Keithley 6514/E Digital-Multimeter, DMM, 6514/E Data Sheet
Product codes
6514/E
LO
W L
E
V
E
L M
E
A
S
U
R
E & S
O
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C
E
A Greater Measure of Confidence
www.keithley.com
1.888.KEITHLEY
(U.S. only)
6514
Programmable Electrometer
Economical Component Testing
Once, electrometers were simply considered too slow to keep up with the
Once, electrometers were simply considered too slow to keep up with the
high throughput that production test applications demand . The Model 6514
is designed for fast, sensitive measurements, providing speeds up to 1200
readings per second with fast integration or 17 measurements per second
with 60Hz line-cycle integration . It offers 10fA resolution on 2nA signals,
settling to within 10% of the final value in just 15ms . A normal-mode rejec-
tion ratio (NMRR) of 60dB allows making accurate low current measure-
ments, even in the presence of line frequency induced currents, which is a
common concern in production floor environments . The instrument’s sen-
sitivity makes it easy to determine the leakage resistance on capacitances
up to 10nF or even on higher capacitances when a series resistor is used .
While the Model 6514 can be easily operated manually using the front
While the Model 6514 can be easily operated manually using the front
panel controls, it can also be externally controlled for automated test
applications . Built-in IEEE-488 and RS-232 interfaces make it possible
I
D
6514 Electrometer
R
L
I
L
= 0
Photodiode
(no incident
light)
–
+
V
BURDEN
CAL V
OFFSET
Total offset
voltage = 0
A/D
figure 2. Dark Current Measurement with burden Voltage Corrected
Leakage
Resistance
R
L
I
L
(error current
due to
V
BURDEN
)
Photodiode
(no incident
light)
–
+
V
BURDEN
A/D
I
D
Electrometer
figure 1. Dark Current Measurement with burden Voltage uncorrected
to
program all instrument functions over the bus through a computer
controller . The instrument’s interfaces also simplify integrating external
hardware, such as sources, switching systems, or other instruments, into
the test system . A digital I/O interface can be used to link the Model 6514
to many popular component handlers for tight systems integration in bin-
ning, sorting, and similar applications .
These features make the Model 6514 a powerful, low cost tool for systems
These features make the Model 6514 a powerful, low cost tool for systems
designed to test optical devices and leakage resistance on low-value capaci-
tors, switches, and other devices, particularly when the test system already
includes a voltage source or when the source current/measure voltage
technique is used to determine resistance .
low Voltage burden
The Model 6514’s feedback ammeter design minimizes voltage offsets in
The Model 6514’s feedback ammeter design minimizes voltage offsets in
the input circuitry, which can affect current measurement accuracy . The
instrument also allows active cancellation of its input voltage and current
offsets, either manually via the front panel controls or over the bus with
IEEE-488 commands .
Dark Current Measurements
When measuring dark currents (Figure 1) from a device such as a
When measuring dark currents (Figure 1) from a device such as a
photodiode, the ammeter reads the sum of two different currents . The first
current is the dark current (I
D
) generated by the detector with no light
falling upon the device (in other words, the signal of interest); the second
one is the leakage current (I
L
) generated by the voltage burden (V
BURDEN
)
appearing at the terminals of the ammeter . In a feedback ammeter, the
primary “voltage burden” is the amplifier offset voltage . This leakage
current represents an error current . Without the use of cancellation
techniques, I
L
= V
BURDEN
/R
L
. Figure 2 illustrates how the Model 6514’s
CAL V
OFFSET
is adjusted to cancel V
BURDEN
to within the voltage noise level
of a few microvolts, so the measured current is only the true dark current
(I
D
) of the photodiode . In a similar manner, offset currents can also be
cancelled . Earlier electrometers used an internal numerical correction
technique in which the voltage burden was still present, so the measured
dark current included the error term I
L
= V
BURDEN
/R
L
.
Voltage burden and Measurement Error
Electrometers provide current measurement with lower terminal voltage
Electrometers provide current measurement with lower terminal voltage
than is possible when making DMM meas urements . As shown in Figure
3, DMMs measure current using a shunt resistance that develops a voltage
(typically 200mV full-range) in the input circuit . This creates a terminal
voltage (V
BURDEN
) of about 200mV, thereby lowering the measured current .
Electrometers reduce this terminal voltage by using the feedback ammeter
configuration illustrated in Figure 1 . The Model 6514 lowers this terminal
voltage still further—to the level of the voltage noise—by canceling out the
small offset voltage that remains, as shown in Figure 2 . Any error signals that
remain are negligible in comparison to those that can occur when measuring
current with a DMM .
Fa
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Fa
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, p
re
ci
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, c
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ge
, vol
ta
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, a
nd
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si
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ts