Category Archives: Scan

Scan of the PLC. Reading inputs, solving logic, setting outputs, communications, etc.

BRX Do-More PLC High-Speed Input Pulse Catch

The High-Speed Input Pulse Catch will set an output that can be seen by the PLC ladder logic scan in response to an input pulse. Inputs that are too fast to reliably be seen by the ladder logic scan time will be seen.
BRX Do-More PLC High-Speed Input Pulse Catch
The BRX Do-More series of programmable logic controllers have built-in high-speed inputs. These inputs can function in Counter, Timer, or Pulse Catch modes. Every CPU will have either 6 or 10 high-speed inputs (HSI) available depending on the model. These inputs can be used for input frequencies from 0 to 250Khz. 250Khz represents 250000 input counts per second that can be coming from devices connected to your PLC like an encoder. Due to the speed of the inputs, they function on the BRX Do-More PLC asynchronous with the PLC scan time.
We will continue looking at the high-speed inputs on our BRX Do-More PLC, by looking at the pulse catch mode. The pulse catch mode will be set up using the Z phase of our incremental encoder. Pulses will be counted using the input directly in the ladder logic and using the pulse catch bit. Comparisons will be made between the two counts and an output will be turned on when different. Let’s get started. Continue Reading!

Productivity 2000 Series PLC Debug Mode

The productivity suite programming software has a debug mode. This will allow you to view and control the rung execution on your ladder logic code. These programming tools allow you to troubleshoot, find, and correct errors in the PLC programming logic.
Productivity 2000 Series PLC Debug Mode
We will be adding a couple of rungs to our exiting start-stop circuit we created last time in our productivity 2000 PLC. Using the debug mode we will explain the scan of the PLC and use these tools to sequence the logic. Let’s get started. Keep on Reading!

PLC Learning Series – Program Cyclic Scan

Programmable logic controllers (PLC) use a cyclic scan. The time that it takes to complete one scan is called Scan Time. Typical scan times range from 10 milliseconds to 10 microseconds. This translates from 0.01 to 0.0001 seconds per PLC scan. Understanding how the program scan will help us in programming and troubleshooting the PLC.

The simplest scan cycle of a PLC consists of 4 steps. Read inputs, execute program, diagnostics, and communication, and update outputs.
We will be looking at each of these steps in a little more detail as we discuss the PLC program cyclic scan. Let’s get started. Keep on Reading!

PLC Training Series – Tutorial for Everyone

Invented in 1968 by Dick Morley, the programmable logic controller (PLC) is a simple rugged industrial computer. This free plc training series is designed for everyone to learn about these controllers. PLCs are constantly evolving and continue to be the best option for a variety of industrial automation applications.
PLC Training Series - Tutorial for Everyone
Even though the PLC is changing, core items remain the same. We will be discussing this in more depth for each of the components mentioned in the picture above. Let’s get started learning about PLCs. Keep on Reading!

Click PLC Modbus ASCII Protocol Communication

We will now look at the click plc modbus ascii protocol. This communication will happen in PLC ladder logic and communicate through the serial port (RS485) to a Solo process temperature controller. Modbus ASCII will be the communication protocol.
Modbus is a communication method used for transmitting information over serial lines between electronic devices. The device requesting the information is called the Modbus Master (Client) and the devices supplying information are Modbus Slaves (Servers). This protocol was originally developed by Modicon systems.
Modbus protocol comes in basically three different types. Ethernet (Modbus TCP) or Serial (Modbus RTU or Modbus ASCII). Modbus TCP and Modbus RTU come as standard protocols in the productivity series of PLCs.
click plc modbus ascii
We will connect the Click PLC to a Solo process temperature controller. This will be done using the Modbus ASCII protocol over serial RS485 communication wire. (Media) The present and set values (PV / SV) will be read from the Solo controller and the set value will be written when required. Let’s get started. Keep on Reading!

Productivity Open P1AM Arduino Time Instructions

Time instructions in our productivity blocks programming (Arduino sketches) consist of runtime (ms), runtime (us), delay ms, and delay microseconds us.
arduino time instructions
We will be looking at each of these instructions that are available for our program using productivity blocks. Delay instructions in our sketches should be used with caution. They will pause our program for the delayed time, not allowing other parts of the program to function. We will be looking at this and the method to do the exact same delay functions without pausing your program.
arduino time instructions
A sample program will be discussed to demonstrate the time functions in our program. Let’s get started. Continue Reading!