“Today’s power management and industrial automation applications often need to send the measurement data of multiple sensors to a local embedded processor for real-time processing, and these embedded processors are optimized for the needs of specific applications.
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Today’s power management and industrial automation applications often need to send the measurement data of multiple sensors to a local embedded processor for real-time processing, and these embedded processors are optimized for the needs of specific applications.
As discussed in this article, the evolution of advanced mixed-signal soc helps to advance the power industry's transition to solid-state metering, while at the same time reducing costs and improving the ability to prevent tampering of readings through multi-phase and multi-channel processing technology. At present, these same basic mixed-signal soc architectures are still providing more effective solutions for lower cost and higher performance energy management, process control and industrial automation applications.
Early solid-state meter designs used multiple ICs to complete the required combination of functions. For example, a microcontroller is responsible for management and control tasks, while multiple a/d converters handle the metering function. Followed by further integration, large meter manufacturers independently developed proprietary asic to handle a/d conversion. However, the continuous evolution of new metering requirements and the pressure of competition have exposed the shortcomings and inflexibility of relying on the combination of fixed-function asic and general-purpose microcontrollers.
With the advent of the highly integrated mixed-signal soc design, a great leap forward has been made in the design of electric meters. The manufacturers of electric meters have obtained single-chip programmable solutions for high-performance, low-cost metering applications, while still providing product differentiation. Ample opportunity.
In addition to the inherent benefits of single-chip SOC integration, a key factor for success is the design of mixed-signal a/d conversion and multi-channel integrated functions. For example, the patented technology single converter technology (single converter technology) in Teridian's 71m651x architecture uses a 21-bit second-order delta-sigma a/d converter, which can handle up to 7 analog inputs and one Programming calculation engine (ce). This 32-bit ce receives and processes all sensor data from the 21-bit a/d converter, and its operation is independent of the on-chip 8-bit microcontroller core responsible for higher-level system management and external interface tasks. This division of functions allows the mixed-signal measurement subsystem to provide high speed, high reliability, and excellent dynamic range without the burden of external interruption or unnecessary processing overhead (see Figure 1).
The experience of the industry has shown that, compared with the architecture that allocates an a/d converter for each channel, the multiplexed system generally provides the lowest cost. However, the multiplexed system uses a switch circuit to scan many input channels, sampling each channel in turn so that a single a/d converter can process the relevant data. Multiplexing provides system designers with uniform gain and offset uniformity, and reduces crosstalk between channels. Therefore, it is a flexible and low-cost solution.
A multiplexed method is particularly suitable for applications that have multiple independent input signals but similar in nature, such as power measurement and many industrial automation applications, including process control sensor measurement and motor control. A key requirement is to save the phase information between the various channels, so that the ce in a multiplexed system can complete “synchronous” measurements on different channels. In addition, compared to the architecture where a separate a/d converter is allocated for each channel, the single converter technology provides lower crosstalk between channels, which is a key advantage in power measurement applications.
The inherent flexibility of the mixed-signal, multi-channel SOC architecture can be fully used to implement various advanced metering functions, from basic residential power metering with 1 phase/2 input to high-end commercial power meters with 3 phase/7 input. It can be programmed to compensate for internal and/or external temperature fluctuations and supports active power, reactive power, rms and other measurement functions, involving almost any combination of various sensor inputs, including resistance splitters, current transformers or rogowski coils.
Figure 1: Teridian’s 71m651x architecture is a typical multiplexing system
This flexibility allows meter manufacturers and power supply companies to further reduce costs, allowing smart metering engines to take full advantage of lower-cost sensor technology. For example, in multi-phase metering, current transformers have been commonly used in neutral wire current measurement to detect power theft, and rogowski coils can be used as a preferred solution because it does not use a metal core, which is very effective for magnetic power theft. The resistance is relatively strong, and the cost is about 20% cheaper than the shielded current transformer. The disadvantage of the rogowski coil is that its differential output must be electronically integrated to provide the required current reading, which in the past required expensive additional external circuitry.
Because these functions can now be processed and implemented internally by a programmable ce, the industry is experiencing a period of dramatic cost reduction. The method is to use rogowski coils to realize the anti-theft function. This is a major advantage for power supply companies operating in developing countries. For example, in China, India, Russia, Eastern Europe, and South America, the rapid growth in power consumption and the risk of power theft must be addressed together.
The inherent flexibility of the programmable, multi-channel mixed-signal soc architecture also makes it an ideal architecture for a variety of other applications. For example, the establishment of an automatic feedback control loop can be easily realized by connecting the input from one or more measuring power, pressure, position, vibration, flow, temperature or humidity sensors and connecting its output to a process controller. Programming logic controller (plc), motion controller or other common control systems in industrial automation systems.
It is also possible to compensate for the special fluctuations of the sensor input by programming the internal calculation engine of the soc, so that the system can be optimized for a specific measurement. By connecting the device to a load cell, it can be used as an equalizer that not only considers commercial and industrial cost issues, but also meets the accuracy requirements. Another important application is to use the device as an “Electronic junction unit”, which is achieved by programming to determine its switching threshold and delay properties and monitoring power line transient interference. The device can be used in industrial power line circuit breakers to protect industrial manufacturing and packaging equipment.
All in all, the use of SOC-based intelligent mixed-signal, multi-channel programmable devices has stimulated the functions and characteristics of metering applications to a new level, and the cost has also been further reduced. At present, the same basic chip-level architecture is ready to create new opportunities for improving industrial automation and control.
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