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Keysight E1412A Digital Multimeter User Guide
Keysight E1412A Multimeter Application Information
Resistance Measurements
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.
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