KEITHLEY

This blog first appeared on the Tektronix website.

This blog first appeared on the Tektronix website.

Lithium-ion batteries produce electricity when a chemical reaction occurs on the anode, releasing ions and electrons that travel to the cathode. The opposite occurs when the battery is charged, lithium ions move from the cathode and collect at the anode. Ideally, the reaction that occurs on discharge is prevented from occurring when the battery is completely disconnected from a circuit. This is not true for practical batteries.

Self-discharge refers to the tendency of a battery to discharge over time, even when nothing is connected to the terminals. This internal current is usually very small, but defects in the battery can cause higher current to flow. The defects can originate from a number of places in the manufacturing line, including conductive contaminants on the electrodes or separator, pinholes in the separator or micro-shorts due to dendrite formation during cycling. A battery with higher self-discharge current will not hold charge at the same level as the other batteries in a pack, leading to reduced performance and increased likelihood of failures.

Measuring Self-Discharge

It is challenging to measure the self-discharge current of the battery directly, as any load on the battery will cause the battery to discharge which changes the measurement. We can characterize the self-discharge behavior of the battery by monitoring the open circuit voltage. The open circuit voltage reflects the state of charge of the battery and will decrease as the battery self-discharges. A defective battery that is charged and allowed to rest will have larger changes in the open circuit voltage over time.

The Keithley DMM7510 is a great option to observe the self-discharge behavior of the battery by monitoring changes in the open circuit voltage. Depending on the discharge current in the battery, it can take days to weeks to see a significant change in the battery’s open circuit voltage. The DMM7510’s 7.5 digit resolution ensures that you can detect smaller changes in the battery’s open circuit voltage, saving valuable test time. On the 10 V measure range, the DMM7510 can measure single microvolts. The DMM7510 is also highly accurate, with an accuracy of 14ppm* on the 10V range, so you can make reliable and repeatable readings. The DMM7510 is equipped with powerful TSP scripting capability so you can easily automate the measurement and data analysis such as pass/fail criteria. The DMM7510 makes measuring self-discharge behavior simple, allowing you to spend less time identifying faulty batteries and more time producing.

*14ppm of reading + 1.2 ppm of range, 10 V range at 1 year

This blog first appeared on the Tektronix website.

1. Taking Measurement Bandwidth into Consideration for High Speed Serial Data

When measuring high speed serial data signals and devices, whether for compliance, for design, or for troubleshooting purposes, measurement bandwidth is an important concern. The measuring oscilloscope can have a large or small bandwidth relative to the signal’s frequency content. What is the correct bandwidth for particular standard? And how has this relationship changed with recent standards?

Here we’ll review the rationale for prescribing the measurement bandwidth, and how that rationale has evolved with the latest standards.

Basic spectral properties of a high-speed serial data signal (Figure 1) show characteristic lobes of energy at the odd harmonics of the signal. The fundamental (1st harmonic) is at ½ of the f_Baud, where f_Baud is the frequency that numerical equals to the symbol rate of the signal, e.g., for a signal at 53 GBd the f_Baud is 53 GHz; and the Nyquist frequency, f_Nyquist, is at ½ of 53 GHz.

The signal of the Device Under Test or DUT (blue) is clearly rolling off quickly, and no usable energy beyond the 2nd harmonic is visible. This is a desired characteristic for signaling at 10s of GBd: high speed energy much past f_Nyquist is not important to the transfer of information: the electrical channel will suppress it anyway; furthermore, it might cause additional undesirable crosstalk. Finally, an attempt at recovery of the highly suppressed energy would be too noisy and would generate a higher error rate than a receiver design that rolls off soon after the necessary minimum, i.e., the Nyquist frequency.

In contrast, a high-speed laboratory signal source (green) might have higher lobes of energy. Yet this too is academic – this source is overdesigned, it will generate too much past the typical DUT transmitter (Tx), and its energy won’t even propagate into the DUT except with extremely high-speed connectors and cables.

 

Figure 1. Basic Spectral Properties of an Amplitude Modulated Signal; also shown is the response of a Bessel-Thomson 4^th order filter (in red) with bandwidth matching the f_Nyquist  i.e., 0.5 * f_Baud as used for PAM4 reference filters.

As mentioned, the BERT signal (green trace example in Figure 1) is extreme in its richness of high frequency energy many times past Nyquist frequency. But since that energy is there, do we need to measure it?

Over the time, various standards have wrestled with this question and established rules for recommending the correct bandwidth. By way of an example, we will use IEEE 802.3 wired / fiber-based signaling to discuss this.

The development of a required measurement bandwidth in the high speed electrical IEEE 802.3 standards is shown in Figure 2 and Figure 3; please note the time range (in years) is approximate.

 

Figure 2. Bandwidth for Measurement of Electrical Standards, over Time (Approximate Time Schedule)

Figure 3. Bandwidth for Measurement of Optical Standards, over Time (Approximate Time Schedule)

The comparison shows clearly that the measurement bandwidth is decreasing over time: why?

The electrical signal (from the Tx to the Receiver or Rx) today is more bandwidth-limited by the media – the lossy channel over which the signal is propagating – than it used to be in the NRZ (PAM2 NRZ) signals. Note that the size of the eye is now, in PAM4 signaling, only about 1/3 of the whole amplitude swing.

It’s also interesting that in optical signaling the measurement bandwidth has been significantly slower – relative to electrical media – for quite a few years. Let us see why.

 

2. Why Measurement Bandwidth Has Decreased over Time

In older, simpler systems, the signal from the transmitter is not exposed to a large loss in the channel. The receiver can recover the reasonably open eye directly or with just a light equalization. See Figure 4.

Figure 4. Simple Electrical Link; Note the Far-End Eye Is Still Mostly Opened

In contrast, complex systems operating at a higher channel loss over f/f_Baud are recovering a very small signal past the Nyquist frequency; significant effort has to be applied, and the eye will typically not open without a large amount of RF gain. However, a large RF gain spells trouble in the form of noise amplification – and noise causes errors in transmission.

 

Figure 5. Complex Electrical Link; Note the Far-End Eye Is Still Fully Closed (3^rd from Right)

As the more complex transmission system (Figure 5) has to perform complex equalization, i.e., equalization with more gain, that system must also filter out most of the noise found at high frequencies, i.e., frequencies above Nyquist. This rapid bandwidth limiting improves noise performance when the transmission channel is highly lossy.

3. Relationship of DUT Receiver Bandwidth to Measurement Bandwidth

The guiding philosophy for measurement bandwidth is that the measurement should observe only a slightly larger spectral window than the DUT receiver.

In simpler systems as were used in the past, this was often implied by the 5th harmonic, rule. In today’s more complex systems, where (as shown above) the channel exhibits a large loss (as a fraction of f/f_Baud), the DUT Rx has to severely limit high frequency noise by rolling off more sharply. This will be somewhat approximated in the measurement system by lowering the measurement bandwidth, e.g., to 3rd harmonic range.

3.1. The Role of 4th Order Bessel-Thomson System

Another consideration is that since the newest – e.g., PAM4 – systems operate with highly noise limited data recovery, it is imperative that the measurement device’s roll-off doesn’t present artifacts into the time-domain view of the signal. The low-pass filter built into an oscilloscope therefore has to be without ringing or large overshoot in time domain. For this reason, a 4th order Bessel-Thomson filter is mandated by the standards. This is a filter design optimized for smooth phase response and smooth voltage transition. Besides specifying the filter, the standard also mandates that this filter has to be followed past the -3 dB point, i.e., if a 40 GHz Bessel-Thomson 4th order filter is specified, it does not mean that a 40 GHz DUT oscilloscope is usable; in fact, even a 50 GHz oscilloscope will not be complaint to the standard because the beneficial Bessel-Thomson roll-off would be truncated too soon.

See Figure 1, red trace, for a Bessel-Thomson 4th order filter matching the signals signaling rate (-3dB at f_Nyquist, as in typical PAM4 standard. Observe how little energy remains after the effect of both the signal roll-off combined with the red-line Bessel-Thomson 4 filter.

What does this mean for today’s standards?

4. Fastest Standards in 2021 / 2022

Electrical standards. The expectation is that IEEE 802.3ck is finishing one of the fastest practical electrical standard, with data throughput of 100 Gb/s per lane, with variants such as the 400GBASE-CR4 or 400GBASE-KR4 or 400GAUI-4, in 2021, and with final ratification likely in mid-2022. The signaling symbol rate of these standards is 53.125 GBd, hence the Nyquist frequency of the signal is 25.5625 GHz.

It is expected that the standard will mandate an oscilloscope measurement bandwidth of 40 GHz bandwidth (i.e., -3 dB) Bessel-Thomson filter of 4th order with the end of controlled roll-off at around 55 GHz. Such acquisition will be fast enough to capture the majority of the signal and its potential fidelity problems while not compromising the SNR of the measured signal with excess bandwidth beyond what is implemented in the DUT receivers.

The OIF-CEI standard uses the same concepts but uses a slightly different filter. We’ll discuss that in a future post.

Optical standards. The measurement of optical signal using PAM4 signaling, aka Optical Direct Detect PAM4 NRZ, has been established for several years now as part of the IEEE 802.3bs effort behind the 400GBASE-DR4 standard. In optical signaling, the considerations for receiver bandwidth are different from those of electrical signaling present in, for example, IEEE 802.3ck. At 53 GBd the optical signal in a single mode fiber experiences relatively little bandwidth roll-off (relative to electrical channels), and for this reason the equalization process is simpler, and there is less impact from reflections on short links, so the optical receiver will not be severely affected by such reflections. Due to these link properties the measurement bandwidth mandated by the optical standards is at only 0.5*f_Baud, i.e., at the Nyquist frequency, as measured on the electrical side of the receiver.

This turns out to be a Bessel-Thomson filter with bandwidth electrical of 26.5625 GHz for 53 GBd signals; in typical single mode systems, the end of controlled roll-off is just past 60 GHz.

Why is there – in optical standards – a difference in bandwidth electrical and bandwidth optical? The optical-to-electrical conversion in an optical receiver squares the power relationship between the optical and the electrical side; therefore, the optical bandwidth is different – higher – than the electrical bandwidth. (The bandwidth is at a fraction of full power; the square-law of a typical O/E changes that ratio.) The optical bandwidth is not used to specify the relationship between the Bessel-Thomson filter and the Nyquist frequency.

In some case the optical link is stressed for capacity “at any cost” in electronics (e.g., very expensive links, such as submarine links between continents). The whole design – including the signal roll-off – is then dominated by concerns for spectral efficiency and much sharper roll-off of transmitter energy and of the measurement tools applies.

Conclusion

The bandwidth for measurements in high speed serial data systems is lower (as a fraction of symbol rate) for higher speed standards than it used to be in less equalized standards of the past. This development simply confirms the design tradeoffs that the link designers have to make today. The measurements are performed with bandwidth of around at the 0.5 * f_Baud, rolling off in a time-domain friendly way of the 4th order Bessel-Thomson filter in most standards. A slightly faster roll-off is likely in the future.

This blog first appeared on the Tektronix Website.

Energy storage device testing is not the same as battery testing. There are, in fact, several devices that are able to convert chemical energy into electrical energy and store that energy, making it available when required.

Capacitors are energy storage devices; they store electrical energy and deliver high specific power, being charged, and discharged in shorter time than batteries, yet with lower specific energy.

Supercapacitors are another type of energy storage device; they share certain characteristics with both capacitors and batteries, achieving higher specific energy than capacitors. Tektronix/Keithley first got involved with testing supercapacitors through our clients in the automotive market that were primarily looking for instruments to characterize supercapacitors in regenerative braking systems.

And then, of course, there are the rechargeable batteries — specifically the Li-ion batteries (LIBs) that started to dominate the market and became a broad new area of test and measurement.

Let’s take a short tour of battery testing.

Graphene and Advanced Cathode Materials Research

Graphene testing and nanotechnology techniques like using carbon nanotubes to control graphene and electrochemical properties caught the attention of our engineers and test specialists. Graphene oxides have been critical to the development of modern Lithium Ion batteries because they help stabilize and improve batteries’ chemical, thermal and electrical properties.

When Li-ion batteries were first being developed, the research involved testing graphite oxides and graphene with composite material. Keithley started to investigate how to characterize and ensure the best electrical conductivity performance at the most reasonable cost.

Keithley’s sensitive low-level measurement solutions and parameter analyzers such as the 4200A are widely used in testing and producing special materials like graphene, specifically in battery cell R&D departments.

Electrical measurements on conductivity were made with a Keithley 622x DC and AC current source and Keithley 2182A Nanovoltmeters connected to a four-probe fixture setup.

Cells Electrochemical Characterization

For a thorough electrochemical characterization, it is necessary to support charge and discharge testing on energy storage devices and batteries, in particular. The electrochemical performance characterization requires two specific measurements: cyclic voltammetry and galvanostatic / potentiostatic charge-discharge cycles.

For these specialized tests, Keithley released the 2450-EC, 2460-EC and 2461-EC Potentiostats, which are specialized versions of our Source Measure Units (SMUs).

SMUs can be programmed to apply a linearly variable electric potential for the electrolysis, while simultaneously scanning and recording the output current. All phenomena are strictly dependent on temperature, so we were typically combining these systems with special dataloggers like DAQ6510 that could track multiple environmental sensor responses in a time-aligned way.

Figure 1: DAQ6510 is a precision data acquisition and logging system that creates a new level of simplicity compared with the often complicated configuration and control found in the industry

Li-Ion Batteries Manufacturing: a quick look into production

Li-Ion battery production is an extremely interesting market; LIBs are a popular choice for several applications that, for simplicity, we will group into three main categories:

• 1. The consumer market, which includes battery-operated IoT, medical wearables, smart home and general portable electronics
• 2. The transportation market, which is in large part the automotive EV battery testing market
• 3. The broad and complex stationary applications market, which includes uninterruptible power supply (UPS), data centers, renewable energy systems (RES), and batteries for grid-level storage.

Each of these main macro applications not only differ in energy and power density requirements, the battery form factor, discharge rate, efficiency, and safety, but must adapt in order to support ever-changing lifetime requirements. This translates to more complex specs, such as the number of charge/discharge cycles and other performance-related parameters.

Also, the needs of each from a test and measurement perspective differ significantly. Over the last several years, many national and international industry projects and consortiums have been created to work throughout the entire battery value stream, growing and sharing their expertise.

Multiple associations in Europe assembled players focused on battery production technology in different departments, from the machine and component supply, raw material provisioning and preparation, electrode production and the stages of assembly, from the cell level to module and pack production. All of these were propaedeutic steps in preparation to support the need for several battery plants in Europe—the so called “Gigafactories”.

These large facilities are supposed to produce battery systems for electric vehicles, which fall in the second of the three aforementioned markets: transportation/automotive.

Battery System Testing in Automotive

An automotive battery system is complex with a lot of electronics incorporated in a solid, protected housing. It contains a battery pack with relatively complex cooling and control systems, electrical and thermal sensors, and some communication wiring. The control unit acts as a “brain” and is called BMS or battery management system.

A battery pack is a system composed of several battery modules. Each battery module is composed of several individual battery cells.

If the chemistry is efficient at the cell level, you need to make sure that the optimization still exists at the module or system/pack level as well.

Different test sets are developed at the cell level, module level and system level. The same test Instrument may find space in different production stages and for different levels of batteries.

Let’s take a quick look at some of the value chain phases.

Cell-level Materials and Subcomponents, Electrode Manufacturing Testing

There is a lot of material (like complex polymers) processing in the early stages of the production of key components used in cell manufacturing. You need to make the separators, the case, the electrodes etc.

Tektronix and Keithley solutions relate to the electrical measurements taken on electrodes for instance. It is necessary to trace the impedance on electrodes to make sure the materials chosen for the anode and cathode do not massively contribute to the battery input impedance and stay in the range of a fraction of an ohm across a certain frequency range. Generally, customers design a specific fixture capable of accessing all interfaces between collectors and other layers; it is a necessary step for the accurate determination of electrical conductivity of different samples. A special chuck can be used to connect to it with the four-point probe technique.

Keithley state-of-the-art Nanovoltmeter 2182A combined with 622x Current AC and DC sources support such measurements. As said in the previous paragraph, these measurements are made mostly in the research stages and considered particularly useful when dealing with electrochemical noise measurements. The DC source applies a very precise constant current on the electrodes while the digital nanovoltmeter measures the correspondent drop in voltage.

Cell-level Assembly, Stacking, Tab Welding, Filling

Before filling the electrolyte into the cell, defective products need to be removed from production. To identify defective products, you can run a test on the insulator (also called the separator) that involves a charging-dwelling-discharging sequence and measure the leakage current.

When issues with the separator exist (membrane problems, decomposition etc.), the failure is easy to detect as the level of current is in the range of tens of mA. When insulation is good, the leakage current can be quite low (in the pico Ampere range). The insulation resistance test is also repeated in the module assembly and pack assembly stages to prove the insulation is good for different parts with respect to ground (chassis).

The Keithley model 6517B Electrometer/ High Resistance Meter offers insulation resistance measurements at various calibrated insulation test voltages. The 6517B has very low current sensitivity and a built-in 1kV voltage source with sweep capabilities. This simplifies performing leakage, breakdown, and high-resistance testing as well as surface resistivity measurement on insulating materials.

Figure 2: Keithley electrometer can embed a high voltage source for testing insulation

Cell level Formation- Aging – End of Line (EOL) testing

The formation and electrical testing of individual battery cells occurs in the last steps of the production line and generally represent a significant bottleneck for mass production.

One of the key characteristics of a battery cell is its performance over the course of its life, so cells are put through an aging process to investigate cell degradation.

A typical characterization of performance over time is achieved by cycling the cells. Cycling is essentially a repeated charging and discharging process.

A current and voltage profile representative of the intended application under typical application-related stress conditions (e.g. temperature variation) is applied to cells.

It is important to note that lifetime requirements for cells, modules, and systems are determined by the application where they will be used (e.g. electrified mobility, Consumer Electronics, etc.).

There are several cycling (charging-discharging) protocols defined by standards for each specific application (e.g. IEC 62660-2).

Depending on the methodology, a programmable power supply source is used to apply a constant current - constant voltage (CC-CV) charge procedure, taking the cell from an initial set voltage to a final set voltage. Then the voltage is fixed, and the current is reduced until a certain capacity is reached.

A discharge cycle is generally applied via a programmable electronic load.

All these cycles are repeated several times with some variable “relaxation” time between charge and discharge.

These tests are typically executed in a temperature chamber; the variation in temperature that a cell experiences is also dependent on the intrinsic thermal variation during charging and discharging.

A multi-channel system based on several source measure units like Keithley SMUs, which capable of measuring while sourcing or sinking, can be used in this stage. The system typically requires multichannel DMMs with specific resolution, accuracy, and stability over time and across environmental conditions.

Figure 3: Keithley Source and Measure units can cycle battery cells with high precision, accuracy and stability

Players compete in introducing the most efficient methodology on end-of-line testing and formation. Meanwhile system integrators challenge themselves in developing efficient test procedures and parameter extraction regarding cell quality monitoring.

Test racks in this space are generally highly automated, involve multiple instrument units, and generally perform the following measurements:

• - Internal resistance measurements (DC)
• - Open circuit voltage (OCV)
• - Leakage current
• - Charge/discharge pulsing

The automation of data collection is critical here and helps the following grading phase, when cells are sorted according to their performance test results.

Internal Resistance and OCV Measurements

The performance of a battery and its efficiency during the charge and discharge process can be evaluated in a few different ways, and there are several indicators to look for. The battery internal resistance characterization is one of them. It basically means accurately characterizing the battery’s changes under several charge/discharge current rates, state of charge (SoC), temperature and other aging indicators.

OCV is the voltage measured at the terminals of the battery after enough rest time (sometimes called relaxation), and it is a key measurement for Li-Ion battery cells.

OCV also varies mostly according to battery SoC and, to a lesser extent, according to the temperature. These details can be used to create a battery equivalent model, which is used to design a battery management system (BMS), in addition to assessing the battery specs and condition.

The internal resistance in the battery accounts for the voltage drop across battery’s terminals when a load is connected compared to no-load voltage and can be derived from OCV measurements.

OCV is generally not just a measurement, but a set of measurements. In fact, we call it the OCV characterization of the battery, and we trace an exhaustive analysis derived from a curve on an SoC versus OCV plane.

To trace this curve, you need to bring the battery to specific states of charge. This is typically performed by charging or discharging current in a pulsed way using a smart source/load then waiting for some amount of rest time, and then measuring the open-circuit potential at the electrodes.

A Keithley SMU like the 2461 is the perfect instrument to perform this test. In fact, it can either source or sink the cell current in a controlled way while measuring the cell current and voltage with a four-wire (Kelvin) connection with contact check. All of this is easily automated and controlled by a programmed embedded microprocessor. This specific SMU offers controlled pulsing capabilities for both charging and discharging.

The accuracy of the voltage measurement in OCV is a discriminating factor for the choice of the instrument. In some cases, the typical 6 ½-digit measurement resolution, the thermal stability, and most importantly, the accuracy of an SMU can be considered insufficient.

For this reason, some test setups involve a special digital multimeter, the Keithley DMM7510, that is a standard in Li-Ion battery cell testing. Its low-noise, 32-bit A-D converter allows 7 ½-digit resolution and metrology grade accuracy.

Busbar Weld Impedance Safety Test Workstation in Battery Packs Manufacturing

A battery module is composed of multiple cells that are connected in parallel or series to achieve the desired voltage output. All cells are laser-welded to a busbar—a long conductor that is isolated from the ground and is responsible for carrying high current for the distribution of power from the battery. The VSH-Busbar weld impedance test characterizes the impedance of the weld. Small resistances in the weld can generate enough heat to degrade the batteries and lead to early failures or unsafe operating conditions. By measuring the resistance before testing the battery operation, defective modules can be quickly removed from the line.

Measuring the impedance of the weld involves sourcing a current across the weld and measuring the voltage to calculate the resistance. Test execution speed and measurement accuracy are the two most important considerations when measuring the weld impedance. This can be done using SMUs like the Keithley models 2460 or 2461 and either the model 3706A System Switch and Multimeter or the model DAQ6510 Data Acquisition and Logging Multimeter System.

The 2460 and 2461 SMUs are capable of sourcing up to 7A for battery systems that require high current. The impedance of the weld can be as small as a few milliohms, so it’s important to use a sensitive enough meter to measure very small voltages. The model 3706A features a 7.5-digit digital multimeter (DMM) and can measure 10s of nanovolts on the 100mV range. Since a battery pack could have close to 80 welds on one busbar, Keithley instruments support mainframes with configurable slots for multi-channel plug-in modules, eliminating the need for rewiring. The process of closing each channel to measure it is obviously automated for speed and efficiency.

Figure 4: A schematic example of an automated system for impedance test in battery production

ATE Design in Battery EOL Testing

When the battery-operated device is a vehicle, things become quite interesting.

First, you tend to deal with a significantly large number of cells to test, and the test equipment is sophisticated and requires very high reliability. ATE design in this application space needs to support multiple tests on multiple devices. The characterization methodologies also need to be simple and a low-cost alternative to the more advanced and higher-resolution scientific alternatives, which tend to be time-consuming and expensive to set up.

At the cell level, there may be “electrochemical workstations” to set up. But when dealing with modules, the focus is on higher current testing. Finally, the test on complete systems (packs) can involve high currents and high voltages (1000A and 1000V or more are quite common today).

Single cell testers are typically multi-channel systems. What matters here is the voltage and current resolution of the measurement and its stability under varying environmental conditions.

BMS ATEs are designed to accurately monitor cell voltages and temperature, and monitoring the changes in impedance is key.

Figure 5: Typical test rack with multichannel high accuracy DMMs and related switching unit

Impedance Measurement of Cells

The battery impedance of cells is a key measurement taken during the formation and aging stages. All batteries experience a reduction in performance with cycling. This can be due to the degradation of one or more components or interfaces. There are different methodologies that can be applied, from electrochemical impedance spectroscopy (EIS) to direct diagnostic measurements.

EIS is a non-destructive technique that provides a considerable amount of information in a relatively short time span while preserving the integrity of the battery. To conduct this test, a small AC signal is applied over a wide frequency range and the response is measured. Measurement methodologies involving a span on frequencies are applied to individual cells, but they aren’t applicable for larger sizes and larger operating power modules. In the automotive battery management system (BMS) space, the test is carried out on multi-cell batteries of varying capacities and mismatched cells have to be carefully tracked. Cell mismatch can occur due to battery overcharge, discharge shorts, or simply because of aging.

The Consumer Portable Battery-Operated Electronics: testing needs

What about the testing needs in the market of IoT, medical wearables, and smart home devices?

Embedded devices used for IoT applications are strictly connected to the battery choice, since this impacts the expected lifetime of the device. Batteries needs to be sized to support device workloads for a long period of time. The battery market for IoT relates to small (also “micro”) batteries with thin, flexible, and sometimes unconventional form factor.

When choosing the right battery for their specific application, designers have to consider multiple parameters, including:

• Battery type and declared specs
• Operating temperature range and storage conditions
• Potential energy losses and circuitry leakage
• Application requested ranges and power consumption profile

Let’s focus on the last bullet for a second. Designers need to be aware of the power consumption profile and precisely control the schedule of each executed task by any of the device units (processors, transmitters, etc.). IoT device workloads are sequences of tasks periodically launched in execution with short-duty cycles.

The rate of discharge is strictly dependent on this power schedule, and the intensity, duration, and frequency of these “power usage” pulses. Also, it’s important to control the voltage range of the application, and be aware of the maximum, nominal, and cut off voltage for each subcomponent to correctly operate it.

Based on all the aforementioned considerations, an embedded designer needs to perform:

• A dynamic model battery simulation
• A dynamic current charge / discharge testing (with pulsing sink capability)

Figure 6 : Battery Simulators need to support modeling like profiles of open circuit voltage and internal resistance as a function of the battery's state of charge

The typical test bench will include:

• A basic oscilloscope operating at max 500MHz (typically lower) like the Tektronix TBS2000B or MDO 3 series
• A multi-channel DC power supply with battery simulation capability (generally linear) like the Keithley 2230 model
• An electronic load, possibly programmable, like that offered by Keithley SMUs
• A DMM with sufficient resolution (DMM6500 when 6 ½ digits is sufficient or for low-power consumption applications, the DMM7510 is recommended to step up to 7 ½ digits)
• An instrument data control software environment (typically PC-based) like Kickstart.

Voltages in this application space do not exceed 10V - 15V max, but current sink in some power-hungry conditions can reach a few Amps (3-4A).

Keithley battery simulators span from the solid 2306 series for production to the 2281S bench solution.

This blog first appeared on the Tektronix website.

Semiconductor manufacturers, validation engineers and reliability engineers can now get faster test script development while automating Keithley test instruments such as SMUs, DAQs or DMMs by downloading the Keithley TSP Toolkit Beta, the new TSP (Test Script Processor) script development environment, which takes the form of a Visual Studio Code extension. In this blog, we’ll explore TSP technology and how the Keithley TSP Toolkit can help you quickly and easily develop test scripts.

What is Test Script Processor or TSP Technology?

Test Script Processor, or TSP, technology is both an instrument automation command set and programming language. TSP-enabled instruments, like Keithley SMUs, DAQs, and DMMs, contain an embedded scripting engine that can execute basic programming functionality and instrument control commands.

You can initiate tests with a single TSP script call from the PC, or run the test on the instrument automatically, without the PC. This drastically reduces test time compared to traditional testing methods using SCPI commands that require individual commands to be sent from the PC to the instrument.

TSP scripts also offer the most flexibility, allowing you to create a wholly custom test system with benefits such as high-speed triggering, parallel testing and increased throughput.

A parallel test instrument configuration using TSP-Link technology.

Quickly and Easily Develop Test Scripts with TSP Toolkit

The Keithley TSP Toolkit is an updated script development environment that includes all the functionality and instrument support of Test Script Builder (TSB) plus many quality-of-life features that improve the development experience.

TSP Toolkit will feature the modern UI of the Visual Studio Code IDE, complete with syntax-highlighting and the increased readability it affords, along with the convenience of the many extensions available on the VSCode marketplace.

Programmers, integrators and those with established automated test frameworks will appreciate having access to other scripting languages like Python in the same environment that they use to write TSP scripts. The Keithley TSP Toolkit extension will also feature autocompletion alongside in-line and hover help, reducing pesky mistakes from copy/pasting TSP commands improperly and eliminating the need to manually parse through dense reference manuals to confirm proper command usage and syntax.

Keithley TSP Toolkit extension command autocomplete feature in action.

Keithley TSP Toolkit command hover help feature in use.

While the Keithley TSP Toolkit extension is open source and is currently in development, a Beta version has been made available on the Visual Studio Code marketplace. The TSP Toolkit Beta can be used to develop automation scripts for all TSP-enabled Keithley instruments.

Keithley TSP-enabled instruments.

The TSP Toolkit Beta is available as a VSCode extension and can be used to develop TSP scripts alongside your other favorite VSCode extensions, such as those for Python, C# and many others.  Download the TSP Toolkit Beta for an improved development experience.

*This blog post first appeared on the Tektronix website.

Data Acquisition (DAQ) is the measurement of electrical or physical things like voltage, current, temperature, pressure, sound, or motion. Converting these signals into digital data is necessary to analyze and store them for further processing. DAQ systems are essential for a wide range of applications, from scientific research and industrial automation to environmental monitoring and medical diagnostics.

Diverse Applications of Data Acquisition Across Fields

Data acquisition plays a pivotal role in a wide array of sectors, enabling the precise measurement and analysis of various physical and electrical phenomena:

1. In Scientific Research: Essential for exploring physical phenomena such as temperature fluctuations, pressure variations, and motion, data acquisition technology also proves vital in medical studies for monitoring key health indicators like heart rate and blood pressure.
2. Within Industrial Automation: Here, data acquisition is integral to controlling and monitoring manufacturing processes. It helps in assessing critical factors such as temperature and pressure in chemical plants and overseeing the functioning of robotic assembly lines, thereby streamlining industrial operations.
3. For Environmental Monitoring: This technology is a key ally in environmental conservation efforts. It aids in tracking important environmental metrics including air quality, humidity, and temperature, and is instrumental in evaluating emissions from industrial plants and analyzing water quality in rivers and lakes.
4. In Aerospace and Defense: Data acquisition is crucial in managing and monitoring complex systems in aerospace and defense applications. It assists in evaluating aircraft engine performance and in the real-time monitoring of various parameters such as temperature and pressure in defense equipment.
5. Within Medical Diagnostics: In the healthcare sector, data acquisition technologies are employed for recording critical physiological data, such as ECG, EEG, and EMG readings. This is particularly crucial during surgical procedures and in diagnostic tests.

Overall, the utility of data acquisition extends across various industries, underscoring its importance in applications that require detailed, accurate, and dependable data collection and analysis. Whether it's advancing scientific research, optimizing industrial processes, protecting the environment, ensuring safety in automotive, aerospace and defense, or aiding medical diagnostics, data acquisition technologies are indispensable.

DAQ Systems

What is a DAQ system?

A DAQ (Data Acquisition) system is a set of components and devices used to measure and collect data from various sensors or transducers. It involves the conversion of physical or electrical signals into digital data for further analysis and processing.

A typical DAQ system consists of three main parts:

1. Sensors or Transducers: These devices convert physical or electrical signals, such as temperature, pressure, or voltage, into measurable quantities.
2. Signal Conditioning Circuits: These circuits amplify, filter, or digitize the signals from the sensors to improve their quality and accuracy.
3. Data Acquisition Device: This device samples and digitizes the conditioned signals and sends them to a computer or other processing unit for analysis and storage. The data acquisition device can be a standalone unit or a plug-in card that connects to a computer's PCI or USB port.

DAQ systems are used in a wide range of applications, including scientific research, industrial automation, environmental monitoring, aerospace and defense, and medical diagnostics. They play a crucial role in measuring, analyzing, and controlling physical or electrical phenomena, enabling researchers, engineers, and technicians to collect and analyze data accurately and efficiently.

How to Choose a Data Acquisition System

Selecting the right Data Acquisition (DAQ) system is crucial for obtaining precise and reliable measurements in various applications. The effectiveness of a DAQ system lies in its ability to accurately meet specific measurement requirements, which involves considering several key factors:

1. Accuracy and Resolution: The core of DAQ system effectiveness is its accuracy, largely determined by the resolution of the analog-to-digital converter (ADC) and the stability of the reference voltage. Opt for systems with higher resolution ADCs and stable reference voltages for more precise measurements.
2. Sampling Rate: Essential for applications involving rapidly changing signals, a higher sampling rate is crucial for high-speed data acquisition and dynamic control systems.
3. Signal Conditioning: Look for robust signal conditioning capabilities, including amplifying, filtering, or digitizing signals from various sensors, to enhance their quality and accuracy. This is particularly important for adapting to different sensor types like thermocouples, strain gauges, and accelerometers.
4. Software Compatibility and Functionality: Ensure the DAQ system comes with user-friendly software that offers effective data visualization tools and supports multiple programming languages. Compatibility with various operating systems like Windows, Linux, or Mac OS adds to the system’s versatility.
5. Channel Count: Consider the number of channels the system can support. A higher channel count increases the system's flexibility and scalability in handling multiple signal types.
6. Environmental Adaptability: Assess the system’s ability to operate under the specific environmental conditions of your application.
7. Budget Constraints: Evaluate the overall cost, which includes the price of the system or device and any additional accessories or software required.

By carefully considering these aspects, you can choose a DAQ system that not only aligns with your specific needs but also ensures a balance between performance, versatility, and budget. This approach guarantees that the selected system can effectively and efficiently handle the required data acquisition tasks.

Enhancing Engineering Decisions with DAQ Systems

Key Insights Gained from DAQ Systems

DAQ systems are instrumental in capturing and recording data from various sensors, crucial for monitoring physical or electrical phenomena. These systems empower engineers with data-driven insights, allowing them to make more informed decisions in areas such as:

• Trends and Patterns Analysis: Engineers use DAQ systems to identify trends in parameters like temperature or pressure, enabling early detection of potential issues.
• Fault Detection and Diagnosis: By analyzing data from DAQ systems, engineers can pinpoint faults in systems, identifying malfunctioning components or sensors.
• Performance Optimization: DAQ data aids in identifying inefficiencies, guiding engineers to optimize system performance and increase productivity.
• Predictive Maintenance: Analyzing data trends helps in predicting maintenance needs, preventing system breakdowns.
• Quality Control: In manufacturing, DAQ systems are pivotal in ensuring product quality, detecting any deviations from required specifications.

Enhancing Data Acquisition with Advanced Techniques

Incorporating Advanced Calibration

Data Acquisition systems today benefit significantly from advanced self-calibration techniques, which employ third-order polynomials. This innovative approach greatly enhances the accuracy of measurements by auto-adjusting calibration coefficients based on predetermined input signals. Such accuracy is indispensable in sectors where precise data collection is critical, including aerospace, defense, and automotive applications.

Importance of Isolation in Measurement Accuracy

Isolation plays a pivotal role in ensuring the accuracy and reliability of DAQ systems. It involves shielding the measurement circuits from potential distortions like electrical noise and voltage discrepancies. Employing isolation techniques, such as galvanic and magnetic isolation, is crucial, especially in high-voltage environments or areas susceptible to electrical interference, to maintain the integrity of the data collected.

Advanced Isolation Techniques for Reliable Measurements

Maintaining the integrity of measurements is a fundamental aspect of data acquisition. DAQ systems often incorporate advanced isolation methods to protect sensitive measurement components from external electrical disturbances. By establishing either physical or electromagnetic barriers, these systems prevent noise or voltage fluctuations from impacting the accuracy of the data, a necessity in environments with high electromagnetic interference or unstable electrical conditions.

Leveraging Signal Streaming and Remote Monitoring

Signal streaming and remote monitoring are groundbreaking advancements in the realm of DAQ. High-speed signal streaming facilitates the real-time capture and analysis of data, essential in dynamic and demanding testing environments. Additionally, remote monitoring capabilities enable operators to manage and visualize data remotely, enhancing operational flexibility and efficiency, particularly in complex, continuously monitored systems.

Keithley Instruments' Advanced DAQ Systems

Overview of Keithley's DAQ Capabilities

Keithley Instruments provides a range of advanced data acquisition systems, known for their accurate measurement capabilities, fast scanning, and versatile setup options. These systems are designed to cater to various measurement and analysis needs in fields like scientific research, industrial automation, and more.

Keithley DAQ6510: Feature-Rich Data Acquisition System

Keithley DMM7510: Digital Multimeter with Real-Time Sampling

Keithley DMM6500: Versatile Bench/System Digital Multimeter

Why Choose Keithley DAQ Systems?

High Accuracy: Keithley Instruments' DAQ systems are designed with high-precision components, including high-resolution ADCs, stable reference voltages, and high-quality signal conditioning circuits, to ensure accurate measurements.

High-Speed Scanning: Keithley Instruments' DAQ systems are capable of high-speed scanning, allowing for fast data acquisition and analysis. This makes them ideal for applications that require real-time monitoring and control.

Flexible Configuration: Keithley Instruments' DAQ systems are designed to be flexible and configurable, allowing users to customize the system to meet their specific measurement requirements. This includes the ability to support multiple sensor types, input/output configurations, and signal conditioning options.

User-Friendly Software: Keithley Instruments' DAQ systems come with user-friendly software that provides data visualization tools and supports multiple programming languages. This makes it easy for users to control and analyze the data from the system.

Industry-Leading Support: Keithley Instruments is known for its industry-leading support, including comprehensive documentation, technical support, and training programs. This ensures that users can get the most out of their DAQ systems and achieve optimal performance.

Overall, Keithley Instruments' DAQ systems are leading the way in terms of accuracy, speed, flexibility, and user-friendliness. Keithley Instruments' DAQ systems are great for many uses, like research, automation, and data collection in different industries. They have powerful parts, can be set up in different ways, and have easy-to-use software. to data acquisition and analysis. to aerospace and defense.

In Conclusion

In the diverse landscape of modern technology, Data Acquisition (DAQ) stands as an indispensable tool across various sectors. From enabling precise measurements in scientific research to optimizing industrial processes, ensuring environmental integrity, and advancing medical diagnostics, DAQ systems have become crucial. Their advanced calibration, robust isolation, and innovative features like signal streaming and remote monitoring exemplify their versatility and adaptability. As the demand for accurate and reliable data collection grows, the importance of DAQ systems in facilitating informed decision-making and driving technological advancement becomes increasingly evident.