Incorporating advanced instrumentation capabilities into a PXI digital multimeter instrument

The use of card modular instrumentation for ATE systems offers test engineers many benefits - including lower acquisition costs, a more compact system footprint, and higher performance when compared to “box based” ATE architecture. In particular, upgrading to the PXI architecture can decrease both the physical and budgetary footprints, while still meeting the overall test requirements. However, for T&M instrument suppliers, incorporating the features and capabilities associated with advanced instrumentation into the PXI form-factor can present several design challenges, particularly in the areas of volume / real estate, noise, power consumption, and measurement stability. Additionally, these demanding requirements can be further challenged when the instrument is required to operate beyond the “normal” temperature range associated with commercial instrumentation. This paper discusses the requirements and techniques used to develop a PXI-based, high performance DMM. A review of the required performance parameters is presented along with an analysis of the alternative design methods employed in order to achieve the necessary performance capabilities without compromising the overall capabilities of the hardware. Areas covered in this paper include a discussion of design techniques which includes the use of multi-function circuitry to reduce overall volume requirements, the conversion of purely analog circuitry into a mixed signal format to reduce volume and power requirements, minimizing power supply noise when replacing a mains-based power supply with isolated and non-isolated DC/DC circuitry and the requirement to operate over an extended temperature range. Additionally, a review of the overall mechanical design with attention to the need to accommodate the noise and airflow considerations associated with the PXI architecture is discussed.