plc
2015年7月28日星期二
Medium programmable control system
Medium plc industrial controller may provide the functionality and flexibility you need, do not have that kind of overhead systems, it is the perfect solution for medium-sized application projects. Select rack-based, modular package design standards and safety certification from the controller. Typical applications include complex machine control, batch processing and building automation.
2015年7月24日星期五
PLC current loop transmission
Application of the current control loop is started in the early 1900s teletype, the earliest use of the 0-60mA loops and later changed to 0-20mA loop, programmable logical controllers system is the first to use the 4-20mA loop.
4-20mA current loop has many advantages. Need to be carefully calculated in the traditional discrete component designs, and compared with the current integrated 4-20mAIC, circuit take up a lot of space.
Any current values measured are representative of certain information. Practical applications, 4-20mA current loop in 0mA to 24mA current range. But 0mA to 4mA and 20mA to 24mA current range for diagnostics and system calibration. Due to lower than 4mA and above 20mA are used for diagnostics, it is believed readings between 0mA and 4mA could indicate a broken wire in the system. Similarly, between 20mA and 24mA between readings can indicate a potential short circuit occurred in the system.
Plus 4-20mA communications Highway Addressable Remote Sensor, which is backward compatible with 4-20mA instrumentation. In HART system uses microprocessor-based intelligent integration of field devices enables two-way communication. The HART protocol capable of carrying additional digital information on the same line 4-20mA analog current signal for process control.
plc analog input output module functions can be divided into several functional groups. Many plc controller manufacturer vendors will integrate these functions as separate modules, each module with features vary with the specific application. Many modules have multiple functions, it can interface with a variety of sensors. However, for specific applications will design special modules or expansion modules, such as in most cases: resistance temperature detector (RTD), sensor, or thermocouple sensor. In general, all modules have the same core functions: analog input, analog output, distributed control (eg fieldbus), interface, digital input and output (I / O), CPU and power supply.
4-20mA current loop has many advantages. Need to be carefully calculated in the traditional discrete component designs, and compared with the current integrated 4-20mAIC, circuit take up a lot of space.
Any current values measured are representative of certain information. Practical applications, 4-20mA current loop in 0mA to 24mA current range. But 0mA to 4mA and 20mA to 24mA current range for diagnostics and system calibration. Due to lower than 4mA and above 20mA are used for diagnostics, it is believed readings between 0mA and 4mA could indicate a broken wire in the system. Similarly, between 20mA and 24mA between readings can indicate a potential short circuit occurred in the system.
Plus 4-20mA communications Highway Addressable Remote Sensor, which is backward compatible with 4-20mA instrumentation. In HART system uses microprocessor-based intelligent integration of field devices enables two-way communication. The HART protocol capable of carrying additional digital information on the same line 4-20mA analog current signal for process control.
plc analog input output module functions can be divided into several functional groups. Many plc controller manufacturer vendors will integrate these functions as separate modules, each module with features vary with the specific application. Many modules have multiple functions, it can interface with a variety of sensors. However, for specific applications will design special modules or expansion modules, such as in most cases: resistance temperature detector (RTD), sensor, or thermocouple sensor. In general, all modules have the same core functions: analog input, analog output, distributed control (eg fieldbus), interface, digital input and output (I / O), CPU and power supply.
2015年7月20日星期一
2015年7月3日星期五
PLC control system and electrical control system distinguish the
PLC control system compared with the electrical control system, there are many similarities, there are many different. The difference is mainly in the following areas:
1) Judging from the control method, the electrical control system control logic hardware wiring, mechanical relay contacts using series or parallel, etc. combined into a control logic connections are many and complex, bulky, power consumption, system configuration, the I would like to change or add functionality more difficult. In addition, a limited number of contacts of the relay, the electrical control system flexibility and scalability is very limited. The PLC technology uses a computer, which controls the way the program logic is stored in memory, to change the control logic simply by changing the program, which is easy to change or increase the system functionality. System wiring small, small size, low power consumption, and PLC-called "soft-relay" is essentially a state of the memory cells, so "soft relay," the number of contacts is unlimited flexibility and scalability plc controller manufacturer system good .
2) From the work point of view, in the relay control circuit, when the power is turned on, the circuit is subject to all relays are in the state, that is, the pull of the relays are energized at the same time, should not be subject to some kind of pull-in relay conditions can not pull, this way of working called parallel work. The plc ethernet module user program is executed cyclically according to a certain order, so that each soft relays are in a cyclical scan cycle turned in by the same conditionality order each relay operation depends on the program scan order, this way of working is called Serial work.
3) Judging from the speed control, relay control system relies on mechanical contact action to achieve control, low operating frequency, mechanical contacts will appear jitter. The PLC to achieve control of program instructions by controlling the semiconductor circuit, high speed, program instruction execution time in microseconds level, and will not appear contact bounce problem.
4) Judging from the timing and the counting control, electrical control system uses the operating time of the relay delay the time control, time delay relay susceptible to ambient temperature and temperature changes, the timing accuracy is not high. The PLC semiconductor integrated circuit as a timer, a clock pulse is generated by a crystal oscillator, high precision, wide time range, the user can set the timer value in the program as needed to facilitate changes, affected by the environment, and the PLC have counted functions, and electrical control systems generally do not have the counting function.
5) From the point of view of reliability and maintainability, since the electrical control system uses a large number of mechanical contact which mechanical wear, arc burns, short-lived, multi-link system, the reliability and maintainability of the more difference. The PLC large number of switching operation performed by non-contact semiconductor circuit to complete its long life, high reliability, PLC also has a self-diagnostic function, able to detect its own fault, displayed to the operator at any time, and can dynamically monitor control the implementation of the program for on-site commissioning and maintenance more convenient.
1) Judging from the control method, the electrical control system control logic hardware wiring, mechanical relay contacts using series or parallel, etc. combined into a control logic connections are many and complex, bulky, power consumption, system configuration, the I would like to change or add functionality more difficult. In addition, a limited number of contacts of the relay, the electrical control system flexibility and scalability is very limited. The PLC technology uses a computer, which controls the way the program logic is stored in memory, to change the control logic simply by changing the program, which is easy to change or increase the system functionality. System wiring small, small size, low power consumption, and PLC-called "soft-relay" is essentially a state of the memory cells, so "soft relay," the number of contacts is unlimited flexibility and scalability plc controller manufacturer system good .
2) From the work point of view, in the relay control circuit, when the power is turned on, the circuit is subject to all relays are in the state, that is, the pull of the relays are energized at the same time, should not be subject to some kind of pull-in relay conditions can not pull, this way of working called parallel work. The plc ethernet module user program is executed cyclically according to a certain order, so that each soft relays are in a cyclical scan cycle turned in by the same conditionality order each relay operation depends on the program scan order, this way of working is called Serial work.
3) Judging from the speed control, relay control system relies on mechanical contact action to achieve control, low operating frequency, mechanical contacts will appear jitter. The PLC to achieve control of program instructions by controlling the semiconductor circuit, high speed, program instruction execution time in microseconds level, and will not appear contact bounce problem.
4) Judging from the timing and the counting control, electrical control system uses the operating time of the relay delay the time control, time delay relay susceptible to ambient temperature and temperature changes, the timing accuracy is not high. The PLC semiconductor integrated circuit as a timer, a clock pulse is generated by a crystal oscillator, high precision, wide time range, the user can set the timer value in the program as needed to facilitate changes, affected by the environment, and the PLC have counted functions, and electrical control systems generally do not have the counting function.
5) From the point of view of reliability and maintainability, since the electrical control system uses a large number of mechanical contact which mechanical wear, arc burns, short-lived, multi-link system, the reliability and maintainability of the more difference. The PLC large number of switching operation performed by non-contact semiconductor circuit to complete its long life, high reliability, PLC also has a self-diagnostic function, able to detect its own fault, displayed to the operator at any time, and can dynamically monitor control the implementation of the program for on-site commissioning and maintenance more convenient.
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