Understanding encoder logic

karivelm

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Join Date
Nov 2006
Location
Quebec
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66
Motor 1800 RPM
Encoder 5000 PPR (pulse per revolution)
Speed of shaft after Gearbox = 0.361 RPM
Input card: 800 KHz in A Quad B mode (16 bit accumulator)

I would like to know how to calculate if my system is OK.
I have a motor (1800RPM) on which we wil install an encoder (5000PPR) there is also a gearbox. At the ouput of the gearbox my the speed is 0,361 RPM.

From my calculations it would take
2,77 mins for a 360 turn of system
so 4986 rotation of the motor for 360
so 5000*4986 = 24930000 pulse for complete turn

My accumulator maixmum is 65 536. Am I missing something? And does anybody have a description on how to program such a system. I know I need at least 1 limit switch to do a '0' on the system....
 
What is the actual reduction ratio of the gearbox - in turns, not in RPM? Don't calculate it from your speed figures. What is the actual specification of the gearbox?
 
What is the make and model of the high speed counter? I ask first because the combination of 800 kHz pulse frequency and only a 16-bit accumulator sounds like a gross mismatch to me, and second because it's impossible to offer any advice on programming or configuring without knowing the specific hardware you're dealing with.
 
The PLCs that are being used is GE90-70, I got a quote for a
IC697HSC700
And for the encoder i got a quote on a HS35 optical encoder...

I have not purchased any material yet...But I need to find out what could be used...to make a functionnal system
 
The good news for you is that using the programming software, you can configure that 90-70 High Speed Counter as what GE calls "Type B", "Type C", or "Type D", all of which give you a 32-bit accumulator. The manual for the module is GFK-1062A. It includes some application examples in Appendix E.
 
If I am using the encoder for Forward and reverse...dont I need to use it as a Type E, A Quad B counter which only has a 16 bit accumulator ?
 
if you need this high resolution on position you willhave to work with some double words. if having overflow then count to max (65536) and then add the rest to it. However i think when putting the decoder on the outgoing shaft you will have enough resolution.
 
Any counter configured for A quad B input is inherently bidirectional. The primary feature of the Type E setup compared to Types B, C and D is the fast (10 microsecond) outputs.

The module has twelve inputs and four outputs. Depending on the configuration, the inputs get interpreted differently by the module's firmware. To summarize the different configurations.

Type B gives you two independent 32-bit counters on the module. Each of the those counters uses six of the inputs and two of the outputs. The six inputs are interpreted as encoder channel A, encoder channel B, preload, disable, and two strobe lines.

Type D gives you four independent 32-bit counters on the module. Each of the those counters uses three of the inputs and one of the outputs. The three inputs are interpreted as encoder channel A, encoder channel B, and marker.

Type C gives you a single 32-bit counter on the module where the accumulator value is the difference between the pulses from two encoders.
 
So if I have three of these installation to do. I will acutally need 3 HSC cards even if there are 12 inputs on the card?

The cards uses inputs enven if they are not wired? Example If I wire an encoder in input 1, and I am using it as type B. So just with this, I have used up 6 inputs and 2 outputs...?
 
So on the programming side does anybody have an example Grafcet of how to program positionning of such a system...

On an HMI I would like to (enter a position 0-180, I know i will porbably need a switch somewhere to do a zero position when the position is lost...)
 
Sometimes I just like to watch the confusion.

Sometimes it is entertaining just watching you guys go through all these calculations and hardware configurations. Now what was the original question? Oh yes...
I would like to know how to calculate if my system is OK.
First I think we need a definition of for the system being OK so we know what to calculate.
 
Basically what I mean by "OK", is that I am looking to control the position of a motorized launder by 1degree through an HMI. I wanted to make sure that I could obtain that degree of precision...

So if I use a 32 bit counter the accumulator can go up to 4.29E09 pulses counted.

From my calculation the maximum that I will count up to is 5000PPR*4986(motor rotation for complete rotation of launder) = 24930000.

This gives a total of 69250 pulses per dergee.

By the way we will not rotate the launder by 360degrees probably a maximum of 180.
 
As far as I know, the 90-70 PLC is not compatible with Grafcet.

Is this an additional function that you want to add to an existing system? If not, the 90-70 sounds like an extremely expensive PLC selection for the task at hand.
 
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