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Old February 6th, 2013, 02:37 PM   #1
Ali Sayghe
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Exclamation analog input in ladder logic

Hi all
I am trying write a program that has analog input from a pressure sensor in a thank that read the pressure sensor for low level and high level when the pump start filling up the tank the motor for gate valve is closed when the water reach the high level the motor for the gate valve will open so the input and the output is:
input I:0/1 from limit switch 1 to turn off the motor when its opening the valve
input I:0/2 from limit switch 2 to turn off the motor when its closing the valve
input I:2/1 analog input from pressure sensor
turn output O/0 when the signal from pressure sensor is low (111)
turn output O/1 when the signal from presser sensor is high (25000)
I have a 1769-IF8 Analog Input Card in a Micrologix 1500 system.
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Old February 6th, 2013, 02:45 PM   #2
passwordg
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Hey, I did not understand what your question is.
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Old February 6th, 2013, 03:05 PM   #3
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Quote:
...Input I:2/1 [is] the analog input from pressure sensor.
Beacause you are using a 1769-IF8 analog module, I think this analog input should be at address I:2.1 or I:2.0. In other words, it must be a word address instead of a bit address.

Quote:
I am trying to write a program...
If you would print your program to a PDF file, or ZIP it to a compresed file, and post it here, I am sure someone can help with your problem.

Your action elements are simple and only two:
"CLOSE VALVE MOTOR" and "OPEN VALVE MOTOR". Put two rungs in your program for those Outputs, and you will have a place to start.

Remember, the Inputs do not control the valve, but instead your PLC outputs control the motor that controls the valve.

Last edited by Lancie1; February 6th, 2013 at 03:08 PM.
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Old February 6th, 2013, 09:55 PM   #4
Ali Sayghe
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Originally Posted by Lancie1 View Post
Beacause you are using a 1769-IF8 analog module, I think this analog input should be at address I:2.1 or I:2.0. In other words, it must be a word address instead of a bit address.

If you would print your program to a PDF file, or ZIP it to a compresed file, and post it here, I am sure someone can help with your problem.

Your action elements are simple and only two:
"CLOSE VALVE MOTOR" and "OPEN VALVE MOTOR". Put two rungs in your program for those Outputs, and you will have a place to start.

Remember, the Inputs do not control the valve, but instead your PLC outputs control the motor that controls the valve.
yes you right i am controlling the valve through the dc motor but my problem is i don't know how can i use less than and more than function to turn the motor whether closing if the level is low or opening if the level is high according to the pressure of the tank the value that indicate low level is 500 and the valve indicate high level 20000 am using the raw/proportional unit for the analog input card. I am using SCP for to scale the input
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Old February 7th, 2013, 07:10 AM   #5
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Originally Posted by Ali Sayghe View Post
..my problem is i don't know how can i use less than and more than function to turn the motor whether closing if the level is low or opening if the level is high according to the pressure of the tank..
The Logic in the Attached Image shows how to do the above with the I/O addresses provided by you in Post #1 and #4.

However, note that if your motor is very slow and the rate of filling is lesser than the rate of emptying through a partially opened valve then you will need to latch the "Open valve" output till it reaches the limit switch because the level may drop before the valve position reaches the limit switch and turn the motor off.

Inversely if your motor is very slow and the rate of filling is greater than the rate of emptying through a partially closed valve then you will need to latch the "Close valve" output till it reaches the limit switch because the level may increase before the valve position reaches the limit switch and turn the motor off.
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File Type: jpg Valve Motor.JPG (22.5 KB, 151 views)
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Last edited by Anirban Hazra; February 7th, 2013 at 07:29 AM.
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Old February 7th, 2013, 07:12 AM   #6
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just a note
is the analogue 0~10V or 4~20 mA
because the min max scaling is different for the two
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Old February 7th, 2013, 05:49 PM   #7
Ali Sayghe
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Originally Posted by Anirban Hazra View Post
The Logic in the Attached Image shows how to do the above with the I/O addresses provided by you in Post #1 and #4.

However, note that if your motor is very slow and the rate of filling is lesser than the rate of emptying through a partially opened valve then you will need to latch the "Open valve" output till it reaches the limit switch because the level may drop before the valve position reaches the limit switch and turn the motor off.

Inversely if your motor is very slow and the rate of filling is greater than the rate of emptying through a partially closed valve then you will need to latch the "Close valve" output till it reaches the limit switch because the level may increase before the valve position reaches the limit switch and turn the motor off.
Thank you very much its really works and i attached the final program
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Old February 7th, 2013, 11:47 PM   #8
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Originally Posted by Ali Sayghe View Post
Thank you very much its really works and i attached the final program
Glad to have Helped.
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