National Instruments CFP-RLY-421 用户手册

In addition, the cFP-RLY-421 has internal protection MOVs to 
prevent excessively high voltage from being applied across the 
contacts. The MOVs are located between the NO and IC contacts 
of each relay. However, National Instruments still recommends the 
use of a protection circuit across an inductive load. The flyback 
protection causes a small leakage current, which is detailed in the 

Proper selection is critical, as the use of a contact-protection device 
can extend contact life. When mounting the protection device, 
always locate it near the immediate area of the load or contact. 
Typically, you should mount a protective device within 18 in. of the 
load or contact.

Typically, contact-protection circuits are provided for an overview, 
but you should thoroughly examine the circuit you are planning 
to use. 

 

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This section has been reprinted with permission from American Zettler, Inc. 

Use in DC applications only.

Use when diode circuit causes too long 
release time.

Use zener diode with zener voltage about 
equal to power supply voltage.

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