Campbell DSP4 Spezifikationen PDF herunterladen (Seite 72)

Section 1. Installation and Maintenance

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1.9.1 Use of Digital I/O Ports for Switching Relays

Each of the eight digital I/O ports (C1 - C8) can be configured as an output port

and set low or high (0 V low, 5 V high) using the PortSet or WriteIO

instructions. A digital output port is normally used to operate an external relay

driver circuit because the port itself has a limited drive capability (2.0 mA

minimum at 3.5 V).

Figure 1.9-1 shows a typical relay driver circuit in conjunction with a coil

driven relay which may be used to switch external power to some device. In

this example, when the control port is set high, 12 V from the datalogger passes

through the relay coil, closing the relay which completes the power circuit to a

fan, turning the fan on.

In other applications it may be desirable to simply switch power to a device

without going through a relay. Figure 1.9-2 illustrates a circuit for switching

external power to a device without going through a relay. If the peripheral to be

powered draws in excess of 75 mA at room temperature (limit of the 2N2907A

medium power transistor), the use of a relay (Figure 1.9-1) would be required.

Other control port activated circuits are possible for applications with greater

current/voltage demands than shown in Figures 1.9-1 and 2. For more

information contact a Campbell Scientific applications engineer.

FIGURE 1.9-1. Relay Driver Circuit with Relay

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Campbell DSP4 Spezifikationen Seite 72