PLC Sequencer Instruction with Example

The PLC Sequencer Instruction (SQO) is an output instruction. SQO instructions can perform the same specific “ON” or “OFF” patterns of outputs that are continuously repeated.

The advantage of sequencer programming over the conventional program is the large savings of memory words.

Typically, the sequencer program can do in 20 words what a standard program does in 100 words. By setting up a sequence of events, sequencers make programming simpler and any future changes easier to make.

The sequencer output (SQO) instruction can be used to control output devices sequentially. The desired sequence of operation is stored in a data file or array, and this information is then transferred sequentially to the outputs.

PLC Sequencer Instruction

In the above block,we have six parameters

File :

Address of the reference sequencer file

Mask :

The address of the mask word or file through which the instruction moves data.

Dest :

Address of the output word or file for a SQO to which the instruction moves data from its sequencer file

Control :

Instruction’s address and control element (3 words) that stores the status byte of the instruction, the length of the file, and the position in the file.

Length :

Number of steps of the sequencer file starting at position 1.

Position :

The word location or step in the sequencer file from/to which the instruction moves data.

Refer the below Block,

Block Description :

On successive false-to-true transitions, the SQO instruction moves a step through the programmed sequencer file, transferring step data through a mask to a destination word.

The done bit is set when the last word of the sequencer file is transferred. On the next false-to-true transition, the instruction resets the position to step one.

Let’s study the block using simple example,

PLC Program

RUNG 0000

Start and stop PB with sequencer input switch is connected with sequencer output block.

Data file-Reference sequence file,

B3:0, B3:1, B3:2 & B3:3 are sets to 1 for reference,

When Sequencer input I:0/2 turns ON for first time,

According to the reference file, O:0/1 turns ON.

Length is 4 & position is 1.

When Sequencer input I:0/2 turns ON for second time,

According to the reference file, O:0/2 turns ON.

Length is 4 & position is 2.

When Sequencer input I:0/2 turns ON for third time,

According to the reference file, O:0/3 turns ON.

Length is 4 & position is 3.

When Sequencer input I:0/2 turns ON for fourth time,

All outputs in the off condition.

Length is 4 & position is 4.

It s like reset, ready to start from beginning again.

Conclusion

We discussed the Sequencer block instruction in Allen Bradley PLC with example.

-END-

Comments

Ferrules and Cross Ferruling

Ferrules are identification labels provided for every wire terminations in an instrument, equipment, or electrical/instrumentation control panels. These tube-shaped sleeves can be inserted easily on each individual wire in a multi-core cable. In earlier days fixed digits/letters are used as ferrules, but now Instrumentation engineers/technicians prints out desired ferrules by using a ferrule printing machine. Typical Ferrule The numbers/ letters on the ferrules will be given as per the approved electrical hook up or loop diagrams. This helps technicians to easily identify a particular loop/wiring from a series of terminal blocks and to troubleshoot the desired terminal connection. Separate numbers on the ferrules distinguish the positive and negative polarities of wires, thus ensure the polarity protection of the instrument. Cross Ferruling As a wire is connected on its both ends, it is quite useful to use a cross reference method for wire identification. Unlike normal ferru...

What is a Torbar? – Averaging Pitot Tubes

The Torbar is employed for flow measurement of liquids, gases, or steam in circular, square, or rectangular section ducts for large flow rates. The Torbar is an insertion type multi-port self-averaging primary sensor for flow measurement. Torbar TORBAR is a set of Pitot tubes mounted on a bar across the pipeline with no moving parts. An averaging Pitot tube is a technology, while TORBAR is a manufacturing brand name. There are several brands available in the market with VERABAR, ANNUBAR, etc. Averaging Pitot Tube Principle Purpose Averaging Pitot tube can be employed when the average velocity of the flow profile, rather than the velocity in a specific point in the cross-section is desired. Averaging Pitot Tubes Principle It measures the differential pressure between the static pressure tap and the tap of full pressure of a stream. Thus such magnitude of differential pressure is directly proportional to the square of the flow rate. Working The TORBAR is designed in such a way that ...

The Method and Process of Siemens PLC Hardware Configuration

The hardware configuration of Siemens PLC can usually adopt the following methods and processes: Determine control tasks and system requirements: Before hardware configuration, it is necessary to clarify the tasks and requirements of the control system, including the requirements for input and output points, control accuracy, speed, and safety. Select the PLC model and module: According to the control task and requirements, select the appropriate PLC model and module, including CPU, I/O module, communication module, power supply module, etc. Assemble the cabinet and install the modules: According to the selected PLC model and module, assemble the cabinet and install the modules, pay attention to the installation sequence, cable wiring, wiring method, etc. Connect the input and output devices: connect the input and output devices with the input and output modules of the PLC, you need to pay attention to the correctness, stability and safety of the wiring. Perform software configura...

TILI Automation

Search This Blog