Modules — Overview
Related Topics:
• PLC Control — Overview
(p. 87)
•
PLC Control Modules — Overview
(p. 394)
•
PLC Control Modules — Lists
(p. 565)
• Switched Voltage Output — Specifications
• Switched Voltage Output — Overview
(p. 59)
•
Switched Voltage Output — Details
(p. 388)
•
Current Source and Sink Limits
(p. 389)
Controlling power to an external device is a common function of the CR800.
On-board control terminals and peripheral devices are available for binary (on /
off) or analog (variable) control. A switched, 12 Vdc terminal ( SW12V ) is also
available. See Switched-Unregulated (Nominal 12 Volt)
(p. 391).
8.4.3.1 Relays and Relay Drivers
Read More See
Relay Drivers Modules — List
(p. 566).
Several relay drivers are manufactured by Campbell Scientific. Compatible,
inexpensive, and reliable single-channel relay drivers for a wide range of loads are
also available from electronic vendors such as Crydom, Newark, and Mouser
(p.
525).
8.4.3.2 Component-Built Relays
Figure Relay Driver Circuit with Relay
(p. 395)
shows a typical relay driver circuit
in conjunction with a coil driven relay, which may be used to switch external
power to a device. In this example, when the terminal configured for control is set
high, 12 Vdc from the datalogger passes through the relay coil, closing the relay
which completes the power circuit and turns on the fan.
In other applications, it may be desirable to simply switch power to a device
without going through a relay. Figure Power Switching without Relay
(p. 395)
illustrates this. If the device to be powered draws in excess of 75 mA at room
temperature (limit of the 2N2907A medium power transistor), the use of a relay is
required.