Truth-Tables, Boolean Equations

A truth table shows how a logic circuit's output responds to various combinations of the inputs, using logic 1 for true and logic 0 for false. All permutations of the inputs are listed on the left, and the output of the circuit is listed on the right. The desired output can be achieved by a combination of logic gates. A truth table for two inputs is shown, but it can be extended to any number of inputs. The input columns are usually constructed in the order of binary counting with a number of bits equal to the number of inputs.


Truth tables are an important tool for evaluating statements and arguments. We can create our own truth tables using following steps:

1. Translate statements of ordinary language.
2. Break all complex statements into smaller parts.
3. Determine how many columns are required.
4. Determine how many rows are required.
5. Determine the truth values of statement letters.
6. Determine the truth values of complex statements.

Scan cycle of PLC

      A PLC program is generally executed repeatedly as long as the controlled system is running. The status of physical input points is copied to an area of memory accessible to the processor, sometimes called the "I/O Image Table". The program is then run from its first instruction rung down to the last rung. It takes some time for the processor of the PLC to evaluate all the rungs and update the I/O image table with the status of outputs. This scan time may be a few milliseconds for a small program or on a fast processor, but older PLCs running very large programs could take much longer (say, up to 100 ms) to execute the program. If the scan time were too long, the response of the PLC to process conditions would be too slow to be useful.

     Special-purpose I/O modules may be used where the scan time of the PLC is too long to allow predictable performance. Precision timing modules, or counter modules for use with shaft encoders, are used where the scan time would be too long to reliably count pulses or detect the sense of rotation of an encoder. The relatively slow PLC can still interpret the counted values to control a machine, but the accumulation of pulses is done by a dedicated module that is unaffected by the speed of the program execution.

Learn about Siemens Logo PLC and its Programming

Getting started with LOGO!

Here's LOGO!
LOGO! is a universal logic module made by Siemens that integrates:

● Controls
● Operator and display panel with background lighting
● Power supply
● Interface for expansion modules
● Interface for a micro SD card
● Interface for an optional text display (TDE) module
● Pre-configured standard functions, for example, on- and off-delays, pulse relay and
softkey
● Timers
● Digital and analog flags
● Inputs and outputs, according to the device type
LOGO! 8 additionally integrates the following components:
● Interfaces for Ethernet communication
● FE (Functional Earth) terminal for connecting to earth ground
● One LED for indicating Ethernet communication status
What LOGO! can do for you
LOGO! offers solutions for domestic and installation engineering applications such as
stairway lighting, external lighting, sun blinds, shutters, shop window lighting and more. It
can also offer solutions for switch cabinet engineering, as well as for mechanical and
apparatus engineering such as gate control systems, air-conditioning systems, and rainwater
pumps.

For More Documents and Software go to Download..............