0:03
Contact and coil instructions are in
0:05
every PLC program. The Productivity
0:08
Suite software comprises more than 82
0:10
instructions organized into 13
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categories for the PLC.
0:14
Contacts and coils are two of those
0:15
categories. Contact instructions include
0:17
NO, NC, NO edge, NC edge, and compare.
0:21
Coil instructions include out, set,
0:23
reset, or out flasher, debounce, timed,
0:26
toggle, program end, and no operation.
0:29
We will be looking at these instructions
0:31
in the Productivity mini PLC P1M6-22
0:34
or 16DR. We will also look at how to
0:37
organize your frequently used
0:38
instructions using the favorites
0:41
Throughout this post, we will tie each
0:43
instruction back to our start-stop motor
0:45
circuit so you can see exactly how they
0:47
apply to real programs.
0:49
Let's get started. Detailed information
0:51
contained in this video can be found at
0:55
A link has been put in the description
0:57
below. The website offers extensive
0:58
links, references, and coding samples,
1:00
making it a one-stop shop for all your
1:03
Once again, that is accautomation.ca.
1:09
Favorites, contact, and coil
1:12
The favorites section is a heading found
1:14
under the instructions window of the
1:16
Productivity Suite software.
1:18
You can open the instructions window by
1:20
clicking on it in the application tools
1:21
panel or use the main menu, tools,
1:30
Right clicking any instruction in the
1:32
list opens a menu that lets you add to
1:34
favorites. Click that option and the
1:36
instruction will now appear under your
1:38
favorites heading at the top of the
1:41
To remove an instruction from your
1:42
favorites, right click on it under the
1:44
favorites heading and select remove from
1:47
Favorites are a great way to separate
1:48
the instructions you use most often from
1:50
the full list. As you work through this
1:52
series and build more complex programs,
1:54
you will find yourself reaching for the
1:55
same handful of instructions repeatedly.
1:58
Adding them to favorites saves time and
2:00
keeps your workflow organized.
2:05
Contacts, contact and coil instructions.
2:09
Contacts are the input conditions of a
2:11
rung. They represent the state of
2:12
boolean tags, physical inputs, outputs,
2:15
or internal bits, [music] and control
2:17
whether power flows through the rung to
2:20
The PLC evaluates logic from left to
2:22
right, top to bottom on each scan. For a
2:24
deeper understanding of how the PLC scan
2:26
works, see this post, understanding the
2:31
NO contact, NO, the normally open
2:33
contact enables power flow in a rung
2:35
when the contact is energized.
2:37
It disables power flow when the contact
2:39
is de-energized. This is the most common
2:41
contact in PLC programming. In our
2:43
start-stop motor circuit, the start
2:48
uses an NO contact. When the physical
2:50
start push button is pressed, the
2:51
contact energizes and power flows
2:55
When the button is released, the contact
2:56
opens, but the sealing contact DO0.1.1.1
3:00
in the parallel branch keeps the rung
3:05
NC contact, NC, [music] the normally
3:07
closed contact enables power flow in a
3:09
rung when the contact is de-energized.
3:12
It disables power flow when the contact
3:14
is energized. This is where most people
3:16
get confused. Just think of a normally
3:17
closed contact as the opposite logic.
3:20
In our start-stop motor circuit, the
3:24
uses an NO contact in the ladder. As we
3:27
covered in the online editing and
3:28
fail-safe wiring post, the physical stop
3:30
button is wired normally closed to the
3:32
input, meaning the input is energized on
3:35
or one in its normal state. An NO
3:37
contact in the ladder therefore passes
3:39
power continuously as long as the stop
3:42
button is not pressed.
3:44
When the stop button is pressed, the
3:46
physical NC contact opens, the input
3:48
drops to off, and the NO ladder contact
3:51
opens, breaking the rung.
3:54
This is the correct fail-safe approach.
3:56
A broken wire or failed button
3:57
de-energizes the input and stops the
4:02
NO edge contact, NOE. The normally open
4:06
edge contact acts as a one-shot input on
4:08
either the rising edge or falling edge
4:11
It allows power flow for exactly one
4:13
scan when the contact transitions from
4:15
de-energized to energized, rising edge,
4:17
or energized to de-energized, falling
4:20
This is sometimes referred to as a
4:22
one-shot in PLC programming. It is
4:24
extremely useful when you need an action
4:26
to happen only once per button press.
4:28
For example, incrementing a counter each
4:30
time a button is pressed rather than
4:32
once per scan while it is held.
4:34
See this post for more details on
4:36
one-shot logic, how to make a one-shot
4:40
NC edge contact, NCE. The normally
4:43
closed edge contact also acts as a
4:45
one-shot, but triggers on the transition
4:47
of a normally closed contact.
4:49
It allows power flow for one scan when
4:51
the contact transitions from energized
4:53
to de-energized, rising edge, or
4:56
de-energized to energized, falling edge.
4:59
Compare contact, CMP. This input contact
5:03
compares two numerical values. Based on
5:05
the selected operand, equal to, not
5:07
equal to, greater than, less than,
5:09
greater than or equal to, or less than
5:11
or equal to, it either enables or
5:13
disables power flow in the rung.
5:16
A practical example, if you have an
5:17
analog temperature sensor reading into
5:21
16DR via an expansion module, you could
5:24
use a compare contact to turn on a
5:26
cooling fan output when the temperature
5:27
tag exceeds a set point. The compare
5:30
contact makes numeric decisions directly
5:32
in your ladder logic without requiring a
5:34
separate math instruction.
5:37
Coils, contact and coil instructions.
5:40
Coils are the output elements of a rung.
5:42
When the rung conditions, contacts,
5:44
evaluate to true, the coil executes its
5:47
The type of coil determines exactly what
5:51
Out coil out provides an output that
5:53
directly responds to the current state
5:55
of the rung. When the rung is true, the
5:57
output is on. When the rung is false,
6:00
the output is off. This is the coil we
6:02
have been using throughout this series
6:04
for the motor output DO0.1.1.1
6:08
in our start-stop circuit.
6:10
The out coil also has a one-shot option,
6:12
which turns the output on for just one
6:14
scan during the transition from off to
6:18
Set coil, set, sets the output into a
6:20
latched on condition when the rung is
6:22
enabled. Once set, the output remains on
6:24
even if the rung condition goes false.
6:27
Reset coil, RST, resets, unlatches, the
6:31
output of a corresponding set coil. The
6:33
output turns off when the reset rung is
6:37
The set and reset instructions work
6:39
together and are an alternative way to
6:40
build a start-stop circuit. Rather than
6:43
using a ceiling contact with an out coil
6:45
as we did in our first program, you can
6:47
use a set coil on the start rung and a
6:49
reset coil on the stop rung.
6:51
Both approaches produce the same result.
6:53
The set-reset method can sometimes make
6:55
the logic easier to read in programs
6:57
with many interlocks.
6:59
See our first program post for the
7:00
ceiling contact approach, P1M622 16DR
7:04
mini PLC first program start-stop motor
7:08
Or out, OR, allows an out coil with the
7:11
same tag to be used in multiple rungs.
7:13
When any rung with that tag is true, the
7:16
Note, while the OR out instruction is
7:18
available, [music] having the same
7:19
output tag controlled from multiple
7:21
rungs can make troubleshooting
7:24
From my experience in the field, this
7:25
should be avoided in most cases. Keep
7:27
your outputs in a single rung where
7:29
possible. It makes maintenance and
7:30
troubleshooting much faster.
7:33
Flasher, FLS, cycles an output bit on
7:36
and off at a programmed rate. You set
7:38
the cycle time in milliseconds.
7:40
When the rung condition is true, the
7:41
output will be on for half the cycle
7:43
time and off for the other half.
7:46
For example, setting the cycle time to
7:48
1,000 milliseconds results in an output
7:50
that flashes 0.5 seconds on and 0.5
7:56
A practical use of the P1M622-16DR would
7:57
be to flash an indicator light wired to
7:59
one of the eight relay outputs to signal
8:01
an alarm or a mode change
8:05
without needing a timer instruction to
8:07
manage timing manually.
8:10
Debounce coil, DBN, eliminates output
8:12
coil chatter caused by rapid on-off
8:14
transitions at the rung condition.
8:17
The rung condition must remain
8:18
continuously on or off for the program
8:21
debounce time before the output
8:22
activates or deactivates.
8:24
Chatter occurs when logic allows a rapid
8:27
oscillation. For example, if a compare
8:29
contact is evaluating a value that is
8:31
bouncing just above and below the
8:33
comparison threshold.
8:36
In our example, the rung condition must
8:37
remain stable for 1,000 milliseconds, 1
8:40
second, before the output changes state.
8:43
This adds a deliberate delay that
8:45
filters out noise without needing a
8:49
Timed coil, TMC, holds the state of the
8:51
output on for a predetermined time after
8:53
the rung becomes true.
8:55
Even if the rung condition goes false
8:57
before the time expires, the output will
8:59
remain on until the time duration
9:02
An output maintained option is also
9:04
available, which keeps the output on
9:06
after the time period as long as the
9:07
rung condition remains true.
9:10
A practical example, pressing a
9:11
momentary push button could trigger the
9:13
time coil to hold a solenoid valve open
9:15
for exactly 5 seconds, regardless of how
9:17
briefly the button was pressed.
9:20
Toggle coil, TGC, changes the state of
9:23
the output each time the rung is
9:24
enabled. If the output is currently on,
9:28
If it is currently off, it turns on.
9:30
This is sometimes called a flip-flop
9:31
circuit. In our example, when the input
9:33
transitions from off to on, the output
9:36
This is useful for applications where a
9:38
single push button needs to act as both
9:40
an on and off control, common in simple
9:42
lighting or fan controls. See this post
9:45
for the logic behind the flip-flop
9:47
circuit, creating a flip-flop circuit in
9:51
No operation coil, NOP, indicates that
9:54
the rung will have no operation. It is
9:56
used as a placeholder in ladder logic,
9:59
for example, when you are reserving a
10:01
rung for future expansion or temporarily
10:03
disabling a rung during development
10:05
without deleting it.
10:08
Program end coil, END, marks the end of
10:11
a task. The Productivity Suite software
10:13
automatically places an end coil at the
10:15
end of your program.
10:16
The PLC will execute all rungs up to the
10:18
end coil on each scan, then restart the
10:22
If you are enjoying this video, please
10:24
hit the like button below.
10:26
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10:27
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10:28
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10:31
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10:32
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10:35
Applying [snorts] what we've learned to
10:36
our start-stop circuit.
10:39
Looking back at the start-stop motor
10:41
circuit we have built throughout this
10:42
series, you can now identify every
10:44
instruction by name. DI0.1.1.1,
10:48
start, NO contact, passes power when the
10:51
start button is pressed.
10:55
stop, NC contact, passes power at all
10:58
times, opens when the stop button signal
11:04
motor sealing branch, NO contact,
11:07
holds the rung energized after the start
11:12
motor out coil, turns the relay output
11:15
on when the rung is true.
11:17
That single rung uses three of the
11:19
contact and coil instructions covered in
11:21
this post. As we build more complex
11:23
programs in the coming post, adding
11:25
timers, counters, and math, you will see
11:27
all of these instructions combined in
11:29
increasingly practical ways.
11:32
Next time, we will look at timer
11:34
instructions in the Productivity Mini
11:39
Many PLC manufacturers offer a range of
11:41
hardware and software.
11:43
All programmable logic controllers share
11:44
similar basic features.
11:47
To see how I would approach learning
11:48
about basic PLCs, click here.
11:51
Click here to see how you can program
11:53
for free with the ACC PLC simulator with
11:55
3D scenes you can program.
