![]() ![]() It is these digital signals that will eventually give our binary value representation in the PLC.īefore getting to know about the A/D converter it’s important to understand what type of analog signal you’re dealing with. This is the component in the PLC analog input card that transforms the analog signal to digital signals. When the analog input signal enters the PLC it goes through an A/D converter or analog to digital converter. The binary number can therefore represent values from -32.768 to 32.767. ![]() So with 1 bit for signing we have 15 bits left for representing the analog value. Because the first bit is used for signing the number, giving it either a positive or negative value. This is only half the truth for PLC’s though. If you remember a little bit about binary numbers you will know, that a binary number with 16 digits can represent values from 0 to 65.535. A word in binary is 8 zeros’ in a row or two bytes (4 zero’s). In many PLC’s an analog signal is represented by a word. But if you combine these bits and thereby create multiple digit numbers, things start to get interesting. As mentioned, this is how digital inputs work. Bits and BytesĪ binary number with one digit is called a bit. I would recommend that you take a look at this tutorial on binary numbers, if you don’t know how they work. Binary is just another way of writing numbers. The system only has two numbers, compared to our 10-base numbering system where we have 10 numbers from 0 to 9. To understand how analog inputs work in a PLC you have to understand binary numbers.īinary numbers is the numbering system used by a PLC or any other computer. Very useful for digital signals, but not for analog. Since a transistor can only be either on or off, these two states will then represent the values 0 and 1.īut this only gives us two states. This is due to the fact that a PLC or a microcontroller is really just advanced electrical circuits made out of transistors. Because what is really going on, is that the PLC works with binary numbers. But that does stop us from working with analog signals. The answer is binary numbers! Representing Analog Signals with Binary NumbersĪs mentioned before a PLC can only work with the two values 0 and 1. We cannot represent it with boolean values, because they can only have the values 0 and 1. The question is now: how do a PLC deal with all these different values? Let’s say you have an analog signal at 5 volts going into the PLC. If you look at the diagram below, you will see that the analog signal can have any value between 0 and 10 volts. And since analog signals are continuous, this signal will always at any time represent a voltage level. This signal can vary from 0 to 10 volts and have any voltage level in between. But what about analog signals? As Wikipedia writes, analog signals are continuous signals that can vary over time.įor example you can have a 0-10 volt analog signal. ![]() They are either 0 or 1 and thereby relatively easy to work with. A PLC can only work with the values 0 and 1. If you’ve read my article about combinatorial logic you will know that a PLC works with boolean values. Analog Signals in the PLCįirst of all, we are going to look at some numbers.
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