An RS-232 to IEEE-488 protocol converter for instrumentation control

Abstract

Instrumentation is defined as "the art and sc1em:e of measurement and control". Instrumentation can be used to refer to the field in which the instrument scientists and engineers work, or it can refer to the available methods of measurement and control and the instruments which facilitate this. Instruments are devices which are used to measure attributes of physical systems. The variable measured can include practically any measurable variable related to the physical sciences. These variables commonly include: pressure, flow, temperature, level, density, viscosity, radiation, current, voltage, inductance, capacitance, frequency, chemical composition, chemical properties and various other physical properties. Instruments can often be viewed in terms of a simple input-output device. For example, if we "input" some temperature into a thermocouple, it "outputs" some sort of signal (this can later be translated into data.) In the case of this thermocouple, it will "output" a signal in millivolts. Instruments communicate with some sort of signal, often adhering to a standard protocol. A protocol is a set of agreed operational procedures to enable data to be transferred between systems. This communication signal may be defined by standards associations such as the Institute of Electrical and Electronic Engineers (IEEE), or it may be a proprietary standard. The IEEE-488 interface protocol is a good example. It began life as an HPIB (HewlettPackard Interface protocol) so as a proprietary standard and in 1975 was defined by the IEEE association as IEEE-488 standard. An interface is the hardware and associated software needed to enable one device to communicate with another. It is a shared boundary for example it may be a piece of hardware (generally plugs and wire) used between two pieces of equipment. These devices are generally connected to some sort of control system by using an interface which responds to the instrument's measurement.