Chapter 8 Tutorial

Actuators and General-Purpose Switching

Snubber Circuits

Whenever a relay contact opens or closes, electrical breakdown or arching can occur between the contacts. This can cause high-frequency noise radiation, voltage and current surges, and physical damage to the relay contacts.

A breadboard area is provided on the HP 34903A to implement custom circuitry such as simple filters, snubbers, and voltage dividers.

The breadboard area provides the space necessary to insert your own components but there are no circuit board traces here. You can build these networks to provide contact protection when actuating ac power line for reactive loads. Although many types of contact protection networks can be used, only RC networks and varistors are described in this section.

 

 

 

Cp

 

 

 

 

 

 

 

 

 

 

IL

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Relay

 

 

 

Varistor

 

 

 

 

 

 

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Rp

 

 

 

 

 

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RC Protection Networks

When designing RC protection networks, the protection resistor Rp is selected as a compromise between two resistance values. The minimum value of Rp is determined by the maximum acceptable relay contact current (Imax). For the HP 34903A, the maximum allowable relay

current (Imax) is 1A dc or ac rms. Thus, the minimum value for Rp is V/Io, where V is the peak value of the supply voltage.

Rp = V = V

Imax 2

Reference Module

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