NI 4070 FlexDMM Reduces Cost by Replacing Multiple Instruments

This tutorial illustrates how the NI 4070 6 ½ digit digital multimeter can reduce system cost by replacing multiple instruments. You can also view an interactive presentation that takes you through this tutorial's material at your own pace.

For additional information and more interactive tutorials on the NI 4070, visit the Digital Multimeter Measurement Tutorial.

Measurement Paradox

Many applications today require both high resolution single-point readings and high-speed waveform measurements. Historically, these applications required engineers to purchase two measurement devices: a digital mulitmeter and a high-speed digitizer. Digital multimeters deliver high-resolution and accurate voltage, current, and resistance single-point measurements. High-speed digitizers and other data acquisition devices are able to perform the high-speed waveform measurements.

The NI 4070 can reduce the cost of these applications because of its unique multifunction capability. The NI 4070 FlexDMM can operate as both a 6 ½ digit digital multimeter and a 1.8 MS/s. isolated, high-voltage digitizer.

This document explains how the NI 4070 can reduce system cost for three specific applications: fuel cell testing, high-voltage flyback measurements, and true power measurements.

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NI 4070 FlexDMM Isolated, Digitizer Mode

When operating as a 1.8 MS/s isolated digitizer, the FlexDMM is capable of acquiring both AC- and DC-coupled voltage and current waveforms up to a maximum of 300 V and 1 A inputs and providing a 300 kHz bandwidth.

You can vary the FlexDMM’s resolution from 10 bits to 23 bits by simply changing the sample rate, as shown in the graph. Figure 1 below illustrates the resolution versus sampling rate of the NI 4070. When acquiring at 1.8 MS/s the NI 4070 has a 10-bit resolution which is comparable to traditional high-speed digitizers that normally deliver 8-bits of resolution. And at 10 kS/s, the FlexDMM operates at 17 bits of resolution.



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Fuel Cell Testing

After years of research, fuel cells, an energy source that relies on oxygen from the surrounding air and hydrogen from an inexpensive source such as natural gas, are becoming inexpensive enough to manufacture and small enough to address many electrical power source needs. A fuel cell directly converts the chemical energy of hydrogen and oxygen into electricity. The production of fuel cells for consumer use is still in the early stages of research and development, and therefore extensive validation and life-cycle testing is needed.

Fuel cell testing pushes the limits of traditional instrumentation. A typical fuel cell test system requires isolation, high-resolution, high-voltage input, and waveform acquisition capability. The built-in signal conditioning of the traditional digital multimeter makes them appropriate for making many of these measurements. However, traditional multimeters provide limited measurement throughput and no waveform acquisition capability. Engineers therefore require an additional instrument, a high-speed digitizer, to make the required waveform measurements, such as measuring the noise ripple on an individual membrane. This approach has proved expensive because it requires multiple instruments and limited throughput due to the lack of integration between the two measurement products.

The NI 4070 FlexDMM unique multi-instrument capability eliminates the need for two instruments for fuel-cell testing and a variety of other applications. This functionality makes the NI FlexDMM ideal for test systems that require both high-accuracy and high-speed measurement devices.

Visit the tutorial below for additional information on fuel cell testing.

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See Also:
Fuel Cell Testing - The NI Way

Test the Ignition Coil Flyback Waveform

Traditional digital multimeters are ideal for many automotive test systems because of their high-voltage and isolation capabilities. However, a challenging application in the automotive industry is the measurement of the flyback voltage on an ignition coil. The ignition coil creates the high voltages used to generate sparks in the engine.

The primary coil generates a flyback waveform that has a peak voltage of 40 to 400 V and is usually on the order of 10 ms in duration. Therefore, an instrument with the ability to measure voltages over 100 V and at a sampling rate over 100 kS/sec is needed. Traditionally, you could measure this waveform using a specialized and expensive digitizer that has high-voltage capabilities. Alternatively, you could use a general-purpose 8-bit oscilloscope with an attenuation probe, but this method reduces your accuracy dramatically.




You now can easily acquire these flyback waveforms using the NI 4070's digitizer capability and use the built-in analysis functions in NI LabVIEW to measure the peak firing voltage, dwell time, and burn time of each high-voltage waveform.

Visit the documents linked below for more information on high-voltage flyback measurements and to download a LabVIEW example program showing how to acquire high-speed waveforms with the NI 4070.

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See Also:
High-Voltage Flyback Measurements
Configure the NI PXI-4070 FlexDMM to acquire high-speed waveforms

Power Measurements

Traditionally, power measurement functionality was only found in specialized power meters because simultaneous measurements of voltage and current waveforms are required.

Using the architecture of the NI 4070 FlexDMM along with LabVIEW analysis functions, you can build a true power measurement system. The system requires two PXI-4070 FlexDMMs: one configured to measure voltage and the other to measure current. Using the NI-DMM instrument driver, you can configure two FlexDMMs to trigger off the same trigger line for tight synchronization. Traditional digital multimeters have asynchronous clocks and do not provide waveform acquisition capabilities and therefore are not able to take power measurements. You can use the FlexDMM to acquire traditional digital multimeter measurements as well as power measurements which minimizes your system cost.

Visit the documents linked below for more information on taking real power measurements with the NI 4070 and to download a LabVIEW example program showing how to use two NI 4070s to make true power measurements.

View interactive presentation

See Also:
Measure Real Power with a Digital Multimeter
Use The PXI-4070 FlexDMM's 1.8 MS/s Digitizer capability to Make Power Measurements

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