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Agilent's LCR meter comes up to speed

Posted: 16 Jan 2006     Print Version  Bookmark and Share

Keywords:Alex Mendelsohn  Agilent Technologies  E4980A  LCR meter 

Some EEs may yawn at an instrument like this, thinking it's sort of mundane in this era of high-speed signal analysis and microwave RF. Nonetheless, Agilent Technologies' E4980A LCR (inductance, capacitance and resistance) metre is a relevant piece of automated or benchtop test gear that's in lockstep with the need to test today's passive components.

Its operation is up to date as well. Previous Agilent LCR meters were operated using the venerable IEEE-488/GPIB General Purpose Interface Bus. These days, however, the ascendancy of USB and LAN control is a given.

As such, the E4980A now includes USB and 10/100-BaseT Ethernet hooks (as well as GPIB), and you can operate the instrument from your Web browser. You can also store data to a USB memory stick. You can also drive this instrument from your desktop PC or notebook.

Modern components
In use, the E4980A can handle small equivalent series resistance (ESR) values, and make low-Z (impedance) measurements. It can also measure and display conductance, admittance, susceptance, dissipation factor, Q and more.

ESR is especially important because the ESR of capacitors is becoming smaller as these parts are crafted to meet high-speed yet low-dissipation applications. The values of components such as tiny chip-capacitors (and semiconductor wafers) are also measured in very low values, too, often just femto-farads (fF).

Stable high-Z measurement capability is needed to accurately measure such tiny values of C. For very low-value caps, ESR can be tough to measure, too. To do it effectively, the E4980A excites devices-under-test (DUTs) at frequencies from 20Hz to 2MHz, exhibiting 4-digit resolution at any frequency in this range.

You can select signal levels from 100?V to 2V (rms) at currents from 1?A to 20mA. This box is accurate and repeatable as well. Voltage accuracy is specified to be within ?10 per cent (plus 1mV rms) at a frequency of 1MHz. Sweep list
The instrument can be set to sweep across 201 pre-listed points. Frequency, measurement range, and stimulus conditions can be set in the list. You can also choose two parameters independently.

With its high-resolution touch screen LCD and 7-digit display, an E4980A can run in six displayed modes to handle the task. Its normal mode gives you basic data about a part under test. A bin no. view is then available for comparison purposes; it can aid rapid device sorting. There's also a BIN count view that can be used for statistical evaluation.

A list sweep view is used when continuous data is needed, and it's backed up by a blank page view that gives you the fastest speed. In the blank page view the display is turned off to shorten refresh times.

Fast measurements
Speaking of speed this box is fast. An E4980A operates at 5.6ms in its shortest measurement time mode, slowing to only 88ms per measurement in its medium speed mode (at 1MHz), and 220ms in its long mode. At 20Hz, it can make a measurement in as short a time period as 330ms.

Similarly, a 100ms measurement can be done at 100Hz. At 100kHz a measurement can be made in as fast as 5.7ms. Adding very little noise in either low impedance or high impedance operation, it can thoroughly reveal the characteristics of inductors and capacitors.

An entry-level option
Not mentioned in the press statement is that Agilent also offers a so-called entry-level option for this instrument. Dubbed the E4980A-5, it's a lower cost model option that offers the same accuracy as its big brother but it operates two to five times slower.

There are other options, too. Agilent's press statement mentions the instrument's support for 40A of DC bias and the DC resistance/voltage/current measurement readout for simultaneous DC characterisation. There's also the 10Vdc source for testing three-terminal devices.

The Option E4980A-001 power and DC bias enhancement lets you apply a 20V (rms) test signal at up to 100mA. This lets you evaluate AC level-dependency, without the need for an adjunct amplifier.

A DC parameter measurement option can also let you simultaneously measure DC resistance, DC current, or DC voltage, as well as impedance. For inductors, inductance and DC resistance can be measured at the same time. You can use this option to measure leakage current of capacitors, too.

Another option lets you apply DC bias to a DUT. Supplying up to 40Vdc at up to 100mA, it lets you perform DC bias vs. impedance measurements. Another DC source option gives you an additional independent DC port. You can use it to measure 3-terminal terminal devices. It lets you control the DUT, add extra bias, and control additional devices at the same time.

Agilent also supports this LCR metre with a variety of test fixtures. Indeed, the box can be used with over thirty different fixtures, and it sports built-in compensation for these. You can also elect to implement an optically-isolated 9-BIN handler (dubbed Option 201). Similarly, a 128-channel scanner interface (Option 301) is for applications requiring a component scanner. A multi-compensation function enables open/short/load compensations to perform scanning measurements independently in each scanner channel in order to minimize inconsistency in measured values between channels.

Both interfaces are also compatible with predecessor Agilent LCR instruments. Speaking of predecessors, just about every E4980A function is compatible with Agilent's earlier 4284A and 4279A LCR metres.

- Alex Mendelsohn
eeProductCenter




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