The Advantages Of Two-wire Transmitter

- Aug 07, 2014 -

Two-wire system refers to the field transmitter and control room instrument contact only two wires, the two lines are both power lines, but also the signal line.

advantage:

1, less susceptible to parasitic thermocouple and voltage drop along the wire resistance and temperature drift effects can be used very cheap and more fine wire; can save a lot of cable and installation costs;

2, the current source output resistance is large enough, the magnetic field coupling induced voltage within the wire loop, will not have a significant impact, because the interference source caused by the current is very small, the general use of twisted pair can reduce interference; And four-wire system must be shielded wire, shielded cable shield to properly ground.

3, the capacitive interference will lead to receiver resistance related to the error, for 4 ~ 20mA two-wire loop, the receiver resistance is usually 250Ω (sampling Uout = 1 ~ 5V) this resistance is small enough to produce significant error, Allow the length of the wire to be longer and longer than the voltage telemetry system;

4, each single display device or recording device can be different in the length of the wire between the different channels for the exchange, not because of the length of the line caused by differences in precision, to achieve decentralized acquisition, decentralized collection of the benefits is: Collection, centralized control.

5, 4mA will be used for zero level, so that open and short circuit or damage to determine the sensor (0mA state) is very convenient.

6, in the two-line output is very easy to add one or two lightning protection devices, is conducive to safe lightning protection.


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