IET Labs SRac Series, User And Service Manual

Page: 13 / 17

5
SRX/SRC Series
5 Operation
Chapter 3
OPERATION
3.1 Initial Inspection and Setup
This instrument was carefully inspected before ship-
ment. It should be in proper electrical and mechanical
order upon receipt.
An
OPERATION GUIDE
is attached to the case
of the instrument to provide ready reference to
speci
fi cations.
3.2 Connections
All SRac have four insulated low thermal emf bind-
ing posts for four-terminal measurements as shown
in Figure 3-1. As an option -bnc is available which
replaces the 4 binding posts with bnc connectors.
The fi fth binding post
GND
is connected to the case.
Figure 3-1: Connections
1
Ω
RESISTANCE STANDARD
MODEL SRac - 1
LO
HI
LO
HI
SENSE CURRENT
GND
HI INPUT
HI SENSE
LO INPUT
LO SENSE
GROUND
Binding Post Function
CURRENT HI Current input from source (e.g. ohmmeter)
CURRENT LO Current return to source (e.g. ohmmeter)
SENSE HI Measurement point for a four-wire ohmmeter
SENSE LO Measurement point for a four-wire ohmmeter
GND Guard or shield
Table 3-1: Connections
3.3 Thermal emf Considerations
High-quality, gold-plated, tellurium-copper bind-
ing posts serve to minimize the thermal emf effects
which would arti
fi cially re fl ect a change in ac resis-
tance measurements. All other conductors within
the instrument, as well as the solder used, contain no
metals or junctions that could contribute to thermal
emf problems.
There nevertheless may be some minute thermal emf
generated at the test leads where they contact the gold
banana jacks. This voltage will also be eliminated if
a meter with so called “True Ohm” capability is used.
Otherwise the generated emf may represent itself as
a false component of the dc resistance measurement.
Always use low emf test leads when working with
SRac models. In particular, avoid brass or steel
conductors.