Nt1310 Unit 1 Research Paper

Words: 1822
Pages: 8

One of the main advantages of 4-20 mA is that you can run 2-wires to the sensor, which saves much cost in long runs, but does have drawbacks. The biggest is the "loading". The sensor "steals" 10V type to operate its electronics. If you’re receiving end uses a 250 ohm resistor (typ), that is another 5V, so your power supply must output 15 V plus wiring drops. Not usually a problem with the typical 24 V power supply. 3-wire systems allow more margin since the signal isn't in series.

Other drawbacks to 4-20 mA are increased sensor complexity, slower response, and less accuracy, particularly if you don't control the 250 ohm sensing resistor. For example, many 5B modules use an external plug-in resistor which can be degraded by pin corrosion. Analog Devices has good explanations of current loops in their data sheets for 4-20 mA chips.

In general, voltage signals are more
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If Repeaters were not used then the signal would degrade over distance and would not have enough power at its destination.
Modbus – this is another communication protocol for serial data communications and is a system that was specifically designed for communications with PLC systems in the industrial environment and is able to allow around 240 devices to communicate with each other on one network. When a command is transmitted using Modbus it is encoded with the address that the command is intended for as well as a checking command to make sure that the data hasn’t been corrupted during transmission. A Modbus command is able to tell a device on the network to carry out a number of actions such as reading an input port controlling an output port or changing the bit stored in a