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Control valve with pneumatic diaphragm actuator and "smart" 4–20 mA positioner which will also feed back the actual valve position and status over the current loop. The 4–20 mA convention was born in the 1950s out of the earlier highly successful 3–15 psi pneumatic control signal standard, when electronics became cheap and reliable enough ...
Older teleprinters used a 60 mA current loop. Later machines, such as the Teletype Model 33, operated on a lower 20 mA current level and most early minicomputers featured a 20 mA current loop interface, with an RS-232 port generally available as a more expensive option. The original IBM PC serial port card had provisions for a 20 mA current ...
In the 1950s, when high gain electronic amplifiers became cheap and reliable, electronic PID controllers became popular, and the pneumatic standard was emulated by 10-50 mA and 4–20 mA current loop signals (the latter became the industry standard). Pneumatic field actuators are still widely used because of the advantages of pneumatic energy ...
This page was last edited on 13 March 2007, at 22:35 (UTC).; Text is available under the Creative Commons Attribution-ShareAlike 4.0 License; additional terms may ...
The sensor circuit is supplied with constant current. A distinguishing feature of the IEPE principle is that the power supply and the sensor signal are transmitted via one shielded wire. Most IEPE sensors work at a constant current between 2 and 20 mA. A common value is 4 mA. The higher the constant current the longer the possible cable length.
Closed-loop regulator circuits using the TL431 are always designed to operate in high transconductance mode, with I CA no less than 1 mA (point D on the current-voltage curve). [8] [7] [2] For better control loop stability, optimal I CA should be set at around 5 mA, although this may compromise overall efficiency. [30] [7]
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The VT100 has various third party and first party boards designed to enhance the capabilities of the device. Most notable of these from DEC themselves are the VT1XX-AB (Advanced Video Option) and the VT1XX-AA (20 mA Current Loop Option). The cards' capabilities and existence are described in Chapter 4 of the VT100 User Guide. [4]