當DI采用24V DC的回路電壓時，DI模塊的門限電壓達到18V DC或者17V DC的時候，DI卡件就認為有信號，認為現場的接點閉合了。判斷1信號的檢測電壓一般為16.8V DC--28.8V DC，低于16.8V DC才被認為是0，部分產品品牌的1信號判斷電壓其至只有15V DC。但是實際上有可能現場的觸點根本就沒有團合，線路上的感應電壓就能達到十幾V DC，這就是我們通常說的干擾造成的假信號。觸點并沒有閉合， 但是有較高的感應電壓，當達到DI卡件門限電壓時就認為有1信號。
When the circuit voltage of the di module is 24 V DC and the threshold voltage of the di module is 18 V DC or 17 V DC, the di card considers that there is a signal and the contact on the site is closed. The detection voltage of judgment 1 signal is generally 16.8v DC -- 28.8v DC, which is considered as 0 only when it is lower than 16.8v DC. The judgment voltage of 1 signal of some product brands is only 15V DC. But in fact, it is possible that the contacts on the site are not agglomerated at all, and the induced voltage on the line can reach more than ten V DC, 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 it reaches the threshold voltage of the di card, it is considered that there is a 1 signal.
而采用48V DC回路電壓的DI卡件，其1信號的門限電壓為36V DC-- 52.8V DC，有的廠家會稍微低一點，但也不會太低?，F場線路感應電壓達到30V DC以上的情況極為少見，這就大大減少了干擾造成的假信號的出現。因此電力行業采用48V DC作為DI卡件的回路電壓，而不是24V DC、36V DC，這是根據現場實際及應用經驗總結出來的結果。那為什么不選60V DC或者110V DC呢？選擇一個合理的門檻，能夠解決主要問題就是合適的解決方案，所以DI卡件的查詢電壓選到48V DC較為合適。
For the di card with 48V DC loop voltage, the threshold voltage of 1 signal is 36V dc-52.8v DC. Some manufacturers will lower it a little, but not too low. It is very rare that the induced voltage of field line reaches above 30V DC, which greatly reduces the false signal caused by interference. Therefore, the power industry uses 48V DC as the loop voltage of Di card, rather than 24 V DC and 36 V DC, which is the result summarized according to the field practice and application experience. Then why not choose 60V DC or 110V DC? Choosing a reasonable threshold can solve the main problem is the appropriate solution, so the inquiry voltage of Di card is 48V DC.
24V DC的DI信號回路還存在信號衰減的問題?，F在流行集中控室的概念，上萬根電纜都接入集中控室。 互相干擾很嚴重， 電纜敷設距離無形之中變長了，電纜越長越容易衰減，因為線阻會加大很多。理論上24V DC的線路可以支撐500m的距離，但是實際上現場問題都比較復雜，很多時候電纜敷設三四百米的時候電壓就已經衰減的明顯了，再加上如果電纜本身指標不夠，那衰減會更嚴重。 結果是，本來信號閉合了，能送一個足夠高的電壓回來；結果，因為衰減，接點閉合了，但是電壓不夠高，DI認為是0信號。適當的提升DI的查詢電壓，可以解決長線路時的信號衰減問題。這也是經過了多年的總結和實驗，發現48V DC是很合適的。線路敷設1km,還可以保證能檢測到信號。
The problem of signal attenuation still exists in the di signal circuit of 24 V DC. Now the concept of centralized control room is popular, and tens of thousands of cables are connected to the centralized control room. Mutual interference is very serious. The laying distance of the cable is virtually longer. The longer the cable is, the easier it is to attenuate, because the line resistance will increase a lot. In theory, a 24 V DC line can support a distance of 500 meters, but in fact, the field problems are quite complex. Many times, when the cable is laid for 300 meters or 400 meters, the voltage has been attenuated obviously. In addition, if the index of the cable itself is not enough, the attenuation will be more serious. The result is that the original signal is closed, and a high enough voltage can be sent back; as a result, because of attenuation, the contact is closed, but the voltage is not high enough, and di thinks it is a 0 signal. Properly increasing the inquiry voltage of DI can solve the problem of signal attenuation in long line. After many years of summary and experiments, it is found that 48V DC is very suitable. When the line is laid for 1km, the signal can be detected.
To sum up, the DCS control system Di card chooses 48V DC as the loop voltage, which is better than 24V DC. At the same time, it needs the equipment related to Di to support 48V DC. I hope the above content is helpful to you. If you want to know more, please click our website: Zhejiang University central control power http://www.eboudy.com