Mitsubishi PLC analog input module programming and use case analysis
(1) Analog input module
The analog input modules commonly used by the FX2N include the FX2N-2AD, FX2N-4AD, FX2N-8AD analog input modules and temperature sensor input modules. The FX-2AD is a 2-channel 12-bit A/D converter module. According to the external connection method and the plc command, the voltage input or current input can be selected, which is an input module with high precision. The range of the analog input can be changed by simple adjustment or according to the instructions of the programmable controller. The reading and writing of data such as the instantaneous value and the set value are performed by the FROM/TO command.
FX-2AD technical indicators
(2) Analog output module
The analog output modules commonly used by the FX2N include the FX2N-2DA, FX2N-4DA, and FX2N-8DA analog output modules. The FX-2DA is a 2-channel 12-bit D/A converter module that is a highly accurate output module. The range of the analog output can be changed by simple adjustment or according to the instructions of the programmable controller. The reading and writing of data such as the instantaneous value and the set value are performed by the FROM/TO command.
FX-2DA technical indicators
(1) Determine the number of the module
On the right side of the basic unit of the FX series programmable controller, up to 8 special function modules can be connected, and their numbers are sequentially programmed from 0 to 7 from the one closest to the basic unit. As shown in the figure: This configuration uses FX2N48 point basic unit, and connects FX-4AD, FX-4DA, FX-2AD 3 analog modules, their numbers are 0, 1, 2 respectively. These 3 modules do not affect the number of the 2 extensions on the right, but they affect the total number of input and output points. The three analog modules occupy a total of 24 points, so the total number of input and output points of the basic unit and the extension can only be 232 points.
(2) buffer register (BFM) allocation
The data communication between the basic unit of the FX series programmable controller and the analog modules such as FX-4AD and FX-2DA is performed by the FROM instruction and the TO instruction. The FROM is the basic unit to read data from the FX-4AD and FX-2DA. The instruction, TO is the instruction to write data from the basic unit to FX-4AD, FX-2DA. In fact, the read and write operations are performed on the buffer registers BFM of the FX-4AD and FX-2DA. This buffer register area consists of 32 16-bit registers numbered BFM#0##31.
(III) Allocation table of FX-4AD module BFM
(four) programming examples
The FX-4AD analog input module is connected to the nearest base unit FX2N-48MR, then its number is N0. If only CH1 and CH2 channels are turned on as the voltage input channel, the average number of sampling times is set to 4 Then, D0 and D1 in the programmable controller respectively receive the average digital quantities of the input quantities of the two channels, and program the ladder program.
Ladder diagram
Case: Refrigeration central air conditioning temperature control
First, the analysis of action requirements
The refrigeration system uses two compressor units. The system requires that the unit does not start when the temperature is lower than 12 °C. When the temperature is higher than 12 °C, the two units are started sequentially, and when the temperature is lowered to 12 °C, one of the units is stopped. A stop is required to start first. When the temperature drops to 7.5 °C, both units stop. When the temperature is lower than 5 °C, the system issues an ultra-low temperature alarm.
Second, the hardware design
In this control system, the temperature point detection can be done using a temperature sensor with a switching output, but some systems have many temperature detection points, or the temperature point is often adjusted according to the ambient temperature change, and many switching temperature sensors are used. , occupying more input points, installation and wiring is not convenient, the temperature signal is converted into a continuously changing analog quantity by the temperature sensor, then the control system of the refrigeration unit is an analog quantity control system. For an analog control system, with programmable controller control, control performance can be greatly improved. Here you can use the FX2N-32MR basic unit and the FX2N-4AD-PT analog input unit to easily realize the control requirements.
Central air conditioning temperature control I / O allocation table
Third, software design
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