Agilent Technologies 34970A, Руководство пользователя, Страница: 307 / 356

307
Chapter 7 Tutorial
Actuators and General-Purpose Switching
4
7
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 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.
RC Protection Networks
When designing RC protection networks, the protection resistor R
p
is
selected as a compromise between two resistance values. The minimum
value of R
p
is determined by the maximum acceptable relay contact
current (I
max
). For the 34903A, the maximum allowable relay current
(I
max
) is 1A DC or AC rms. Thus, the minimum value for R
p
is V/I
o
,
where V is the peak value of the supply voltage.
Relay
Contact
C
p
R
p
Varistor
I
L
R
L
R
p
V
I
max
-----------
V
2
---- = =
34970A Refresh UG.book Page 307 Wednesday, February 17, 2010 12:34 PM