All You Need To Know About Siemens PLC Analog Programming. – Multipurpose Engineering & Industrial Automation
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Nowadays, PLCs regulate both digital and analog signals. The input relays of PLC support both digital and analog inputs. Some models of Siemens PLC have built-in analog inputs. In most circumstances, we need to acquire an Analog Module separately [1]. Analog Module Consists of both input and outputs. The input side of an analog module is Analog to Digital Converter (A to D). Later in this blog, we will discuss briefly the Analog Modules. Siemens PLC Analog Programming enables both unipolar and bipolar inputs [5].

Learn Siemens PLC Analog Programming at Multipurpose Engineering & Industrial Automation.

What is Analog Programming? 

Analog signals are continuous signals that change value over time. Thus, the PLC analog signal will range from 0 to 10v or 4 to 20ma. So, it is logical to say that the value of the PLC analog signal will vary between 0 to 10v or 4 to 20ma.   


For example, take the above picture. If we give our PLC any analog current input, the value will fluctuate between 4ma and 20ma.  
So, how does a PLC handle an input signal that fluctuates between 4ma and 20ma?  
PLC handle these continuously changing value by converting them into binary bits.  A bit is the smallest unit of data in computing and digital communications. Its name is a binary digit. The bit represents one of two logical states [6]. 

Our PLC will convert 10V to 32000 bits if you give it 10V. The Detailed Calculation will be done later in our blog. 
An A/D Converter is required to convert analog to digital signals which are also known as Analog to Digital Converter [1]. Analog signals change their values, phase angle, and position continuously. Whereas Digital Signal will always act on two states high and Low. The values of digital signals are always fixed to 0 and 1. Siemens PLC has various Modules. Analog Programming requires a basic understanding of Siemens PLC. Such as the reading, writing, and wiring procedure of Siemens PLC.  

To learn more about Siemens PLC, read our article ‘How to Learn Siemens PLC Very Easily & Quickly‘.

Siemens PLC has various kinds of analog extension modules to serve these purposes. But before working with all these modules, you must understand how Siemens PLC works.

Analog to Digital Converter (A/D)

An A/D Converter is used as the PLC’s input in an analog module. To have a clear understanding please look at the picture below, 

Siemens PLC Analog Programming | Analog I/O Expansion Module
Siemens S7 200 PLC EM 235 Analog I/O Expansion Module [3]

We will show you how to program Siemens PLCs using analog signals. Moreover, we will also help you with the PLC analog input wiring procedure. 
As PLC is a microcontroller that only understands bits, we need analog to digital converters. The A/D Converter will convert the input signals into bits. These bits allow us to control or monitor our loads. 

Digital to Analog Converter (D/A)

In an analog module of PLC digital to analog converter is used as the output of the PLC. To control our PLC with bits, we need to convert our input signal to bits. But we cannot control or operate our load using bits. So, to control our output, we need to convert digital bits into analog signals[4].  
Siemens PLC analog programming and various analog programming modules are covered in detail by Multipurpose Engineering & Industrial Automation.

Siemens PLC Analog Programming — Input Scaling

Scaling is a crucial part of any kind of PLC analog programming training. Scaling is required to operate our load in a certain analog input value[5].  

As an example of Siemens PLC Analog Programming, consider the s7 200 PLC’s analog module. So, if we want to turn on a load at a certain voltage level it will be hard to do so.  

Thus, we need to convert these scattered 0 to 32000 values to raw 0 to 10v. By doing a simple math we can do so. 
Here, 32000 stands for 10v 
so 1V = 32000/10 = 3200   
if 1v = 3200 
so 5v = 3200×5 = 16000 
By doing these simple math steps we can easily scale our analog input values. And we can operate our loads to certain voltage value. This is an aspect of the PLC Analog Programming training at Multipurpose Engineering & Industrial Automation. 

Siemens PLC Analog Programming — Output Scaling

Analog output scaling is the same as input scaling. But there is a twist. Let us take an example to understand it more clearly. Assume we need to turn on a load when the analog output is 2v. it will turn on another load when the analog output is sent 6v. Finally, when the PLC analog output is 9v, both loads turn.  

Also, the value it is sending whether it is urate or not.   
The calculation process is the same as before,  
First, we need to convert the binary coded decimal value to an accurate raw value 
we know, 
10v = 32000 v 
1v = 32000/10 
2v = (32000/10) ×2 
    = 6400 
We need to set our output value to 6400. When the D/A converter sends this value, our load turns on. Learn how to program Siemens PLCs using analog inputs and outputs from Multipurpose Engineering & Industrial Automation.

Siemens PLC Analog Programming — Input Wiring 

Before starting any wiring, we must go through the PLC manual properly. Wiring of analog entities is easy but sensitive as well. There are various analog inputs. The most used analog inputs are,

  1. Voltage Input
  2. Current Input

For the wiring of Voltage input, we need two ports  

  1. A+ port = The voltage source’s positive supply will be linked here (for EM 235 Analog expansion module).  
  2. A˗ port = We’ll connect the voltage source’s ground or common supply here.
Wiring of voltage and current input for S7 200 PLC EM 235 analog extension module [3].  

For the wiring of current input, we need 3 ports  

  1. RC and C+= we need to short these two ports with a wire if we want to use current input. These two ports together will act as the positive supply for current input.  
  2. C˗ = This port will be the current input’s negative supply.  

Siemens PLC Analog Programming — Output Wiring

PLC analog and output wiring share similarities but there are always some differences. For starters, we have similar output points such as,

  1. Voltage Output
  2. Current Output

The analog output wiring of Siemens PLC is comparatively easier than the input wiring. To see the wiring process please see the picture given below, 

Output Wiring of Siemens s7 200 PLC EM 235 analog extension module [3]

For the wiring of voltage output we need only two ports

  1. M0 = the negative supply or point of the load will connect to this port. 
  2. V0 = the positive supply or point of the load will connect to this port. 

For the wiring of current output, we need only two ports

  1. M0 = the negative supply or point of the load will connect to this port. 
  2. I0 = the positive supply or point of the load will be connected to this port. 

The best PLC Analog Programming training center will show you how to wire PLC analog inputs and outputs. 


We discussed Siemens PLC analog programming, Siemens PLC analog module, and its wiring technique earlierWe also learned about analog input and output scaling for Siemens S7 200 PLC analog programming.  


[1] 2021. Learn-/Training Document. [online] Available at: <> [Accessed 16 September 2021]. 

[2] PLC Academy. 2021. PLC Analog Input and Output Programming | All About PLC Analog Input and Output Signals and Programming. [online] Available at: <> [Accessed 16 September 2021]. 

[3] Automation, S., 2021. S7-200 Programmable Controller System Manual. [online] Available at: <> [Accessed 16 September 2021]. 

[4] Amatrol. 2021. PLC Analog Training | Siemens S7300 Series | Adds to 890-PECB. [online] Available at: <> [Accessed 16 September 2021]. 

[5] Automation, S., 2021. S7-200 Programmable Controller System Manual. [online] Available at: <> [Accessed 17 September 2021]. 

[6] 2021. Bit – Wikipedia. [online] Available at: <> [Accessed 17 September 2021].