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This paper traces the development of small field data acquisition and analysis systems. The impact of some significant recent advances in microelectronics on the design of field test systems is detailed. Techniques for the exploitation of newly developed microelectronic devices to design field test systems based on the concepts of distributed computing and modular hardware and software organization are discussed. The paper concludes with a description of a recently developed test system which embodies the newly available capabilities.

An important design objective for an automotive air-conditioning system is ensuring sufficient oil return to the compressor. Maintaining proper lubrication of the compressor extends compressor life and thus minimizes warranty and consumer replacement costs. An automotive air-conditioning test stand capable of monitoring transient system parameters was utilized. Real-time oil concentration data were obtained using an optical, oil-concentration sensor installed in the liquid line. The mass flow rate of the refrigerant-oil mixture and the evaporator superheat were varied with an electronic expansion valve. Steady-state oil concentration data are presented for both saturated and superheated evaporator exit conditions. Experimental oil concentration data taken during system startup and quasi-steady compressor-clutch-cycling conditions are also presented. Steady-state results show that oil return rate is maximized by maintaining a two-phase condition at the evaporator exit.