As a PLC professional technician, I have encountered multiple projects where the number of input points available for the Programmable Logic Controller (PLC) is limited. This limitation can be due to budget constraints, space limitations, or simply the design of the system. However, as a professional, it is our responsibility to find efficient solutions to overcome these challenges. In this article, I will share some tried and tested methods for PLC to save input points without compromising on functionality or performance.
The first method is to use analog inputs instead of digital inputs. Analog inputs are capable of reading a wide range of values, unlike digital inputs which can only register a binary signal (ON or OFF). By using an analog input, multiple sensors or switches can be connected in parallel and the PLC can differentiate between their varying values. This can significantly reduce the number of input points needed, as instead of using one digital input for each sensor, we can use one analog input for multiple sensors.
Another approach to save input points is by using a multiplexer. A multiplexer is a device that can select one of several inputs and forward the selected input to a single output. In PLC systems, a multiplexer can be used to reduce the number of analog inputs needed. By connecting multiple sensors to the inputs of a multiplexer, and then connecting the output of the multiplexer to a single analog input of the PLC, we can save a considerable number of input points. However, this method can only be used when the sensors are not required to be read simultaneously.
An often overlooked method to save input points is by utilizing the spare outputs of the PLC. Most PLCs have a few spare outputs that are not being used in the current system. These outputs can be configured as inputs, saving the need for additional I/O modules. However, this method can only be used if the input signals are not time-critical, as the PLC will scan the outputs before scanning the inputs, causing a slight delay in response time.
For systems that require a large number of inputs from sensors with the same specifications, the use of a remote input/output (I/O) module can be a cost-effective solution. Remote I/O modules are connected to the PLC via communication networks and can be placed at a remote location, reducing the need for additional I/O modules near the PLC. This method can save significant costs, as remote I/O modules are generally less expensive than local I/O modules. However, it is essential to consider the communication network's limitations, such as distance and bandwidth, before implementing this method.
Another efficient way to save input points is by implementing a shift register. A shift register is a type of memory unit that stores data in a sequential manner. In PLC systems, a shift register can be used to store the status of multiple input signals. This method can be beneficial when there is a requirement to monitor multiple input points in a sequential manner, such as in a conveyor belt system. By using a shift register, we can save the need for multiple inputs, as the status of each input can be stored and monitored as it moves through the register.
Lastly, the use of input grouping can also save input points in a PLC system. Input grouping involves connecting multiple sensors or switches in series, and then connecting them to a single input of the PLC. This method is commonly used for safety circuits, where multiple sensors need to be activated to shut down a system. By using input grouping, we can save on the number of input points, as only one input is required for a group of sensors. However, it is crucial to ensure that the sensors are functioning correctly and are appropriately wired in series, as a malfunction in one sensor can cause the entire group to fail.
In conclusion, as PLC professionals, it is essential to be resourceful and find creative solutions to save input points in PLC systems. By utilizing methods such as using analog inputs, multiplexers, spare outputs, remote I/O modules, shift registers, and input grouping, we can save on costs, space, and time without compromising on the functionality or performance of the system. I hope this article has given you some valuable insights and can help you in your future projects. Remember, as professionals, it is our duty to continuously learn and adapt to new challenges to deliver efficient and effective solutions.