There are many ways to measure the power consumption of an electronic message centre (EMC). One could add up the power supplies and heaters; or calculate consumption for each light-emitting diode (LED) and set the duty cycle at 65 per cent; or calculate an average that is much less than the sign’s maximum power level.
测量电子信息中心（EMC）的电源功耗有很多种方法。有能够计算电源供给和加热器的合计功耗；或者计算每个发光二极管（LED）的功耗并将其设置为65%的负载率；或者计算出比整个标识的最大功率级低得多的平均值。
With a typical EMC, 95 per cent of the power is used by direct current (DC) power supplies to provide stable, regulated voltage to the LED modules. The other five per cent is used by the cooling fans and standby idling current.
一个标准EMC直流电源供给的95%都用于为LED模组提供稳压电源。剩余5%电源供给用于冷却风扇和备用空载电流。
Duty cycle
负载率
The duty cycle of an LED-based EMC relates directly to the sign’s brightness and its degree of power consumption.
以LED为基础的EMC负载率，与整个标识的亮度和电源功耗级是直接相关的。
Using ambient light sensors, EMCs can be brightened or dimmed based on the client’s needs. That is not to say the electronics within the sign can accommodate ‘medium-bright’ or ‘dim’ LEDs. Rather, they can only turn the LEDs on—i.e. to full brightness—or off. Dimming effects are instead accomplished through the clever trick of changing the duty cycle of the LEDs.
在EMC中采用外部光敏元件，可以根据客户的需求调整其亮度。这并不是说标识内部的电子元件能够将LED调节成‘中等亮度’或‘昏暗’状态。相反地，它们只能将LED点亮——即最大亮度，或熄灭LED。昏暗状态则是通过改变LED负载率实现的。
This process, which involves adjusting the amount of time each LED is on or off, is commonly referred to as Class D modulation. A ‘medium-bright’ LED has a 50 per cent duty cycle, as it is only on for 50 per cent of the time. A ‘dim’ LED has a duty cycle of 10 per cent, as it is on for only 10 per cent of the time and off for the other 90 per cent. A dimmer control for LED illumination of a room works on a similar principle, changing the duty cycle to dim the lights.
调整每个LED亮或灭间隔的过程，通常称之为D类调制。‘中等亮度’的LED负载率为50%，因为它只亮整个时间段的一半。‘昏暗’的LED负载率则为10%，因为它仅亮整个时间段的10%，剩余90%的时间段都是灭的。房间内的LED照明亮度调整也是相似的原理，通过改变负载率使得灯变暗。
The relationship between duty cycle and power consumption is a 1:1 ratio. If the duty cycle is increased by 10 per cent, then the power consumption rises by 10 per cent, too.
负载率和电源功耗之间的关系是其比率为1:1。如果负载率增加了10%，那么电源功耗也会上升10%。
Minimum, average and maximum
最小、平均、最大功率级
An EMC’s minimum and maximum power levels are determined by its number of LEDs and their brightness. An EMC might consume 1,000 W in sunny daytime conditions at a 90 per cent duty cycle, for example, before being dimmed at night to a 10 per cent duty cycle and consuming only 150 W. Given the various duty cycles within a 24-hour period, the average power consumption of the sign may realistically be around 400 W.
EMC最小和最大功率级是由LED的数量和亮度来决定的。例如，在晴朗的日间条件下，LED的负载率为90%，EMC的功耗大概为1000W；而在夜间，LED负载率为10%的情况下，功耗只有150W。在24小时期间内采用多种不同负载率情况下，标识的平均电源功耗大概为400W。
A true root mean square (RMS) ‘clamp amp’ power meter can be used to measure consumption of electricity, but an EMC—with all of its various components—is not so simple to summarize. Other issues include: what kinds of messages the sign is displaying (e.g. still ../images or full-motion video); how many LEDs are lit to display these messages, in which colours; and which duty cycles are used, for how long.
一个精确的‘钳位放大器’用于电耗功率的测量，但是要测量由各种不同器件组成的EMC的电耗不是那么简单的。其他问题包括：该标识显示的是哪种信息（例如，静止图像或全动感视像）；显示这些信息需要点亮多少LED，哪种颜色的；采用多大的负载率。
With these factors in mind, one of the better approaches is to determine the absolute highest possible ‘peak’ power consumption of a given sign. This scenario would entail every LED being illuminated at a 90 per cent duty cycle. At the other end of the spectrum, shutting all of the LEDs off will yield the sign’s lowest possible power consumption.
考虑到这些因素，其中一种比较好的测量方法就是，确定标识的最高功耗值。该方案需要每个LED的负载率均为90%。另一方面，熄灭所有的LED就能得到该标识的最低可能功耗值。
The ratio between these two ends of the spectrum is usually about 10:1, e.g. with maximum power of 1,000 W and minimum power of 100 W.
这两个极端值之间的比率通常为10:1，举例来说，当最大功耗为1000W时，最小功耗为100W。
The maximum/peak power consumption is important to understand so electricians can select the right breaker for the sign, as they can ascertain the servicing requirements. The average power consumption, on the other hand, is important to understand so the client can estimate ongoing electricity costs to run the sign.
理解最大/峰值功耗对电工来说是很重要的，他们能够根据标识的服务需求为其选择适当的适配器。另一方面，功耗平均值也是非常需要了解的，因此客户可以估计连续运行此标识所需要的电费。
Permits and codes
许可和准则
Power consumption does not have any obvious impact on acquiring permits or following local sign codes, but it is indirectly related, in the sense that sign brightness is often considered a public safety issue. A sign that is too bright at night, in particular, may not be permitted for fear of distracting drivers on the road.
电源功耗对于获得许可或遵守当地标识准则来说没有任何明显的影响，但它们属于间接相关联，在这个意义上讲，标识亮度通常被视为公共安全问题。特别是晚上不允许出现太亮的标识，否则会分散司机的注意力。
Fortunately, EMC manufacturers have pioneered optimal ‘formulas’ for properly blending colours and light so as not to disturb nearby traffic patterns. At the same time, they are also optimizing visibility and legibility. Amber LEDs, for example, are the easiest to read for colour-blind passersby, while many municipalities are banning red.
幸运的是，EMC制作商已经推出了LED颜色亮度调配的最佳方案，如此就不会干扰到过往的车辆了。同时，他们也在不断优化标识的可见性和易读性。例如，琥珀色的LED对色盲路人是最易识别的，然而许多自治市却禁用红色。
Components
元器件
Most EMCs are built similarly, but not with the same quality of components. Standard components mean replacements can be sourced as needed from a local store. Odd non-proprietary plugs and cables, on the other hand, cannot easily be bought off the shelf. This is why it is better—both for the manufacturer and for the customer—to use standard plugs, cables and connectors.
大多数EMC都非常相似，但是其使用的元器件的质量却是不同的。标准的元器件意味着替代品可以从当地商店内采购。而特殊的非专属插头和电缆却很难从现有成品中购得。这就是使用标准插头、电缆和连接器对于制作商和客户都更加有利的原因。
Processing and compression
加工和压缩
Dedicated read-only memory (ROM) state machines, also known as programmable logic arrays (PLAs), offer high processing speeds in the 200 MHz range, without needing additional heat sinks and fans to ensure their reliability. One might wonder why so much ‘horsepower’ is needed for a simple EMC; the answer lies in the aforementioned Class D modulation of the LEDs.
专用的只读存储器（ROM）状态机也是以可编程逻辑阵列（PLAs）而著称，提供200MHz范围内的高速处理性能，无需额外的散热器和风扇来确保其可靠性。你或许想要知道为什么简单的EMC需要如此大的‘马力’；答案就是前面提到的LED D类调制。
If a sign has a refresh rate of 100 Hz, then it must clock out 128 bits of data for one line of LEDs from left to right, 100 times per second. This modulation rate of data transmission is expressed as 12,800 baud (Bd), representing 12,800 bits per second. Such a rate is easy to achieve, even with old chips, but there is an additional burden when using Class D modulation. To achieve a greyscale of 256 for a red, green and blue (RGB) display, the data rate goes up from 12,800 to 3,276,800 Bd.
如果标识的刷新频率为100Hz，那么它必须在一行发光二极管中，从左到右以每秒100次的速度输出128位数据。这种数据传输调制频率用12800波特（Bd）来表示，指的是每秒钟12800位。这样的频率即使是用旧的芯片也很容易实现，但是当使用D类调制时会产生额外的负荷。为了实现256灰度级的红绿蓝（RGB）显示效果，其数据频率要从12800波特上升到3276800波特。
That is about 3 MHz, which may not seem like a big deal, but the requirements do not stop there. For the sign’s colours to be dimmed at night, a minimum greyscale of 32 must be added to the 256, which brings the sign up to 100 MHz.Many older chips were limited to only 10 MHz, but there are inexpensive 1-GHz 32-bit microprocessors today that are up to the task at hand.
这大概有3MHz，它或许并不是多么大的数据，但是对速率的需求却不会停止于此。要想在夜间呈现昏暗的标识颜色，最小的32灰度级要增加为256灰度级，这样该标识的刷新频率就会达到100MHz。许多较旧的芯片频率只能达到10MHz，但是目前已经开发出便宜的1-GHz的32位微处理器，来解决手头上的业务。
That would be sufficient, of course, if an EMC only featured one line of 128 LEDs. Rather, the average EMC features 64 lines of each of three colours (i.e. RGB) of LEDs, boosting the processing speed requirements from 100 MHz to 20 GHz—a level of microprocessing technology that is not available today. This certainly poses a challenge for designing a full-colour LED EMC that can display full-motion video.
当然，如果EMC只含有一行128个LED，那就足够了。相反地，通常的EMC都含有64行三色（即RGB）LED，促进了处理速度需求从100MHz上升到20GHz——目前尚不可用的微处理技术。这就为制作全色LED的全动感视像EMC提出了一个挑战。
Yet, such signs obviously already exist in the real, despite the technology seeming to be impossible. The answer is to ‘cheat,’ using compressed video files. This process involves several data compression algorithms.
然而，这样的标识现实中已经是存在的，尽管目前的技术似乎还无法实现。这种情况下就属于‘作弊’，采用的是压缩视频文件。该过程包含几个数据压缩算法。
The first algorithm is horizontal. If an RGB pixel exhibits cyan brightness of 128 out of 256 greyscale, for example, then there is a good chance the pixel next to it is equally bright. There is no point in using valuable bandwidth by transmitting two pixels when one will do the job, set with 1-bit parity to indicate the neighbouring pixel is the same colour. Doing so achieves 50 per cent compression.
第一个算法是水平位置。例如，如果一个RGB像素展品是256灰度级的128青色亮度，那么很有可能旁边的像素也是同样的亮度。当一个像素就可以达到期望效果时，利用宝贵的带宽来传递两个像素是毫无意义的。这样做就达到了50%的压缩率。
The second algorithm is vertical and works in exactly the same way. By taking advantage of redundancy compression, it becomes possible to display an image with only 25 per cent of the original video information.
第二个算法是垂直位置，基本原理是一样的。利用冗余压缩就能够显示出只有25%原始视频信息的图像。
The third algorithm relates to time. When a single frame of video is displayed, there is a high probability the next frame is the same. Time compression is more significant than horizontal and vertical algorithms combined, as it can achieve compression somewhere in the neighbourhood of a 10:1 ratio.
第三种算法是关于时间的。当播放一帧视频时，下一帧很有可能是一样的。时间压缩比水平、垂直位置的组合算法更重要，因为它可以实现附近某个位置的压缩比例为10:1。
With all three algorithms in effect, a 1-GB video file can be compressed to just 25 MB, without destroying any of the original video information. With ‘destructive’ algorithms, the net compression of file size is even more impressive, but the displayed image is of lower quality. In some cases, however, highly destructive algorithms are cleverly designed enough that it is hard for the average passerby to notice a large-scale EMC is missing data.
三种算法都生效的情况下，一个1-GB的视频文件可以被压缩到只有25MB，并且不会破坏任何原始视频信息。在‘毁灭性’算法下，净压缩文件大小更加令人印象深刻，但是显示图像的质量却很低。然而，在某些情况下，高度毁灭性算法的巧妙设计，使得普通路人很难注意到遗漏数据的大型EMC。
In these ways, the sign industry has been able to source Video Graphics Array (VGA) or Digital Visual Interface (DVI) output from computers and use compression software to drive content effectively onto EMC screens.
通过这些方法，标识行业就能够通过源视频图形阵列（VGA）或数字可视化界面（DVI）从计算机输出，高效地使用压缩软件将内容驱动到EMC屏幕上。 |
