Relative and Math
7-5
Measuring high resistance devices
— When using offset-compensated ohms to measure
high resistance values, an appropriate source delay must be used to provide settled readings.
There is a rise time associated with high ohms measurements. For normal ohms measurements,
you can watch the reading change on the display. When it stops changing, you know you have
the final, settled reading. For offset-compensated ohms, this process is not as straight forward
since the source is constantly changing between two values. If measurements are performed
while the source is still rising (or falling), incorrect offset-compensated ohms readings will
result. Therefore, it is imperative that an adequate source delay be used to make sure that mea-
surements occur while the source is at its final, settled values.
Settling times are drastically different from one type of resistor to another. Another factor
that affects settling time is the test setup (i.e., cabling, fixturing, and guarding). These variables
make it necessary for the user to characterize his test system to assure that the source delay set-
ting is adequate.
NOTE
Source delay is set from the source configuration menu (press CONFIG > select
SOURCE I (or V) > select DELAY). See “Source delay” in Section 3 for details.
Varistor alpha
This math formula is used to determine ALPHA (
α
), which is the logarithmic ratio of two
voltage measurement points on a non-linear V-I curve and is expressed as follows:
where:
V1 is the voltage measurement at the first I-Source point.
V2 is the voltage measurement at the second I-Source point.
The log (x) function uses the absolute value of x.
When configuring this math function, you will be prompted to enter the two I-source values.
See
Front panel math operations
.
Voltage coef
fi
cient
High value or high-megohm resistors exhibit a change in resistance with a change in applied
voltage. This effect is known as voltage coefficient. The voltage coefficient is the percent
change in resistance per unit change in applied voltage and is defined as follows:
where:
∆
R = R2 - R1
∆
V = V2 - V1
R1 is the resistance measurement at the first source point.
R2 is the resistance measurement at the second source point.
V1 is the voltage measurement at the first source point.
V2 is the voltage measurement at the second source point.
If sourcing voltage, you will be prompted to enter the two V-source values. If sourcing cur-
rent, you will be prompted to enter the two I-source values. See
Front panel math operations
.
α
I2 I1
⁄
(
)
log
V2 V1
⁄
(
)
log
--------------------------------
=
Coefficient%
∆
R
R2
∆
V
×
----------------------
=
100%
×
Содержание 6430
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Страница 78: ...2 14 Connections ...
Страница 98: ...3 20 Basic Source Measure Operation ...
Страница 138: ...5 30 Source Measure Concepts ...
Страница 156: ...6 18 Range Digits Speed and Filters ...
Страница 168: ...7 12 Relative and Math ...
Страница 176: ...8 8 Data Store ...
Страница 202: ...9 26 Sweep Operation ...
Страница 248: ...11 22 Limit Testing ...
Страница 310: ...16 6 SCPI Signal Oriented Measurement Commands ...
Страница 418: ...17 108 SCPI Command Reference ...
Страница 450: ...18 32 Performance Verification ...
Страница 477: ...A Specifications ...
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Страница 499: ...C DataFlow ...
Страница 503: ...D IEEE 488BusOverview ...
Страница 518: ...D 16 IEEE 488 Bus Overview ...
Страница 519: ...E IEEE 488andSCPI ConformanceInformation ...
Страница 523: ...F MeasurementConsiderations ...
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