11.1 Cable Transmission of Analog Voltage and Current Signals 10.000 ft of cable 是t 1.5- 1.0 10 1001,000 10,000100,000 Frequency, w Hz R=100,000ohms -100° -200° (d) -300° |会wl叶 1.0 0.8 =100 ohms 0.6 =300 ohms 7000 ft of cable 0.4 voltage source 0.2 =1,000ohms internal resistance 0 R=100,000ohms 10 le] 100 1,000 10,000 Frequency,Hz Figure 11.1d e:some typical simulation results. /18 11.1 Cable Transmission of Analog Voltage and Current Signals Current loop:a hard-wired (cable)data-transmission technique widely utilized in the process industries,usually a 4-to 20-mA range. Transmitters are available which convert millivolt,thermocouple,RTD frequency,slidewire potentiometer,or bridge-circuit inputs into a proportional output current.Fig.11.2 shows the. Ac line power Up to 10,000 ft required at this end only 80-Vsystem power supply A 4 to 20 mA 4 to 20 mA Line Digital current resistance ammeter transmitter Thermo couple Figure 11.2 Remote sensor site The Two-wire Version Central control room Current Loop of 4 to 20mA The transmitter is a true current source,which makes the system relative immune to induced noise voltages and line resistance changes (within the 3550 limit)11.1 Cable Transmission of Analog Voltage and Current Signals Figure 11.1d & e: some typical simulation results. 5/18 11.1 Cable Transmission of Analog Voltage and Current Signals z Current loop: a hard-wired (cable) data-transmission technique widely utilized in the process industries, usually a 4-to 20-mA range. z Transmitters are available which convert millivolt, thermocouple, RTD, frequency, slidewire potentiometer, or bridge-circuit inputs into a proportional output current. Fig.11.2 shows the. Figure 11.2 The Two-wire Version Current Loop of 4 to 20mA z The transmitter is a true current source, which makes the system relative immune to induced noise voltages and line resistance changes (within the 3550 Ω limit). 6/18