|Product Performed to Expectations:||9|
|Specifications were sufficient to design with:||10|
|Demo Software was of good quality:||8|
|Product was easy to use:||9|
|Support materials were available:||10|
|The price to performance ratio was good:||10|
|TotalScore:||56 / 60|
Data acquisition serves a number of important purposes in engineering, but I hadn’t grasped what modern systems were capable of until I got to explore the . It turns out that it can provide within a single instrument virtually an entire test-bed for key areas of product design and test. I hadn’t expected that!
There's an 11-minute video review, to accompany the text:
In the past, I’d used a data acquisition system from Hioki, part of its HiCorder family. They are quite nice all-in-one instruments with an integrated display and printer, but they are less general-purpose than the DAQ970A. Mine is a old unit, with only four channels and 8-bit resolution. It works fine for specific use-cases (such as automotive) but it’s not really all that useful for design or test engineers. It has some advantages like fast logging (at up to 500 ksample/sec) but it doesn’t have a lot of memory. Really it is like an electronic chart recorder.
The DAQ970A on the other hand doesn’t just perform logging or chart recording type features. It offers data manipulation, and control functionality too. Before getting into the details, it is easier to see what use-cases it will help in.
To provide a feel for what the DAQ970A would be good for, here are examples of tasks:
By looking at the examples, it can be seen that many different categories of use-cases are emerging.
There’s the parallel tasks – the DAQ system can be used to reduce overall time to complete, by allowing many similar items to be tested simultaneously, perhaps in similar conditions, such as battery testing.
There’s also the ‘multiple helping hands’ tasks, where many diverse attributes (such as different voltage levels, current and temperature) can be probed to gain better insight into a design.
There are logging tasks where the system may need to capture data on a trigger, or at a fixed interval, for days on end perhaps.
There are science tasks where to gain better understanding, sensors may be deployed in different locations, and data collected centrally.
There are also automation tasks, where based on inputs or outputs or stimulus, conditional things need to be done.
In summary, this non-exhaustive list reveals a very large span of use-case for data acquisition. I hoped to see if the DAQ970A really could perform for many of these categories.
From a birds-eye view the DAQ970A looks like a bench digital multimeter (DMM), with relay cards plugged into the back. There’s more detail to it however, and the diagram below seeks to explain it another layer down. Up to three cards can be plugged in, and they can have analog or digital functionality. The analog functionality is used to get signals into the DMM portion of the system. The digital functionality is used to act on logic signals, or provide controls to external hardware and alarms. The digital functionality bypasses the DMM of course.
Different cards can be inserted to suit different needs. If only analog functionality is needed then all three slots could be loaded with the same analog card for instance. Unlike older traditional data acquisition systems which measured only voltage and needed a sensor or transducer for other measurements, the DAQ970A can directly handle (amongst other thing) measurements of capacitance, resistance and temperature and even frequency.
The analog cards are known as Multiplexer or Scanner cards, because many input analog signals can be multiplexed in the time domain, to attach to the single DMM inside the chassis.
In a testbed there may be a requirement to switch around signals and so Switch and Matrix cards are also available. They can switch any signal (power, analog or digital or even RF depending on the particular card).
Finally there’s a ‘Multifunction’ card that has lots of digital inputs and outputs, as well as a couple of analog outputs driven from a DAC.
In total there are eight different possible cards that are available, and it is up to the user to determine which ones are required. They all have their strengths for particular use-cases. The core cards are the Multiplexer cards, since without them, no analog signals can reach the DMM.
Scratching the surface even deeper, there are several further important core features in the hardware for data acquisition that are worth mentioning. Firstly, the measurements are isolated – not just from ground, and not just from the DMM hardware inside the unit, but also between each channels, for most of the cards. So, unlike (say) a typical oscilloscope and probes, you can wire the channels with no need to worry about maintaining a common reference point between them. Another key feature is that owing to the importance of temperature measurements in engineering, there is extreme flexibility for this, built-in to the hardware. Thermocouples can be used directly wired into most of the multiplexer cards (except the single-ended relay card). There’s no need for a cold junction, the card itself will do the compensation. The cards monitor their own temperature, close to the screw terminals, to perform this compensation. The DAQ970A also supports other temperature sensors too (RTD and thermistors), so it’s very flexible. Another very useful feature is that the processing system can perform custom calculations on-the-fly, which is handy for transforming a measured voltage or current (from say a sensor) into a more useful or meaningful quantity. An example use-case for this could be to set the DAQ970M to measure the voltage from a light sensor and display the result in lux.
For review, I had the card, which offers multiplexing combinations of up to twenty 2-wire analog sources into the DMM, or ten with 4-wire sensing (used for measuring low resistances accurately). I unfortunately didn’t have a switching/matrix or multifunction card, but it is possible to use the back panel alarm capabilities as a kind of output to control external equipment (see later).
The switching topology for the module cards are provided in user documentation, but the DAQ970A conveniently provides a display showing the information too, as shown below.
On the right, the banks of orange and yellow circled relays are used to switch one of 20 inputs into the internal multimeter, provided the green relay is closed, and the blue relay too if one of the orange inputs is to be connected.
For 4-wire resistance measurements, the blue relay is opened, and the purple relay is closed.
The DAQ970A records the number of relay operations in non-volatile memory, so that the user can desolder and swap out individual relays as they approach the end of their life (or swap out the entire module).
The TFT screen is really lovely – it is viewable in all directions, bright, with some dimming only at extremes when the instrument is above the user. The menu, fonts, palette choices and screen layout is good and it is all easy to read to my eyes.
The buttons feel great, and they are laid out well. The soft keys are used extensively, which is fine too.
The screen capture capability is not intuitive (it could in theory be resolved in a software update). It is convoluted (needing more than half a dozen keypresses through the soft keys), and unfortunately buggy. I had to resort to using the PC screen capture from the browser interface to the instrument.
Apart from that, the firmware was generally un-buggy (although sometimes the browser interface needed refreshing), and the instrument did not crash during the time reviewing it. It provided confidence that it could be left logging for long periods with no crashes hopefully! : ) The instrument was always responsive.
Although most things are intuitive, I must admit a few times I really did need to dig around lots to find the odd configuration item. Fortunately there’s a cool help menu built-in with contents page, that was handy for the times when I didn’t want to dig into the manual but wanted a quick pointer to do a task. Also, for any button, if it is held down for a second or so, a help page pops up : ) It’s really neat.
In terms of noise, there is a fan, and it is audible. It’s not crazy-loud (it can be 35 dBA according to the specs), perhaps the volume of a small desk fan, and it would get tiresome if it was on every day nearby. It is possible that due to the chassis design (which by nature is blocked partially, to allow the module cards to slide in), the airflow ends up being noisier. Due to where the instrument may be used, it’s likely that environmental chambers or production or test environments will be far noisier anyway.
The DAQ970A has a 6.5-digit multi-meter internally, so it can be imagined that it is going to be an accurate precision data acquisition device which, in many use-cases, may exceed the required accuracy and resolution by a long shot. Some temperature measurement scenarios (such as hot water systems) only need accuracy of a few degrees C. My old Hioki HiCorder only has 8-bit resolution.
What does 6.5 digits really mean in practice? To put it in perspective, one would expect (and it does reach) an accuracy in places approaching two orders of magnitude better than (say) a Fluke 87V handheld meter (a device that is fairly accurate). A good 6.5 digit meter will approach the DC voltage accuracy measuring limits of world calibration lab standards as they were coming into the second half of the 20th century. It was enough for Nobel prize winners in Physics : ) 6.5 digits can offer really an incredible level of accuracy for measurements.
The accuracy is specified across many tables in the DAQ970A datasheet (PDF). The chart below is an attempt to provide an indication of accuracy in some easy-to-understand manner. It shows what error to expect when measuring voltage, which is perhaps the core function of a DAQ system. The way to use it, is to look up the measured value on the x-axis, and the intersection on the vertical axis will indicate the maximum plus/minus error in volts.
(Note: To simplify down to this single chart, some assumptions were made; that the measurement is at room temperature, and done in a suitable range, i.e. that you’re not measuring a 1mV signal in the 300V range, and that you’re not measuring at high speed, and that the measurement is done within a year of calibration).
Incidentally, in terms of a like-for-like comparison for this aspect, the Keithley/Tektronix DAQ6510 is almost a near dead match in performance with the DAQ970A.
It can be seen from the chart that the Keithley model performs better in the lower ranges (slightly!) but that’s only with certain cards. Some of the cards will perform slightly worse than the DAQ970A in those ranges. They are both fantastically accurate. The Keithley model has the advantage of being directly usable up to 1000V, whereas the DAQ970A is designed for up to 300V.
When DC measurements are made rapidly, DMMs sample the voltage for an amount of time known as the integration time. Ideally they take advantage of sampling at the same time at each power cycle (50Hz or 60 Hz depending on region) and sampling for a period longer than one power cycle length. When sampling for less time (i.e. at a rate higher than 50 or 60 Hz), some small error is introduced. That error looks like an additional noise on top of the reading.
The graph here shows that additional maximum RMS noise value to expect, based on the measured value (assuming the best range is used for the measured value). To use it, look up the measured voltage on the x-axis, and then look vertically to the line indicating the integration time, and read off the maximum additional noise value in microvolts RMS.
So, up to 10V, one can expect additional noise less than 200uV RMS at integration times of less than 1/50 of a power cycle period (i.e. sample rates of approximately 2500 Hz or 3000 Hz). At a lower sample rate of approximately 250 or 300Hz (i.e. 0.2 PLC), then the maximum additional noise for a signal lower than 10V would be 50uV RMS. At 10 PLC (i.e. 5 or 6Hz readings) the additional noise is not observable and is off the chart.
One immediate competitor is the Keithley DAQ6510, because it performs fairly similar tasks. I do not own one, so I can only compare against some of the paper specs. It has strengths and weaknesses compared to the DAQ970A.
Two main functional differences are that the DAQ6510 exposes the DMM functionality to front panel banana jack sockets, so it can serve as a bench meter too, and secondly, it has a very high speed logging capability, although the measurements drop down to 16-bit resolution for that.
For design lab use, the exposed DMM functionality is nice to have, however for testbed use it doesn’t see so useful. For design use a dedicated bench DMM instrument may be preferable anyway, since that is such a core device to have in a lab.
The DAQ6510 high speed logging seems unique and attractive.
The DAQ6510 will perform close to the DAQ970A (there is a hair-thin difference in performance in some places), and costs are similar. The DAQ6510 has no external outputs (for alarms) without an optional card, whereas the DAQ970A has them built-in. There are two interface module slots on the DAQ6510, whereas the DAQ970A has three slots. One module on the DAQ6510 has a scan speed that is almost twice that of the DAQ970A (but of course that speed is only attained if other slower modules do not need switching for a test). The DAQ970A directly supports strain gauges, but the DAQ6510 doesn’t. The DAQ6510 supports an in-built scripting system, whereas the DAQ970A would need to be attached to a computer for that. The environmental operating conditions for the DAQ970A are slightly better than the DAQ6510.
Each module has an approximate price of around $600 USD, which is the same ballpark as for other manufacturer data acquisition system cards too. It’s a cost that could pale into insignificance compared to the cost of actually wiring them up, which could take a couple of days depending on what you’re precisely doing. For my use-cases as an instrument for varied testing suitable for a design engineer, I wished to semi-permanently wire up the module to some lengths of wires.
STEP files are available of the module plastic enclosure, and the DAQM970A itself too, so that wiring can be planned both inside the module, and as part of the entire system/testbed. The diagram shown below was drawn to scale, so that it can be printed and used as a template to design wiring layouts manually (or of course it could be designed using the correct CAD software).
For my use-cases, I decided to allocate eight of the 20 channels in a 4 x 4-wire configuration that could be useful for low resistance measurements (or any resistance or voltage measurement in 2-wire mode).
Next, four channels were allocated for additional voltage or resistance measurements in a 2-wire configuration, and finally four more channels were allocated for temperature measurement with thermocouples.
This still left me with spare channels for any future additions.
The module card also has a common output, which is useful to attaching to external test equipment, so that was brought out via a pair of wires too.
Incidentally, as a suggestion, since the optimal cables (for your application) might be hard to find, it is sometimes cheaper to just build your own custom composite cables. That’s what I did in the end, since I didn’t want to spend hundreds of $$$ on reels of shielded cable. Instead, I purchased some 20 AWG silver-plated copper wire with PTFE insulation, and twisted it myself to reduce noise pickup, and put shielding braid over it. All the shields were connected to the common output connection, to reduce the amount of shield wiring. The thermocouples were shielded too. In the photo above, the blue wires are all the shielding connections.
Once all that was done, it was tidied with some cable ties and nylon braid over the metal shielding, and the clear lid was snapped on top of the module.
It was a lot of wiring! It took me an entire weekend.
Still, it means now I can rapidly use the DAQ970A for many diverse tasks, with a good chance that it may not need to be re-wired often.
Using the DAQ970A to get basic measurements is very smooth. I was surprised because the user manual is laid out in an order that describes button functions, rather than workflow! The first steps to be done are not the first button functions described in the user manual. It’s a good thing the instrument is fairly easy to use : )
Once the instrument is powered up, it auto-senses the card type, and then it is up to the user to configure what measurement is required on which wires. To do that was simple. Hit the Configure button, and then the use the cursor keys to traverse the channels available on the module (they are numbered from 101 upward, because the module is in the slot labelled 100.
For any channel where wiring has been attached, the soft-keys can be used to select a measurement type. That’s enough to get the device working. To give a taste of using the instrument, the diagram below shows a workflow, in this case for configuring a thermocouple.
As another example, in the screenshot below, channel 107 (i.e. the 7th channel in slot 100) was set to measure DC voltage.
Once the channel has been configured, press the Monitor button, and the DAQ970A provides a familiar multimeter-style display (the example here is showing temperature).
And, like the best modern bench meters, it can display the measured results with different views:
As part of the testing, I wanted to try different example applications. One was to see how the DAQ970A could be used as a traditional chart recorder. For this application, the Keysight BenchVue software was used. BenchVue supports hundreds of Keysight instruments (and can work to an extent with standards-based communications with third party instruments too).
The software recognises instruments plugged into the network (I used the Ethernet connection on the DAQ970A and plugged it into the router/switch) and allows you to interact with them in different ways.
One way is to download an application specific to the test instrument, and it appears as a fully integrated app inside BenchVue. In the case of the DAQ970A, the app provides a way to configure channels, scan settings, and how the data is to be displayed, and ultimately saved or exported too.
For the chart recorder scenario, I connected a channel to the mains supply (via a special safety transformer that reduces the voltage by 100:1) in order to observe the mains voltage. The aim was to see if the mains supply sagged or increased over time. The ‘strip chart’ view was perfect for this use case!
The screenshot below shows how multiple views of the data (in real time) can be displayed. Multiple channels can be collected, so (say) current consumption could be monitored at the same time as the voltage.
The screenshot below shows the mains voltage was around 246V (2.46V on the chart) but sagged to 244V. I placed marker flags at those points, and the software allows for annotations so that the detail can be explored later. In my case, that sagging occurred when the oven was turned on : ( My home is more than 130 years old, and although the mains supply to the home isn’t quite that old! clearly there’s room for improvement.
The strip chart worked well, and it was possible to set the X-axis to real time, instead of relative time since the start of the test.
It is also possible to export the data at any time from BenchVue (even during a test run) to applications like Excel and Matlab. The Matlab export was very smooth. It generates a .mat file that contains a vector (or array) for each channel, and also a vector of timestamps.
I needed to manipulate the timestamp – not sure why – but in any case by trial and error this worked for me in case anyone else needs to do it, to output an understandable time in UTC:
It appears the 1601 is Windows NT time format.. Anyway, once you’ve performed this manipulation, plotting a chart is easy:
plot(timeseries, Trace_name); datetick('x', 'HH:MM:SS');
For straightforward data logging scenarios there is no need to attach a computer. The instrument can be used as-is and it logs to internal memory. By plugging in a USB memory stick, data can be recorded indefinitely. Once the device starts scanning, it will create a folder with two files. One file contains the configuration, and the other contains the recorded data.
In production lines some procedures may accidentally damage the end product (it may not be accidental, it’s not unknown for some manufacturers to deliberately damaging the sharpness of blades for instance, for early replacement). The act of screwing in a circuit board into the chassis could flex it too much and cause lower yield due to parts cracking. The procedure should be tested in that case, and the DAQ970A could help production teams increase their yield.
For design engineers, the positioning of components and the design decisions on how the board is mounted can be critical for performance. When doing (say) 24-bit ADC implementations, the slightest flexing of the board or components could cause additional errors in readings. I wanted to see how use the DAQ970A for these types of scenarios.
For this test, I used an example 160x80mm PCB intended for an audio project, and chose a suitable location on the board. If the sensitive area is not known, then multiple locations would need to be selected. A couple of strain gauge sensors were attached using superglue.
Strain gauges can be used in several different electrical arrangements, and the DAQ970A supports these (bridge arrangements, and also single strain gauges directly connected). The easiest to connect up is the direct method, and 4-wire connections were used (2-wire is supported too). The gauge parameters can be directly entered into the channel configuration settings.
Once this is done, pressing the Monitor button will immediately start showing the measurements in micro-strains (i.e. change in length in parts per million). There’s likely to be an offset (the strain gauges were 350 ohm nominal, but there was a slight difference), and it is easy to compensate for that because the DAQ970A allows for offset and gradient adjustment using the Math button. I added an offset value to get the micro-strain value close to zero. The measured strain value went negative when the gauges were flexed downwards.
BenchVue was used to capture 20 scans worth of data. For the screenshot below, the PCB was flexed by hand, lightly, at the end. It can be seen that one sensor recorded several times as much strain compared to the other. In fact, the flexing the board down in the way that I did, caused slight strain in the upward direction in the other plane. That would have been near-impossible to tell without taking such measurements!
Armed with this information, if that area of the board is sensitive to such strain, action could be taken at the design stage, such as adding slots to prevent as much flexing in that area when the board is screwed down.
Even with these low-cost strain gauges in the bridge-less configuration, very slight flex (several parts per million) was observable.
The screenshot below shows the trend view on the instrument, when the board was clamped at one end, and a 5 gram weight was placed at the other end. The locations marked 1 and 2 indicate when the weight was added, and when it was lifted. This shows that a 1.6mm circuit board of 160x80mm, will exhibit about 6 micro-strains of flex close to the center of it, in the long direction, when 5 grams weight is placed at the long end of it.
With additional filtering, it would be possible to detect a 1 gram weight on the PCB too.
In summary, it was impressive how easy it was to integrate strain gauges into a testbed. Ordinarily dedicated strain gauge measurement instruments can cost thousands of dollars, so it’s nice that the DAQ970A can handle it, in many configurations.
In a previous job I had to test dozens of circuit boards for identifying patterns to the failures, to see if it was a production issue or not. I didn’t have such a measurement instrument, otherwise the strain measurement feature would have helped immensely.
For this scenario, the aim was to determine the temperature across a board in a reflow oven. Usually an oven may have one or two temperature sensors for its control loop, but measuring the temperature on the object itself can be more helpful. This of course needs to be done whenever the object changes (or changes significantly). This is common when (say) baking paint onto products. There are dedicated test tools for such purposes, but I couldn’t see why the DAQ970A could not be used for this, provided all the temperature sensors can reach from the instrument into the oven.
As shown earlier, the DAQ970A supports thermocouples, RTDs and thermistors for measuring temperature. Thermocouples are great for high temperatures, and they are low cost. The way thermocouples work requires the temperature of the far end to be known, and the module card has built-in temperature sensors on the PCB for this.
Extending the length of thermocouples isn’t easy (it requires special extension wire) and so it is better to just buy them in the required length. For this test, 2 meter long thermocouples were used, so that they could reach into the oven easily. Four locations were chosen, to cover the left, center, and back and front areas of the oven, and the thermocouples were taped to a pad on scrap PCBs of a typical size used with this oven.
The oven is old and has a drawer with a slightly warped front which is no longer flush when closed (there is a gap of 1-2mm in places).
Although the DAQ970A can store all results internally and export them, for this application it was decided to also examine the automation capabilities, because there could be scenarios where data needs synchronising and collecting from multiple DAQ970A instruments. It was decided to use Matlab for the test automation directly, instead of just exporting the results to Matlab.
The DAQ970A programmability documentation was good enough to quickly get up to speed building the automation. A simple program was created that would repeatedly scan across all the thermocouple channels, and dynamically plot the chart. The program is attached, and could be modified for other purposes.
This test was extremely useful to helping better understand the oven behaviour with circuit boards (more tests could be done to explore temperature variations across a specific board). The oven was programmed to reach 110 degrees C within a certain period, and then to reach 210 degrees C. After that, it vents out to rapidly cool. It was found that at the peak, the center was the hottest, and compared to that, the back and sides were 12 degrees cooler, and the front was 28 degrees cooler : ( At the end of the reflow cycle, when the fans kicked in, the center cooled most rapidly too.
The measurements were clean despite the 2 meter long thermocouples (they were shielded for about 1 meter) and it’s likely that profiling in larger ovens could be achieved in this manner too. Since test automation was used, it is also possible to use multiple DAQ970A instruments for profiling temperatures across extremely large areas and gathering the data in real-time across the network.
These measurements provided a great amount of insight; the cycle is fairly accurate at the center of the oven, but work needs to be done to improve the seal at the front.
There are many ways to have programmable behaviour with the DAQ970A, and a couple of them have been used so far in this review (BenchVue, and Matlab).
Benchvue allows test flows to be created graphically. Compared to other methods, BenchVue could be easier to use for beginners. It may also be quicker to use. Personally, for what it’s worth, I’d suggest that it is worth a try, but ultimately if you have a choice, it is also definitely worth trying out other tools too, in case you like them – especially since modern programming languages are a lot easier to dive into nowadays.
In some environments, LabView is prevalent. Python or Matlab are other options.
Like all really decent instruments, the DAQ970A offers both network and USB connectivity. The network option is excellent if the instrument is to be used in a lab. For field work with a laptop, USB connectivity is really helpful. SCPI commands work with both methods of course.
Another useful feature for automation purposes is the alarm output capability. There are four logic level outputs (3.3V logic) on the back of the DAQ970A, on a DB9 connector. The normal way of using these is to pick a channel, and assign high or low thresholds, and then link the alarm to them. When the threshold is exceeded, the display changes color and the alarm is raised (it can optionally be latched, or can follow the input as it goes in or out of the threshold).
However, if you’re desperate for just a single SCPI controllable output (and don’t want to purchase another module that has output capability) then there is a way to do it. The method is to not assign the alarms to any channels, and instead merely change (via SCPI) the alarm mode from normally high (the default) to normally low, or vice versa. By doing that, the outputs will change logic level. It’s a hack but is may be useful occasionally (e.g. to trigger another piece of equipment).
The DAQ970A can change the way engineers work. Tests can be run in parallel, or information can be extracted from a circuit or system at different parts of it simultaneously. There are many use-cases, and this review attempted to cover several of them. Throughout, the instrument was easy to use on its own, but it was a very smooth experience capturing data remotely with a PC too. It’s a nice, easy-to-use instrument with a great display and in-built help capability.
The instrument was used in several configurations; standalone, and with automation software (BenchVue and Matlab). The user manual and programmability reference guide was sufficient to work with, and everything went smoothly.
The DAQ970A can replace data loggers and chart recorders; it was useful for monitoring the mains supply, and it can record indefinitely to USB.
The in-built strain gauge capability is extremely useful for examining if circuit boards (or other products) are being damaged or suffering stress when inserted into enclosures.
When heating items in an oven, it came in handy to be able to check oven consistency, and for examining if the particular items are being heated evenly.
In a lab the DAQ970A could replace a lot of standalone equipment. In my case, I found I no longer needed to use handheld temperature loggers with their awkward methods of pulling off data to a PC, and I can finally ditch the chart recorder + printer, which suffered from low resolution, and low number of channels.
It’s a fantastic all-in-one instrument for probing lots of signals simultaneously, and without messing about flying blind to some measurements due to the time it takes creating similar conditions multiple times to do tests with single-channel equipment. The DAQ970A is a worthwhile addition as a primary instrument in a design lab, or even for scientists.
Thanks for reading.