TRiLOGI Version 5 supports eight
sequencers of 32 steps each. Each sequencer uses one of the first eight counters (Counter
#1 to Counter #8) as its step counter. Any one or all of the first eight counters can be
used as sequencers "Seq1" to "Seq8".
To use a sequencer, first define the sequencer name
in the Counter table by pressing the <F2> key and scroll to the Counter Table. Any
counter to be used as sequencer can only assume label names "Seq1" to
"Seq8" corresponding to the counter numbers. For e.g. if Sequencer #5 is to be
used, Counter #5 must be defined as "Seq5". Next, enter the last step number for
the program sequence in the "Value" column of the table.
Construct a circuit that uses the special function
"Advance Sequencer" [AVSeq]. The first time the execution condition for the
[AVseq] function goes from OFF to ON, the designated sequencer will go from inactive to
step 1. Subsequent change of the sequencer's execution condition from OFF to ON will
advance (increment) the sequencer by one step. This operation is actually identical to the
[UPctr] instruction.
The upper limit of the step counter is determined by
the "Set Value" (SV) defined in the Counter table. When the SV is reached, the
next advancement of sequencer will cause it to overflow to step 0. At this time, the
sequencer's contact will turn ON until the next increment of the sequencer. This contact
can be used to indicate that a program has completed one cycle and is ready for a new
cycle.
Accessing individual steps of the sequencer is
extremely simple when programming with TRiLOGI. Simply create a "contact" (NC or
NO) in ladder edit mode. When the I/O window pops up for you
to pick a label, scroll to the "Special Bits" table as follow:
Special Sequencer Functions
Quite a few of the ladder logic special
functions are related to the use of the sequencer. These are described below:
Advance
Sequencer - [AVseq]
Increment the sequencer's step
counter by one until it overflows. This function is the identical to (and hence
interchangeable with) the [UpCtr] function.
Resetting Sequencer - [RSseq]
The sequencer can also be reset to
become inactive by the [RSseq] function at any time. Note that a sequencer that is
inactive is not the same as sequencer at Step 0, as the former does not activate the
SeqN:0 contact. To set the sequencer to step 0, use the [StepN] function described next.
Setting Sequencer to Step N -
[StepN]
In certain applications it may be
more convenient to be able to set the sequencer to a known step asynchronously. This
function will set the selected sequencer to step #N, regardless of its current step number
or logic state. The ability to jump steps is a very powerful feature of the sequencers.
Reversing a Sequencer
Although not available as a unique
special function, a Sequencer may be stepped backward (by decrementing its step-counter)
using the [DNctr] command on the counter that has been defined as a sequencer. This is
useful for creating a reversible sequencer or for replacing a reversible "drum"
controller.
Other Applications
a. Driving Stepper Motor
A sequencer may be used to
drive a stepper motor directly. A two-phase stepper motor can be driven by four transistor
outputs of the controller directly (for small motors with phase current < 0.5A) or via
solid-state relays. The stepper motor can be driven using a sequencer that cycles through
Step#0 to Step#3 (full-step mode) or Step#0 through Step#7 (half-step mode). Each step of
the sequencer is used to energize different phases of the stepper motor. A clock source is
needed to drive the stepper motor through its stepping sequence. The stepping rate is
determined by the frequency (which is equal to 1/period) of the clock source.
Clock pulses with periods in multiples of 0.01
second can be generated easily using the "Clk:.01s" bit and an [Upctr] function.
For e.g., to generate a clock source of period = 0.05s, use "Clk.01s" to feed to
an [Upctr] counter with Set Value = 4. The counter's contact (completion flag) will be
turned ON once every 5 counts (0,1,2,3,4), which is equivalent to a 0.05 sec. clock
source.
b. Replacing a Drum Controller
A drum controller can be replaced easily by a sequencer if the timing of the
drum's outputs can be divided into discrete steps. Assuming a drum controls two outputs
with the timing diagram shown in the following figure:
This can be replaced by an 8-step sequencer. Step 1
(e.g "Seq1:1") turns ON and latch Output A using [Latch] function, Step 2 turns
ON and latch Output B, Step 4 turns OFF Output A using the [Clear] function, and Step 6
turns OFF Output B. All other steps (3,5,7,0) have no connection.
