Speed Calculations

escoplcguy · Jan 11, 2011

Hello all, i have a hydrolic cylinder that has to run at 1 inch per second till it hits full stroke (40 inches) than retract. i have a transducer in the cylinder that can measure the distance of the cylinders stroke. i need to develop a screen that shows the actual "real time" speed of the cylinder. how can i do this....

also, the cylinder has a 4-20mA directional valve that is controlled by an analog output card,the cylinder needs to auto correct itself if while running it starts to move faster than 1 in/s..could i accomplish this using a PID instruction??

i am using a plc-5. but they may make me swap the plc-5 to a micrologix 1100 due to the etherent capabilities

thanks for your help!!

califflash · Jan 11, 2011

Is the transducer 4-20mA? Are you talking about displaying the status of the cylinder on the 1100 screen? Are you using a seperate HMI? Why not get a ethernet converter for the SLC-5 or something like a red lion that does HMI and ethernet conversion. Is this new, a recycled SLC-5, or an upgrade????

Information please!

escoplcguy · Jan 11, 2011

transducer is 4-20mA, i am talking displaying the real time speed on the current HMI which is a PV600 the HIM is simple i just want to display the tag that would be the speed. this is just a R&D project im working on the PLC-5 was a spare i had, i also have a micrologix1100 sittig at my desk, i chose the plc-5 just to test and be sure the processor and cards still worked; the MLX1100 i already knew it worked. all i want to know is can i determine the speed of the cylinder as it travels down and up. speed in inches per second.

hope thats enough info if you need more let me know

James Mcquade · Jan 11, 2011

escoplcguy,

your profile indicates that you are a student, so this is my question - is this a classroom assignment?

regards,
james

escoplcguy · Jan 11, 2011

haha i dont know why or where it says that, and no it is not a classroom assignment i graduated in '03

Tom Jenkins · Jan 11, 2011

1) You can control cylinder speed with a PID loop.

2) Speed is ds/dt. Your cylinder is moving slowly, so use a timer and divide the distance moved in the time increment by the time increment. The result is velocity.

escoplcguy · Jan 11, 2011

what do i set the timer at 99999 so that it continusly runs??

can you show me an example??

leitmotif · Jan 11, 2011

Tom Jenkins said:
1) You can control cylinder speed with a PID loop.

2) Speed is ds/dt. Your cylinder is moving slowly, so use a timer and divide the distance moved in the time increment by the time increment. The result is velocity.

Equation for ds/dt is
(Old position - new position)/(old time - new time)

Dan Bentler

escoplcguy · Jan 11, 2011

so i use a sub instruct and subtract the transducer by itself?? and divide that by doing the same thing with the counter??

leitmotif · Jan 11, 2011

escoplcguy said:
so i use a sub instruct and subtract the transducer by itself?? and divide that by doing the same thing with the counter??

Basically yes excepy I would use a timer for the time calculation

Dan Bentler

TConnolly · Jan 11, 2011

Lets talk about your controller and its capabilities first. What kind of position control and velocity control precision do you require? What kind of load are you moving and how is it supported? What size is the cylinder bore? What is the pump pressure

Depending on the answer to those questions you may need to seriously reconsider using a PLC - you may need a hydraulic motion controller since a PLC is is just plain too slow for precision hydraulic control.

Hopefully Peter will enter the discussion - be ready to answer some detailed questions. The more info we have the better answer you will get.

escoplcguy · Jan 11, 2011

the speed is already accurate. the cylinder is mounted on a stand and just moves straight downward. they just want to see the speed of the cylinder and if something caused the speed to change auto correct it back to 1 in/sec.....currently the speed is at 1 in per second. just want to display that speed through the PLC onto an hmi screen.

escoplcguy · Jan 11, 2011

fyi....speed was achieaved by using stop watch and adjusting the directional valve to be opened just a bit.

OkiePC · Jan 11, 2011

I would recommend that you calculate the distance travelled every 1/2 second in raw units, then scale that number to inches per second for display. Most HMI won't update much faster than that anyhow, and if they do, a jittery number can be hard on the eyes.

So, every 1/2 second (self resetting TON), subtract the new_position from the old_postiion and store it as raw_counts_per_half_second, then MOV the new_postiion into the old_positiion register for the next calculation.

Then multiply that number by the units to inches scale factor times two (to get whole seconds).

Peter Nachtwey · Jan 11, 2011

Some thought should be put into what kind of accuarcy is required and if this is achieveable with the current equipment.

Speed Calculations

escoplcguy

Member

califflash

Member

escoplcguy

Member

James Mcquade

Member

escoplcguy

Member

Tom Jenkins

Lifetime Supporting Member

escoplcguy

Member

leitmotif

Member

escoplcguy

Member

leitmotif

Member

TConnolly

Lifetime Supporting Member

escoplcguy

Member

escoplcguy

Member

OkiePC

Lifetime Supporting Member

Peter Nachtwey

Member

Similar Topics