Basic PLC operation

Plc logic controllers can be simple and to what extent? We have a common household space heater.
Heater member sealed in a container, ease of system communications. This concept can be extended to a remote control home thermostat heater, communication distance of a few meters, usually voltage control.
Now, we are in this small, simple process control system to be expanded on the basis of which the control and configure a plant need?
Long-distance transmission line impedance, EMI and RFI voltage control scheme makes implementation very difficult, in this case, the current loop is a simple and effective solution. Kirchhoff's law by the current loop current loop at any point is equal to all other points in the current, which can offset the impact of the transmission line impedance. Because the loop impedance and bandwidth (a few hundred ohms and "100Hz), EMI and RFI spurious pickup issues are minimized. digital output plc system is useful for properly controlling such a factory production system.

PLC basic instruction Overview

FX series plc temperature control module basic logic instructions 20 or 27, stepping instruction 2, features more than 100 instructions (different series vary).
FX2N plc intelligent controller a total of 27 basic logic instructions, which contains 20 basic logic instructions some sub-series PLC Programmable Logic Controller.
Instruction fetch and output instruction (LD / LDI / LDP / LDF / OUT)
(1) LD (instruction fetch) a normally open contact and left instruction bus connection, a normally open contact each logical row starting with this directive.
(2) LDI (negated instruction) a normally closed contact and left the bus connection instruction, a normally closed contact each logical row starting with this directive.
(3) LDP (transition instruction fetch) normally open contact with the left leading edge detection instruction bus connected only at the rising edge of the specified bit device is turned on when a scan cycle (from the OFF → ON).
(4) LDF (falling instruction fetch) normally closed contacts of falling edge detection instruction and left the bus connection.
(5) OUT (output command) coil for driving instruction, also known as output instruction.

Analog output module expansion

Here take a 12 bit analog output as an example, the design will use 12 bit D/A conversion chip MAX531 to realize the number of conversion. We then output the operational amplifier at MAX531, micro smart plc ,adjust the analog output to 0 ~ 5V, and output the hardware circuit of the output part as shown in Figure 3. Here, MAX531 is the 12 serial D/A, with a high conversion speed, MAX531 has internal reference voltage, both 10# pin (REFOUT) is 2.048V, so the full range of D/A conversion is 2.048V. And the output signal is a standard 0 ~ 5V, plc input output modules ,therefore, to a level of operational amplifier to max531 output 0 ~ 2.048v signals into 0 ~ 5V signal.

Analog sampling values transfer

MAX187 has an internal reference voltage, both 4 # pin (REF) is 4.096V, therefore, compact plc ,A / D conversion of the full range of 4.096V. The input signal is 0 ~ 5V, therefore, to add an op amp to 0 ~ 5V 0 ~ 4.096V after converted into MAX187. AT89C52 the P1.3 and chip select (CS) MAX187 connected, AT89C52 the P1.4 terminal and serial clock signal (SCLK) MAX187 is connected to the serial data output of AT89C52 the P1.5 and MAX187 (DOUT) connected. Value stored in the microcontroller memory analog sampling, plc analog input module and then by the microcontroller serial port to send to the PLC. A / D conversion of the C51 program is as follows,

#include
#include
sbit IC4_S = P1 ^ 4;
/ * AD input port settings * / sbit IC4_D = P1 ^ 5;
sbit IC4_C = P1 ^ 3;
void input (void)
{Unsigned char idata i;
unsigned int idata result = 0x0000;
IC4_C = 0;
/ * CS terminal is low * / for (i = 0; i <12; i ++)
{Result = result << 1;
  IC4_S = 0; / * clock terminal generates a clock pulse * /
IC4_S = 1;
if (IC4_D) result ++;
  / * Read from the serial data output of the A / D conversion data * /}
  IC4_C = 1; / * CS side is high * / pdat [1] = result;}

Analog input module expansion

Here take a 12 bit analog input as an example, analog signal to 0 ~ 5V standard voltage form into the signal input, plc digital input application 12 bit MAX187 conversion chip A/D realize analog conversion.

MAX187 is the 12 serial A/D, with a high conversion speed, the sampling frequency is 75kHz, input module plc and it is suitable for the process control of higher precision.

Taking into account the high frequency interference in the real industrial scene, the low-pass filter is used before the sampling signal MAX187.

PLC analog output module with low cost expansion

Programmable controller (hereinafter referred to as PLC) due to the high reliability, simple programming, strong versatility, small size, compact structure, installation, plc analog output module maintenance is convenient wait for a characteristic, and in industrial control has been widely used. General PLC module for the following categories, switch quantity input module, switch module output, analog input module and analog output module.

In the industrial control especially process control in the field of analog acquisition and control needs to be more, more and need of PLC Analog input and output module, and analog input and output module is more expensive and increase the analog input and output module increases the cost and reduce the price of the entire system, limit the application of PLC. This paper presents a method of extended analog input output module,  high-speed counter modules communication based on trying to solve this problem.

The role of the PLC input and output module

PLC input module is used for receiving, the various parameters of production process. (start stop input) output module plc  ,input module plc

The PLC output module is used to send can be obtained after computing the controller programming information, programmable logic controller manufacturer  and implementing agencies through the outside to complete all kinds of industrial field control. (the output)

1, have good anti disturbance ability.
2, can meet the requirements of all kinds of industry scene signal