If you need to convert data, this module translates analog forms into digital forms before storing this reconfigured information in its image table. Individually utilize all six channels with software for compatibility with two- or three-wire RTD or direct resistance input devices. These six channels or inputs are compatible with typical four-wire sensors; however, they do not use the fourth wire. The Allen-Bradley IR6 is a compact input module series that provides two programmable excitation current values 0. This is available for open-circuit all wires , short-circuit excitation and return wires only , and over and under-range detection and indication. In addition, these compact input modules offer both single-ended or differential inputs and high accuracy rating.
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These are all basic PLC functions implemented in ladder logic. In this ladder logic example, there are two inputs. When the start button is released, the relay will still be activated, because of the latch in ladder rung 2. This latching will be broken when the stop button is activated. You might wonder why the stop button in this example is normally open.
And the reason for that, is that you should use normally closed as stop button , to avoid dangerous situations under failure. When you push the button the first time, the output will be activated. Now, when you push the button for the second time, the output will deactivate and turn off.
The single push button has two functions: on and off. Push on push off logic can be done in several ways. It can be done by using ladder logic and boolean logic instructions or it can be done with a counter. It can even be done with PLC rising edge and falling edge triggers or with shift registers. The blog has a lot of very useful information about PLC programming and especially ladder logic.
Take a look at the blog and see the many ladder logic examples. Generally speaking, you have three types of PLC timers available in ladder logic. The on-delay timer , the off-delay timer and the retentive timer or pulse timer. Its name comes from the fact, that the on delay timer delays its output from the on signal. When the preset time is up, the output of the on delay timer will turn on. If the input is turned off before the count down finish, the time will reset.
So, as long as the input is true or on, the enable output will be true. Second output is the done output DN. Look at this great video for more info about the on delay timer. You can also check out my own video about the on delay timer: PLC Program Example with Off Delay Timer The off delay timer works just like the on delay timer with one exception.
Instead of starting the count down from the signal at the input turns on, the off delay timer starts to count down from the signal turning off at the input signal. The example below is from Sakshat Virtual Labs. When you are heating something, you often have some sort of cooling too. A good example of that is a heating oven. The oven is heated by an electrical heater, and in the side there are ventilation motors to cool the oven after use.
The electrical heater and the cooling fans should turn on simultaneously. Why the cooling fans has to turn on too, is to circulate the hot air and spread the heat. Since both the fans and the heater has to start at the same time, the two outputs should work simultaneously. But keep in mind, that the cooling fans has to run for some time, after the heater is turned off. This is the exact function of an off delay timer, and the ladder logic example looks like this: Example of motors with cooling in ladder logic.
Off delay timer for extra delay. The time only pauses if the input is turned off before the count down is finished. When the input is turned on again, the timer continues counting down from where the time was paused. The word retentive even means to retain , and that is what retentive timers do. They retain the time they have counted when the input is off.
With the use of a retentive timer to control a motor with an automatic lubrication system, they have made a great practical example. The video illustrates some great examples and the basics of PLC timers. Finally I will encourage you to take a look at my video about the pulse timer. The pulse timer is used for generating pulses of a specific length and is very useful in ladder logic: Ladder Diagram for Motor Control Motor control can be done with a PLC program.
Here are some examples of ladder diagrams for motor control. When the motor speed is sufficient, the connection is switched to delta. This is due to the high current AC motors use when starting. To switch between the star and the delta relay, a timer is used. It includes a lot explination and a lot of great power and control circuit diagrams.
Example 5 is on page The DOL is made of a contactor usually 3-phase contactor , an overload relay like the thermal relay, and some connections in between. Sometimes you might have to use a smaller relay between the PLC output and the coil of the contactor. Make sure you always check the ratings of the PLC outputs you are using. All examples of how to use PLC programming and ladder logic to solve real problems. At many schools, universities and even companies you will get the challenge to make a traffic light ladder logic diagram.
The traffic light PLC program is a combination of timers to control which lights are turned on and for how long time. But some sort of interlock must be there to prevent the green light to be on in multiple directions. A PLC program like the traffic light is a little more complicated and therefore are a lot more solutions to. For inspiration you can look at these good examples of traffic light ladder diagrams: The first ladder logic example is from Engineer On A Disk, which is a marvelous site full of great articles.
In the example you will get all the ladder diagrams and step-by-step instructions and explanation. This is a great example because of all the explanation it gives. You will be introduced to the actuators motors , sensors and switches and a step-by-step guide to how to make the PLC program. At last you will see the example ladder logic for the bottle filling application.
Before you check out this application, be sure to include counters in your program. For a bottle filling plant, it is very important to keep track of how many bottles that went through the system. For this you can use the PLC counter instructions. In fact a PLC program is a great way to make an elevator control. But before you start looking at ladder diagrams and PLC program examples for elevator control, some safety issues are important to know about. You might want to incorporate a safety relay in the system.
Here are the things you need to know before you start to build a PLC elevator control: Mechanical safety No elevator control without mechanical parts. All these parts has to be tested and verified to make sure that they will last. Electrical safety Be sure to follow the rules and regulations for electrical safety. This includes proper grounding, using the right circuit breakers, wire gauges and so on. In the elevator examples you will be looking at, there will be a lot of interlocks, to prevent some functions to run at the same time.
This is a highly critical point.
1769-IR6 | Allen-Bradley | Resistance Input Model
Allen-Bradley 1769-IR6 (1769-IR6) Input Module
Allen Bradley Compact RTD/Resistance Input Module: 1769-IR6