Agilent E1412A Multimeter Application Information
31
Power Dissipation
Effects
When measuring resistors designed for temperature measurements (or other
resistive devices with large temperature coefficients), be aware that the
multimeter will dissipate some power in the device-under-test. If power
dissipation is a problem, you should select the multimeter's next higher
measurement range to reduce the errors to acceptable levels. Table 2-3
shows several examples.
Settling Time
Effects
Both the E1412A has the ability to insert automatic measurement settling
delays with the
TRIG:DEL
command. These delays are adequate for
resistance measurements with less than 200pF of combined cable and device
capacitance. This is particularly important if you are measuring resistances
above 100k
. Settling due to RC time constant effects can be quite long.
Some precision resistors and multi-function calibrators use large parallel
capacitors (1000pF to 0.1
F) with high resistor values to filter out noise
currents injected by their internal circuitry. Non-ideal capacitances in cables
and other devices may have much longer settling times than expected just by
RC time constants due to dielectric absorption (soak) effects. Errors will be
measured when settling after the initial connection and after a range change.
Errors in High
Resistance
Measurements
When you are measuring large resistances, significant errors can occur due
to insulation resistance and surface cleanliness. You should take the
necessary precautions to maintain a “clean” high-resistance system. Test
cables and fixtures are susceptible to leakage due to moisture absorption in
insulating materials and “dirty” surface films. Nylon and PVC are relatively
poor insulators (10
9
ohms) when compared to PTFE insulators (10
13
ohms).
Leakage from nylon or PVC insulators can easily contribute a 0.1% error
when measuring a 1M
resistance in humid conditions.
Making High-Speed
DC and Resistance
Measurements
The multimeter incorporates an automatic zero measurement procedure
(autozero) to eliminate internal thermal
EMF
and bias current errors. Each
measurement actually consists of a measurement of the input terminals
followed by a measurement of the internal offset voltage. The internal offset
voltage error is subtracted from the measurement for improved accuracy.
This compensates for offset voltage changes due to temperature. For
maximum reading speed, turn autozero off. This will more than double your
reading speeds for dc voltage, resistance, and dc current functions. Autozero
does not apply to other measurement functions.
Table 2-3. DUT Power Dissipation
Range
Test Current
DUT
Power at Full Scale
100
1mA
100
W
1k
1mA
1mW
10k
100
A
100
W
100k
10
A
10
W
1M
5
A
25
W
10M
500nA
2.5
W
Summary of Contents for Agilent E1412A
Page 2: ......
Page 10: ...8 Contents Notes...
Page 14: ...12 Notes...
Page 15: ...13 Notes...
Page 16: ...14 Notes...
Page 26: ...24 Agilent E1412A Multimeter Module Setup Chapter 1 Notes...
Page 194: ...192 Agilent E1412A Multimeter Error Messages Appendix B Notes...
Page 201: ...Index 199 Index Agilent E1412A User s Manual and SCPI Programming Guide...
