No need to plan your future analysis… Go straight aheadLatest updated: November 26, 2020
It is time to demystify a false truth. You really do not always need to add points in the record settings of BT-Lab® and EC-Lab® in order to obtain highly accurate measurements.
For while it might seem logical that the greater the number of points, the higher accuracy the results, this is not actually the case. Because with EC-Lab® and BT-Lab®, more points do not mean more prizes.
Record frequency and time base: two different entities
Before we enter into the detail of how this can benefit you, it is important to understand the differences between the two terms:
“Time base” is independent of user settings and relates solely to the instrument itself. It refers to the minimum time between 2 actions/steps (in control mode). Points acquired during this time base may not be visible to users but they are used for processed data, for example, battery capacity, dQ/dV and energy calculations.
“Record frequency” is a parameter chosen by users in their settings. It refers to the number of points recorded by unit of time. It is sometimes also called the “Sampling rate”. Expressed in hertz (Hz), it can also be seen in time units (seconds): frequency = 1 / time. The recorded points are available for all export files and graphs.
Both of these entities may, or may not, be inter-related. It really depends on each instrument and the way it has been designed. The following table indicates the relevant specifications of Bio-Logic instruments and software:
|EC-Lab® software||EC-Lab® Express||BT-Lab® software|
|Minimum record time/Maximum sampling rate||200 µs/5 kHz*||14 µs/71 kHz*||2 ms/500 Hz|
|Time base/Time base frequency||200 µs/5 kHz||14 µs/71 kHz||2 ms/500 Hz|
* down to 1 µs/1 MHz with Analog Ramp Generator (ARG) option
So, why are these differences important?
Because of their architecture, some instruments on the market do not process data at the time base but only at the record frequency , so in such cases, it would actually be true that in order to increase the accuracy of a measurement, you would need to increase the number of acquisition points in the system’s user settings.
Great results all the time… just go straight ahead
However, EC-Lab® and BT-Lab® work differently as presented in the schematic below. Bio-Logic has specifically designed an instrument intended to generate highly accurate and precise analyses and data processes. Indeed, most of the variables are directly processed by the embedded software (called firmware) and not by the software on the computer. Thus, record frequency and time base can be separated!
This allows users to obtain perfect results without pre-planning or having to think about the number of points needed to analyse data after the test. Therefore, you don’t need to record a lot of data. This will generate smaller files to archive and increase the reactivity of the software during test and analysis.
Every acquisition point counts: A simple example
It is especially relevant for extensive variables and derivatives such as charge variables. For example, battery capacity calculation, which is a charge, is time dependent and is calculated based on the following formula:
The schematics below illustrate a theoretical example of the influence on record frequency vs time base. On the left, a user, let’s call her Arya, has set a record every 10ms, using a BCS-800. In order to calculate the capacity, she carries out the integral of current vs time. The result is then compared to the one obtained using process data from BT-Lab® software (i.e. “Summary per protocol and cycle”). However, they are slightly different; Arya is surprised and cannot understand which of the results is actually correct!
In fact, the figure on the right illustrates what the instrument is doing for you. In addition to the record points set by Arya, the system is also acquiring points every 2ms (for a BCS-800). The capacity calculated from these results is much more accurate than the one from the figure on the left.
It might also be difficult to select the proper points on the graph to carry out the analysis, especially during a cyclic voltammetry. Carrying out graph calculations using the integral can lead to significant analysis errors.
Moreover, for battery testing in CC (constant current), recording in both dE (5-10mV) and hundreds of seconds (120s) is usually enough for a good graph analysis. For processed data, your instrument will automatically carry out the calculations for you.
To conclude, you really do not need to record many points. Our instruments and software have been purpose-built to ensure accuracy and precision.
There is just no need…Just go straight ahead!