Overcome Test Challenges with Truevolt Series Digital Multimeters

Overcome Test Challenges with Truevolt Series Digital Multimeters
Keysight Technologies
Overcome Your Test Challenges with
Truevolt Series Digital Multimeters
34465A and 34470A
Application Compendium
A compendium of six 34465A and 34470A
test challenge application briefs
Introduction
In a rack or on a bench real-world signals are never flat. They have some level of AC signal riding on top from power line
noise, other environmental noise, or injected current from the meter itself. How well your meter deals with these extraneous factors and eliminates them from the true measurement makes a big difference to your accuracy. Behind the scenes,
Keysight’s Truevolt Series digital multimeters (DMMs) account for measurement errors created by these real-world factors
so you can be confident in your measurements.
Truevolt DMMs utilizes an analog-to-digital converter that enables a patented metrology-grade architecture. Using this
architecture, Keysight delivers a good balance of measurement resolution, linearity, accuracy, and speed at a value price,
all derived and guaranteed per ISO/IEC 17025 industry standards.
Some of the key test challenges for which the Truevolt Series DMMs are especially well suited are included in the
following application briefs:
Achieving Enhanced Digital Multimeter Accuracy in the Presence of Temperature Variation............... 3
Measuring Difficult AC Signals with a Digital Multimeter......................................................................... 8
Measuring Low Current Consumption with a Digital Multimeter........................................................... 17
Faster Data Analysis with Graphical Digital Multimeter Measurements............................................... 23
Simultaneous Measurements with a Digital Multimeter.........................................................................30
Making Simpler DC Power Measurements with a Digital Multimeter....................................................36
03 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Achieving Enhanced Digital Multimeter Accuracy in
the Presence of Temperature Variation
Overview
Accurate measurements with a benchtop or system Digital Multimeter (DMM) are very important. However, an often overlooked
specification adder is the Temperature Coefficient (TC). The basic premise of a TC specification is that if you are using your DMM at a
temperature that is not the same temperature at which you calibrated the instrument, then you need to add an error to account for the
TC specification. Most DMMs are calibrated in a temperature controlled environment, nominally at 23 °C. However, often times DMM’s
are used in real-life environments where the temperature is not the same as the calibration lab. See how the latest Truevolt Series
DMMs can help minimize this TC specification adder.
Making highly sensitive, accurate measurements
in a lab with variable temperature
Making DMM rack measurements when the internal
system temperature is higher than ambient
You need to make highly sensitive measurements with your DMM,
while maximizing accuracy. However, the temperature of your lab
can vary by a few degrees over the course of a day. This temperature
variation has a direct impact on the accuracy of your measurements
and can affect the quality of your data; especially if your lab’s
working temperature is not the same as the temperature at which
the DMM was calibrated.
You have mounted your DMM into a rack. Like a good system
designer, you have controlled air flow and temperature monitoring.
Even with these precautions, the internal temperature of your
system is 15 °C higher than ambient due to the other instruments
in your system. With a 15 degree rise, your DMM reading
specifications are now higher than design tolerances with the
TC specification adders. Since you designed in a Truevolt Series
DMM with autocalibration, you can reduce the TC adders up to
5x and still stay within your specification budget for your DMM
measurements.
The Truevolt Series DMMs for Keysight Technologies features
built-in autocalibration designed to help minimize errors due to
temperature drift. Using these instruments allows you to make
your measurements with the added assurance that autocalibration
will help adjust for any errors.
04 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Achieving Enhanced Digital Multimeter Accuracy in
the Presence of Temperature Variation (continued)
DMM specifications
If you look at a DMM datasheet you will normally find 90-day and 1-year specification
columns. These columns are populated with percentage of reading and of range, and
are based on the measurement that you are taking. Table 1 shows the datasheet for the
new 34465A 6.5 digit DMM. The inclusion of 24 hour, 90 day, 1 year, and TC columns are
common for high-end DMMs.
To calculate your accuracy specification, consider an example when the DCV 10-V range
is used to measure 9 V. In this case, your 1-year specification (based on Table 1) would
be calculated as 0.0035% reading+0.0005% range, or: 9 V * 0.003%+10 V * 0.0004% =
0.00027 + 0.00004 = 0.00031 V
Consequently, the accuracy you would expect is 9 V ± 0.31 mV
If your measurement environment—the ambient temperature where the DMM is operating—
is not the same as the temperature of the DMM calibration, then you need to consider
the TC error adder. For example, a unit was calibrated at 22 °C, but is operating at 40 °C
inside of a test system. Such a rise in temperature is common in test sets inside of a
system rack. We need to add in error due to TC specifications. From Table 1, the right
most column contains the TC specification. For each degree C, the specification adder is:
9 V * 0.0005%+10 V * 0.0001% = 0.000045 V+0.00001 V = 0.000055 V (0.055 mV)
For the Truevolt 34465A DMM, the 1-year specification applies for temperatures ± 2 °C
of the calibration temperature. If you are outside of the 2 °C range, in our example the
threshold is 24 °C, then you need to add in the TC specification for each degree. In the
example cited here that would mean adding in 16 °C of TC adder.
The total specification for this example would be: 9 V ± (0.00032 + 16 * 0.000055) =
9 V ± 0.00119 V (1.19 mV), which represents a 385 percent increase in your potential
measurement error!
Specification ± (% of reading + % of range)
Range
24 hours
TACAL ± 1 °C
90 days
TACAL ± 2 °C
1 year
TACAL ± 2 °C
2 years
TACAL ± 2 °C
Non ACAL
temperature
coefficient/°C
With ACAL
temperature
coefficient/°C
DC voltage: 34465
100 mV
0.0030 + 0.0030
0.0040 + 0.0035
0.0050 + 0.0035
0.0065+ 0.0035
0.0005 + 0.0005
0.0002 + 0.0005
1V
0.0015 + 0.0004
0.0025 + 0.0004
0.0035 + 0.0004
0.0050 + 0.0004
0.0005 + 0.0001
0.0002 + 0.0001
10 V
0.0010 + 0.0003
0.0020 + 0.0004
0.0030 + 0.0004
0.0045 + 0.0004
0.0005 + 0.0001
0.0002 + 0.0001
100 V
0.0020 + 0.0006
0.0035 + 0.0006
0.0040 + 0.0006
0.0055 + 0.0006
0.0005 + 0.0001
0.0002 + 0.0001
1000 V
0.0020 + 0.0006
0.0035 + 0.0006
0.0040 + 0.0006
0.0055 + 0.0006
0.0005 + 0.0001
0.0002 + 0.0001
Figure 1. Shown here are the 34465A DCV specifications.
Please refer to the Truevolt Series DMM data sheet, publication number 5991-1983EN, for additional specification details.
05 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Achieving Enhanced Digital Multimeter Accuracy in
the Presence of Temperature Variation (continued)
Truevolt autocalibration
The new 34465A and 34470A Truevolt Series DMMs feature autocalibration (ACAL),
which greatly reduces temperature drift error. ACAL is the built-in ability of the DMM to
compensate for temperature drift and internal errors. This is also known as self calibration. The only other Keysight DMM with ACAL is the high-end 3458A with its high-end
price;
a bestselling 8.5-digit DMM. The new 34465A and 34470A Truevolt DMMs at 6.5 digits
and 7.5 digits, respectively, are lower performance and with prices at a fraction of the
cost of the 3458A.
The 34465A and 34470A Truevolt DMMs feature ACAL circuitry that adjusts the
calibration for DCV, OHM and the internal Analog-to-Digital Converter (ADC) circuitry.
Keysight designers were able to optimize the calibration for cost, accuracy and speed.
The ACAL operation is a short 15 to 20 seconds; greatly improved over the 3458A ACAL
DMM operations, which could take 12 minutes to complete.
With this improved ACAL, Keysight is able to optimize the circuit design to offer a
high-end DMM that is price competitive with non-ACAL DMMs. This economical solution
is ideal for high accuracy needs in DCV and Ohms functions, both of which are often the
most challenging measurements for engineers needing the most accuracy.
In a higher accuracy DMM, temperature stability is a larger factor. Temperature variations
affect voltage and ADC accuracy. With the 34465 and 34470A, the base specifications
are applicable for TCAL ± 2 ˚C. This means that the specification would apply for a range
of 21 ˚C to 25 ˚C if the unit was calibrated at 23 ˚C. While this range is tighter than most
6.5-digit DMMs, it is also wider than the 3458A, which is specified at TCAL ± 1 ˚C.
Because the 34465A and 34470A DMMs have a built-in temperature reference, it is
easier to track the temperature at which your instrument was calibrated. The calibration
menu shows what the current temperature is, the calibration temperature and the
temperature change. Figure 1 illustrates the new information available in the calibration
screen.
Figure 1. Shown here is the new 34465A and 34470A DMM calibration screen.
06 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Achieving Enhanced Digital Multimeter Accuracy in
the Presence of Temperature Variation (continued)
Better accuracy with ACAL
Now let’s take a look at the specifications for the 34470A and see how the accuracy
limits change if you perform ACAL. Using the same scenario previously presented
(9-V DC reading, 10-V range, 22 ˚C cal temperature, and a 40 ˚C operating temperature),
we can calculate the specifications using the table in Table 2;
1-year base accuracy = 9 * 0.0016% + 10 * 0.0002% = 0.000144 + 0.00002 = 0.000164 V
(0.164 mV)
The base 1-year accuracy using a 34470A will be 9 V ± 0.164 mV.
There are two options for you here, depending on whether you choose to do an ACAL
or not. If you skip the ACAL step, you would use the TC adder for the non-ACAL column.
For each degree Celsius outside of the TCAL ± 2 ˚C, you would add in the following:
9 V * 0.0005% + 10 V * 0.0001% = 0.000045 V + 0.00001 V = 0.000055 V (0.055 mV)
In this example, the base specification is applicable for 22 ˚C + 2 ˚C = 24 ˚C. Since we are
operating at 40 ˚C, we need to multiply our TC adder by 16 degrees (40 ˚C-24 ˚C = 16 ˚C).
Consequently, the final calculation is:
9 V ± (0.000164 + 16 * 0.000055) = 9 V ± 0.00104V (1.04 mV)
The TC adder increases the error potential to 1.04 mV. This is over 600 percent of the
original specification!
However, since we can use the ACAL, we can greatly reduce the TC error. By performing
an ACAL shortly before our most accurate measurements, we can usually assume that
the temperature will not change by more than 2 ˚C.
Accuracy specification: DC voltage and resistance, automatic calibration (ACAL) capable,
Specification ± (% of reading + % of range)
Range
24 hours
TACAL ± 1 °C
90 days
TACAL ± 2 °C
1 year
TACAL ± 2 °C
2 years
TACAL ± 2 °C
Non ACAL
temperature
coefficient/°C
With ACAL
temperature
coefficient/°C
DC voltage: 34470
100 mV
0.0030 + 0.0030
0.0040 + 0.0035
0.0040 + 0.0035
0.0045 + 0.0035
0.0005 + 0.0005
0.0001 + 0.0005
1V
0.0010 + 0.0004
0.0015 + 0.0004
0.0020 + 0.0004
0.0025 + 0.0004
0.0005 + 0.0001
0.0001 + 0.0001
10 V
0.0008 + 0.0002
0.0013 + 0.0002
0.0016 + 0.0004
0.0020 + 0.0002
0.0005 + 0.0001
0.0001 + 0.0001
100 V
0.0020 + 0.0006
0.0032 + 0.0006
0.0038 + 0.0006
0.0040 + 0.0006
0.0005 + 0.0001
0.0001 + 0.0001
1000 V
0.0020 + 0.0006
0.0032 + 0.0006
0.0038 + 0.0006
0.0040 + 0.0006
0.0005 + 0.0001
0.0001 + 0.0001
Table 2. Shown here are the 34470A DCV specifications.
Please refer to the Truevolt Series DMM data sheet, publication number 5991-1983EN, for additional specification details.
07 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Achieving Enhanced Digital Multimeter Accuracy in
the Presence of Temperature Variation (continued)
Using the new TC column with ACAL specifications, the TC adder is now:
9 V * 0.0001% + 10 V * 0.0001% = 0.000009 V + 0.00001 V = 0.000019 V (0.019 mV)
Multiplying by sixteen degrees we get:
9 V ± (0.000164 + 16 * 0.000019) = 9 V ± 0.000468 V (0.468 mV)
While the TC adder is still a large effect over the base specifications, the overall accuracy
with ACAL is much better than the specifications without ACAL. The accuracy is widened
by 285 percent and is more accurate than a non-ACAL DMM’s specifications.
Table 3 compares the accuracy specifications for the 34465A and 34470A DMMs when
used with the following scenario: 9 V, tested on a 10-V range, calibrated at 22 ˚C, used
at 40 ˚C.
Model
Input
voltage/range
Base spec
at 22 ˚C
Specs w/TC
at 40 ˚C
Specs w/TC and
ACAL @ 40 ˚C
34465A
9 V/10 V range
± 310 µV
± 640 µV
± 424 µV
34470A
9 V/10 V range
± 164 µV
± 494 µV
± 278 µV
Table 3. 9-V input on a 10-V range, with calibration temperature at 22 ˚C and operating temperature at 40 ˚C.
For reference, Tables 4 and 5 are provided to allow you to compare the performance of
the two DMMs.
Model
Input
voltage/range
Base spec
at 22 ˚C
Specs w/TC
at 40 ˚C
Specs w/TC and
ACAL @ 40 ˚C
34465A
50 V/100 V range
± 2.6 mV
± 8.2 mV
± 5.8 mV
34470A
50 V/100 V range
± 2.5 mV
± 8.1 mV
± 4.9 mV
Table 4. 50-V input on a 100-V range, with calibration temperature at 22 ˚C and operating temperature at 40 ˚C.
Model
Input
voltage/range
Base spec
at 22 ˚C
Specs w/TC
at 40 ˚C
Specs w/TC and
ACAL @ 40 ˚C
34465A/34470A
10 KΩ/10 KΩ
range
± 0.45 Ω
± 1.57 Ω
± 0.93 Ω
Table 5. 10-KΩ input on a 10-KΩ range, with calibration temperature at 22 ˚C and operating temperature at 40 ˚C.
Summary
The operating temperature of your DMM can affect the accuracy of your readings. A
DMM with ACAL capabilities can greatly minimize your TC errors. With an operation time
of less than 20 seconds, ACAL is a task that you can run often to ensure optimal accuracy,
as shown in the tables. The new 34465A and 34470A Truevolt Series DMMs can help
ensure that your readings are accurate, even with temperature errors.
08 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Measuring Difficult AC Signals with a Digital Multimeter
Overview
Ideal AC signals used in electronics and power supplies are considered to be sinusoidal waveforms. In the real world; however, AC
voltages and currents are anything but ideal. Instead, they can take on widely varying shapes and values. See how the Keysight Truevolt
Series of digital multimeters (DMMs) can help you more quickly and easily characterize, analyze and understand your AC waveforms.
Measuring high peaking AC signals
Characterizing an energy harvesting device
You are designing a switching power supply and need to
characterize the apparent power factor when the supply is loaded.
With a capacitive load, the input current is not a pure sinusoid.
Often times, it is a signal that has large peaks compared to its
Root-Mean-Square (RMS) level. This can lead to measurement
errors when using a DMM. Using the Truevolt Series of DMMs
from Keysight Technologies you can obtain accurate AC current
measurements, even if the peak value is 10 times greater than
the RMS value.
With new technology comes new measurement challenges. In the
energy harvesting industry, for example, the signal levels are low
and often non-repetitive. Devices like piezoelectric generators
create AC signals from intermittent or continuous mechanical
stress. Characterizing these types of signals requires excellent
measurement resolution and the ability to discern non-continuous
waveforms. The Truevolt Series of DMMs not only measures these
types of low-level signals, but can also help you visualize ugly
AC signals with its digitizing capability.
09 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Measuring Difficult AC Signals with a Digital Multimeter (continued)
Understanding your AC waveform
Not every signal is going to be ideal—that’s a fact. It’s also a fact that as humans, it is
easier to understand things if we can visualize them. This is especially true for waveforms.
Using the digitizing capability of the 34465A and 34470A Truevolt DMMs, you can
visualize and characterize your AC waveforms to help you better understand their shape.
Traditionally this has been accomplished using an oscilloscope, but these instruments
are often limited to two digits of amplitude resolution. With a Truevolt Series DMM, you
can digitize your waveforms with a minimum of 4½ digits and up to 7½ digits of resolution.
The 34465A and 34470A DMMs have deterministic sampling intervals and sampling
modes that allow you to digitize your signal. Other digitizing capabilities available in
the DMMs include the ability to digitize directly from the front panel using the graphical
display and advanced trigger configurations (e.g. level-based triggering and logging
measurements to memory for post analysis).
For those who prefer using a PC for digitizing, Keysight’s BenchVue software can be
used to set up the measurement. Both BenchVue and the Truevolt DMM front panel allow
you to visualize your signal with more resolution than you would typically get from an
oscilloscope. Furthermore, using a DMM for digitizing has the added benefit of allowing
you to digitize current or voltage without the complexity of external current shunts,
clamps or voltage dividers.
Measurement tip
With the Truevolt Series of DMMs
you can analyze your AC measurements using the built-in statistics,
trend chart or histogram displays.
You can also save your readings to
an internal storage, a USB thumb
drive, or use BenchVue software to
easily transfer your reading to a PC.
www.keysight.com/find/BenchVue
10 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Measuring Difficult AC Signals with a Digital Multimeter (continued)
Higher crest factor helps you get the whole signal
While digitizing waveforms might allow you to see a few cycles of the waveforms, if you
are interested in the RMS amplitude or frequency of your AC waveform over time you’ll
need to make AC measurements. The Truevolt Series of DMMs use a proprietary digital
AC circuit that enables faster AC measurements and higher accuracy when compared to
older DMM architectures.
One AC component that is often overlooked is the crest factor. The Truevolt Series of
DMMs not only have one of the highest crest factor measurement capabilities in their
class, but also are able to measure double that possible with previous generation DMMs.
The crest factor is defined as the ratio of peak value to RMS value in a waveform.
Mathematically it can be expressed as:
Crest Factor (peak-to-RMS ratio) = (peak value)/(RMS value)
Figure 1 depicts an extreme case where the peak value is much higher than the
RMS value.
Figure 1. This image illustrates an AC signal with a large peak to RMS value.
Measurement tip
The Truevolt Series of DMMs
connected to your PC via a USB
cable can be accessed like a USB
drive. Your DMM shows up as a
drive. You can access your saved
readings by simply dragging and
dropping to your PC.
11 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Measuring Difficult AC Signals with a Digital Multimeter (continued)
A DMM’s crest factor represents how much of the total energy from the peak value will
be included in an AC measurement. Ideally, you would like to include as much of the total
energy in the waveform as possible to get an accurate measurement. For a measuring
instrument, the crest factor expresses the size of the dynamic range for an input signal.
We define the crest factor as the size of the dynamic range based on rated range value
(RMS value). Since the Truevolt Series of DMMs have a crest factor rating of 10, it is
possible to measure an input signal whose peak value is ten times larger than that of
the rated range value.
Consider, for example, the readings of a 34401A DMM that uses an older analog AC
circuit design compared to the measurements of a 34465A DMM with the improved
digital AC. Note that many DMMs out on the market today still use older analog AC circuit
designs. Figure 2 shows the digitized input signal using the built-in digitizing capability
of the 34465A DMM. Notice that the majority of the energy is around 1-V RMS, but the
signal has a very high peak, close to 10 V. It is in this area where the measurement
accuracy of the 34465A DMM makes a difference.
Figure 2. Shown here is digitized AC voltage with large crest factor.
12 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Measuring Difficult AC Signals with a Digital Multimeter (continued)
Figure 3 shows the AC readings that were obtained from two DMMs employing BenchVue
software. The 34465A DMM readings are on the bottom panel, while the older 34401A
DMM readings are on the top. Notice that the readings on the 34465A DMM are higher
than that of the 34401A DMM’s readings. The difference is 52 mV, which equates to a
6 percent amount error. This error is significant compared to a normal AC specification
of less than 0.2 percent.
Figure 3. This display compares two parallel DMM readings. The reading taken with the 34465A DMM, at the
bottom, measures the complete AC signal and hence, explains the higher reading value.
Measurement tip
You can use the dual display
features of the 34465A/34470A
DMMs to measure frequency
concurrently with your AC signals.
See more dual display modes with
the following Keysight application
brief “Faster Data Analysis with
Graphical Digital Multimeter
Measurements” publication
number 5992-0421EN.
13 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Measuring Difficult AC Signals with a Digital Multimeter (continued)
Another area where crest factor is important is when measuring pulsed signals. That’s
because for many DMMs it can be challenging to accurately read the RMS voltage/current
when a signal level that has an “on” period is followed by a period where no activity
occurs. With the larger crest factor of the Truevolt Series of DMMs; however, you can
achieve better accuracy—even when the pulse ratio changes.
As an example, consider a 7-V RMS sine wave running at 10 KHz, which translates to a
period of 10 ms. Any 6.5-digit DMM will measure this type of signal with minimal issues.
Where the Truevolt Series of DMMs standout; however, is when the number of sine
pulses in the input signal is reduced. Figure 4 shows a digitized pulsed waveform with a
single sine pulse of 0.1 ms, followed by a quiet period of 9.9 ms. The total period is still
the same at 10 ms. The new signal represents a drop in power of 100:1, while the RMS
voltage drops 10:1, when compared to the original.
Figure 4. Shown here is an example of a digitized waveform.
14 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Measuring Difficult AC Signals with a Digital Multimeter (continued)
Given these results, we would expect that the voltage would be one tenth of our original
signal’s 7 V. The expected result should be 0.7-Vac. However, as can be seen in Figure 5,
only the Truevolt Series DMM gives an accurate reading of 0.69987 V. The older analog
AC measurement produces a 0.4677 V reading! The old DMM now has an error of 0.23 V
or 35 percent from nominal! Again, it is the Truevolt Series DMM’s superior handling of
crest factor that enables a more accurate measurement on this challenging signal.
Figure 5. In this graphic, 1/10th of the V RMS is measured accurately by the 34465A (bottom measurement).
15 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Measuring Difficult AC Signals with a Digital Multimeter (continued)
Green energy example
Energy harvesting is the industry term for scavenging and accumulating ambient energy
that has historically been deemed unusable, and converting it to a usable power source.
Examples of ambient energy sources include solar, wind, vibrations from a motor, or even
RF energy from ambient radio transmitters. Today there are a number of devices on the
market to harvest these sources, and electronics manufacturers are continuing to
investigate methods for making them more efficient.
One such device that is used to convert mechanical vibrations to usable power is a
piezoelectric generator (Figure 6). This device is designed to harvest the otherwise wasted
vibration energy and convert it to power that can be used directly or saved to a battery.
However, the power generated by this type of device is understandably small — often
times, its maximum power output is less than 1 mW and this depends on the magnitude
of the vibration source.
Figure 6. In this image a piezoelectric generator is attached to a vibration source — in this case, a fan.
The AC performance of the Truevolt Series of DMMs can be useful for characterizing
energy harvesting devices such as piezoelectric generators. These generators are typically
mounted on mechanical devices with very irregular vibration cycles. As such, the current
output of these generators can vary from a very large signal to a small signal. With a
Truevolt Series DMM, you can visualize the current and then measure the AC signals
accurately. Figure 7 shows a digitized current that starts with a large magnitude (when
the device is vibrating) and decays rapidly. The digitized picture also shows the AC
nature of piezoelectric devices.
Figure 7. The digitized current from a piezoelectric generator device.
16 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Measuring Difficult AC Signals with a Digital Multimeter (continued)
Since we now know that our device outputs an AC signal, we can measure the AC current
of the device and characterize this over time and different conditions. In Figure 8, you
can easily see that the vibration source has varying “on” periods and quiet periods. By
using an AC measurement, we can measure the total RMS current generated. We can
then use the in-box statistics to understand the value of our average output current. We
also can save and transfer the readings to a PC for further analysis. With the improved
AC techniques of the Truevolt Series of DMMs, you can trust these results to be accurate.
Figure 8. Shown here is the characterization of a piezoelectric generator connected to a
vibration source.
Summary
The Truevolt Series of DMMs can accurately measure your AC signals. Whether you have
a typical AC signal or a signal that is more challenging, you can use its digitizing feature
to help you visualize and better understand your signal. You can then use its AC
measurements to characterize your signals.
17 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Measuring Low Current Consumption with a Digital Multimeter
Overview
DMMs measure current. It’s one of the basic functions of a digital multimeter (DMM). These instruments are the go-to tool for most
engineers and technicians when they need to make current or voltage measurements. Keysight has added additional current ranges to
the Truevolt DMM series that allow you to measure a wider range of currents than other 6.5 digit DMMs. Learn some of the details on
how expanded current ranges can help your measurements.
Characterizing the power consumption of a
battery powered device
You are tasked with characterizing the power consumption of a
battery powered device. Designers have optimized the device’s
current draw, but need complete measurements of the current
from sleep mode to full operating load. To fully characterize the
device’s different current cycles, you decide to use a 34465A DMM.
Its’ 1-µA DC current range provides the pico-amp resolution
needed to accurately characterize the sleep mode. It also has a
high range, 10 A, which allows you to measure a wide range of
currents for your battery powered device when operating in full
load conditions.
Testing the current draw of a low leakage diode
You are testing the current draw of a low leakage diode. To do so,
you need pico-amp resolution, but with the ability to measure
forward currents with dozens of mA’s. While you can perform
these measurements with a more expensive electrometer, you
might also be able to make them using a stable DC power supply
and a new Truevolt DMM. The 34465A/34470A Truevolt DMMs
feature a low DC current range of 1 µA, which allows for pico-amp
resolution with less than 100 pA accuracy (1 year specs, depending
on current reading) to accurately characterize leakage current.
With a no-open circuit range change up to 3 A, you can characterize
your device’s backward and forward current without breaking the
circuit.
18 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Measuring Low Current Consumption with a Digital Multimeter
(continued)
DMM current readings
Measurement tip
Many 6½ digit DMMs are limited to a 1-mA low current range when measuring DC. This
offers a best case resolution of 1 nA. Other DMMs offer a 100-µA or 200-µA range,
which in turn offers 100-pA resolution.
When measuring very small currents
be sure to null your readings before
your crucial measurement. Doing
so removes any system related
offsets, allowing the measurement
to be more accurate.
The new 34465A and 34470A Truevolt Series of DMMs feature a low current range of 1 µA,
which in turn offers an exceptional 1-pA resolution. The new Truevolt DMMs also offer
extended current ranges that are simply not available with other DMMs in this class. The
new current ranges include 10 µA, 1 µA on the low end, and a 10-A range on the higher
end (Figure 1). With pA resolution on the 1-µA range, the potential current measurements
range from 1 pA to 10 A, resulting in 13 orders of magnitude to be measured by these DMMs.
Accuracy specifications: DC current and other DC functions
Specification ± (% of reading + % of range)
Range/frequency
24 hours TCAL ± 1 °C
90 days TCAL ± 5 °C
1 year TCAL ± 5 °C
2 years TCAL ± 5 °C
Temperature
coefficient/°C
1 μA
0.007 + 0.005
0.030 + 0.005
0.050 + 0.005
0.060 + 0.005
0.020 + 0.010
10 μA
0.007 + 0.002
0.030 + 0.002
0.050 + 0.002
0.060 + 0.002
0.015 + 0.006
100 μA
0.007 + 0.001
0.030 + 0.001
0.050 + 0.001
0.060 + 0.001
0.015 + 0.004
1 mA
0.007 + 0.003
0.030 + 0.005
0.050 + 0.005
0.060 + 0.005
0.015 + 0.005
10 mA
0.007 + 0.020
0.030 + 0.020
0.050 + 0.020
0.060 + 0.020
0.020 + 0.020
100 mA
0.010 + 0.004
0.030 + 0.005
0.050 + 0.005
0.060 + 0.005
0.020 + 0.005
1A
0.050 + 0.006
0.070 + 0.010
0.080 + 0.010
0.100 + 0.010
0.050 + 0.010
3A
0.180 + 0.0020
0.200 + 0.020
0.200 + 0.020
0.230 + 0.020
0.050 + 0.020
10 A
0.050 + 0.0010
0.120 + 0.010
0.120 + 0.010
0.150 + 0.010
0.050 + 0.010
DC current
Figure 1. Shown here are all of the new current ranges available with the 34465A and 34470A Truevolt Series of DMMs.
Please refer to the Truevolt Series DMM data sheet, publication number 5991-1983EN, for additional specification details.
19 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Measuring Low Current Consumption with a Digital Multimeter
(continued)
Burden voltage
When measuring low levels of current, burden voltage can be a concern. Burden voltage
is the change in potential created when current flows through the shunt resistor of a
DMM. While this is not normally a concern, very sensitive components must be aware
of the voltage, especially if the DMM is placed in series in the return path as shown in
Figure 2. By adding a small voltage above the low of the power supply, the low of your
device might well be above your design tolerance.
If the burden voltage gets sufficiently large, the offset voltage on the return path might
cause a problem; depending on your device. The burden voltages of the 34465A and
34470A DMMs are shown in Figure 3.
Figure 2. Shown here is the DMM in series on the return path.
DC and AC current burden voltage at full scale
DC current range
Burden voltage
1 μA
< 0.0011 V
10 μA
< 0.011 V
100 μA
< 0.11 V
1 mA
< 0.11 V
10 mA
< 0.027 V
100 mA
< 0.27 V
1A
< 0.7 V/0.05 V1
3A
< 2.0 V/0.15 V1
10 A
< 0.5 V
1. The second burden voltage can be obtained by using the 10 A range input.
Table 2. This table represents the burden voltages of the different current ranges of the 34465A and 34470A.
Measurement tip
Consider moving the DMM in
series to the positive side of your
power supply. If you can increase
the voltage to accommodate for
the burden voltage, you can still
supply the correct voltage to your
device and measure current.
20 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Measuring Low Current Consumption with a Digital Multimeter
(continued)
Dynamic current measurements
Dynamic current measurements can be quite complex due to the DMM range change
based on the level of current you are measuring. Keysight offers specialized instruments
(e.g., the Keysight N6782A SMU) that can digitize power, voltage and current without
ranging issues. While this may be a great solution for current characterization, the
solution is a bit more expensive than using a Truevolt DMM. In situations where budget
or flexibility is a concern, the Truevolt DMM allows you to accomplish many of the same
measurements.
Whether you are measuring the reverse and forward bias current of an LED or the
sleep/operating mode current of a battery powered device, you will have a very large
difference between the two modes of operation.
Figure 4 illustrates a simple block diagram for battery drain analysis. You can effectively
monitor the power drain from your battery powered device using one DMM to monitor
the voltage and another DMM to monitor the current. On the Truevolt DMMs, the 10-A
input is separate from the low current input. This setup uses the low current input.
Figure 4. This block diagram depicts a battery drain analysis using two DMMs.
Measurement tip
Using the Truevolt DMM digitizing
capability and High Speed (HS)
option, you can measure fast
changing characteristics while
measuring with a time resolution
with a time resolution of 20 µs. To
effectively digitize with accurate
timing, ensure that auto zero and
auto ranging is turned off. This
eliminates the timing variation
that occurs when the DMM makes
additional readings for the auto
zero or switching to a different
range.
21 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Measuring Low Current Consumption with a Digital Multimeter
(continued)
Figure 5 shows a typical current profile of a portable radio transceiver. As you can see,
the current draw is complicated with a wide range of sleep, standby and active modes.
The dynamic range of the current is large because the operating currents are drawing
approximately 30 to 40 mA, while the standby currents are only 1 to 10 µA.
In order to get accurate readings for both ranges with a DMM, you need to take multiple
reading sweeps with different ranges. One method for capturing the current profile
would be to run the Device-Under-Test (DUT) multiple times to capture the sleep and
standby modes separately and then the operating mode currents. In the first capture,
set the DMM to the 100-mA range and 0.001 plc (20 µS per sample). This will capture
the complete current signal, including the active mode values between 30 to 40 mA,
but provides less resolution on the lower current measurements.
Figure 5. Shown here is a current profile from a portable radio.
Figure 6 shows a trend chart view of the currents read using a 34465A DMM. Notice
that the lower current measurements seem to be very uniform, which is due a loss of
resolution. To measure the low current values, you need to take another measurement
at a lower current range. Once you have captured the readings, the data can be saved
to memory and analyzed on a PC.
Figure 6. This operating current was captured with the 34465A DMM. Shown here is the DMM front panel.
Measurement tip
You can use Keysight’s BenchVue
software to control and trigger
both DMMs simultaneously. Use
the digitizing mode of the DMM
to ensure 20 µS/sample timing.
Note that the datalogging mode in
BenchVue includes PC overhead
that can interfere when precise
timing is required.
22 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Measuring Low Current Consumption with a Digital Multimeter
(continued)
Next, you can set the DMM to a lower current range for the standby and/or sleep
currents. Figure 7 shows a graphical data capture, using BenchVue, of the standby
currents measured by the top graph. The bottom graph shows the DCV readings. Figure 8
shows the statistics and actual readings from the data set. The currents captured range
from approximately 2 to 10 µA. They were captured with the DUT in standby mode, thus
allowing for a single range current capture. Anything above 120 percent of the range will
result in an overload condition.
Figure 7. These two graphs illustrate the digitized DCI (top image) and DCV (bottom image) consumption.
Summary
With extended current ranges and
digitizing capabilities, the 34465A and
34470A Truevolt DMMs can effectively
characterize dynamic currents. Whether
your DUT is drawing high current at
10 A or you need to measure lower
current in the pico-amp region, the
new Truevolt DMMs have the features
and measurement capabilities to be a
workhorse instrument on your bench.
Figure 8. Shown here are the statistics and actual readings from the data set captured in Figure 7.
23 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Faster Data Analysis with Graphical Digital Multimeter Measurements
Overview
New modern DMMs allow you to analyze your setup and data using only the front panel. The Truevolt Series of DMMs—the 34460A,
34461A, 34465A, and 34470—offer other methods for gaining insight into measurement data, without having to first transfer that data
to a PC. Truevolt DMMs feature a large graphical display and built-in math functions that show measurement trends, statistics, and
histograms all in a single, compact unit. With advanced analysis and data collection methods on the 34465A and 34470A, it may even be
possible to run an entire analysis using only the DMM. See how the Truevolt Series DMMs can help you more quickly analyze your data.
Analyzing changes with time
Identifying noise in your design
You need to characterize the drift of a precision resistor in your
design. Rather than setting up a program or using your PC, you
decide to use your Truevolt DMM’s trend chart feature to gather
the data. After allowing the design to heat up for 20 minutes, you
start to see nonlinear behavior in the resistor. With the pan, zoom
and cursor capability of the new 34465A/34470A DMM’s, you
identify the instant the measurement goes nonlinear. As a result
of this discovery, you decide that the resistor is not performing to
specification and that you need to evaluate other parts.
You are troubleshooting a switching DC power supply that
appears to work well. However, there is some behavior that
drops the voltage out of tolerance. Using your Truevolt DMM you
characterize the power supply’s output. By switching between
trend chart and histogram mode you identify that the power
supply’s noise is not Gaussian and is skewed toward the lower
end of
regulation. Your analysis only takes 10 minutes and was
accomplished without a computer.
24 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Faster Data Analysis with Graphical Digital Multimeter Measurements
(continued)
Trend charts show direction
If you expect a measurement to remain constant, only measure it once. That’s because
in the real world values drift with time, track other parameters, or vary in complex ways
with outside influences. You can set the trend chart display on the 34461A, 34465A, and
34470A DMMs to display the most recent data over the last minute, or to display all of
the data collected since the last time the readings were cleared (Figure 1).
An example of a common secondary measurement would be the ability to measure the
frequency of an AC signal, as shown in Figure 1.
Histograms tell all about the data
When the lowest digits of a reading are changing constantly and sometimes too quickly
to visually track, it is important to know the nature of that variation. The histogram
provides insight by showing the distribution of the measured values (Figure 2). The
average, distribution shape, and standard deviation are all critical information for
understanding the variation phenomena.
Figure 1. The trend chart display shows direction and reading anomalies.
Figure 2. The histogram show data distribution.
25 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Faster Data Analysis with Graphical Digital Multimeter Measurements
(continued)
Secondary measurements
With the ability to have secondary measurements run concurrently with your primary
measurement, you can gather two types of information at a glance; for example, a
thermistor temperature measurement (primary) and the resistance measurement made
on the thermistor (Figure 3). For further information on secondary measurements, see
the Keysight Technologies application brief “Simultaneous Measurements with a Digital
Multimeter” publication number 5992-0419EN or the Truevolt DMM datasheet, publication
number 5991-1983EN.
Figure 3. The Truevolt DMMs allow secondary measurements to run concurrently
with a primary measurement.
Advanced DMM triggering
If the traditional DMM triggering model was insufficient for your testing needs, then the
new Truevolt DMMs may have just the solution for you. Traditional DMMs either make
measurements right after you configure the measurement (immediate trigger), do a single
measurement, or trigger from an external source via the External Trigger port. Higher-end
DMMs like the 34465A and 34470A have additional modes wherein a combination of
trigger settings, delay times, number of samples per trigger, and pre-trigger settings
can be used to provide concise data (Figure 4).
Using the DMM’s advanced trigger modes you can set a level trigger that will start making
measurements when the desired level is reached (Figure 5). You can also set a trigger
delay to wait a defined time after the trigger event. Another useful setting is the ability to
define the number of samples after a trigger is received, which helps to ensure a number
of continuous measurements after the trigger event, rather than just a single reading per
trigger.
Figure 4. The 34465A/34470A DMMs feature advanced trigger modes.
Figure 5. The Truevolt DMMs’ advanced trigger modes allow designers to set a level trigger.
26 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Faster Data Analysis with Graphical Digital Multimeter Measurements
(continued)
New acquisition modes
In addition to the traditional continuous measurement mode, the 34465A and 34470A
DMMs provide data logging and digitizing modes from the front panel. These new modes
are accessible from the Acquire menu located on the front panel. To start the acquisition,
you simply press the Run/Stop button.
Data logging
The 34465A and 34470A DMMS feature a new data logging mode for front panel usage.
Found under the Acquire menu, the mode allows you to get readings at a constant sample
interval to effectively log your data over time. You can easily set your sample interval
(e.g., how often you want to make a measurement) and your total duration (e.g., how long
or how many readings you want to make). You can also choose your start time by defining
either a delay time from when you press RUN or a start time in terms of Hour/Min/Sec.
Data logging allows you to stream directly to a .csv file on either the DMM’s internal
memory or a USB thumb drive connected to the front panel of the DMM. You may log up
to 100 hours or 360 million readings, whichever is less (Figure 6). In data logging mode,
you may sample as fast as 1000 samples/second. Because the data logging feature is
optimized for precision timing in its readings, some features are not available, such as
the level trigger and external trigger.
Exporting to a .csv file allows you to analyze your data on a computer (Figure 7). The .csv
file includes the start time and measurement interval (in seconds); allowing you to extract
the time that your measurement was taken.
Figure 7. CSV data file from Truevolt DMM.
Measurement tip
Figure 6. Data logging allows you to log up to 100 hours or 360 million readings.
You can set the DMM’s real-time
clock to your local time. Truevolt
DMM’s ship from the factory with
Greenwich Mean Time (GMT)
standard. Setting the clock to your
local time allows for start times to
be more intuitive for analysis.
Measurement tip
Figure 8. A Truevolt DMM shows up like a drive
on your PC.
With a USB connection to your
PC, Truevolt DMMs show up like a
drive on your PC (Figure 8) Using
the Easy File Access, you can drag
and drop files from or to your DMM
without additional software. This
is an easy method to get readings
from your DMM to your PC for
analysis.
27 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Faster Data Analysis with Graphical Digital Multimeter Measurements
(continued)
Digitizing mode
The Truevolt DMM digitizing mode allows you to sample at the maximum rate and analyze
your data from the front panel. With a 50-kHz sampling rate, you can take a measurement every 20 µs (Figure 9). The slowest rate for digitizing is 100 ms. The digitizing mode
sends data to the DMM’s measurement memory, which can keep up to 2 million readings
with the optional memory (50,000 readings standard). After the readings have completed,
you can store the readings to a .csv file.
In addition to the fast sampling, the digitizing mode allows you to setup a level trigger
to start your readings. You can set the level and polarity at which you want to start the
triggering of the measurement. You can also select the number of pre-trigger readings to
digitize. This allows you to keep measurements that happen before your trigger level has
been reached.
Figure 9. A 50-KHz sampling rate allows you capture fast changes in your signal.
28 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Faster Data Analysis with Graphical Digital Multimeter Measurements
(continued)
Pan/zoom/cursors
If you are using the histogram or trend chart display modes, you have additional features
for analysis. For readings in measurement memory, you can pan or zoom into your data.
With zooming, you can enlarge portions of your data for viewing. Panning allows you to
move the display screen to the measurement sample number that you want to view.
Figure 10 shows a digitized reading that looks similar to the Keysight logo. In Figure 11,
the DMM has zoomed into a number of readings to show how individual sine waves
actually make up the total logo.
Figure 10. Digitized data of 1.2 million readings.
Figure 11. Zoomed/panned in data that shows individual sine waves.
29 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Faster Data Analysis with Graphical Digital Multimeter Measurements
(continued)
The new cursor functionality in the trend chart allows you to place two X and Y cursors
on your data (Figure 12). Each cursor shows the time (from a start time of 0 seconds)
and the measurement value for where the cursor is placed. While this feature has been
commonly used in oscilloscopes for years, it is new to DMMs and only available on
Truevolt DMMs.
Histograms include cursor functionality as well (Figure 13). Histogram cursors allow you
to select which bin to view and show the number of occurrences and percentage of total
readings that the bin has accumulated. The span feature includes between the cursor
information about the range of the readings, the number of readings, and the percentage
of readings between the cursors compared to the total readings.
Measurement tip
If you need to control multiple
DMMs or a mix of instruments, and
analyze their data, use Keysight’s
BenchVue software for your PC.
BenchVue supports all Truevolt
DMMs, along with more than 200
other Keysight instruments.
Figure 12. The Truevolt DMMs allows you to place X and Y cursors on your data.
Conclusion
Figure 13. Histogram cursors.
Setting up a computer connection
for data collection and analysis can
take too much time, especially if you
are measuring a single parameter.
It is clear that a single value does
not provide much insight into the
performance of your DUT over time or
in response to outside interference.
A picture, on the other hand, can
offer much richer insight with just a
single glance. Now, with the Truevolt
Series DMMs’ new graphical display,
advanced analysis modes, and built-in
math functions, the ability to turn lots
of data into results that can be quickly
analyzed is at your fingertips—all this
with just simple front-panel menu
entries. Using the Truevolt DMMs you
can now meet your testing goals faster
than ever before.
30 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Simultaneous Measurements with a Digital Multimeter
Overview
Traditionally, digital multimeters (DMMs) have been single-measurement instruments. In some cases; however, system designers want
the ability to track more than one parameter on their signal. Doing so often provides complementary data that can make measurements
significantly easier to understand. With the right architecture and design, DMMs can now make secondary measurements. See how the
Truevolt Series DMMs helps designers make secondary measurements without ever having to change the instrument’s configuration.
The advanced functionality on the 34465A and 34470A (e.g., expanded math functions) also means that designers can now analyze
their data faster.
Making more confident measurements
Making dual measurements in less time
A test engineer wants to monitor the temperature inside of an
environmental chamber and needs a high level of confidence that
the measurements are accurate. A 34465A DMM is selected due
to its ability to log data and provide simple trend charts. A 5-KΩ
NTC thermistor is used to spot check for accuracy.
A system designed to apply a linear force to a small structure has
the ability to provide an oscillating force with an AC signal and
a constant force with a DC signal. The system designer wants to
keep track of both signals concurrently in order to characterize
how much force is being applied. Using a Truevolt DMM with its
ability to make secondary measurements, he is able to read both
the DC and AC components of his control signal at the same time.
The engineer notices that the thermistor has a temperature error
of a few degrees. To understand the error, the secondary display
on the Truevolt DMM is turned on and temperature and resistor
readings are read at the same time. According to the datasheet
for the thermistor, it should read 25 ºC at 5 KΩ. The engineer’s
probe is put inside of a calibrated chamber set to 27 ºC, but the
probe reads 25 ºC with a 5-KΩ resistance reading, a two degree
error. After a bit of characterization, the engineer decides that
he can simply add an offset value to adjust for the offset of his
thermistor.
31 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Simultaneous Measurements with a Digital Multimeter (continued)
Two measurements one screen
Secondary measurements are defined as auxiliary measurements that augment information provided by a main primary measurement function. Depending on the function,
you can measure complementary data that traditionally would have taken two different
operations and function changes to acquire. The table illustrates all secondary
measurement capabilities of the Truevolt DMMs.
Primary measurement
function
34460A secondary
measurement function
34465A/70A secondary
measurement function
DCV
ACV
ACV, peak, pre-math
ACV
Frequency
DCV, frequency, pre-math
2-wire, 4-wire resistance
Pre-math
DCI
ACI
ACI, peak, pre-math
ACI
Frequency
DCI, frequency, pre-math
Frequency
Period
Period, ACV, pre-math
Period
Frequency
Frequency, ACV, pre-math
Temperature
Sensor
Sensor, pre-math
Ratio
Input/Ref
Input/ref, pre-math
Capacitance
Pre-math
Continuity
None
Diode
None
Table 1. Secondary measurement capabilities supported by the Truevolt DMMs.
An example of a common secondary measurement would be the ability to measure the
frequency of an AC signal, as shown in Figure 1.
Figure 1. AC voltage with frequency.
32 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Simultaneous Measurements with a Digital Multimeter (continued)
With the advanced secondary features of the 34465A and 34470A DMMs, the secondary
measurements provide more information than is possible with other DMMs. As an
example, Figure 2 shows the primary measurement of DC voltage (DCV) with a secondary
measurement of AC voltage (ACV). This is an especially important measurement if your
signal has both an AC and DC component.
In DCV mode, there are two additional secondary measurements that can be made to
provide insight into your signal: Peak and Pre-Math. The Peak measurement, as shown in
Figure 3, keeps track of the minimum and maximum DCV readings read by the DMM. This
is similar to the information that is available from the statistics display.
Figure 2. DC voltage (primary) and AC voltage (secondary) measurements.
Figure 3. Peak measurement of DCV.
33 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Simultaneous Measurements with a Digital Multimeter (continued)
Pre-Math is also a very valuable measurement because it allows you to see modified
readings and raw readings in one screen (Figure 4). You can even modify your primary
display by applying useful math functions to your data (e.g., a null value or scaling) or
filtering your data (Figure 5). See Adding Math Enables Faster Analysis section for more
information on applying math function.
Once you have applied the desired math function, the secondary display will display
the raw reading without the math. This is useful for determining if the applied math is
correct, and if the readings are within the expected range.
Figure 4. A DCV signal with dB scaling with the Pre-Math measurement.
Figure 5. A with the null value applied with the raw measurement on the secondary display.
34 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Simultaneous Measurements with a Digital Multimeter (continued)
With the temperature measurement capabilities included on Truevolt DMMs, you might
also want to see what the sensor readings are in volts or ohms, depending on your sensor
(Figure 6). All four Truevolt DMM models provide this capability on the secondary display.
Figure 6. Sensor readings displayed on the secondary display for a given
temperature measurement.
Another useful feature of the dual display is the ability to provide raw measurements
when you are using the DCV ratio function. With the addition of the second display, you
can read the ratio, the input voltage, and the reference voltage in one glance (Figure 7).
The DCV ratio is a function measured by comparing the voltage on the Input terminals
divided by the reference voltage. The reference voltage is the difference of two separate
measurements. These measurements are the DC voltages from the HI Sense terminal to
the LO Input terminal and from the LO Sense terminal to the LO Input terminal. Figure 8
shows a simple DCV ratio diagram.
Figure 8. Basic DCV ratio diagram.
Figure 7. With the Truevolt DMM dual display, you can view 2 voltage
measurements when using the DCV ratio function.
35 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Simultaneous Measurements with a Digital Multimeter (continued)
Additional information
Adding math enables faster analysis
A key advantage of the 34465A/34470A Truevolt Series DMMs is that they feature
additional Math functions as compared to their predecessors, the 34460A and 34461A.
These earlier Truevolt DMMs allow you to Null readings to zero out your measurement
offsets, set Limits for your readings, and show statistics. The newer 34465A/34470A
DMMs provide the same capabilities, but they also include a Smoothing filter and Scaling
(Figure 9).
The Smoothing filter is useful if you want to average out statistical outliers. Applying the
smoothing filter means the DMM uses a moving average (boxcar) filter to reduce random
noise. You may change the filter response by choosing Fast/Medium/Slow (Figure 10).
The slower the filter gets, the more readings are used in the filter.
Additional Scaling features are available on the new DMMs as well. You can now change
the readings on your front panel by scaling the readings with either a dB, dBm, %, or
Mx-B scaling (Figure 11). For dB scaling, the result is the difference between the input
signal and the stored dB-relative value reference. The dBm Scaling is a result based on
the calculation of power delivered to a reference resistance (Ref R), relative to 1 milliWatt.
The % scaling shows a percent change from a reference value, while the Mx-B allows for
linear scaling with an offset operation.
Figure 9. Math functions available in the 34465A/34470A DMMs.
Figure 10. Smoothing filter options.
Figure 11. Options for scaling.
Summary
Advanced dual-screen measurements not only allow you to get more information
concurrently, they also allow you to check your raw data compared to your adjusted
measurements. Using the Truevolt Series DMMs to make dual measurements, you not
only save time and but also gain more information than is possible with other similar
instruments.
36 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Making Simpler DC Power Measurements with a Digital Multimeter
Overview
Many applications need to measure power. In fact, it can be the more intuitive parameter for your specific test. For many years, the
DMM has served as the “go to” solution for measuring power. While DMMs can measure both current and voltage, their internal
architecture inhibits their ability to measure both at exactly the same time. Using a few different techniques; however, you might be
able to get a good V/I measurement from your benchtop DMM. Those measurements can then be used to calculate DC power. This
brief describes several methods that can aid you in making simple DC power measurements using a single Truevolt Series DMM.
Measuring DC voltage and current with a single
digital multimeter
You are tasked with measuring the power consumption of a
Bluetooth® speaker, which is normally powered from a battery.
The operating voltage of the speaker is 19.2 V and the current
consumption ranges from a few hundred micro-amps to a few
amps. You would like to keep the voltage stable and monitor the
current to understand the power consumption in terms of watts.
Using a Truevolt Series DMM and internal math scaling of the
current measurement, you can use a simple math function to
multiply a known voltage with the measured current signal. This
will provide you a reading in watts. With the display capabilities
and low current ranges of the Truevolt Series DMMs, you can do
make your power measurements with just a single DMM.
Measuring watts with a digital multimeter
You have a lower power DC-to-DC converter and need to
monitor the voltage and current consumption at the same time
to understand its efficiency. This typically takes one DMM to
measure the voltage, and one to monitor the current. With the
help of a stable external shunt resistor and a Truevolt Series
DMM, you can accurately measure lower power voltage and
current at intervals very close to each other. With knowledge
of the limitations of this method, you can get an accurate and
precise measurement of your DC power characteristics.
37 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Making Simpler DC Power Measurements with a Digital Multimeter
(continued)
Measuring Power with a DMM
The most basic equation in DC power is an extension to Ohm’s law, given by:
P=V*I
The typical configuration used to monitor power with DMMs is to have one DMM monitor
voltage, while another one measures the current. The power is then calculated on a PC.
Figure 1 shows a typical DC power measurement configuration.
+
+
–
PS
–
+
A
DUT
+
–
DMM1
DCV
–
DMM
DCI
Figure 1. This diagram represents a typical DCV and DCI measurement configuration using two DMMs.
A dual DMM configuration is needed to monitor voltage and current at the same, or very
nearly the same time. This approach is highly flexible, allowing you to measure a wider
variety of voltage and current levels. However, it does add complexity because you need
to monitor two DMMs. Also, if you want to control the timing of the readings such that
they are close to each other, you will likely need some sort of PC program to control the
multimeters. Often, you might not have the resources for this type of approach or even
the time to create and debug the program.
Some engineers assume they can use a single DMM to measure voltage and current at
the same time since there are two different ports, one for voltage and one for current.
There are a couple of issues with this approach. The first is that most DMMs do not support both readings without an internal configuration change. Internal relays will change
state, ranges change, and circuits might be disrupted. Thus, the timing of the voltage
and current readings is often unpredictable. Another issue is that the ports share the
same common LO terminal. Unless you are very careful with how you wire your test, you
might actually damage your DMM or Device Under Test (DUT) by applying a dangerous
floating voltage on either the current or voltage terminals. Because of this, many DMM
manufacturers do not allow for simultaneous voltage and current measurements.
Measurement tip
Instruments that are dedicated to
measuring power include Keysight’s
N6705B and N6715B DC power
analyzers. For AC power analysis,
Keysight offers the new PA2200
IntegraVision power analyzers. Go
to www.keysight.com for more
information.
38 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Making Simpler DC Power Measurements with a Digital Multimeter
(continued)
Using scaling to get readings in watts
Often in power measurements, you might have a constant voltage or current source and
the other factor varies. For example, if you have a constant voltage, the power varies
because the current is changing. Many times you would like to see your DMM readings in
terms of watts, as this makes the readings more intuitive. If you have a constant parameter, such as a constant voltage, you can make a single voltage reading and then use
the same DMM to measure current. Finally, you can convert your current measurements
to watts in real time with a simple scaling operation on either the Truevolt 34465A or
34470A DMM.
For this example, a DC voltage reading was taken at the DUT inputs as shown in Figure 2.
The DMM was then moved in series with the DUT on the return path. This is done to
measure current as shown in Figure 3. After enabling mathematical scaling on the DC
current reading, a gain was applied to the readings.
Figure 2. Shown here is a DCV reading at the inputs to the DUT.
+
PS
–
+
–
Vburden
+
A
DUT
–
DMM
DCI
Figure 3. The DCI current can be measured using the configuration shown here.
39 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Making Simpler DC Power Measurements with a Digital Multimeter
(continued)
In Figure 4, you can see that the gain applied was the same DC voltage reading taken in
Figure 1. The reading in yellow is the total watts that are measured (V*I) and is updated
constantly as the DCI measurement changes. Also, note the raw DC current reading in
the secondary measurement in blue. You may enable or disable the secondary measurement as needed. In the math menu, you may also enter in a user defined unit (max 4
characters) that allows the displayed measurement to be shown in watts.
Measurement tip
If you need to measure currents
higher than the 10-A range
available on the Truevolt Series
DMMs, consider using external
shunts on the DC volts terminal or
current transformers. You can still
use the math scaling functions to
convert the measurements to the
units that you expect.
Measurement tip
Burden voltage is the change in
potential created when current
flows through the shunt resistor
of a DMM. Be aware of the burden
voltage and the effect it can have
on the accuracy of your power
measurements.
Figure 4. This screen displays the watt reading given the gain and raw current readings shown.
Measure voltage and current at nearly the same time
If your voltage or current is not constant, the method previously outlined might not be
right for you. Fortunately, there is another method available on the Truevolt Series DMMs
that measures both voltage and current at close intervals to one another. This method
involves the use of an external resistor to convert a DC voltage measurement to current,
again utilizing Ohm’s law.
The Truevolt Series DMMs have a DC voltage ratio measurement that normally takes two
DCV measurements and reports the ratio between them. The connection diagram for
the measurements is shown in Figure 5. The ratio is the voltage on the Input terminals
divided by the reference voltage. The reference voltage is the difference between two
separate measurements, the DC voltages from the HI Sense terminal to the LO Input
terminal and from the LO Sense terminal to the LO Input terminal. For the purposes of
this discussion, the LO input terminal and LO Sense terminal are shorted together. This
reduces measurement errors caused from floating DCV1 and DCV2.
40 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Making Simpler DC Power Measurements with a Digital Multimeter
(continued)
Sense
Ω4W
+
HI
HI
200 Vpk
DCV2
–
Input
VΩ
LO
LO
!
10A
1000 VDC
750 VAC
1
+
DCV1
–
500 Vpk
3A
Figure 5. Shown here is the ratio diagram for the two DCV measurements.
Note that the reference measurements must be within the range of ±12 VDC. Also, the
reference voltage is always autoranged.
Utilizing the DCV ratio, we can put an external resistor on one side of the ratio measurement. Normally, the DCV ratio measurement reports the ratio; however, Keysight offers a
secondary measurement that reports both DCV1 and DCV2. Using this feature, located
in the DMM’s display menu, we can see the two voltage measurements independently of
the ratio measurement (Figure 6).
Figure 6. Here, the Input/Ref measurements are displayed independent of the ratio measurement.
41 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
Making Simpler DC Power Measurements with a Digital Multimeter
(continued)
To make a current measurement, a shunt resistor can be placed on either side of the ratio
measurement. Figure 7 shows an example configuration for using the DCV1 and DCV2
measurements to make separate DC voltage and current measurements.
DUT
+
Rload
+
DCV1
DMM
PS
–
–
External shunt
–
+
DCV2
DMM
Figure 7. This configuration can be used to make seperate DCV and DCI measurements.
We can convert the DCV2 reading into current by dividing the reading by the value of the
shunt resistor using Ohm’s law (I=V/R). In this case, the 34330A current shunt was used
and has a value of 0.001 ohms. The current reading would then be:
-000.165 mV/.001 Ohm = 165 mA
To get more resolution on the current readings, a larger shunt resistor can be used.
Other DCV ratio measurement considerations
The LO sides of the two voltage measurements (DCV1 and DCV2) require some consideration. The difference in potential between Sense LO and Input LO cannot exceed 12 V.
Doing so might damage the DMM or cause either reading to be in error. Keep in mind that
any difference between the LO Sense and Input LO will add error to the reference reading
because this voltage is directly related to the reference voltage (see the DCV ratio above).
As a recommendation, if you cannot put the current sense resistor in series with the low
side of your circuit, then put the current sense on the high side. Make sure; however, that
the LO connections are shorted together and expect a negative DCV1 reading.
Figure 8 shows a recommended block diagram for the case where you cannot separate the
grounds to insert a current measurement. Look closely at the DCV1 polarity. It is reversed
so that the LO input is connected to the LO Sense input of DCV2.
External shunt
–
+
+
PS
–
DCV2
DMM
DUT
Rload
–
DCV1
DMM
+
Figure 8. This DCV1 and DCV2 configuration is used for an earth grounded circuit.
Measurement tip
If you do choose an external shunt,
make sure it is stable enough and
large enough to handle the current
that will be passing through.
Keysight offers the 34330A current
shunt, which can handle 15 A of
continuous current with very low
drift. It is a precision 0.001-ohm
resistor housed in a plastic case
surrounded by epoxy, and is
designed for minimal drift under
power.
42 | Keysight | Overcome Your Test Challenges with Truevolt Series Digital Multimeters - Application Compendium
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© Keysight Technologies, 2015
Published in USA, April 30, 2015
5992-0750EN
www.keysight.com
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