A Compact Capacitance Meter for High Speed Production Test
Introduction to a compact, highly accurate capacitance meter designed for high speed measurements
The 4288A meter is housed in a 3/4-sized rack enclosure compared to the full 19" rack-mount 4278A. This smaller footprint allows users to dramatically downsize autohandlers used for production-line testing of chip capacitors. The instrument measures capacitance over ranges of 0.00001 pF to 20.000 µF at 1 kHz and 0.00001 pF to 1.50000 nF at 1 MHz. It can evaluate other key capacitor parameters, such as dissipation factor, quality factor (Q), equivalent series resistance (ESR) and conductance (G). The meter is well suited for testing most ceramic, film and mica capacitors. Table 1 lists the instrument's main specifications.
In terms of measurement speed, the new capacitance meter is approximately 30 percent faster than its predecessor. The 4288A provides two measurement modes -- short and long. The shorter test time results in somewhat less accuracy than the longer test time. The measurement time using the short mode is 6.5 ±0.5 ms, or a worst-case value of 7 ms. The measurement time using the long mode is 16.5 ±1.0 ms, or a worst-case value of 17.5 ms. The basic accuracy using the long mode and either test frequency (1 kHz or 1 MHz) is 0.07 percent for capacitance measurements and 0.0005 for dissipation factor measurements. The accuracy "drops" to 0.085 percent for capacitance measurements and 0.00065 for dissipation factor measurements when using the faster short mode.
The 4288A allows up to ten test setups (instrument configurations) to be stored in its electronically erasable programmable read-only memory (EEPROM) versus a single stored measurement setup (using a memory card) with the 4278A instrument. All of the options available for the 4278A are now standard features in the 4288A. Notable among these is software-selectable frequency-shift capability to make adjustments of +2, +1 and 1 percent from the nominal 1 kHz and 1 MHz test frequencies. The 4288A features a separate load reference for each of the measurement channels when using a scanner. In the 4278A, a single load reference was distributed across all four channels. The 4288A is equipped with open/load/short calibration and compensation, with support for as many as 64 channels of multiple compensation. The 4288A can be set for use with cable lengths of 0, 1 and 2 m while maintaining compensation.
For ease of integration with automatic parts handlers and scanners used in capacitor ATE systems, the 4288A offers a choice of electronic links, with GPIB, handler and scanner interfaces. The capacitance meter has a built-in comparator with a nine-bin sorting limit as the primary parameter and high/low limits for the secondary sorting parameter. Independent of the comparator, a "low C reject" function helps to differentiate poor-performing capacitors from bad test connections by rejecting judgments due to incomplete handler contacts.
In addition to its high performance levels, the 4288A reduces maintenance costs by extending the calibration interval to one year, and it consumes only 35 W of power at 100 VAC. The price for the 4288A capacitance meter is $9,900. Additional information is available at www.agilent.com.
Santa Rosa, CA (800) 452-4844.
Circle No. 301