Agilent Technologies 34901A User Manual page 389

Chapter 8 Tutorial
Actuators and General-Purpose Switching
The maximum value for R
Therefore, the limits on R
V
< R
I
max
Note that the actual value of the current (I
by the equation:
V
I =
o
R
Where V is the peak value of the source voltage and R
of the load. The value for I
protection capacitor (C
In determining the value of the protection network capacitor (C
are several things that you will need to consider. First, the total circuit
capacitance (C
relay contacts does not exceed 300 Vrms. The equation for determining
the minimum allowable circuit capacitance is:
≥
C (I
tot
where L is the inductance of the load and I
calculated earlier.
The total circuit capacitance (C) is actually made up of the wiring
capacitance plus the value of the protection network capacitor C
Therefore, the minimum value for C
the total circuit capacitance (C). Note that the actual value used for C
should be substantially greater than the value calculated for C.
Using Varistors
Use a varistor to add an absolute voltage limit across the relay contacts.
Varistors are available for a wide range of voltage and clamp energy
ratings. Once the circuit reaches the voltage rating of the varistor, the
varistor's resistance declines rapidly. A varistor can supplement an RC
network and is especially useful when the required capacitance (C
too large.
386
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is usually made equal to the load resistance R
p
can be stated as:
p
< R
p L
L
will be used to determine the value of the
o
).
p
) must be such that the peak voltage across the open
tot
2
/ 300) x L
o
) in a circuit is determined
o
is the resistance
L
is the current value
o
should be the value obtained for
p
.
L
), there
p
.
p
p
) is
p