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%
×
Summary of Contents for 6430
Page 26: ......
Page 32: ......
Page 78: ...2 14 Connections ...
Page 98: ...3 20 Basic Source Measure Operation ...
Page 138: ...5 30 Source Measure Concepts ...
Page 156: ...6 18 Range Digits Speed and Filters ...
Page 168: ...7 12 Relative and Math ...
Page 176: ...8 8 Data Store ...
Page 202: ...9 26 Sweep Operation ...
Page 248: ...11 22 Limit Testing ...
Page 310: ...16 6 SCPI Signal Oriented Measurement Commands ...
Page 418: ...17 108 SCPI Command Reference ...
Page 450: ...18 32 Performance Verification ...
Page 477: ...A Specifications ...
Page 489: ...B StatusandErrorMessages ...
Page 498: ...B 10 Status and Error Messages ...
Page 499: ...C DataFlow ...
Page 503: ...D IEEE 488BusOverview ...
Page 518: ...D 16 IEEE 488 Bus Overview ...
Page 519: ...E IEEE 488andSCPI ConformanceInformation ...
Page 523: ...F MeasurementConsiderations ...
Page 539: ...G GPIB488 1Protocol ...
Page 557: ......