National Instruments CFP-RLY-421 用户手册

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Wire an external power supply to the load and IC terminal of the 
individual channel as shown in Figure 2. This method of wiring 
keeps the electrical connections of the cFP-RLY-421 within safe 
current limits. 

Figure 2.  Connecting a Load

The cFP-RLY-421 has eight SPST (Single-Pole-Single-Throw) 
electromechanical relays. The power-up state is off (open) to 
ensure safe installation. In the ON state, the NO and IC contacts 
connect to form a short circuit. In the ON state, there is an effective 
resistance of 100 m

Ω between the NO and IC terminals, which 

causes a voltage drop. For example, if the current is 1.5 A, the 
voltage drop across the NO and IC terminals is 0.15 V.

The amount of current the relay can switch depends on the voltage, 
the type of load, and ambient temperature. Refer to the 

 section for more information

.

When inductive loads are connected to the relays, a large 
counter-electromotive force may occur at relay switching time 
because of the energy stored in the inductive load. These flyback 
voltages can severely damage the relay contacts and greatly 
shorten the life of the relay.

It is best to limit flyback voltages by installing a flyback diode 
across an inductive DC load or a metal oxide varistor (MOV) 
across an inductive AC load. Refer to the 

 section for more information.

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To next channel

cFP-RLY-421

IC

NO

V

C

V

SUP

COM

or

AC

Sourcing

Load