Actually, you can use any range you choose! But if you do, you will have to design and manufacture both the transmitter and receiving controller to match.

The 4-20 ma range is a "standard" adopted by tradition and also ANSI 50.1, and most process instruments and controllers use it. It was developed during a time when teletypewriters used a 20 ma current loop for communications, so parts for that type of circuit were readily available. There once was a 10-50 ma current loop, but it has pretty much faded out.

It does have several advantages:

• The 4 ma "bottom of span" signal allows the receiver to detect a broken wire or failed instrument.
• Since the loop current never falls to zero, the instrument can be loop powered, allowing for two-wire devices.
• 20 ma is low enough to be made intrinsically safe, making it easier to apply in hazardous locations.
• The constant-current feature of a current loop cancels out voltage drop errors due to long wiring runs (of course this would also be true if you selected different current values for zero and span).
• The 4-20 ma signal dropped across a 250 or 500 ohm resistor creates very convenient 1-5V and 2-10V voltage ranges, respectively, also fairly standard in the industry.

So, while technically a manufacturer could use 7-17.3 ma or 6.2-21.1V as their range, who would buy their pressure transmitter? No one! That's both the beauty and trap of a "standard". There is a huge investment out there in process controls that use 4-20 ma. That's the real reason, Im afraid. You will not change that until you find a different range that has some huge benefit over the current (pun intended) standard.

A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information.[1] Where at least one process in one device is able to send/receive data to/from at least one process residing in a remote device, then the two devices are said to be in a network.

Networks may be classified according to a wide variety of characteristics such as the medium used to transport the data, communications protocol used, scale, topology, and organizational scope.

Communications protocols define the rules and data formats for exchanging information in a computer network, and provide the basis for network programming. Well-known communications protocols are Ethernet, a hardware and Link Layer standard that is ubiquitous in local area networks, and the Internet Protocol Suite, which defines a set of protocols for internetworking, i.e. for data communication between multiple networks, as well as host-to-host data transfer, and application-specific data transmission formats.

Computer networking is sometimes considered a sub-discipline of electrical engineering, telecommunications, computer science, information technology or computer engineering, since it relies upon the theoretical and practical application of these disciplines.

Before the advent of computer networks that were based upon some type of telecommunications system, communication between calculation machines and early computers was performed by human users by carrying instructions between them. Many of the social behaviors seen in today's Internet were demonstrably present in the 19th century and arguably in even earlier networks using visual signals.

• In September 1940, George Stibitz used a Teletype machine to send instructions for a problem set from his Model at Dartmouth College to his Complex Number Calculator in New York and received results back by the same means. Linking output systems like teletypewriters to computers was an interest at the Advanced Research Projects Agency (ARPA) when, in 1962, J.C.R. Licklider was hired and developed a working group he called the "Intergalactic Network", a precursor to the ARPANET.
• Early networks of communicating computers included the military radar system Semi-Automatic Ground Environment (SAGE), started in the late 1950s
• The commercial airline reservation system semi-automatic business research environment (SABRE) which went online with two connected mainframes in 1960.[2][3]
• In 1964, researchers at Dartmouth developed the Dartmouth Time Sharing System for distributed users of large computer systems. The same year, at Massachusetts Institute of Technology, a research group supported by General Electric and Bell Labs used a computer to route and manage telephone connections.
• Throughout the 1960s Leonard Kleinrock, Paul Baran and Donald Davies independently conceptualized and developed network systems which used packets that could be used in a network between computer systems.
• 1965 Thomas Merrill and Lawrence G. Roberts created the first wide area network (WAN).
• The first widely used telephone switch that used true computer control was introduced by Western Electric in 1965.
• In 1969 the University of California at Los Angeles, the Stanford Research Institute, University of California at Santa Barbara, and the University of Utah were connected as the beginning of the ARPANET network using 50 kbit/s circuits.[4]
• Commercial services using X.25 were deployed in 1972, and later used as an underlying infrastructure for expanding TCP/IP networks.

Today, computer networks are the core of modern communication. All modern aspects of the public switched telephone network (PSTN) are computer-controlled, and telephony increasingly runs over the Internet Protocol, although not necessarily the public Internet. The scope of communication has increased significantly in the past decade, and this boom in communications would not have been possible without the progressively advancing computer network. Computer networks, and the technologies needed to connect and communicate through and between them, continue to drive computer hardware, software, and peripherals industries. This expansion is mirrored by growth in the numbers and types of users of networks from the researcher to the home user.