CHAPTER 23 Alarm Event Programming - CengageCHAPTER 23 Alarm & Event Programming ... hen the mo tely...
Transcript of CHAPTER 23 Alarm Event Programming - CengageCHAPTER 23 Alarm & Event Programming ... hen the mo tely...
CHAPTER 23 Alarm & Event Programming
Objectives
After completing this chapter, you should have the knowledge to:
Understand alarm programming.
Apply the various techniques to capture alarm and event information.
Many PLC applications require some form of alarming when abnormal conditions or events occur. PLCs are
well suited for this task and in fact, many PLC manufacturers provide special instructions designed just for
this purpose. Some of these special instructions will be covered later in this chapter.
Alerting operating or maintenance personnel of abnormal conditions or problems saves time and increases
machine or process up‐time. When detailed alarming is provided, many problems can be resolved by
operators themselves rather than calling a technician to find the problem saving time and increasing
productivity.
When a PLC system is connected to one of the many HMI interfaces available on the market today, the HMI
can provide all of the alarming functions necessary with minimal additional PLC programming. Most HMI
software packages provide some form of alarming and event recording. These HMI systems continually
monitor the PLC’s internal data files or tags and based on how the HMI is programmed will alarm accordingly.
When HMI interfaces with built‐in alarming features are not part of the overall system or when events must
be captured faster than an HMI system can monitor, the alarming and event recording must be programmed
in the PLC. This chapter is dedicated to showing the reader some of the techniques and instructions used to
program alarm and event information in PLCs.
BASIC ALARM LOGIC
Alarms and events can be triggered from digital information such as a motor failing to start or run. They can
be triggered from process analog values such as a high temperature or low pressure. Whether monitoring a
digital or analog value the end result is the same, a bit or tag is typically set to a 1 or ON indicating that a
problem has been detected. Figure 23‐1 illustrates an example of this basic logic.
R
an
an
an
w
m
Af
sw
th
fr
ot
A
re
pr
Bo
be
ung 1 in Figur
n alarm if the
nalog temper
n internal bit
with an actual
monitored by a
fter studying
witch is turne
herefore the m
raction of a se
ther PLC logic
similar probl
eached 101° f
rocess, the op
oth problems
elow in Figure
re 23‐1 monit
e motor is not
rature input (
or tag that, w
output that i
an HMI interf
Rung 1 in Fig
ed ON, the sta
motor alarm
econd may no
c that uses th
lem can be se
for only a spli
perator may n
s described ab
e 23‐2.
Figu
tors the moto
t running whe
N7:1) and ala
when ON, ind
illuminates a
face system.
gure 23‐1, you
atus input fro
will be ON fo
ot seem like m
is alarm infor
een in the sec
t second caus
not know wh
bove can be c
re 23‐1 Basic
or on/off swit
en the switch
arms if the te
icates an abn
light, sounds
u should see a
m the motor
r a fraction o
much but it ca
rmation or fa
cond rung wit
sing the high
at happened
corrected wit
Alarm Logic
tch and corre
is in the ON
mperature ex
normal condit
a horn, or lef
a basic proble
starter does
f a second as
an trigger fals
lsely turning
th the over te
temperature
.
h some simp
Example
sponding mo
position. The
xceeds 100° F
tion. This inte
ft as an intern
em with this a
not change s
s the motor co
se alarms tha
on an alarm o
emperature a
e alarm to tur
le changes to
otor starter st
e second rung
F. In both run
ernal bit or ta
nal memory a
alarm logic. W
state immedia
ontactor chan
t can cause p
output.
larm. If the te
rn ON shuttin
o the alarm lo
tatus input to
g monitors an
gs the output
g can be repl
address that i
When the mo
ately and
nges state. Th
problems with
emperature
g down the
ogic as shown
set
n
t is
aced
is
otor
his
h
In
al
Th
ex
th
ac
ab
C
Ca
ci
m
th
th
n the first run
larm is activa
he second run
xample we ha
he alarm set‐p
ction. See Ch
bnormal mot
CAPTURING
apturing and
rcuit as was s
meaning the a
he alarm rete
his chapter.
g an On‐Dela
ted which is e
ng uses a sea
ave used the
point before t
hapter 22 for
or conditions
G ALARM E
retaining ala
shown in Figu
larm status w
ntive as show
Figur
y Timer (TON
enough time
ling circuit to
start push bu
the alarm can
an example o
s.
EVENTS
rm informatio
ure 23‐2, Rung
will be lost if t
wn in Figure 2
re 23‐2 Enhan
N) has been ad
for the moto
o seal‐in the a
utton as the r
n be reset. Th
of a motor fau
on can be do
g 2 and some
he processor
23‐3. Other m
nced Basic Ala
dded that allo
r contactor to
alarm until the
eset method.
he start butto
ult and monit
ne in multiple
e means to re
r loses power
methods, such
arm Logic
ows for a sma
o change stat
e alarm is res
. Of course, t
on can be rep
toring logic th
e ways. A sim
est the alarm.
. Latching ins
as moving da
all delay befo
te and preven
set by the ope
he temperatu
placed with al
hat can be use
mple method i
This method
structions can
ata, will be d
ore the motor
nt a false alar
erator. In our
ure must be b
most any des
ed to alarm
is to use a sea
d is non‐reten
n be used to m
iscussed later
r
rm.
r
below
sired
aling
ntive,
make
r in
Yo
Th
pu
A
So
ra
m
to
ch
an
ch
in
cu
ti
al
ou will notice
his is done to
ushed while t
ANALOG RA
ome applicati
apid rate of ch
move, and bit
o the evaluati
hanging the t
nalog value (F
hange is store
nstruction and
urrent analog
mer is done.
larm on a dec
e in Figure 23‐
o ensure that
the alarm is s
ATE‐OF‐CH
ions require t
hange and ala
instructions t
ion period (30
imer preset v
F8:1) that wa
ed in F8:2 and
d requires a c
g value when
This logic mo
creasing rate
Fi
‐3 that the ala
the alarm rem
till active.
HANGE ALA
that analog va
arm if such a
to create a ra
0 seconds). Th
value. Rung 4
s stored at th
d can be chan
corresponding
the PLC is firs
onitors for a p
of change or
igure 23‐3 Lat
arm reset (un
mains set for
ARM LOGI
alues such as
condition exi
te of change
his evaluation
compares th
he end of the
nged to any d
g unlatch inst
st started so t
positive (incre
both if desire
tching Alarm
nlatch) rung is
the entire PL
C
temperature
ists. The logic
alarm. Rung
n period can
e current ana
last evaluatio
esired value.
truction to res
that a false al
easing) rate of
ed.
Logic
s located abo
LC program sc
e, pressure, le
c in Figure 23‐
2 in Figure 23
be set to any
alog value sto
on period. Th
The alarm o
set the alarm
larm is not ge
f change, wh
ove the alarm
can if the star
evel, etc. be m
‐4 uses a time
3‐4 is a free r
y desired valu
ored in F8:0 w
e maximum a
output is latch
m. Rung 1 is us
enerated the
ich can be ea
set (latch) ru
rt button is
monitored for
er, compare,
unning timer
e by simply
with the previ
allowable rat
hed using the
sed to store t
first time the
asily changed
ung.
r a
set
ious
e of
latch
the
e
to
Figur
e 23‐4 Rate‐oof‐Change Alaarm Logic
A
Ea
bo
en
an
ye
w
de
ha
Th
te
de
ex
Th
an
bo
ANNUNCIA
arly alarming
oards used a
ngraved on th
nnunciators w
et acknowled
was acknowled
epending on
ad occurred (
he PLC ladder
emperature a
escribed abov
xample on ho
he over temp
n internal me
oard.
ATOR LOGIC
methods use
light behind a
he window. W
would use thr
ged by the op
dged, the alar
the state of t
(flashing), wh
r logic to mim
alarm as was s
ve. The “Flas
ow to program
perature alarm
emory addres
C
ed an annunc
an opaque w
When the alar
ree modes to
perator, the a
rm window w
the alarm. Op
ich are still ac
mic the early a
shown in Figu
sher” contact
m this flasher
Figure
m could be a
s monitored
iator board to
indow. The o
rm was active
indicate an a
alarm window
would stop fla
perators could
ctive (illumin
annunciators
ure 23‐2 and a
is a ½ second
r.
e 23‐5 Basic A
hardwired ou
by an HMI th
o notify oper
paque windo
e the window
alarm conditio
w would flash
ashing and eit
d monitor the
ated), and wh
is shown Figu
added the ne
d On/Off inte
Annunciator T
utput to a ligh
at has been p
ators of prob
ow would hav
w would be illu
on. If the ala
h indicating th
ther remain il
e annunciator
hich were not
ure 23‐5. Her
ecessary logic
rnal memory
Type Logic
ht on an annu
programmed
blems. These a
ve the name o
uminated. Th
rm had been
he problem. O
lluminated or
r board and te
t active (non‐
re we have us
c so that the a
y address. See
unciators boa
to mimic an
annunciator
of the alarm
hese alarm
triggered bu
Once the alar
r turn off
ell which alar
‐illuminated).
sed the same
alarm functio
e Chapter 22 f
rd or it could
annunciator
t not
m
rms
.
over
ns as
for an
be
If
B
be
w
yo
at
Ch
In
w
hu
w
Th
Th
sh
you only hav
ut if you have
ecome cumb
way to handle
ou recall from
t the bit level
hapter 6 wou
n the example
words of data.
undreds of al
word, file, and
he first step i
Word
Word
unackn
Word
Word
still ac
he second ste
hown in Figur
ve a handful o
e more than a
ersome requi
a large numb
m Chapter 6 “
to make logi
uld be strongl
e that follows
Later in this
arms at one t
bitwise oper
s to create fo
1 (N7:0) Raw
2 (N7:1) Curr
nowledged.
3 (N7:2) Ackn
4 (N7:3) Unac
tive.
ep is to progr
re 23‐6.
of alarms to p
a handful or e
iring addition
ber of alarms
Digital Logic G
cal decisions
y recommend
s we will prog
chapter we w
time. We wil
rators can be
our (4) integer
Alarms – this
ent Alarms –
nowledged Al
cknowledged
am each of yo
Figure 2
program, then
even a few hu
nal programm
is to use bitw
Gates” that d
. If you are no
ded before pr
gram the alarm
will show how
l use the Alle
used.
r memory wo
s word contai
contains all c
arms – conta
d Alarms – con
our raw alarm
3‐6 Alarm Sta
n the method
undred alarm
ming time, me
wise logic alon
igital logic no
ot familiar wit
roceeding.
m logic for 16
w you can take
en‐Bradley PLC
ords (16 bit) a
ins the actual
current alarm
ains the status
ntains the sta
m bits using o
atus Logic Usi
d shown in Fig
s to deal with
emory usage,
ng with word
otations such
th digital logi
6 alarms (one
e this basic a
C‐5 for this ex
and label as fo
l alarm bits se
ms that are eit
s of all ackno
atus of all una
one of the 16
ing N7:0 Bits
gure 23‐5 will
h, then this m
and scan tim
and file mov
as AND, OR,
ic notations t
16 bit word)
pproach and
xample, but a
ollows:
et in your use
ther acknowle
wledged alar
acknowledged
bits available
work just fin
method may
e. A much be
ve instruction
XOR, etc. ope
hen a review
by manipula
deal with
any PLC with
er program.
edged or
rms.
d alarms that
e in word N7:0
ne.
etter
s. If
erate
of
ating
t are
0 as
Th
w
us
un
To
23
sh
he third step
we are using tw
sing logical op
nacknowledg
o better unde
3‐8a (unackn
hown for easy
is to program
wo Compute
perators in th
ged alarm wo
Figure 2
erstand what
owledged) an
y of understa
m the logic to
(CPT) instruc
he expression
rds.
23‐7 Logic to
each express
nd Figure 23‐8
nding.
Figure 2
find all unack
ctions to perfo
ns of each com
Find Unackno
sion is doing i
8b for acknow
23‐8a Unackn
knowledged a
orm this task.
mpute instruc
owledged and
in the two CP
wledged alarm
nowledged Al
and acknowle
. You will not
ction to updat
d Acknowled
PT instruction
ms. Only the f
arm Matrix
edged alarms
ice in Figure 2
te the acknow
ged Alarms
s refer to the
first five bits
s. In Figure 23
23‐7 that we
wledged and
e matrix in Fig
of each word
3‐7
are
gure
d are
In
in
n step four we
nto the ackno
e program the
wledged alar
Figure
e logic to clea
rm word whe
Figu
e 23‐8b Ackno
ar the unackn
n the acknow
ure 23‐9 Alarm
owledged Ala
nowledged ala
wledged push
m Acknowledg
rm Matrix
arms and mo
button is pre
ge Logic
ve the curren
essed. See Fig
nt alarms (N7
gure 23‐9.
7:1)
St
Re
in
tep five uses
efer to the m
nstruction of F
another CPT
atrix in Figure
Figure 23‐10.
instruction to
Figure
e 23‐11 to be
o update the
e 23‐10 16‐Bi
etter understa
current alarm
t Alarm Logic
and the logica
m word (N7:1
c Example
al operation b
). See Figure
being perform
23‐10.
med in the las
st CPT
R
al
st
bo
lo
on
M
To
ty
pr
m
ch
pl
un
N
co
co
ungs 3, 4 and
larm such as w
tate. This info
oards, or sou
ogic is that it o
ne scan.
MULTIPLE A
o increase the
ype instructio
rogram in Fig
monitor the st
hanging the le
lan to increas
nacknowledg
7:0 through N
ontain the sta
ontains all ack
d 5 in Figure 2
whether the
ormation can
nding a horn
operates in a
ALARM &
e number of a
ons that opera
gure 23‐12 rep
atus of 80 (16
ength or word
se the numbe
ged and ackno
N7:4 contain
atus of all cur
knowledged a
Fig
23‐10 monitor
alarm has be
be used in m
if there are a
single scan a
EVENT CA
alarms (abov
ate on multip
places the CP
6x5) alarms. Y
ds to operate
er in the futur
owledged) as
the raw alarm
rrent alarms,
alarms and N
ure 23‐11 Cu
r all 16 alarm
en acknowled
any different
any unacknow
nd will trap t
PTURING L
e sixteen) is a
ple words at o
T, MOV, and
You can incre
e on. It is reco
re that you cr
shown in Fig
ms that are pr
both acknow
12:0 through
rrent Alarms
s and provide
dged, unackn
t ways such as
wledged alarm
he status of a
LOGIC
a simple matt
one time such
CLR instructi
ease or decrea
ommended th
eate a separa
ure 23‐12.
rogrammed i
ledged and u
h N12:4 the un
Matrix
e the user wit
nowledged, or
s turning on w
ms. The real b
any alarm eve
ter of replacin
h as the Allen‐
ons with FAL
ase the numb
hat if you hav
ate file for ea
nto the user
unacknowledg
nacknowledg
th status info
r currently in
warning light
benefit to this
en if the alarm
ng the CPT ins
‐Bradley FAL
, COP, and FL
ber of alarms
ve a large num
ch alarm stat
PLC logic. N1
ged. N11:0 th
ged alarms.
rmation on e
an active ala
s or annuncia
s type of alarm
m was only on
structions wit
instruction. T
LL instructions
by simply
mber of alarm
tus (raw, curr
0:0 through N
hrough N11:4
each
arm
ator
m
n for
th file
The
s that
ms or
rent,
N10:4
Figure 23‐12 Alarm Logic Example For Up To 80 Alarms
The reset output instruction that follows each FAL instruction ensures that the FAL is reset before the next
program scan so that no alarms are lost.
The examples shown so far in this chapter are only some of the many ways that alarming information can be
handled in the PLC. Most HMI systems today have very extensive alarming and event recording capabilities
that make programming alarm logic in the PLC almost obsolete. The questions you must ask yourself is, does
the HMI update fast enough to capture your alarms without adding additional PLC logic.
ALLEN‐BRADLEY LOGIX5000 ALMD & ALMA INSTRUCTIONS
The Allen‐Bradley Logix family of PLC processors has two alarm/event instructions designed specifically for
monitoring digital and analog data for abnormal conditions as programmed by the user. These Logix‐based
alarm instructions are available for use in relay ladder, structured text, and function block diagram programs.
The advantage to using these two instructions is that when an alarm is detected, the controller will publish
the event to FactoryTalk View Alarms and Events servers that propagate alarms to FactoryTalk View SE
clients (HMIs) that subscribe to receive notifications.
The Digital Alarm (ALMD) instruction detects digital alarms based on Boolean (true/false) conditions. The
instruction is an output instruction that obtains its alarm condition from the rung condition. Some of the
features of the ALMD instructions include alarm acknowledge, latch, minimum duration timer, alarm
counter, time stamp, severity, etc.. Figure 23‐13 Rung 1 shows and example of the ALMD instruction.
The Analog Alarm (ALMA) instruction detects analog alarms based on the level or rate of change of an analog
value. The instruction is an output instruction and is typically placed on an unconditional rung. Some of the
features of the ALMA instructions include alarm acknowledge, high and high/high limits, low and low/low
limits, dead band, rate‐of‐change, minimum duration timer, alarm counter, time stamp, severity, etc.. Figure
23‐13 Rung 2 shows an example of the ALMA instruction.
Because of the many features of both of these instructions it is not practical to include a complete
description here. Please refer to the manufacturer’s instruction manual for a complete description.
C
M
al
W
ca
pr
pr
al
un
al
M
th
an
Chapter Su
Many PLC app
larming is pro
When program
aptured, annu
rogrammed i
rogram is larg
larms at one t
ncommon to
larms.
Most HMI syst
he need for P
nd data files t
F
mmary
lications requ
ovided, mach
mming alarm
unciated, ack
n conjunction
ge with many
time which w
find PLC prog
tems today ha
LC programm
that contain t
Figure 23‐13 A
uire some for
ine or proces
logic, the pro
nowledged, a
n with the log
y alarms it ma
will save time,
grams that ha
ave extensive
med alarm log
the machine o
Allen‐Bradley
m of alarming
s down‐time
ogrammer sho
and reset. In s
gic that contro
ay be easier to
increase PLC
ave been crea
e alarming and
gic. These HM
or process inf
y ALMD and A
g when abno
can be minim
ould take into
small PLC pro
ols the machi
o create dedi
C scan time, a
ated with ded
d event captu
MI systems can
formation suc
ALMA Instruct
rmal conditio
mized which i
o consideratio
ogram applica
ine or proces
cated alarm l
and decrease
dicated progr
uring features
n be program
ch as pressur
tions
ons occur. Wh
n turn increa
on how alarm
ations the ala
ss. On the oth
logic to proce
memory usag
am files for ju
s that can red
mmed to moni
re, level, runn
hen adequate
ses productiv
ms will be
rm logic can
her hand, if th
ess and updat
ge. It is not
ust handling
duce or elimin
itor the PLC t
ning, fault, etc
e
vity.
be
he PLC
te all
nate
ag
c.
R
Review Que
1. What p
2. How d
3. Write
100° F
4. In Figu
5. In the
estions
pair of PLC in
oes the logic
the alarm log
.
ure 23‐12 wha
PLC logic belo
structions ca
al XOR instru
gic that will al
at would you
ow, when wil
n be used to
ction work?
arm if a proc
change to inc
l the flow ala
capture and
ess temperat
crease the nu
arm be active?
retain alarms
ture should ri
umber of alar
?
s?
ise above 250
rms to 128?
0° F or fall bellow