iET SRL Series, Руководство по эксплуатации

Страница: 13 / 17

5
SRL Series
5 Operation
3.2.3 Connections for values
³
100 M
W
Values ≥100 MΩ have two insulated, low thermal
emf binding posts for two-terminal measurements as
shown in Figure 3-3. The third binding post, labeled
GROUND
, is connected to the case. The fourth
binding post, labeled GUARD , is connected to an
internal case that contains the resistor.
Figure 3-3: Connections for values
³
100 M
W
Binding Post Function
HI Input from source (e.g. ohmmeter)
SENSE LO Measurement point
GROUND Shield
GUARD
Interrupts leakage from the internal resistor to
the case and other components of the unit
Table 3-3: Connections for values ³ 100 M W
RESISTANCE STANDARD
MODEL SRL - 100M
Temperature Coeffi cient: 5 ppm/°C
Maximum Voltage: 1000 V
100 M W
LO
HI
GROUND
GUARD
HI INPUT
HI SENSE
LO SENSE
LO INPUT
GROUND
GUARD*
*If no GUARD point exists on the measuring instrument,
it may be connected to GROUND .
3.3 Thermal emf Considerations
High-quality, gold-plated, tellurium-copper binding
posts serve to minimize the thermal emf eff ects which
would artifi cially refl ect a change in dc resistance
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
SRL models. In particular, avoid brass or steel
conductors.