ABB SCYC51020 58052582H PLC控制备件

ABB SCYC51020 58052582H PLC控制备件

有时这被称为四相PSK，4-PSK，或4-（同QuadratureAmplitudeModulation）正交幅度调制。(虽然QPSK和4-QAM的根本概念不同，但产生的调制无线电波完全相同。)QPSK在星座图上用了四个点，围绕一个圆等距分布。通过四个相位，QPSK可以对每个符号进行两位编码，如图所示格雷编码为了最小化比特误码率(BER)——有时被误认为是BPSK的两倍。

数学分析表明，与BPSK系统相比，QPSK可用于使数据速率加倍，同时保持相同的 带宽的信号，或者保持BPSK的数据速率但是将所需带宽减半。在后一种情况下，QPSK的误码率为完全一样作为BPSK的BER当考虑或描述QPSK时，持有不同的观点是一种常见的困惑。传输的载波可以经历多次相位变化。

假设无线电通信信道是由诸如联邦通信委员会给定规定的(最大)带宽，QPSK相对于BPSK的优势变得明显:在相同的误码率下，QPSK在给定的带宽内传输的数据速率是BPSK的两倍。付出的工程代价是QPSK的****机和接收机比BPSK的更复杂。然而，随着现代电子学技术，在成本上的惩罚是非常温和的。

与BPSK一样，在接收端存在相位模糊问题差分编码实践中经常使用QPSK。

在用户程序执行阶段，PLC总是按由 上而下的顺序依次地扫描用户程序(梯形图)。在扫描每一条梯形图时， 又总是先扫描梯形图左边的由各触点构成的控制线路,并按先左后右、先上后下的顺序对由触点构成的控制线路进行逻辑运算,然后根据逻辑运算的结果，刷新该逻辑线圈在系统RAM存储区中对应位的状态;或者刷新该输出线圈在I/O映象区中对应位的状态;或者确定是否要执行该梯形图所规定的特殊功能指令。即，在用户程序执行过程中，只有输入点在I/O映象区内的状态和数据不会发生变化，而其他输出点和软设备在I/O映象区或系统RA存储区内的状态和数据都有可能发生变化，而且排在上面的梯形图，其程序执行结果会对排在下面的凡是用到这些线圈或数据的梯形图起作用;相反,排在下面的梯形图，其被刷新的逻辑线圈的状态或数据只能到下一个扫描周期才能对排在其上面的程序起作用。

ABB SCYC51020 58052582H PLC控制备件

Sometimes this is called four-phase PSK, 4-PSK, or 4- QuadratureAmplitudeModulation. (Although the fundamental concepts of QPSK and 4-QAM are different, the modulated radio waves generated are exactly the same. QPSK uses four points on the constellation diagram, which are equally distributed around a circle. Through four phases, QPSK can encode each symbol with two bits. As shown in the figure, Gray coding is to minimize the bit error rate (BER)-sometimes mistaken for twice that of BPSK.

Mathematical analysis shows that compared with BPSK system, QPSK can be used to double the data rate while maintaining the same bandwidth, or to keep the data rate of BPSK but halve the required bandwidth. In the latter case, the bit error rate of QPSK is exactly the same. As the BER of BPSK, it is a common confusion to hold different views when considering or describing QPSK. The transmitted carrier can undergo multiple phase changes.

Assuming that the radio communication channel is the (maximum) bandwidth specified by the Federal Communications Commission, the advantages of QPSK over BPSK become obvious: at the same bit error rate, the data rate transmitted by QPSK in a given bandwidth is twice that of BPSK. The engineering cost is that the QPSK * * * machine and receiver are more complicated than BPSK. However, with the development of modern electronic technology, the cost penalty is very mild.

Like BPSK, QPSK is often used in differential coding practice with phase ambiguity at the receiving end.

In the user program execution stage, PLC always scans the user program (ladder diagram) in order from top to bottom. When scanning each ladder diagram, always scan the control circuit composed of contacts on the left side of the ladder diagram first, and perform logical operation on the control circuit composed of contacts in the order of first left and then right, first up and then down, and then refresh the state of the corresponding bit of the logic coil in the system RAM storage area according to the result of logical operation; Or refresh that state of the corresponding bit of the output coil in the I/O map area; Or determine whether to execute the special function instruction specified in the ladder diagram. That is, in the process of user program execution, only the state and data of the input point in the I/O image area will not change, while the state and data of other output points and soft devices in the I/O image area or the system RA storage area may change, and the program execution result of the ladder diagram ranked above will play a role in the ladder diagram ranked below that uses these coils or data; On the contrary, in the ladder diagram arranged below, the status or data of the refreshed logic coil can only work on the program arranged above it in the next scanning cycle.

ABB SCYC51020 58052582H PLC控制备件