By measuring the phase-sensitive ratio of the voltage between two electrical ports of the device and the resulting current flowing through the same, an LCR meter allows to measure the absolute impedance and phase, as well as its real and imaginary parts. Rohde & Schwarz recently introduced a new family of LCR meters.
The impedance measurement is essential for characterizing the electrical properties of different devices and materials. Specialized equipment, like an LCR meter, is used to measure impedance parameters such as capacitance, inductance, and resistance. By measuring the phase-sensitive ratio of the voltage between two electrical ports of the device and the resulting current flowing through the same, an LCR meter measures the absolute impedance and phase, as well as its real and imaginary parts.
The relevant impedance parameters can then be derived through a user-defined equivalent circuit model. Because impedance varies with frequency, a more accurate and reliable measurement is achieved performing the measurement at different frequencies (frequency sweep).
Rohde & Schwarz LCX LCR meter
Rohde & Schwarz recently introduced a new family of LCR meters: the R&S LCX. The new test equipment, shown in Figure 1, measures impedance at a given operational point of the device under test, which is typically an inductor, a resistor, a filter, or a similar component. Used to determine passive linear components in floating conditions, the measurement can also be swept over a range of frequencies, an operation typically done in R&D departments, on production, or wherever there is a need for material and device characterizations.
“The three key factors of our brand-new R&S LCX equipment are accuracy, frequency range, and impedance range,” said Philipp Weigell, director of product management and planning for Power Supplies & Meters at Rohde & Schwarz. “If you need to study and characterize standard or non-standard components, like in material science, you need an LCR meter, where frequency can be swept over a wide range up and down.”
Built on R&S long-term experience, the R&S LCX series (which includes the LCX100 and the LCX200 models) complements the features of two major pillars: the R&S HM8118 LCR bridge (an entry-level LCR meter with up to 200-kHz frequency range) and the MFIA (a faceless impedance analyzer with wide frequency range of 1 to 5 MHz and high impedance range of 1 mΩ to 1 TΩ). The MFIA unit was originally developed by Zurich Instruments, acquired last year by Rohde & Schwarz.
The R&S LCX100 model is really meant as a one-to-one replacement of the HM8118 and covers the frequency range from 4 Hz to 300 kHz. The R&S LCX200 can be software-upgraded to different frequency ranges. It has an upper frequency of 500 kHz, which can be further extended to 1 MHz or 10 MHz using software options when needed.
“Internally, the instrument can always operate at 10 MHz and is calibrated up to that frequency value,” said Weigell. “This gives the possibility to upgrade with a simple software key code, whenever you actually need more frequency.”
The LCX series is not just a full replacement for the previous HM8118 equipment but adds new and outstanding features, such as:
- The application space has been extended with a higher frequency and test voltage range.
- Logging mode and faster measurements enable more manufacturing applications. The fast-logging function records all measured values up to 10× per second.
- A large and high-resolution display with capacitive touchscreen and virtual keyboard enables faster operation. The display can also be used for graphical representation of measurements.
Both LCR meters feature high measurement speed, accuracy, and versatile measurement capabilities, making them the ideal instruments for component R&D, component production, material research, device characterization, education, service, and QA. Thanks to their wide measurement ranges, the instruments are also suitable for applications with extremely low and extremely high impedances. With an extended frequency range from 4 Hz to 10 MHz, the R&S LCX family is suitable for devices operating at conventional 50-Hz or 60-Hz domestic power frequencies and 400 Hz for aircraft and aerospace, as well as everything from low-frequency seismic sensors to high-power communication circuits operating at several megahertz.
Three measurement times are available:
- Fast: less than 15 ms
- Medium: less than 100 ms
- Slow: less than 500 ms
The basic accuracy is ±0.05 % for impedance measurements and ±0.03° for phase measurements.
“New technologies drive up the frequency range,” said Weigell. “Higher switching devices require test equipment able to operate at higher frequencies, analyze margins, and perform four-corner testing and aging analysis.”
The R&S LCX can be used both as a general-purpose LCR meter and as an impedance analyzer for dynamic impedance measurement. In the first case, it measures equivalent series resistance and equivalent series inductance of electrolytic capacitors and DC-link capacitors. Moreover, users can test transformers and measure DC resistance in addition to the full range of impedance measurements. Through an option activated using an ordered keycode, the equipment can operate as an impedance analyzer, supporting dynamic impedance measurements with the frequency, voltage, or current as the swept parameter. This feature allows investigation of components with impedance values varying at different frequencies and levels.
To measure capacitors and inductors at different operating points, an adjustable DC bias is required for many applications. Both R&S LCX test equipment internally generate a DC bias voltage of up to 10 V. Optionally, DC bias voltages of up to 40 V can be applied at an external connection on the rear panel (R&S LCX-K108 option) using a standard DC power supply.
“Obviously, we have hard-coded some buttons to reach the most frequently used functions very quickly,” said Weigell. “There is also a save-and-recall feature, which makes it easy to save and recall frequently used settings, or presets. Three instrument settings can be accessed directly on the touchscreen, while other settings can be stored freely.”
Figure 2 shows the three instrument settings, or presets, that can be called directly on the touchscreen. Alternatively, voltage, current, and frequency values can be set using the rotary knob in the middle of the instrument (Figure 1). Less frequently used functions are menu-operated.
“With the launch of the R&S LCX series, we address the full LCR meter market needs with our portfolio,” said Weigell. “Compared with other competitors’ products, we are able to provide a 5× frequency range, which is a major achievement. Obviously, there are always new applications coming, which can be addressed via additional test fixtures.”
