Selection of low-cost analysis of the input module plc

PLC because of its high reliability , simple programming , versatility , small size, compact structure, convenient installation and maintenance , etc. , and in the industrial control has been widely used . PLC modules are generally divided into the following categories : switch input modules , digital output modules , analog input module , analog output modules. Industrial  plc digital input output module control, especially in the field of process control and control need to collect more than analog , input module plc thus PLC analog input and output modules require more, and analog input and output modules are more expensive, increase the analog input and output modules increases the cost and reduces the cost of the entire system , input module plc limit the application of PLC. This paper presents a communication -based analog input and output modules extension method seeks to solve this problem based  Programmable Input Module on analog communication input, output module extension methods
PLC analog input module 12 extend all the way to where the analog input , for example, in the form of an analog signal standard 0 ~ 5V input voltage signal feeding side, the application 12 A / D conversion chip MAX187 analog- digital conversion. MAX187 is a 12-bit serial A / D, has a high conversion rate , the sampling frequency is 75kHz, suitable for high precision here all the way 12-bit analog output , for example, the design will be  plc intelligent controller using 12 D / A converter chip MAX531 to achieve the number of touch conversion. We MAX531 op amp output termination , the analog output is adjusted to 0 ~ 5V, the output part of the hardware circuit shown in Figure 3 . Here , MAX531 is a 12-bit serial D / A, has a higher conversion rate...