Power Dissipation Effects; Settling Time Effects; Errors In High Resistance Measurements; Making High-Speed Dc And Resistance Measurements - Agilent Technologies Agilent E1412A User Manual

Power Dissipation
Effects
Settling Time
Effects
Errors in High
Resistance
Measurements
Making High-Speed
DC and Resistance
Measurements
Chapter 2
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.
Table 2-3. DUT Power Dissipation
Range
100
1k
10k
100k
1M
10M
Both the E1412A has the ability to insert automatic measurement settling
delays with the
TRIG:DEL
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.
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
9
poor insulators (10 ohms) when compared to PTFE insulators (10
Leakage from nylon or PVC insulators can easily contribute a 0.1% error
when measuring a 1M resistance in humid conditions.
The multimeter incorporates an automatic zero measurement procedure
(autozero) to eliminate internal thermal
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.
Agilent E1412A Multimeter Application Information
DUT
Test Current Power at Full Scale
1mA 100W
1mA 1mW
100A 100W
10A 10W
5A 25W
500nA 2.5W
command. These delays are adequate for
and bias current errors. Each
EMF
13
ohms).
31