How to choose an RLC meter

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Ruční nebo stolní, to je oč tu běží
Probably the first question of anyone who needs to measure impedance - the basic variable of every LCR meter, besides phase angle - and the values of inductance, capacitance, resistance and many other parameters derived from it (e.g. ESR equivalent series resistance, loss factor D/tanδ, quality factor Q, admittance, reactance, etc. etc.) typically used to measure capacitors, inductors, and resistors, is whether he will make do with a simple handheld instrument costing a few thousand dollars, or whether he will need a benchtop instrument with a higher accuracy class, wider frequency range, and overall better capabilities. In this article we will focus on the latter group, i.e. benchtop instruments designed for both laboratory and industrial use.
Ruční RLC metr

Table RLC meters - what measurement frequency?

So if you are clear that you cannot afford to pay a few thousand crowns for a device, the main decision criterion is the measuring frequency. For simpler industrial measurements, an instrument with a relatively narrow range of measurement signal frequencies, or measurements at only one or a few discrete frequency values, is often sufficient; in this case, you can choose the basic LCR Meter IM3523 or its twin IM3523A from our range. The frequency of the test signal is adjustable from 40 Hz to 200 kHz for these two models; DC resistance measurements are of course also possible. A top measurement speed of up to 2 ms per sample and a range of support functions such as a comparator of measured values with predefined limits, automatic sorting of results into groups or storage of measurement conditions for quick recall later are ideal for automated deployment in production lines.

At a slightly higher price level are instruments with extended lower or upper frequency bandwidths. For measurements from as low as 1 mHz (but again up to a maximum of 200 kHz) there is the pair of LCR Meter IM3533 and IM3533-01 (the one with -01 also "knows" transformers - displaying N, M and ΔL parameters and has a directly built-in Analyzer mode for swept measurements). Compared to the basic industrial models IM3523/IM3523A with a monochrome display and push-button control, these RLC meters have a touch screen display, which offers a slightly more user-friendly setup and measurement under laboratory measurement conditions. At the other "frequency" end of this price range is the IM3536 with a frequency range from 4 Hz to 8 MHz. At first sight identical to its IM3533/IM3533-01 siblings, but thanks to its increased limit up to 8 MHz and thus versatility it is now practically the bestseller of this category.

But what else?

So we should have the basics - we know that we are not satisfied with a manual meter, that we need to measure at this or that frequency and that we are interested in such and such parameter. But at this point, another set of questions often comes up: is it possible to measure a given parameter at a continuously varying frequency (i.e., frequency sweep)? How to measure correctly on voltage or current dependent samples? What are the possibilities of contacting the samples under test?
Let's go in order: if the key requirement is the analysis of a test sample over a certain frequency band, there are basically two options - the first is to choose a higher category of instrument, namely, for example, the LCR analyzer IM3570 or IM3590, which allow you to set the frequency range directly in the instrument and then display not only a numerical listing of the measured values of a given parameter for a specific frequency, but above all the complete waveform in a graph directly on the display. These two models are designed for testing, for example, piezoelectric elements, multilayer ceramic capacitors and electrochemical materials and components (typically in the battery industry). A second, significantly more economical option for frequency measurement is to use the freeware LCR Meter Sample Application, which allows the user to predefine the frequencies over which he needs to measure a given parameter and then simply use one of the LCR meter's communication interfaces to start the measurement from a connected PC. The output of such a measurement is then a set of values from which a graph can easily be created in Excel (or other program using a csv file exported by the application). Below is a window from this application, in which the key parameters for frequency sweep are defined (of course it is also possible to use Voltage and Current Sweep modes):

Sweep measurement

A common issue is also the so-called biasing, or applying voltage (e.g. for electrolytic or ceramic capacitors) or current (e.g. for inductors) to a given sample before the actual measurement. Due to the usually limited internal power supply of RLC meters, an external power supply is usually used for this purpose; the RLC meter itself must be supplemented with a special adapter in this case. This measurement setup (RLC meter + power supply) can then be controlled using the again freeware program Sequence Maker:

Sequence maker

The last of the above key issues is usually the issue of sample contacting. When it comes to manual measurements of common electronic components with physically easy to reach pins (resistors, coils, capacitors), the solution is usually easy - there are different types of probes to choose from for the standard four-wire measurement method used in RLC meters. All that is needed is to select a probe corresponding to the desired frequency range of measurement. Alternatively, tweezers are also available (in this case the contacting is done in a two-wire way).

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In addition to these, let's say fully manual probes, another variant is the test fixturing, which still allows manual clamping of the sample to be measured (typically miniature SMD components) in a precisely defined position, but the way the sample is clamped is in a way a semi-automated solution. This largely eliminates the risk of incorrect contacting. Finally, there is the last option, a fully automated solution used on production lines. This option is usually part of a complex solution where the customer defines the contacting method according to its own internal regulations and outsources the production of the test station to specialized manufacturers of single-purpose equipment.

Conclusion

If you've read this far, we hope you're a little clearer on which direction to take. Still, it may be that you haven't yet found what you were looking for; the article above, for example, didn't mention anything about yet another category of RLC meters - impedance analyzers, which are capable of measuring at significantly higher frequencies, even in the order of units of GHz. These instruments, at a much higher price level, use a different measurement principle (as opposed to the Automatically Balanced Bridge Method of the four-wire models described above), namely the high-frequency RF-IV method. For basic information on this issue and the suitability of different measurement methods for different applications, see for example here.

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