The Secret Of Getting Rid Of Noise On Your Analog Signal

Allot of times in industrial environments we get noise on the analog signal input to PLC's or other controllers. The noise can be generated by motors, bad wiring, etc.

Placing a 1- 100 uF capacitor on the input signal and ground (common to the cabinet)  will reduce the noise that the input is receiving.

If you have any questions, or need further information please contact me.
Thank you,
Garry

Here’s a Quick Way to Understand PLC Inputs and Outputs

The term I/O means Input/Output. I/O can come in two different types; Discrete or Analog
Most people starting out leaning about programmable logic controls (PLC) are taught all about discrete input and outputs. Data is received from devices such as push-buttons, limit-switches etc. and devices are turned on such as motor contactor, lights, etc. Discrete input and output bits are either on or off. (1 or 0)
The following program will show a motor control circuit stop start.
Motor off:

Motor on:

Analog inputs
Common input variables for analog are temperature, flow, pressure, etc. They are converted to an electrical signal into a PLC analog input. Standard electrical signals are 0 - 20 mA, 4 - 20 mA, 0 - 10 volts DC, -10 - 10 volts DC.
Note: It is recommended that a 4 - 20 mA signal is best. If voltage is required, a resistor can be added to get a voltage input.

Analog outputs
Common output variables for analog are speed, flow, pressure, etc. They are converted from a word in the PLC to the output of the analog. The range of signal is then outputted to the device to control the position, rate, etc. Standard electrical signals to the device are 4 - 20 mA, 0 - 10 volts DC, -10 - 10 volts DC.

Both Analog Inputs and Outputs use words to determine the signal going to or from the device.
Example: 4 - 20 mA current Input - 8 bit resolution
4 mA = 000000002 = 0016
20 mA = 111111112 = FF16
Example: 4 - 20 mA current Output - 8 bit resolution
 0016 = 000000002 = 4 mA
 FF16 = 111111112 =20 mA

For a review of numbering systems, follow the link below:
What everyone should know about PLC numbering systems

Let me know if you have any questions or need further information.

Here's a Quick Way to Convert Grey Code into Binary for PLC

Grey Code
Grey Code is used because only one bit of data will change at a time. The following chart shows the conversion of Grey Code to Binary.

Number	Binary Code	Grey Code	Number	Binary Code	Grey Code
0	0000	0000	8	1000	1100
1	0001	0001	9	1001	1101
2	0010	0011	10	1010	1111
3	0011	0010	11	1011	1110
4	0100	0110	12	1100	1010
5	0101	0111	13	1101	1011
6	0110	0101	14	1110	1001
7	0111	0100	15	1111	1000

It is important for absolute encoders because if the power is interrupted the encoder will know where it is within the one bit.

Example:
Power is interrupted when the encoder is between 7 and 8. If we are looking at Binary Code all of the bits would be effected and we would not be sure as to what number we are looking at for the encoder. Therefore we have lost position. In Grey Code only one bit changes so we will still be able to tell if we were on 7 or 8 if the power was interrupted.

The following sample PLC program will convert 4 bit grey code into binary code.
This code was written in an Automation Direct PLC software called Do-more Designer.

Do-more Designer Software
How to use video's for Do-more Designer Software

Contact me for the above program. I will be happy to email it to you.
Thank you,
Garry

What Everybody Ought to Know About PLC (Programmable Logic Controller) Numbering Systems

Programmable Logic Controllers (PLC) are the same as computers. They only understand two conditions; on and off. (1 or 0 / Hi or Low/ etc.) This is known as binary. The PLC will only understand binary but we need to display, understand and use other numbering systems to make things work. Let's look at the following common numbering systems.

Binary has a base of two (2). Base means the number of symbols used. In binary the symbols are 1 or 0. Each binary symbol can be referred to as a bit. Putting multiple bits together will give you something that looks like this: 100101112. The 2 represents the number of symbols/binary notation. Locations of the bits will indicate weight of the number. The weight of the number is just the number to the power of the position. Positions always start at 0. The right hand bit is the 'least significant bit' and the left hand bit is the 'most significant bit'.

Let's look back at our example to determine what the value of the binary number is:
 100101112 =
We start with the least significant bit and work our way to the most significant bit.
1 x 2⁰ = 1 x 1 = 1
1 x 2¹ = 1 x 2 = 2

1 x 2² = 1 x 2 x 2 = 4

0 x 2³ = 0 x 2 x 2 x 2 = 0

1 x 2⁴ = 1 x 2 x 2 x 2 x 2 = 16

0 x 2⁵ = 0 x 2 x 2 x 2 x 2 x 2 = 0

0 x 2⁶ = 0 x 2 x 2 x 2 x 2 x 2 x 2 = 0

1 x 2⁷ = 1 x 2 x 2 x 2 x 2 x 2 x 2 x 2 = 128

 100101112  = 1 + 2  + 4 + 16 + 128

 100101112  = 151

Note that the we just converted the binary number to our decimal numbering system. The decimal numbering system is not written with a base value of 10 because this is universally understood.

To be sure we have the concept down, let's take a look at our decimal numbering system the same way as we did the binary.

Decimal has a base of ten (10). The symbols are 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9. 

15110 =

1 x 10⁰ = 1 x 1 = 1

5 x 10¹ = 5 x 10 = 50
1 x 10² = 1 x 10 x 10 = 100
15110 = 1 + 50 + 100
151 = 151

Hexadecimal has a base of sixteen (16). The symbols are  0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E and F. Hexadecimal is used to represent binary numbers. F16 = 11112 
Every for bits of binary represent one hexadecimal digit.
In our original binary number we now can convert this to hexadecimal.
 100101112
The least significant four bits are:
01112 =
1 x 2⁰ = 1 x 1 = 1
1 x 2¹ = 1 x 2 = 2

1 x 2² = 1 x 2 x 2 = 4

0 x 2³ = 0 x 2 x 2 x 2 = 0

01112 = 1 + 2 + 4 + 0 = 716

The most significant four bits are:

10012 =

1 x 2⁰ = 1 x 1 = 1

0 x 2¹ = 0 x 2 = 0

0 x 2² = 0 x 2 x 2 = 0

1 x 2³ = 1 x 2 x 2 x 2 = 8

10012 = 1 + 0 + 0 + 8 = 916
Therefore:
 100101112 = 9716 
We can now convert this hexadecimal number back into decimal
9716 =

7 x 16⁰ = 7 x 1 = 7

9 x 16¹ = 9 x 16 = 144
9716 = 7 + 144 = 151

The following chart will show all of the combinations for 4 bits (nibble) of binary. Its shows the Binary, Decimal and Hexadecimal (Hex) values. It is interesting to not that Hex is used because you still have only one digit (Place Holder) to represent the nibble of information.

Binary	Decimal	Hexadecimal	Binary	Decimal	Hexadecimal
0000	00	0	1000	08	8
0001	01	1	1001	09	9
0010	02	2	1010	10	A
0011	03	3	1011	11	B
0100	04	4	1100	12	C
0101	05	5	1101	13	D
0110	06	6	1110	14	E
0111	07	7	1111	15	F

ASCII (American Standard Code for Information Interchange)

Two nibbles (8 bits of data) together form a byte. A byte is what computers (PLC) use to store and use individual information. So it will take one unique byte to represent each individual numbers, letters (upper and lower case), punctuation etc. www.AsciiTable.com

Example:

Chr 'A' = 4116 = 010000012

Chr 'a' = 6116 = 011000012

Chr '5' = 3516 = 001101012

Each time you hit a key on your keyboard, the following 8 bits of data get sent.

A word is made up of two bytes, or 4 nibbles, or 16 bits of data. Words are used in the PLC for holding information. The word can also be referred to as an integer.

Long word / Double word is made up of 4 bytes, or 8 nibbles, or 32 bits of data. Long words are used for instructions in the PLC like math. 

Hey what about negative numbers?

So far we have talked about unsigned words. (Positive numbers)

Signed words can hold negative numbers. Bit 15 (most significant bit) of a word is used to determine if the word is negative or not. 

The following table shows you the signed vs unsigned numbers that can be represented in the PLC.

HEX	8000	BFFF	FFFE	FFFF	0000	3FFF	7FFE	7FFF
Signed	-32768	-16385	-0002	-0001	00000	16383	32766	32767
Unsigned	32768	49151	65534	65535	00000	16383	32766	32767

Memory retentiveness:

When working with PLC's look at the memory tables to determine what will happen if power is removed from the device. Will the bits go all off or retain their prior state? 

Usually there will be areas that can be used in the PLC for both conditions.

As you can see PLC numbering systems and computers are very much related and it all boils down to individual bits turning on and off. The interpretation of these bits will determine what the value will be.

Reference: 

http://www.learn-c.com/data_lines.htm

http://computer.howstuffworks.com/bytes.htm

Let me know your thoughts, or questions that you have on PLC numbering systems.