IET Labs SRC-10T-Tnetwork, Руководство пользователя и обслуживания

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1
SRC-Tnetwork
1 Introduction
Chapter 1
INTRODUCTION
1.1 Introduction
The SRC-Tnetwork is a standard resistor de-
signed for calibration of various electrometers and
megohmmeters.
The SRC-Tnetwork is a high resistance standard
that uses 3 lower value resistors confi gured in a T
network to create a higher resistance.
1.2 T-Networks
For high resistance measurements a T-network is
often used with instruments such as electrometers
and megohmmeters equipped with a guard termi-
nal.
A T-network uses low value resistors to achieve
what electronically looks like a high value resistor.
The basic operation of a T-network is three resis-
tors are place in a T confi guration and connected
to the positive, negative and guard terminals of the
megohmmeter.
The ratio of the resistors then determines the eff ec-
tive resistance value that will actually be displayed
by the megohmmeter.
The advantages of the T network is that low value
resistors are used that can be easily and accurately
measured as compared with trying to calibrate a
single high value resistor.
This technique is used quite often in calibration
where it is diffi
cult to accurately calibrate a resistor.
A T-network is illustrated in Figures 1.2 and 1.2
along with the formula to calculate the eff ective
resistance.
Guard
Positive Negative
R1
R2
R3
It In
Ig
Effective R =
R1 + R2 R3
R2 R3
*
R3
Figure 1.1: T-Network Model
Figure 1.2 illustrates an example T-network com-
prised of two 1 GΩ resistors and a single 10 kΩ
resistor to create a T-network that has an eff ective
resistance of 100 TΩ.
Figure 1.2: T-Network Example