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🔎 In this video, you'll learn about the "Dead Zero" problem in 0-20 mA signals and how it affects PLC systems.
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👉 We’ll explain:
✅ What the Dead Zero problem is
✅ Why it happens in 0-20 mA signals
✅ How it impacts PLC readings
✅ Simple ways to identify the issue
💡 This tutorial is perfect for beginners and professionals working with PLCs and industrial automation.
🚀 Watch now and improve your troubleshooting skills!
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0:07
in this video I will discuss about dead
0:12
zero
0:14
problem the previous videos we discussed
0:18
about 4 to 20 milliamp right the four
0:24
represents the zero scale reading or 0%
0:28
of the process variable
0:30
so it is 0 percentage and the 20
0:34
represents
0:35
the full scale value and it represents
0:39
the 100% of the process
0:42
variable so this concept is very
0:45
clear now what I will do I will assume 0
0:50
to 20 milliamp as the range instead of 4
0:57
to20 okay
1:00
I assumed 0 to 20 milliamp as a range
1:05
instead of 4 to 20 in this
1:09
video the zero represents the 0% of the
1:14
process variable or zero scale and 20
1:18
represents the full scale value which is
1:21
100% of the process variable
1:31
now I will go to the same
1:34
example we have a tank and there is a
1:38
level transmitter which measures the
1:40
tank
1:42
level this transmitter range is 0 to 20
1:47
milliamp when the tank level is
1:51
0% transmitter sends 0 milliamp to the
1:57
PLC and the PLC calculate the equivalent
2:01
tank level and display the tank level on
2:04
the
2:06
computer if the tank is full then
2:10
transmitter sends 20 mamp to the PLC PLC
2:14
updates the tank level status on the
2:18
graphics if the tank is
2:21
50% then transmitter sends 10 mamp to
2:26
the
2:27
PLC again plc calculates the equivalent
2:31
tank level and displays on the
2:36
computer okay in this video you have to
2:40
remember one point main point which is
2:46
transmitter range it is 0 to 20
2:49
Mila
2:52
Okay let's say the present tank level is
2:55
0
2:57
percentage then how much current the
3:00
transmitter will send it is 0 milliamp
3:04
current signal it will send it to the
3:08
PLC PLC calculates the level and updates
3:11
the computer
3:14
Graphics now I will take one
3:19
table the first one is tank level the
3:22
present tank
3:24
level right now how much percentage is
3:26
there tank level 0% so I will
3:31
zero next one is level transmitter right
3:35
now what is the level transmitter output
3:38
it is 0
3:39
milliamp so I will enter 0
3:43
milliamp right now how much current the
3:46
PLC is receiving it is zero so I will
3:51
enter 0
3:53
milliamp so what is the computer status
3:56
how much it is there level reading on
3:59
the computer it is 0 percentage so I
4:02
will enter 0
4:06
percentage
4:08
okay let's say due to some
4:13
reason the cable the wire between the
4:16
transmitter and the PLC is damaged or
4:22
broken then what
4:25
happens
4:27
see the wire is broken
4:30
between transmitter and PLC due to any
4:34
reason there may be a short circuit
4:37
there may be a open circuit there may be
4:39
a sensor
4:41
failure this level sensor may be a
4:44
failure some damage is
4:47
happened okay in this case what happens
4:51
again we will
4:55
check now I will update the table again
5:03
see the tank level is 0
5:06
percentage right now it is 0 percentage
5:09
see I am using yellow color for the
5:12
readings this case is for the broken
5:15
wire or sensor
5:20
failure that level transmitter is
5:22
sending 0 milliamp so 0
5:27
milliamp but the wire is
5:31
broken the PLC is not receiving any
5:35
input from the
5:38
transmitter okay so in this case the PLC
5:43
receives how
5:44
much default value is zero so it will
5:48
receive 0
5:51
milliamp and the PLC calculates the 0
5:56
milliamp into the equivalent level value
5:59
and and updates the computer which is 0
6:03
percentage if you see if you compare
6:06
these two cases the first one and the
6:08
second
6:10
one you will not find any
6:13
fault okay this is the
6:17
problem the PLC don't know whether the
6:21
reading is true reading or false
6:25
reading in the second case it is dead
6:29
zero
6:30
the line is dead the wire is dead the
6:33
sensor is dead still the PLC is
6:37
displaying
6:40
0% this is the problem with the zero if
6:45
the zero scale value or lower range
6:49
value if it is zero then it will be
6:53
difficult for PLC to identify the fault
7:00
now you can some people can say right
7:03
now both are same values even though the
7:05
second one is faulty reading but it is
7:08
matching with the first
7:10
one the values are matching but we don't
7:14
know whether the zero is a true reading
7:19
true measurement or due to some faulty
7:23
line or due to some sensor
7:27
damage now I will take one more case yes
7:29
You
7:31
observe so this is the dead zero problem
7:35
which is highlighted here now I will
7:38
take one more example see I will
7:41
increase the tank
7:44
level now the tank level is
7:47
50% I will enter 50
7:50
percentage
7:51
okay the level transmitter sending 10
7:56
milliamp that is why the level
7:58
transmitter output is 10
8:00
milliamp but the wire is still
8:04
broken so how much the PLC will
8:07
receive
8:09
zero
8:10
PLC receives 0 milliamp that means it
8:14
will not receive anything the default
8:16
state is zero the starting state is zero
8:19
that is why it will receive zero you see
8:22
the PLC unlock input right now is 0
8:25
milliamp but the level transmitter is
8:27
sending 10 milliamp
8:32
and again the PLC calculates the level
8:36
signal based on the 0 milliamp and it
8:39
will update the computer
8:41
reading which is 0
8:44
percentage so this is also a faulty
8:48
reading right the present level is
8:51
50%
8:53
but the PLC is receiving 0
8:56
milliamp that is why it is showing zero
9:01
level this is very serious concern if
9:04
you do not address
9:06
this it may lead to the
9:09
accidents damage to the equipment and
9:13
human beings
9:17
right also one more important point you
9:22
have to remember when understanding this
9:25
dead zero
9:28
problem you have to consider the plcs
9:31
from the 1970s
9:34
1980s in that era
9:39
okay with the modern technology we have
9:42
lot of diagnostic softwares uh
9:45
diagnostic Hardware available we can
9:48
easily detect the faulty readings faulty
9:52
circuits faulty lines short circuit open
9:56
circuit sensor
9:58
failure okay
9:59
okay
10:01
but these 4 to 20 milliamp are
10:04
introduced during
10:07
19 uh 60s 1970s at that time so at that
10:12
time the plcs don't have any inbuilt
10:16
Diagnostics or inbuilt advanced Safety
10:20
Futures so if you are already working in
10:23
Industry do not compare present
10:27
technology present PLC future Futures to
10:30
solve this
10:32
problem you have to solve this problem
10:36
without using any
10:39
modern technology I mean modern safety
10:44
Futures okay so this is the dead zero
10:48
problem which was faced during
10:50
the 1970s 1980s at that
10:56
time so I will discuss the solution in
10:59
the next video
#Computers & Electronics