# Plc ladder diagram for analog signal

#### irfan16

Joined Dec 29, 2011
12
Dear All

My input signal to PLC is 0~24V
I want to activate green led at out put of PLC when input voltage to plc is 10 volt..and red led when input voltage is 24v..

Kind Regards

Urfee

#### kubeek

Joined Sep 20, 2005
5,751
Statistically speaking, the leds would never light up because the voltage will never be exactly 10 nor 24V. You need to specify some intervals, like green led is on when V>10V or 9.9V<V<10.1V.
Then you need to set up some comparators to get logic signals out of the continuous variabels, then make the PLC logic.

#### strantor

Joined Oct 3, 2010
5,540
I do not recognise the 0-24V analog signal. are you sure that is correct? All PLCs I know of, standardize on 0-10V, 4-20mA, and rarely 0-60mA or 0-20mA. Never seen 0-24V. In any case, depending on what PLC you have & what software I can't walk you step by step unless I know what you are using. You should have a symbol library that contains analog comparator functions like >, <, $$\leq$$, $$\geq$$, $$\neq$$. do you have these symbols?

#### anotheruser1

Joined Dec 6, 2011
30
Its doable, but I need to know what programming software you are using and the processor

#### GetDeviceInfo

Joined Jun 7, 2009
1,844
Look up your cards input impedance configured as 0-20ma, calculate the appropriate dropping resistor that gives full scale current, Scale for full range, and off you go. Some older PLCs require specific multiple port read/writes to read your conversion, but most now is a simple port read. A simple looping compare and output will have you up and running.

#### irfan16

Joined Dec 29, 2011
12
Statistically speaking, the leds would never light up because the voltage will never be exactly 10 nor 24V. You need to specify some intervals, like green led is on when V>10V or 9.9V<V<10.1V.
Then you need to set up some comparators to get logic signals out of the continuous variabels, then make the PLC logic.
Dear Sir

My input signal is 4~20mA. Actually I want to outputs. one output when input is 7 to 9mA, Second ouput when input is 13 to 16mA. And third out put will enrgise when input is 18 to 20mA.CAN U GUIDE ME HOW I SHOULD DEVELOP LADDER LOGIC..IF U SEND ANY EXAMPLE OF WRITTEN PROGRAM IT WILL SURELY VERY HELPFUL.. I am using ABB PLC AC500, CODESYS V2.3

#### irfan16

Joined Dec 29, 2011
12
I do not recognise the 0-24V analog signal. are you sure that is correct? All PLCs I know of, standardize on 0-10V, 4-20mA, and rarely 0-60mA or 0-20mA. Never seen 0-24V. In any case, depending on what PLC you have & what software I can't walk you step by step unless I know what you are using. You should have a symbol library that contains analog comparator functions like >, <, $$\leq$$, $$\geq$$, $$\neq$$. do you have these symbols?
My input signal is 4~20mA. Actually I want to outputs. one output when input is 7 to 9mA, Second ouput when input is 13 to 16mA. And third out put will enrgise when input is 18 to 20mA.CAN U GUIDE ME HOW I SHOULD DEVELOP LADDER LOGIC..IF U SEND ANY EXAMPLE OF WRITTEN PROGRAM IT WILL SURELY VERY HELPFUL.. I am using ABB PLC AC500, CODESYS V2.3

#### strantor

Joined Oct 3, 2010
5,540
My input signal is 4~20mA. Actually I want to outputs. one output when input is 7 to 9mA, Second ouput when input is 13 to 16mA. And third out put will enrgise when input is 18 to 20mA.CAN U GUIDE ME HOW I SHOULD DEVELOP LADDER LOGIC..IF U SEND ANY EXAMPLE OF WRITTEN PROGRAM IT WILL SURELY VERY HELPFUL.. I am using ABB PLC AC500, CODESYS V2.3
I dont have access to your codesys software, but heres how it would look like in RSLogix500. Pay attention to the "source B" numbers, you will need those.

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