cycle time of a revolving wheel

hi,
what is the easiest way for measuring the cycle time of a revolving wheel with a single sensor and an s7 300 plc ?

i need the time values between sensor pulses. this time values are about 0,5 - 1,5 seconds.

the code should not be affected from PLC programe cycle.

thanks

set urself up a one second clock memory pulse, use the rising edge to pulse a counter which counts to 6. Count the pulses from the sensor in this time and multiply by 10 to get pulses per minute or RPM.

Sounds like a homework puzzle so i will leave it to you to figure out the logic for it.

LH

Longhorn said:

set urself up a one second clock memory pulse, use the rising edge to pulse a counter which counts to 6. Count the pulses from the sensor in this time and multiply by 10 to get pulses per minute or RPM.

Sounds like a homework puzzle so i will leave it to you to figure out the logic for it.

LH

Click to expand...

clock memory times are too long for this app.
i need time values of max 10ms resolution.

Why do you think we have a crystal ball to get the basic values?
Much simpler to tell us up front.

Do I correctly infer you have no idea of what the RPM is? It is really simple 8th grade math to figure out the time for one revolution.

If you have no idea of what the two values are it seems to me you have no idea of what your process is and you are nowhere near ready to even tinker with a PLC.

Dan Bentler

leitmotif said:

Why do you think we have a crystal ball to get the basic values?
Much simpler to tell us up front.

Do I correctly infer you have no idea of what the RPM is? It is really simple 8th grade math to figure out the time for one revolution.

If you have no idea of what the two values are it seems to me you have no idea of what your process is and you are nowhere near ready to even tinker with a PLC.

Dan Bentler

Click to expand...

OUCH!!

Don't forget we were ALL in 8th grade once [maybe twice in "TNY"'s case].

LOL

Just wait, tny asked a valid question. He stated that he needed to measure short time periods rather accurately and implied that the scan time variance would not be fine enough resolution. Maybe guidance in the high speed capabilities (if any) of the system he mentions would be in order. A long term timing of multiple occurances seems to be ruled out by his question. Homework or not, it appears he has give some thought to the matter.

By the way, his previous posts seem to indicate other than 'homework'.

tny said:

hi,
what is the easiest way for measuring the cycle time of a revolving wheel with a single sensor and an s7 300 plc ?

i need the time values between sensor pulses. this time values are about 0,5 - 1,5 seconds.

the code should not be affected from PLC programe cycle.

thanks

Click to expand...

What is the minimum time the sensor pulses will be on for ?

Which CPU will you be using ?

Do you have to worry about the case where the wheel is stopped and is just on the edge of the sensor resulting in counts due to vibration ?

Will you consider adding a counter card ?

leitmotif said:

Why do you think we have a crystal ball to get the basic values?
Much simpler to tell us up front.

Do I correctly infer you have no idea of what the RPM is? It is really simple 8th grade math to figure out the time for one revolution.

If you have no idea of what the two values are it seems to me you have no idea of what your process is and you are nowhere near ready to even tinker with a PLC.

Dan Bentler

Click to expand...

the time values between the pulses are necessary to calculate the diameter of the wheel angry guy. if you do not have any technical comment please do not pollute this thread.
and may be you should hang out with friends more to learn how to speak like other people.

bernie_carlton said:

Just wait, tny asked a valid question. He stated that he needed to measure short time periods rather accurately and implied that the scan time variance would not be fine enough resolution. Maybe guidance in the high speed capabilities (if any) of the system he mentions would be in order. A long term timing of multiple occurances seems to be ruled out by his question. Homework or not, it appears he has give some thought to the matter.

By the way, his previous posts seem to indicate other than 'homework'.

Click to expand...

it's nice to see right-minded people here

L D[AR2 said:

What is the minimum time the sensor pulses will be on for ?

Which CPU will you be using ?

Do you have to worry about the case where the wheel is stopped and is just on the edge of the sensor resulting in counts due to vibration ?

Will you consider adding a counter card ?

Click to expand...

the pulses are 50 msec long. (on time)
the cpu is cpu314.
the stopping point is not important. i think there will not be any vibration problem but anyway i used a positive edge trigger after the input on my program.
and sure if necessary i may add a counter card.

the siemens 314 cpu and has counter inputs but they are already used to get data from encoders.

today i tried a way to calculate the time values between pulses by using normal timers, with no any hw interrupt, high speed counter etc. i simulated the pulses (50 msec pulse on - 250 to 1450 msec off) and i saw that the code works on an empty plc with 1 msec cycle times.

but with the cycle times of 30-40 msec with all codes, the code calculates the times with 20-30 msec excess.

step7 is not installed on this pc so i can not copy the code here, i'm sorry. i will add tomorrow.

regards

Set your cyclic interrupt time to 10ms in the h/w config.

Perform your processing in OB35 based on the fact that OB35 will run every 10ms.

To ensure the process image is up to date you have to load the peripheral byte of the input you are using and copy it to the process image e.g.

thanks, this will be very useful for me

L D[AR2 said:

To ensure the process image is up to date you have to load the peripheral byte of the input you are using and copy it to the process image e.g.

Click to expand...

does it mean, when the inputs are read as pib, they are used like immediate inputs on s7-200 plcs?

and, i knew that the ob35 is 100msec interrupt, how can i set the ob 35 to 10msec?

regards.

H/W config - double click on CPU then select Cyclic interrupts

Yes - L PIB reads from the peripheral, copying to IB make the inputs avaiable using A Ix.y

i did a similar project 6 months ago.
i used a timer to produce puls every 10ms and then i used a counter to count how many pulses there were when the input was low and then restarted the counter when the input was high