Sql

r5rouse · Nov 16, 2013

Hello,
I'm new here. Feel free to abuse me for asking noob questions... it wont hurt my pride.

I'm looking for information on RS LOGIX sequencers.

Specifically, what would you use the SQL function for?

I'm trying to set up a sequence of electro-pneumatic selenoids that fire two double acting cylinders and a spring loaded gripper.

The cylinder positions are sensed through reed switches.

So far, I've set up an SQC function that steps an SQO through steps.

i'm using binary files to compare inputs and set outputs.

it works ok.. but I'm wondering what the SQL would do if I were to add it..

I'm also wondering where I'd add it in the ladder diagram.

Doug-P · Nov 16, 2013

Which processor are you using? Some PLC5s have a Sequential Function Chart capability. This functions much like a sequencer but is more versatile.

Lots of folks 'roll their own' by using state machine logic.

r5rouse · Nov 16, 2013

I'm using a micrologix 1500.

I'm just controlling a mechatronics classroom lab set. There's some versatility, but I don't have relays available to use solid state logic.

Lancie1 · Nov 16, 2013

I'm wondering what the SQL would do if I were to add it..

The idea is that you can save some steps and some ladder logic by using a sequencer output instruction that does several functions, such as keep up with what position or step the sequence is on, and then set the correct outputs for that step, then repeat the process.

Normally, a Sequencer Load instruction is needed to load the sequence of steps into the Sequencer memory stack. The SQL instruction may only need to be active one time, usually the First PLC Scan (unless the sequence changes).

From the RSLogix Help files:

Rockwell Software
Sequencer instructions are used typically to control automatic assembly machines that have a consistent and repeatable operation. Use the sequencer input instruction to detect when a step is complete; use the sequencer output instruction to set output conditions for the next step. Use the sequencer load instruction to load reference conditions into the sequencer input file.

The primary advantage of sequencer instructions is to conserve program memory. These instructions monitor and control multiples of 16 discrete outputs at a time in a single rung.

SQL [Sequencer Load]

Description
On successive false-to-true transitions, the SQL moves a step through the sequencer file, loading a word of source data into the current element of the sequencer file. The source of this data can be an I/O storage word address, a file address, or a program constant.
You may use indexed or indirect addressing in this instruction.

Entering Parameters
File is the address of the sequencer file. Make sure to use the file indicator (#). This file stores the reference data for monitoring inputs.
Source can be a word address, file address, or a program constant (-32768 to 32767). If the source is a file address, the file length equals the length of the sequencer load file. The two files will step automatically, per the position value.

Control is the control file address, the control element (3 words) that stores the status byte of the instruction, the length of the file, and the position in the file. Do not use this address for any other instruction. Status bits in the control file include:
11 = ER (error bit)
13 = DN (done bit)
15 = EN (enable bit)

PS: State-machine logic is not necessarily solid-state logic. State-machine logic is rather a method where you try to identify all possible states for each part of a machine, and write logic to handle those states.

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r5rouse

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Doug-P

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r5rouse

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Lancie1

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