Hello. 1
In this video we are going to learn encoder basics for understand encoders. 2
We need to know perfectly how optocoupler works in here. 3
You can see structure of how optocouplers are working in led in here. 4
Led goes high and then after led goes high transistor goes high. 5
And in here zero volt from here. 6
From this point is clear and the five volt DC is cut and encoder connected to Motor shaft for the give 7
the position of the shaft with resolution precision with the pulses and the meant by resolution is number 8
of encoders that one cycle can measure in here. 9
You can see sample of encoder standard resolutions. 10
For example if the resolution is here four thousand two hundred so one cycle is to three hundred and 11
sixty degree and 360 degree divide by four thousand two hundred. 12
So that encoder can measure every zero point zero eight hundred fifty seven degrees and if we have a 13
encoder with the four thousand two hundred resolution so it can measure each zero point zero eight five 14
seven degrees and encoders divided into two according to detection technology and optical sensing encoders 15
and magnetic sensing encoders and encoders divided into two according to group we can say to group and 16
this group is created by output type incremental encoders and absolute encoders. 17
And if we say absolute encoders can be classified as follows. 18
So according to communication technology absolute encoders can be to group and parallel type and they're 19
serious type and parallel type encoders parallel type absolute encoders divided into two types. 20
A single turn and multi turn there are separate conductors for each output. 21
For example eight conductors are used for a eight bit output, serial type absolute encoders divided into two 22
types as single turn and multiturn also. 23
In this communication technology the output that is made with different electronical protocols and two 24
conductors are used for example serial synchronous interface SSI serial asynchronous 25
interface and interbus and profibus and canbus etc. for the serial type absolute encoders 26
Another important issue is the working of and working on signal voltage of encoders. Encoders are 27
produced at two operating voltages TTL and HTL so TTL encoders are supplied that typical 24 volt DC 28
voltage value between 5 volt +/-%10 and HTL encoders are supplied between 10 to 30vdc 29
and given output signal. 30
This is the difference between HTL and TTL and again during this election it should be taken into consideration 31
whether the absolute encoders will output in gray code or binary code which code is going to give us 32
from absolute encoders. 33
That is another important point. 34
Another important point is the operating voltage of encoders.Incremental encoders it generates the signal 35
in the rate of resolution one round for example the incremental encoder with the resolution of three 36
thousand six hundred sends 3600 pulses to drive. 37
For example vfd in one round and the driver collects this pulse and converts them into position 38
information. 39
When the motor rotates rotates in both directions this pulse. 40
This is really important point. 41
Now this pulse will be produced and the incremental encoder sends three signals to the driver to distinguish 42
the direction and detect 0 crossing point. 43
Another important point for the encoders the figure below shows in here a and b and Z signal.The Z signal 44
is 0 crossing signal and output just give an output. 45
Only once in a turn after one turn is completed in here for example we can get just once the Z signal. 46
Note that the A and B signals in the figure are 90 degree phase apart. 47
In here you can see in here we have a 90 degree phase apart and these signals output differently in 48
fast to differentiate two direction of rotation in the forward rotation of the motor. 49
The A signal will output before B signal and another important point B signal will output before 50
the A signal when the motor direction change and other really important point is here. 51
Inverter or drive will provide direction information based on the priority of these signals. 52
You can see schematic of the channels A and B and Z and according to Time the outputs are in here. 53
You can see it in here . 54
A ,When the motor goes forward before B just goes high 90 degree is here or motor goes in other direction 55
so B becomes high before A 56
So let's take a look to encoder 0 test. 57
Another really important point in here although the zero signal seems unnecessary. 58
After one turn is completed it is really important for the testing to encoder.The encoder needs to pulse 59
at the rate of the resolution in one turn. 60
For example the resolution of encoder seven thousand two hundred then it turns fifteen point five turns 61
after these turns. 62
We need to get seven thousand two hundred multiply fifteen point five and equals one hundred eleven 63
thousand six hundred pulses from the motor from the encoder. 64
And if we get this value from the encoder we can say our encoder is working for example after one resolution. 65
We need to get for example three thousand six hundred pulses from drive but we are getting six 66
Three thousand five hundred pulses inside of the drive we are monitoring it. 67
Imagine like this. 68
So that means the malfunction in the optical circuit in the encoder or magnetic noise is because of 69
magnetic noise or connection is losing looseness on the cable that connects the encoder to try. 70
So these are maybe the problems of our encoders and speed limitation of encoder is another 71
really important point. 72
When you are choosing your encoder there is a speed limitation inside of the encoders so you can find 73
it with this formula. 74
Maximum electrical speed of encoder equals maximum for frequency response. 75
Divide by pulses per revolution multiply 60 seconds per minute. 76
So imagine we know the RPM or maximum electrical speed is this is it our encoder is spinning five 77
thousand RPM and its produces pulses at two hundred and fifty hertz. 78
But how can we know this. 79
How can we find this. 80
For example if it is three PPR , PPR means pulse per revolution and encoder so fifty five thousand. 81
This is our turning speed or electrical speed equals B so maximum frequency response we don't know 82
divided by three because it's three PPR. 83
Then multiply by 60. 84
So in this calculation we can get these maximum frequency response or two hundred and fifty hertz. 85
So according to our PPR pulse per revolution or maximum frequency response or maximum electrical speed. 86
So what we know for the encoder but we need to find maximum electrical speed after you buy your encoder 87
you need to know maximum frequency response and divide it by pulse per revolution and multiply it 88
by 60 seconds per minute and you are going to get your maximum electrical speed. 89
So for the encoders there is a disk and also led and also light source like this in here. 90
We have a led and in here we have optical devices a and b and in here we have one axe to turning for the 91
encoder and this is disc. 92
So this is turning first. 93
This is looking to a channel a is the outside B is inside channel. 94
So because of this structure ,90 degree phase apart is existing. 95
So when this led is looking first to a channel and after encoder is turning it is looking in here just 96
for example right here it is detecting A optical devices and giving A pulse and 90 degrees later it 97
is seeing or detecting suddenly B optical devices and giving B pulse. 98
In here you can see it how it is continue. 99
And after one turn it is the take it is giving a Z or Z pulses to us ,so we can understand the encoder 100
structure with these images. 101
Just focus these images than you are going to understand the logic under of encoders. 102
So in here we will after each side. 103
We are getting output pulses and the output pulses of the incremental encoders are produced in 104
NPN and PNP and open collectors circuits as well as circuits such as push pull and NPN + PNP and 105
the line driver. 106
So the important thing is here the outputs of the open collector in these schematic cannot be directly 107
connected to drive or vfd.these or any other devices. 108
So you can see in here open collector structure circuit structure and the push pull circuit structure 109
and the line driver circuit structure in these images. 110
So Let's go to magnetic encoder. 111
So although they are not preferred very much because of their low resolution we will briefly talk about 112
their existence. 113
What is happening inside of the main magnetic encoders magnetic encoder is the magnetic one of the optical 114
incremental encoder so many NS permanent magnets Poles are listed on the magnetic disk in here you 115
can see an N and S poles in here. 116
And this is how a affect device in here and it is going to detect these poles and in here we have a magnetic 117
rotor. 118
So with the shaft this pulse rotates and the hall element generates attention because of this tension. 119
When they pass in front of the hall element sensitive to the magnetic field so the voltage is raised 120
in the electronic circuit of the magnetic encoder because of the tension generating tension the voltage 121
is going to up or raised and it is given to the driver in the form of pulses. 122
So it is giving a pulse because of the poles are detected by hall device and because of this detection 123
it generated tension after this tension the voltage is raised and it became a pulse. 124
So absolute encoders what is happening for the absolute encoders and absolute encoders gives 125
the real position of the shaft. 126
For example in here all this is our shaft. 127
-- 128
Let's divide it this connected to the shaft into nine parts like in here and line parts will be positions 129
our positions and we will created four tracks in each position. 130
So in here for example if the 1 1 0 1 signal is resolved received from the absolute encoder. 131
Let's take a look. 132
1 1 0 1 in here as binary code. 133
So it will say Ah ! I am at sixth position so we will say our encoder position is 6. 134
Then we can understand the absolute position of our motor or devices. 135
So for being absolute encoder can be seen below and for this actually provide the resolution of the 136
encoder when passing regions give the position information will be obtained according to our binary number. 137
So for the absolute encoders according to binary code we can divide our motor positions to 9 or 138
a little more. 139
Or for example 5 position we can create it like this. 140
We can get absolute encoder gives a really real position of the shaft to us in here also you can 141
see for example information 1 1 0 1 on the encoder output indicates that this rotor is in fifth position 142
1 1 0 1. 143
Where can we see the blacks ones are 1 and 1 and 0 and 1 as decimal eleven so it gives to us to another 144
example in here. 145
Our motor is stopping or waiting at the fifth position. 146
The biggest value that you can get into binary number code with the four bits. 147
If you are working with the four bit is you can divide it maximum 16 position dividing the shaft into 148
sixteen positions provides a precision of one turn is 360 degree. 149
So if we divided equally to 16 part we will get twenty two four point five degree after each position. 150
We are going to move twenty two point five degree. 151
This is absolute and real position. 152
So in table we can get angular sensitivities and the resolutions of absolute encoders as can be seen 153
as sixteen with absolute encoders can measure zero point zero zero fifty five degree fastness in here 154
we can see sixteen bit resolution in here so we can use this formula two exponential by sixteen so 155
this value is goes to this value, sixty five thousand five hundred and thirty six . 156
Remember this was equal, 157
One word value. 158
From the previous lessons or lectures. 159
So if we divide by 300 than 60 degree divide 160
divide this one sixty five thousand five hundred thirty six. 161
So we will get this value. 162
So what can we say. 163
Sixteen bit absolute encoder can measure zero point zero zero 55 degree fastness an absolute encoders 164
can be produced to output in binary code as well as in the gray code the 0 and 1 fields on the disks 165
of the encoders that output in gray code are placed according to this code. 166
So this is binary code. 167
This is gray code structure. 168
So the reason for the choosing. 169
Another important point is here. 170
The reason for choosing gray code is that the data communication is security better than binary code. 171
This is really security or safe according to binary code for grey code this code looks at the change 172
in transition from one bit to the next bit in the next bit. 173
After a bit if there is a same number it's a grey code is zero. 174
If there is a different number the grey code is one. 175
Let us check out this fifty six as decimal as binary 1 1 1 0 0 0. 176
So if we put it all together from under and upper side look now 0 and 0 , so similar 177
So the grey code is 0 , 0 0 is similar. 178
So Grey code is 0 .0 and 1 179
So the grey code becomes 1 , 0 than 1 and1 so our output is 0 and 1 and 1 again. 180
So this is the same number is grey code is 0 and 1 and 0. 181
So our grey code becomes 1. 182
So if we put it together we will get this value 1 0 0 0 1 0 0 0 as grey code. 183
The production of absolute encoders requires very thin technology compared with the incremental encoders. 184
And this caused absolute encoders to be more expensive than incremental encoders. 185
This is really important point another really important point in case of power failure or if the driver 186
fails during the application since the location information will be deleted from the drivers memory 187
due to number of pulses sent by incremental encoders. 188
The system must be brought to the zero point and the application must be started again in absolute encoders. 189
When electricity comes the signal from the encoders will give the real location information and the 190
application can be continued from where it left off. 191
This is really important. 192
Absolute encoders should be used if the system is able to continue operating from where it left off after 193
the arrival of electricity or if reaches to zero point of electricity is arrives. 194
And if the material remaining in the system increases to the point of passing to the zero point 195
it will increase the cost. 196
In fact there is another encoder that is the mixture of these two encoders but that gives absolute value. 197
So this encoder operates incrementally but by counting battery pulses with a microprocessor install 198
on it it performs the necessary calculations and sends absolute value to the drive in here also some 199
very thin technology is produced by very thin technology encoders and incremental encoder. 200
This in here an absolute grey code encoder structure is here so I'm finished for this video. 201
See you in the next video.