273
Chapter 7 Plug-in Modules
Protection Networks
4
7
In designing RC protection networks, the protection resistor, R
p
, is
selected as a compromise between two values. The minimum value of R
p
is determined by the maximum acceptable relay contact current (Io). The
maximum allowable relay current (Io) is 2 amps ac rms or 2 amps dc.
Thus, the minimum value for R
p
is V/Io, where V is the peak value of the
supply voltage.
R
p
= V/Io = V/2
Equation 1
The maximum value for R
p
is usually made equal to the load resistance,
RI. Therefore, the limits on R
p
can be stated as:
V/Io < R
p
< RI
Equation 2
Note, the actual value of Io in a circuit is determined by the equation:
Io = V/RI
Equation 3
Where V is the peak value of the source voltage and RI is the resistance
of the load. Equations 1 & 2 use Io as the maximum allowable relay
current to determine the minimum value of R
p
. The value for Io
calculated in Equation 3 will be used to determine the value of the
protection capacitor, C
p
.
In determine the value of the protection network capacitor C
p
, there are
several things that need to be considered. First, the total circuit
capacitance (C) must be such that the peak voltage across the open relay
contacts does not exceed 353 volts peak (250 V rms = 353 Vp). The
equation for determining the minimum allowable circuit capacitance is:
C
≥
(Io/353)
2L
Equation 4
where L = the inductance of the load and Io is the value calculated in
Equation 3.
In reality, the total circuit capacitance (C) is made up of the wiring
capacitance plus the value of the protection network capacitor C
p
.
Therefore, the minimum value for C
p
should be the value obtained for
the total circuit capacitance, C, from Equation 4. Indeed, the actual
value used for C
p
should be substantially greater than the value
calculated for C.
Summary of Contents for Agilent 3499A
Page 13: ...1 1 Quick Start ...
Page 27: ...2 2 Front Panel Operation ...
Page 55: ...3 3 System Overview ...
Page 77: ...4 4 Features and Functions ...
Page 113: ...5 5 Remote Interface Reference ...
Page 164: ...164 5 ...
Page 165: ...6 6 Error Messages ...
Page 173: ...7 7 Plug in Modules ...
Page 256: ...256 Chapter 7 Plug in Modules 44475A Breadboard Module 7 ...
Page 261: ...261 Chapter 7 Plug in Modules 44476B Microwave Switch Module 4 7 The 44476B is shown below ...
Page 286: ...286 Chapter 7 Plug in Modules Terminals and Connections Information 7 ...
Page 288: ...288 7 ...
Page 289: ...8 8 Application Programs ...
Page 299: ...9 9 Specifications ...
Page 343: ...343 Chapter 9 Specifications 44475A Breadboard Module 4 9 ...