This section will look at the basics of data loggers and chart recorders and how they compare to oscilloscopes, and look at the products on the market similar to the B&K Precision / Sefram DAS240-BAT to understand how it is positioned in the market.
Oscilloscopes, Data Loggers & Chart Recorders – Similar, but Different!
I think the majority of readers would be familiar with an oscilloscope. This is basically a piece of test equipment that takes in a signal (usually a voltage, from a probe) and plots it on the screen over time. Usually this is done over a short time-base, but with digital storage oscilloscopes, longer timebases are now possible with a sampling rate that is reduced due to internal memory constraints. Many oscilloscopes may have more than one channel (2 or 4) allowing the plotting of multiple signals simultaneously on the one screen. Others may allow for X-Y mode where one signal controls the X-axis of the plot while another controls the Y-axis. Many times, oscilloscope circuits are optimised for speed, for high bandwidth signals (>>1MS/s), while sacrificing vertical resolution (e.g. 8-bits).
Generally speaking, oscilloscopes are designed to “wait” until a trigger event occurs, then record/display the signals coming in at a given rate until the buffer (screen) is full and then wait for the next trigger event. This is great for signals that happen infrequently, but perhaps are very short in duration. They are not designed to look at a signal continuously or record continuously (although some can at low rates, e.g. PicoScope) – for many basic models, there is a “rearm delay” for the trigger resulting in some acquisition blind time (i.e. a gap where the signal cannot be seen).
Conversely, data loggers generally do the opposite. They are designed from the outset to record data on a continuous basis at a high resolution (e.g. 12 to 24-bits) with more channels (often >>4), but in return, their sampling rates are often lower (<1MS/s). Some data-loggers are designed without much of a user interface, designed to plug into a computer for long term recording or just to dump data quietly to a memory device (e.g. SD card) over prolonged periods. These are invaluable for troubleshooting or validating slow-changing signals (e.g. changing physical quantities in a process control operation) over a long time.
A chart recorder, as the name implies, serves a similar purpose to a data logger but instead traditionally records trends and changes in signal to a paper record, similar to the way seismographs are depicted in movies. While paper recording is on the way out, some standalone data loggers have a chart-recorder-like interface which allows for visualising the data trends over long periods of time in a more flexible manner, on the device itself rather than requiring download and analysis on a computer.
The B&K Precision / Sefram DAS240-BAT is called a Multi-Channel Recorder, but is basically a portable data logger and chart recorder in one unit. It has a maximum sample rate of 1kS/s on a single channel, with a 16-bit resolution, so is most suitable for slowly changing quantities.
Of note is that there are some devices which try to blur the likes – for example, the Hioki HiCorder, Yokogawa ScopeCorder, Dewetron and Astronova units which offer higher sample rates and continuous recording capabilities as well. So in essence, oscilloscopes, data loggers and chart recorders all do similar things differently – with different time scales, memory depths, vertical resolution and sample rates.
Market Survey
To see what was on offer on the market for a multi-channel data logger, I put myself in the shoes of someone looking to purchase such a unit. Specifically, I was looking for units which were capable of standalone operation with an independent user interface display, not reliant on a PC for operation. I also looked for data loggers which were flexible in terms of their channel functions with universal input channels, rather than specialised, niche, industry-specific designs. It had to be portable, for test and measurement usage, rather than panel integrated or a desk/rack-bound mainframe/modular system. Finally, to keep things in the realm of reasonable cost, it had to have moderate sample rates of less than 1MS/s, excluding high-end options such as the Hioki HiCorder, Yokogawa ScopeCorder, Dewetron and AstroNova units to name a few.
The results of the market survey are as below:
Key players in the market include Hioki, Grant, Graphtec, MadgeTech, Fourtec, TandD and B&K Precision/Sefram. The results are sorted by price, with the exception of the review unit in the leftmost column. Attributes have been colour-coded on their general desirability. The standard disclaimer applies – the information is supplied in good faith based on my own independent research based on information provided by manufacturers and suppliers. It does not take into account how the units actually perform in real life and other parameters not captured by these parameters. Prospective buyers are to verify the units meet their needs and perform their own independent research prior to purchase. I will not be held responsible for any errors, omissions or consequences which may arise directly or indirectly as a result of using or inability to use the information provided.
The multi-channel data logger market spans a wide range for pricing and capabilities. At the low-end of the market resides relatively low-channel-count units with basic monochrome matrix LCD interfaces, limited expansion capabilities and recording capacity, some of which can be powered by standard sized batteries. Towards the higher end of the market, smaller colour LCDs become available along with greater expandability and improved accuracy.
The B&K Precision/Sefram DAS240-BAT is almost the most expensive single unit in this round-up, but compared to the competition, it does stand out on a number of key parameters. Its integrated 20-base channels of analog input and 12-channels of digital input are amongst the best, with the expandability to 200-channels being unique amongst the competition. The input range is also the widest of all units, offering the best sensitivity for small voltages. The accuracy compares well with the competition, with the 1ms minimal sampling time being comparable to the best from many of the peers (although some are capable of as low as 0.25ms). But where the DAS240-BAT excels is in the offered channel modes, calculations, display size and resolution, storage capacity and battery life. This may justify its higher price tag compared to the competition, although if 10-channels is enough for you and expandability is not a requirement, the DAS220-BAT is relatively competitively priced compared to its peers while offering very similar advantages otherwise.
That being said, the most expensive unit is actually a combination of units – the Hioki LR8410 base unit and LR8510/8511 remote sensing unit. This data acquisition system has the distinction of using Bluetooth for remote channel interface units, allowing for less clutter, smaller and lighter units, which is an innovative take on the multi-channel data recorder. The downside to this is a more limited expandability, slower maximum sampling rate, more limited memory, limited battery life and higher cost. The other units within the round-up are relatively conventional by comparison.
Conclusion
Oscilloscopes, Data Loggers and Chart Recorders all perform a very similar function of being able to record and display input parameters over time (or parameter versus parameter), but do so at different scales. Oscilloscopes tend to be optimised for high-bandwidth rapid events that happen infrequently and are designed to capture a “buffer” of data at every trigger event (with short acquisition blind periods in-between), while data loggers and chart recorders are designed to capture data continuously to monitor more slowly-changing inputs. Oscilloscopes tend to have fewer channels and lower vertical resolution, favouring higher sample rates while data loggers and chart recorders tend to favour more channels being sequentially sampled and higher vertical resolutions with a lower sample rate. Data Loggers may be optimised for logging without a user interface, depending on a PC, while Chart Recorders formerly used paper as a recording medium leading to an inflexible and bulky solution. Modern multi-channel recorders blur the lines between Data Logger and Chart Recorder by offering both in the same box – such as the B&K Precision/Sefram DAS240-BAT. There are other devices which further blur the distinction, offering new combinations of channels, sample rate, memory depth and vertical resolution to meet various needs.
The B&K Precision/Sefram DAS240-BAT is almost the most expensive single unit in this round-up, but compared to the competition, it does stand out on a number of key parameters. Its integrated 20-base channels of analog input and 12-channels of digital input are amongst the best, with the expandability to 200-channels being unique amongst the competition. The input range is also the widest of all units, offering the best sensitivity for small voltages. The accuracy compares well with the competition, with the 1ms minimal sampling time being comparable to the best from many of the peers (although some are capable of as low as 0.25ms). But where the DAS240-BAT excels is in the offered channel modes, calculations, display size and resolution, storage capacity and battery life. This may justify its higher price tag compared to the competition, although if 10-channels is enough for you and expandability is not a requirement, the DAS220-BAT is relatively competitively priced compared to its peers while offering very similar advantages otherwise. Compared to the other options from Hioki, Grant, Graphtec, MadgeTech, Fourtec, TandD, the market seems to have many older solutions which have more limited monochrome LCD/small colour LCD user interfaces, small memory capacity and limited battery powered options. The only other interesting contender was the Hioki LR8410/8510/8511 combination which offered all-wireless Bluetooth-connected channel interfaces, but at a higher cost with other trade-offs.
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This post is part of the B&K Precision/Sefram DAS240-BAT Multi-Channel Recorder RoadTest Review.
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