setting a timer with an MI

[muckingfuddle]

Hey all, I need to adjust the time of a timer dependent on an MI bit, basically i need the timer to increase or decrease with a speed signal, 

 

for example on average, it takes 20 seconds for 1 rotation of a drum on a piece of test equipment, but some operators prefer to run the tester faster and some slower so if the tester wants to run a slower test one drum rotation will take longer, and if the tester runs a faster test a drum rotation will take less time.

 

The test equipment only wants to do 1 rotation and its speed is determined by 0-10v signal to a DC speed controller hence the MI bit

i want to hit a start button and the timer automatically stop after one rotation, there is no facility for an input to determine one rotation as it never has a set start position.

 

Any help will be greatly appreciated 

[Ausman]

1 hour ago, muckingfuddle said:

there is no facility for an input to determine one rotation as it never has a set start position.

Without a physical indication of where the drum is, your request is not possible. You need to think this through........ How is the plc going to know when one rev from the triggered starting point is complete?  It can't.  You need some sort of connection, the simplest/most reliable being an inductive that triggers once every rev, or gives a fixed number of senses per rev that you can then relate to a full rev.  Even if you have such an inductive set up for many counts per rev, you are still going to have an inaccuracy due to rotation count errors caused by an inherent lack of precision.

cheers, Aus

[Joe Tauser]

1 hour ago, muckingfuddle said:

dependent on an MI bit

I'm guessing you mean MB bit.  And you want to increment / decrement the timer by some amount.  But as Aus points out, you can't control the number of revolutions without an index pulse.  So you'll need to figure out how fast to make the drive run as well for a given rotation time.

This can be back-calculated with some uncertainty if you know the drive speed needed for the 20 second rotation.  Hopefully you're not looking for exactly one rotation with this method.

To answer your immediate question, the Store TP block can be used to move a new preset to the timer.  Timers are 32 bit animals, so you'll need to work with an ML and add or subtract some number of 0.01 increments to your timer when the up or down button is pressed.

If you've already beat on this, post some code and some data regarding the drive speed / rotation time and we can be more helpful.

Joe T.

[muckingfuddle]

The drum is stationary and is started by pressing the start button,  one rotation takes X amount of time at Speed Y. this machine works like this and has for 40 years it currently has a 10k pot that goes into a timer and has some setpoints, all i need to know is how to change a timebase when i change the speed of the drum, the drum is about 1 foot in diameter and only runs for 1 rotation accuracy is not 100% critical if it runs for a fraction of a turn longer its not too critical. 

 

 

[muckingfuddle]

Just now, Joe Tauser said:

I'm guessing you mean MB bit.  And you want to increment / decrement the timer by some amount.  But as Aus points out, you can't control the number of revolutions without an index pulse.  So you'll need to figure out how fast to make the drive run as well for a given rotation time.

This can be back-calculated with some uncertainty if you know the drive speed needed for the 20 second rotation.  Hopefully you're not looking for exactly one rotation with this method.

To answer your immediate question, the Store TP block can be used to move a new preset to the timer.  Timers are 32 bit animals, so you'll need to work with an ML and add or subtract some number of 0.01 increments to your timer when the up or down button is pressed.

If you've already beat on this, post some code and some data regarding the drive speed / rotation time and we can be more helpful.

Joe T.

i dont need to increase or decrease rotations, it only runs one rotation and thats it test over,  the speed is manually selected using up or down buttons, i know how long 1 rotation takes depending on speed so all i need to do is basically T1 to 10 seconds when speed 6Rpm is selected, and T1 to 60 seconds when 1 RPM is set and so on. this is for a tester for the paper industry 

[Ausman]

So is the manual selection dictating a series of jumps in speed, or a smooth rise/fall according to how long the button is pushed?

[muckingfuddle]

Ausman 

 

the speed will be set prior to the test dependent on the operator, the test must be at a steady speed or it will not work correctly, but the test can be done at any speed between 1RPM and 60 RPM, this is all determined by the scientist running the test, some believe a slow test is the correct way some believe a fast test is better

 

 

[Joe Tauser]

Don't over-think it-

This is what you do to change the timer preset to a known number.

Joe T.

[Ausman]

9 minutes ago, muckingfuddle said:

the test must be at a steady speed or it will not work correctly

you've misunderstood the question.   I've changed it slightly.

[muckingfuddle]

 

Ok this did it perfectly, thanks Joe for pointing me in the right direction.

[Ausman]

That's the sort of thing my question was relating to.

cheers, Aus

[muckingfuddle]

10 minutes ago, Ausman said:

That's the sort of thing my question was relating to.

cheers, Aus

i guess i didnt explain it very well LOL. it works well now i just need to tune it to the machine.

Thanks Pau;l