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PLC Tutorial: Learn the Dead Zero Problem in 0-20 mA Signals
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May 23, 2025
🔎 In this video, you'll learn about the "Dead Zero" problem in 0-20 mA signals and how it affects PLC systems. 👉 Full Course Here - https://bit.ly/Free-PLC-4-20-mA-Course 📆 Free Offer Ends on March 4, 2025, at 1:01 AM PST or until coupons run out! 🎁 Due to high demand, FREE coupons are now available for a few more days! But hurry—only while they last! ⏳ 👉 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! #plc #learn #signals
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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
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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
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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
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transmitter range it is 0 to 20
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Mila
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Okay let's say the present tank level is
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0
2:57
percentage then how much current the
3:00
transmitter will send it is 0 milliamp
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current signal it will send it to the
3:08
PLC PLC calculates the level and updates
3:11
the computer
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Graphics now I will take one
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table the first one is tank level the
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present tank
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level right now how much percentage is
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there tank level 0% so I will
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zero next one is level transmitter right
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now what is the level transmitter output
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it is 0
3:39
milliamp so I will enter 0
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milliamp right now how much current the
3:46
PLC is receiving it is zero so I will
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enter 0
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milliamp so what is the computer status
3:56
how much it is there level reading on
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the computer it is 0 percentage so I
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will enter 0
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percentage
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okay let's say due to some
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reason the cable the wire between the
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transmitter and the PLC is damaged or
4:22
broken then what
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happens
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see the wire is broken
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between transmitter and PLC due to any
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reason there may be a short circuit
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there may be a open circuit there may be
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a sensor
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failure this level sensor may be a
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failure some damage is
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happened okay in this case what happens
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again we will
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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
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see I am using yellow color for the
5:12
readings this case is for the broken
5:15
wire or sensor
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failure that level transmitter is
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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
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transmitter okay so in this case the PLC
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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
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second
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one you will not find any
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fault okay this is the
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problem the PLC don't know whether the
6:21
reading is true reading or false
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reading in the second case it is dead
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zero
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the line is dead the wire is dead the
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sensor is dead still the PLC is
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displaying
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0% this is the problem with the zero if
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the zero scale value or lower range
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value if it is zero then it will be
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difficult for PLC to identify the fault
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now you can some people can say right
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now both are same values even though the
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second one is faulty reading but it is
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matching with the first
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one the values are matching but we don't
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know whether the zero is a true reading
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true measurement or due to some faulty
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line or due to some sensor
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damage now I will take one more case yes
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You
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observe so this is the dead zero problem
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which is highlighted here now I will
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take one more example see I will
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increase the tank
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level now the tank level is
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50% I will enter 50
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percentage
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okay the level transmitter sending 10
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milliamp that is why the level
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transmitter output is 10
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milliamp but the wire is still
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broken so how much the PLC will
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receive
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zero
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PLC receives 0 milliamp that means it
8:14
will not receive anything the default
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state is zero the starting state is zero
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that is why it will receive zero you see
8:22
the PLC unlock input right now is 0
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milliamp but the level transmitter is
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sending 10 milliamp
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and again the PLC calculates the level
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signal based on the 0 milliamp and it
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will update the computer
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reading which is 0
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percentage so this is also a faulty
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reading right the present level is
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50%
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but the PLC is receiving 0
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milliamp that is why it is showing zero
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level this is very serious concern if
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you do not address
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this it may lead to the
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accidents damage to the equipment and
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human beings
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right also one more important point you
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have to remember when understanding this
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dead zero
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problem you have to consider the plcs
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from the 1970s
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1980s in that era
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okay with the modern technology we have
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lot of diagnostic softwares uh
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diagnostic Hardware available we can
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easily detect the faulty readings faulty
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circuits faulty lines short circuit open
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circuit sensor
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failure okay
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okay
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but these 4 to 20 milliamp are
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introduced during
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19 uh 60s 1970s at that time so at that
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time the plcs don't have any inbuilt
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Diagnostics or inbuilt advanced Safety
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Futures so if you are already working in
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Industry do not compare present
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technology present PLC future Futures to
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solve this
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problem you have to solve this problem
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without using any
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modern technology I mean modern safety
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Futures okay so this is the dead zero
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problem which was faced during
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the 1970s 1980s at that
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time so I will discuss the solution in
10:59
the next video
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