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Showing results for tags 'ALLEN BRADLEY'.
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ALLEN BRADLEY Allen Bradley PLC Subroutines
leizuofa posted A plc and hmi english article in PLC programming learning
JSR, SBR, and RET instructions are used to direct the controller to execute a separate subroutine file within the ladder program and return to the instruction following the JSR instruction. Allen Bradley PLC Subroutines The SBR instruction must be the first instruction on the first rung in the program file that contains the subroutine. Use a subroutine to store recurring sections of program logic that must be executed from several points within your application program A subroutine saves memory because you program it only once. Update critical I/O within subroutines using immediate input and/or output instructions (IIM, IOM), especially if your application calls for nested or relatively long subroutines Otherwise, the controller does not update I/O until it reaches the end of the main program (after executing all subroutines) Outputs controlled within a subroutine remain in their last state until the subroutine is executed again. When the JSR instruction is executed, the controller jumps to the subroutine instruction (SBR) at the beginning of the target subroutine file and resumes execution at that point. You cannot jump into any part of a subroutine except the first instruction in that file. The target subroutine is identified by the file number that you entered in the JSR instruction. The SBR instruction serves as a label or identifier for a program file as a regular subroutine file. The instruction must be programmed as the first instruction of the first rung of a subroutine. The RET instruction marks the end of subroutine execution or the end of the subroutine file. The rung containing the RET instruction may be conditional if this rung precedes the end of the subroutine. In this way, the controller omits the balance of a subroutine only if its rung condition is true. -
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ALLEN BRADLEY AENT Module in Rockwell PLC – Remote IO Adapter
xiangjinjiao posted A plc and hmi english article in PLC programming learning
In industrial automation, there are three types of IOs – Local, Remote, and Distributed. It defines whether the IOs are in a local electrical panel or a remote network panel. It is decided based on the location of field instruments from the panel. Different types of automation manufacturers have corresponding modules in their make, for working with remote IOs. One such famous brand is Rockwell. In Rockwell PLC, the most used network adapter for IO communication is the AENT module. This module can be connected at a location other than the local PLC and is connected to it through Ethernet communication. The corresponding IOs are interfaced with the AENT module. In this post, we will see the concept of the AENT module in Rockwell PLC. AENT Module in Rockwell PLC As discussed earlier, an AENT module is a type of remote IO adapter. The module does not have any CPU in it; it is just a network interface used to communicate field IO’s with the main PLC through Ethernet IP protocol. That means no logic can be written in the module as it will only read and write data of IO modules configured with it to the main PLC CPU. You can connect a maximum of 64 IO modules with an AENT module, for interfacing. It is generally identified by the 1734-AENT series. Not only IO data, but you also get each and every diagnostic of the IO’s through this module. This makes troubleshooting much easier. The module communication takes place through Ethernet IP protocol, and it has RJ45 ports in it for this. It can communicate in either half-duplex or full-duplex mode. The standard power supply for this module is 24V DC. IP Address Configuration There are three general methods through which IP address is set in the module – By setting the switches on it (it has three numbers which denote the last three digits of the IP address) Using BootP/DHCP software available from Rockwell Using IP configuration software available from Rockwell. Once you set the IP address, you can then use the module for your communication with the main PLC. In the PLC software (Studio 5000), the IO modules must be configured in this AENT module. These modules then communicate their IO status to the main CPU through the AENT module. This module can be used in star topology or tree topology. LED Diagnostics The module has the following LED in it for diagnostics – module status, network status, network activity, POINT Bus status, System power, and Field power. You can get a detailed description of each of the LEDs by reading its catalog. This helps in the detailed troubleshooting of the module. One thing to be noted is that the power supply connected to the module can drive only a maximum of 10 IO modules; so, a power supply module is required after every 10 modules connected in the AENT. Chassis Size One of the most important terms related to this module is chassis size. Chassis size means the number of modules connected with AENT. For example, if 19 IO modules are used, then you must set the chassis size in the AENT configuration to 20. The adapter stores this chassis size setting in non-volatile storage. When the adapter’s non-volatile chassis size does not match the actual number of modules present on its backplane, the adapter will not make any I/O connections. Also, once you are online, you are required to set this size online apart from offline configuration. After this step only you can use the module for communicating IO values with the main CPU. AENT module is a higher range of adapter and so, is used only with three types of PLCs – Control Logix, Compact Logix, and Flex Logix. In this way, we saw the concept of the AENT module used in Rockwell PLC. -
ALLEN BRADLEY One-Shot Rising and Falling Edge Instructions in Rockwell PLC
xiangjinjiao posted A plc and hmi english article in PLC programming learning
In any PLC, it is important to understand how its instructions have been written. The basic understanding is the same in all the languages; the difference is how it is illustrated. If we are clear with the instructions, then we can work with any type of PLC software. One of the most widely used brands in automation is Rockwell. There are many different types of instructions in it for programming. In that, there are two instructions that are mostly required in any PLC logic. They are – One-shot rising edge and one-shot falling edge. In this post, we will see the working of these two instructions. One Shot Rising Edge (OSR) In PLC programming, you must have heard two common types of objects – positive peak and negative peak. A positive peak means that it takes a trigger only when the variable changes from 0 to 1. The output of this object comes in a trigger pulse type. Now, instead of the variable state, there is one additional instruction in PLCs where you get the trigger output of the whole rung. This means, that when the whole rung or condition changes its state from 0 to 1, then the output will come in a pulse-type trigger condition. This is rising trigger instruction in PLC. In Rockwell PLC, it is called one-shot rising edge instruction. Refer to the below image for understanding. As you can see, the instruction takes two inputs in its condition. Both are written as NO logic; meaning when both are on, then only the condition is true. Now, when this happens, the instruction has two variables in it – storage bit and output bit. The function of the storage bit is to store the condition state. When both the bits turn on and the condition changes from 0 to 1, then the storage bit gets updated as 1 and passes on this value to the output bit. The output bit turns on for a very short duration of time, in milliseconds. This pulse output can then be used by the PLC programmer in his logic. As long as the condition is true, the storage bit does not change. As soon as the condition becomes false, the storage bit is updated with 0. When again the condition becomes true, then the output bit turns on as a pulse. This shows that this instruction is very useful when you want to turn an output by only a pulse, and this pulse must be generated only when the whole condition is true, and not when a single variable becomes true. One Shot Falling Edge (OSF) Now, take an example where it is required to take action when the system is stopped. This means, that when the condition becomes false from true, then some action must be taken. And the action must be done in a trigger type; it should not be continuously on. This is called a negative peak. To execute this function, either a negative peak must be taken from the variable or the negative peak must be taken from the whole condition as discussed earlier. For the second type, one-shot falling edge instruction is used in Rockwell PLC. Refer to the above image. There are 2 NO conditions in the rung, and the output of this rung is connected to the OSF block. The block has two bits – storage and output. The storage bit is used to store the condition of the rung. When the condition becomes true, then the storage bit is updated to 1. When the condition becomes false from true, then the storage bit is updated to 0 and the output bit becomes 1 in a pulse form. The cycle repeats again when the condition becomes true once again. The output bit is in pulse form and is on for a very short time, in milliseconds. This shows that this instruction is very useful when you want to turn an output by only a pulse, and this pulse must be generated only when the whole condition is false, and not when a single variable becomes false. In this way, we saw the one-shot rising edge and one-shot falling edge instructions in Rockwell PLC.
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