Campbell Scientific CR1000KD CR800 and CR850 Measurement and Control Systems - Page 313
Relays and Relay Drivers, 2.4.3 Component-Built Relays
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Section 8. Operation Figure 100: Control port current sourcing 8.2.4.2 Relays and Relay Drivers Several relay drivers are manufactured by Campbell Scientific. For more information, see the appendix Relay Drivers (p. 541), contact a Campbell Scientific applications engineer, or go to www.campbellsci.com. Compatible, inexpensive, and reliable single-channel relay drivers for a wide range of loads are available from various electronic vendors such as Crydom, Newark, Mouser, etc. 8.2.4.3 Component-Built Relays Figure Relay Driver Circuit with Relay (p. 314) 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 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. 314) illustrates a circuit for switching external power to a device without using 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 is required. 313
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