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Sensor Platforms and Wireless Networks
Published in Kirk A. Phillips, Dirk P. Yamamoto, LeeAnn Racz, Total Exposure Health, 2020
As is evident from the table, each method of interfacing has its own tradeoffs. In general, the thinner the gauge or longer the wire, the harder it is to pass and resolve electronic signals at the other end. A simple voltage will dissipate with distance, so current loop (typically 4–20 mA) analog transmission is used in industrial settings for longer wire runs. Higher-level protocols and encoding methods present in RS232 (a simple interface of typically two to four wires—send, receive, power, ground) or RS422/485 (similar to RS232 but uses two wires each for send and receive in order to provide for a differential voltage) can extend range significantly. Yet, higher-level protocols and encoding methods as listed in the table can send and receive data even faster, although always with a tradeoff of distance. However, it is important to keep in mind that within the context of sensors, the distances from a hardwired sensor to its platform device is typically very short (on the order of a few meters). More importantly, the interface needed by a particular sensor of interest must be the primary concern when choosing what interface to use.
Sensor Networks and Communication
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
The 4–20 mA current loop is a widely used method for transferring information from one station (the transmitter) to another station (the receiver). Therefore, this system allows for only two stations. A typical current loop system assigns a sensing range (e.g., 0 °C–100 °C) to the current range between 4 and 20 mA. A loop exists (i.e., two wires) between the transmitter and receiver. The transmitter can impress a certain current in the loop (using a controlled current source) so that the receiver can measure the current in the loop (e.g., by placing a small resistor in series with the loop and measuring the voltage drop across the resistor). After measuring the current, the receiver can then determine the present level of the sensed signal within the defined sensing range. This method uses current signaling, instead of voltage signaling, and therefore is relatively unaffected by potential differences between the transmitter and the receiver. This is similar to the benefit of differential (voltage) signaling, which also requires two wires. Another characteristic of this method is that it is not primarily digital in nature, as many other sensor communication systems are. The measured value can vary continuously in the range of 4–20 mA and therefore can easily represent an analog sensing range, rather than a set of digital signals. Also, the signal is continuously variable and available. Another characteristic of this method is that the integrity of the loop can be verified. As long as the loop is unbroken and the transmitter is in good working order, the current in the loop should never fall below 4 mA. If the current approaches 0 mA, then the receiver can determine that a fault exists—perhaps a broken cable. These systems are widely used in various process control industries (e.g., oil refining) for connecting sensors (transmitters) with control computers. Because one station is always the transmitter and one station is always the receiver, this is a unidirectional, half-duplex communication system.
Development of an Advanced AC Drive for the Heating Circulation Pumps with Dry-Rotor Using a Synchronous Reluctance Motor
Published in Electric Power Components and Systems, 2023
The ideal current response must not be too slow, but it must neither contain a high overshoot. High-current loop bandwidth can lead to instability. After PI control parameters were calculated, they were experimentally tuned for this study. The dq-axis current response of the current loop bandwidth at 1500 rpm and different load conditions are shown in Figure 23. Motor phase currents at full load shown in Figure 24.