What is the definition of "SQI"?
Sequencer input. An instruction in a PLC ladder program in which input data is compared for equality with data that has been stored in memory.

## PLCs Training

Class Information
 Tooling U-SME classes are offered at the beginner, intermediate, and advanced levels. The typical class consists of 12 to 25 lessons and will take approximately one hour to complete.
 Class Name: Sequencer Instructions for PLCs 330 Description: This class covers sequencer instructions for PLCs. Difficulty: Advanced Number of Lessons: 12 Language: English, Spanish

Class Outline
• Objectives
• Sequential Control of Processes
• Mechanical Sequencers
• PLC Sequencers vs. PLC Counters
• File and Destination Fields
• Control Parameters and Status Bits
• Length and Position Parameters
• Sequencer Output Instructions
• Sequencer Input and Load Instructions
• A Sample Sequencer Application
• Summary

Class Objectives
• Describe sequential control of processes.
• Describe mechanical sequencers.
• Distinguish between PLC sequencers and PLC counters.
• Describe the file and destination fields for sequencer instructions.
• Describe how sequencer masks work.
• Describe control parameters and status bits for sequencer instructions.
• Describe length and position parameters for sequencer instructions.
• Describe how sequencer output instructions work.
• Describe sequencer input and load instructions.
• Give an example of a sequencer application.

Class Vocabulary

Vocabulary TermDefinition
The number of time units or counts that have accrued. When the accumulated value equals the preset value, the done bit is enabled.
A single numerical unit in the binary number system. Bit is short for BInary digiT.
Circular or cylindrical machine components that convert rotational movement into linear movement.
A type of mechanical timer that uses cams arranged along a shaft to alternately press down and release switches that control different timing elements of a system.
The process of linking two or more sequencers together to expand their capability. Also known as chaining.
The process of linking two or more sequencers together to expand their capability. Also known as cascading.
A sequencer data file composed of three words that tell the processor how the sequencer is structured. CONTROL holds the status bits, the length, and the position of the sequencer.
A device that counts, calculates, or keeps a record of the number of times something happens. PLC counters exist as a set of instructions inside the PLC microprocessor.
A defined area in a PLC that stores bits of information. Some PLCs refer to data files as registers.
A field in a sequencer instruction that specifies the output image address at which the sequencer instructions will be enabled. DEST is used for SQO only.
Done bit. A bit that activates the output and resets the sequencer program after the last sequencer file is completed. The done bit is one of the most frequently used status bits.
DN. A bit that activates the output and resets the sequencer program after the last sequencer file is completed. The done bit is one of the most frequently used status bits for PLC applications.
Counting in a downward or decreasing direction. Counting 3, 2, 1, and so on is a down count.
A circular or cylindrical machine component that uses pegs to convert rotational movement into intermittent electrical contact.
Enable bit. When the enable bit is true (1), the sequencer executes an output or load instruction.
EN. A bit that causes the sequencer to execute an output or load instruction when the bit is true (1). The enable bit is one of the most frequently used status bits.
A bit that is ON.
A condition in which the status of all the input bits matches the status of all the bits in the current step of the sequencer. Equality is measured in the SQI instruction.
Error bit. A bit that is set when an error has occurred in the sequence.
ER. A bit that is set when an error has occurred in the sequence.
A sequencer that controls the order of steps of a process, but not the amount of time the steps take.
Found bit. A bit that is set when all of the non-masked bits in the source word match the corresponding bits in the sequencer word.
A placeholder in an instruction that is used for inputting information.
A field in a sequencer instruction that contains the address of the data file containing the sequencer program. FILE tells the PLC where to find the sequencer instructions.
A letter code given to each type of data file to make it easier for the programmer to identify the files.
The specific bit number assigned to each type of data file so that it easily can be found within the ladder logic program.
FD. A bit that is set when all of the non-masked bits in the source word match the corresponding bits in the sequencer word.
The default position of a robotic arm when it is at rest or ready to begin a new cycle.
A parameter of a sequencer that tells the PLC how many steps must be taken to complete the sequence.
A feature used in sequencer instructions to enable or disable specific bits in a memory word. MASK tells the PLC which inputs or outputs are controlled by the sequencer, and which ones are not.
A named value or range of values that define or characterize a process.
The process of picking up an object or part in one location and placing it in another location. Pick and place robots use sequencers to complete their tasks.
Programmable logic controller. A processor driven device that uses logic-based software to provide electrical control to machines.
An element of a sequencer instruction that tells the PLC what step of the sequencer is currently being run.
A value set in advance that triggers a timer or counter action. When the accumulated value equals the preset value, the done bit is enabled.
A data file in a PLC that stores bits of information. Some PLCs refer to registers as files.
A connected series of events that occurs in a certain order. In manufacturing, sequential control is required for many applications.
A type of program control instruction for PLCs that determines the order in which a group of processes is performed.
SQC. An instruction in a PLC ladder program in which input data is compared for equality with data that has been stored in memory. Also known as sequencer input.
SQI. An instruction in a PLC ladder program in which input data is compared for equality with data that has been stored in memory. SQI is typically used to monitor or troubleshoot machines.
Program instructions for a PLC ladder program that control the order in which a group of processes is performed.
SQL. An instruction in a PLC ladder program that loads the current data into the sequencer step by step. SQL does not use a mask.
SQO. An instruction in a PLC ladder program that determines the output conditions for the next step of the process. SQO cannot be enabled until certain conditions are met.
A field in a sequencer instruction that specifies the address of the input data. SOURCE is used for SQI only.
Sequencer compare. An instruction in a PLC ladder program in which input data is compared for equality with data that has been stored in memory. Also known as sequencer input.
Sequencer input. An instruction in a PLC ladder program in which input data is compared for equality with data that has been stored in memory.
Sequencer load. An instruction in a PLC ladder program that loads the current data into the sequencer step by step.
Sequencer output. An instruction in a PLC ladder program that determines the output conditions for the next step of the process.
A bit that controls the condition or state of the PLC sequencer. The two most frequently used status bits are enable (EN) and done (DN).
A sequencer that controls the amount of time of a process, as well as the order of steps.
Counting in an upward or increasing direction. Counting 1, 2, 3, and so on is an up count.
A combination of up counters and down counters that allows you to increase and decrease values by increments of 1.
A defined and specific number of digits grouped together. For most PLCs, a word consists of 16 digits.