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浙大中控分析DCS控制系统DI卡件采用24VDC还是采用48VDC?

2021-09-06 16:42:40 来源:http://www.sdjkyqyb.com/ 53

当DI采用24VDC的回路电压时,DI模块的门限电压达到18VDC或者17VDC的时候,DI卡件就认为有信号,认为现场的接点闭合了。判断1信号的检测电压一般为16.8VDC--28.8VDC,低于16.8VDC才被认为是0,部分产品品牌的1信号判断电压其至只有15VDC。但是实际上有可能现场的触点根本就没有团合,线路上的感应电压就能达到十几VDC,这就是我们通常说的干扰造成的假信号。触点并没有闭合,但是有较高的感应电压,当达到DI卡件门限电压时就认为有1信号。
When Di adopts 24VDC loop voltage and the threshold voltage of Di module reaches 18vdc or 17vdc, di card considers that there is a signal and that the field contact is closed. The detection voltage of judgment 1 signal is generally 16.8vdc-28.8vdc, and it is considered as 0 when it is lower than 16.8vdc. The judgment voltage of 1 signal of some product brands is only 15Vdc. But in fact, it is possible that the on-site contacts are not combined at all, and the induced voltage on the line can reach more than ten VDC, which is what we usually call the false signal caused by interference. The contact is not closed, but there is a high induced voltage. When the threshold voltage of Di card is reached, it is considered that there is a 1 signal.
而采用48VDC回路电压的DI卡件,其1信号的门限电压为36VDC--52.8VDC,有的厂家会稍微低一点,但也不会太低。现场线路感应电压达到30VDC以上的情况为少见,这就大大减少了干扰造成的假信号的出现。因此电力行业采用48VDC作为DI卡件的回路电压,而不是24VDC、36VDC,这是根据现场实际及应用经验总结出来的结果。那为什么不选60VDC或者110VDC呢?选择一个合理的门槛,能够解决主要问题就是合适的解决方案,所以DI卡件的查询电压选到48VDC为合适。
For Di cards with 48VDC loop voltage, the threshold voltage of 1 signal is 36vdc-52.8vdc, which will be slightly lower by some manufacturers, but it will not be too low. It is rare that the induced voltage of the field line reaches more than 30VDC, which greatly reduces the occurrence of false signals caused by interference. Therefore, the power industry adopts 48VDC as the loop voltage of Di card instead of 24VDC and 36VDC, which is the result summarized according to the field practice and application experience. Then why not choose 60VDC or 110VDC? Choosing a reasonable threshold can solve the main problem is the appropriate solution, so the query voltage of Di card is 48VDC.
24VDC的DI信号回路还存在信号衰减的问题。现在流行集中控室的概念,上万根电缆都接入集中控室。互相干扰很严重,电缆敷设距离无形之中变长了,电缆越长越容易衰减,因为线阻会加大很多。理论上24VDC的线路可以支撑500m的距离,但是实际上现场问题都比较复杂,很多时候电缆敷设三四百米的时候电压就已经衰减的明显了,再加上如果电缆本身指标不够,那衰减会更严重。
The 24VDC Di signal circuit also has the problem of signal attenuation. Now the concept of centralized control room is popular, and tens of thousands of cables are connected to the centralized control room. The mutual interference is very serious. The cable laying distance is virtually longer. The longer the cable, the easier it is to attenuate, because the line resistance will increase a lot. Theoretically, the 24VDC line can support a distance of 500m, but in fact, the field problems are more complex. In many cases, the voltage has attenuated obviously when the cable is laid for three or four hundred meters. In addition, if the index of the cable itself is not enough, the attenuation will be more serious.
结果是,本来信号闭合了,能送一个足够高的电压回来;结果,因为衰减,接点闭合了,但是电压不够高,DI认为是0信号。适当的提升DI的查询电压,可以解决长线路时的信号衰减问题。这也是经过了多年的总结和实验,发现48VDC是很合适的。线路敷设1km,还可以保证能检测到信号。
As a result, the original signal is closed and can send a high enough voltage back; As a result, the contact is closed due to attenuation, but the voltage is not high enough, and di considers it as a 0 signal. Properly increasing the query voltage of DI can solve the problem of signal attenuation in long lines. After years of summary and experiment, it is found that 48VDC is very suitable. When the line is laid for 1km, it can also ensure that the signal can be detected.
综上所述,DCS控制系统DI卡件选择48VDC做为回路电压是有它优于24VDC的地方,同时这就需要与DI相关的设备支持48VDC。
To sum up, 48VDC is selected as the loop voltage of Di card of DCS control system, which is better than 24VDC. At the same time, it needs the equipment related to Di to support 48VDC.
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