Electronic Design

Unique Nullmeter/Nanovoltmeter Improves Calibration Precision

Let's say you're performing a critical calibration or measurement in a bridge configuration. You have your choice of a high-resolution digital multimeter and an analog nullmeter with nanovolt resolution and its mirrored zero-center meter. Which instrument should you trust to produce the closest measurement to zero? When "nearly nothing" isn't good enough, go with the analog meter.

But finding a calibration-grade nullmeter/nanovoltmeter these days isn't easy. Popular calibration instruments such as the Fluke 845AD, Hewlett-Packard HP419A, and Keithley 155 nullmeters have been discontinued. So where do you go for a superior day-to-day calibration laboratory meter?

Today, your best choice may be PPM Instruments' AVM-2000. Designers can use this nullmeter/ nanovoltmeter as a standalone analog voltmeter or in conjunction with Kelvin-Varley dividers and other calibration lab equipment where high-sensitivity radiometric processes are used.

Older nullmeters have become impossible to maintain, forcing calibration lab engineers and techs to use newer digital meters. While digital meters are good, they're far more difficult to use. Also, they can't produce the precision that can be achieved with a superior analog meter. Many calibration professionals prefer analog null techniques to digital.

But finding a meter to do the job has become a challenge. The AVM-2000 solves the problem by allowing calibration engineers to use the tried and proven nullmeter and ratio standards that provide orders of magnitude greater accuracies compared to what's achievable with even the best digital meter.

Combined with a traditional large, zero-center meter, the AVM-2000's extreme sensitivity and wide range of selectable filters let operators achieve critical null indications where comparisons in the range of one part in 108 to 109 or greater are readily achievable. The AVM-2000 is just about the only instrument of its type currently available that can do this.

And the really good news is that the functionality and operability of this instrument ensure that it can be used with a wide range of existing calibration procedures "as currently written." This protects your investment by eliminating the rewrite and redesign of many infrequently used but critical procedures.

Consider the full-scale range from 100 nV to 1000 V. That 100-nV full-scale range has a 2-nV resolution that easily surpasses earlier competitive instruments by an order of magnitude. The unit also has 21 ranges with a 1-3-10 sequence. The front end uses an amplifier with an extremely high commonmode rejection of 80 dB, input impedances ranging from 1 mΩ to 1 GΩ, and gains from 103 to 108.

Precision-adjustable offset voltage and selectable low-pass filters also are available. The amplifier has an isolated single-ended output available on the back panel to connect to other devices such as related meters, chart recorders, data-acquisition systems, or digital instruments. Designers can use this input amplifier separately as a flexible instrument amplifier.

The AVM-2000 can be used as a traditional analog meter with its mirrorbacked dual-scale zero-center meter. But it also incorporates modern digital technology for mode selection and display. An LCD shows operating mode, range, output level, and any input offset level. The range selection is by rotary knob, while other functions are pushbutton selected.

Furthermore, the AVM-2000 may be ac-line powered or battery powered. Its internal rechargeable batteries operate the instrument for up to 50 hours. This mode provides total independence and isolation from common-mode signals generated through the power line and building wiring, minimizing errors induced by ground loops and other wiring-related noise.

The AVM-2000 costs $5950 fully optioned and with all accessories. Call PPM for further details.

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PPM Instruments

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