TABLE OF CONTENTS Learning Objectives. On completion of this chapter the reader will have a knowledge on:
Common Instrument Interfaces
4 20 MA Current Loop
60 MA Current Loop
RS 232, RS222, and RS485
Concepts of GPIB, Advantages of GPIB
VISA Programming, Attributes of VISA, Advantages of VISA
Instrument interfaces play pivot role in all kind of digital equipments. It is the job of these equipments to make a symbiotic liaison between the external environment data and the process data. The information that received by these instrument aids in conditioning so the data available could be relied more efficiently Some of the main considerations for PC based instrument interfaces depends on the type of connector (pinouts) on the instrument, type of cables needed, electrical properties involved, signal levels, grounding, cable length, communication protocols used, and the software drivers available. This section describes the operation and characteristic features of serial communication devices such as 4 20, 60 mA current loops along with the RS232C standard. The IEEE standard GPIB is also detailed in later part of this section. VISA, which is a high level API capable of controlling VXI, GPIB, or Serial instruments. It also makes the appropriate driver calls depending on the type of instrument interfaced with PC.
Current-mode data transmission is the preferred technique in many environments, particularly in industrial applications. This section describes the design of a 4 20 mA current loop using the MAX1459 sensor signal conditioner.
Current-mode...
