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Rotation speed of a vent measurement

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Hi all, 

 

I need to measure the rotation speed of a vent. For this I have to do the following:

 

Mount a proximity sensor (5V) which detects when the vent blades are in the detection area and will generate a difference in the voltage read by an AI. The AI is linked to a MI which reads the voltage from the AI

I need to store in a counter how many times the MI is changing the value and at every minute to take the value from the counter divide it by 60 and to put the result in a MB. 

 

Do you guys have any idea on how to do this? 

 

Thanks and appreciate your input.

 

Cheers, 

Marius

 

 

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Hi Marius,

What is a PLC model you use?

What is a proximity sensor output? PNP? NPN? Push/pull?

What is a vent rotation speed range and number of blades?

What is a vent power source and voltage? AC/DC?

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Hi Alex, 

 

PLC model: V1210

Sensor: not sure what type is. I bought it from here: http://www.ebay.com.au/itm/191473719568?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Vent rotation speed range: 0-100 rpm, and 7 blades. Does not have an electrical power source as is wind powered.

 

Basically with this construction I will be able to calculate the wind speed without buying an anemometer. 

 

Cheers, 

Marius

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Hi Marius,

 

Like Alex says, more info needed.  But for now I am assuming that your "vent" is actually some sort of blower with blades.

 

I do this a lot and my routine is a good quality inductive from Sick or similar.  You get a straight forward 24v digital output that you read using one of the high speed counter inputs to allow for any times the count might be an issue related to scan times, unless it is going to be fairly slow and you know for sure that every "on/off" change will be read correctly at every speed it runs at.   You then use a normal DI.

 

I always mount the sensor so that it is reading something from the slowest moving part of the blades.  Most of the time I can easily achieve a mounting to read from the steel bolts in the hub.  Perfect for good, error free inductive operation.  I have had a few odd times where I have had to make a special end cap for the motor shaft that mounts as an extension on the motor fan end, and is a series of lobes that the inductive reads.  You can often buy this sort of thing off the shelf.

 

Once you have the inductive reading ok you can work the maths any way you like to arrive at your rpms.  This really relates to how many pulses you are going to get per second, to enable good accuracy.  You accumulate the pulses into a count, and then at whatever interval works best you do the maths and reset it to zero to start again.  So the more pulses per second the better, as you can get a faster responding measurement.

 

cheers,

Aus

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Using an analog proximity sensor to measure rotation may end up being problematic.

 

 

You'll need to test that the analog signal is between a range, and then increment a counter based on that condition, then divide that counter by the number of blades * 60 to get RPM. 

 

You will need to make sure that there is some sort of "locking" mechanism to prevent the counter from picking up noise on the input signal to prevent counting rotations that never happened.  Ideally you only want to catch the peak value when the blade passes under or over the sensor.

 

 

I think the best way would be look for a drop from the peak output by installing the sensor where the change in signal would be the largest and only detect that change.

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Hi again Marius,

 

that sensor gives you a digital output, and as it is 5V I guess you were planning on using the AI in 0-10v mode to read when it goes on and off as it would be able to read that voltage level directly.  However, I think you will likely get time interval problems doing this.  My suggestion would be to interface a small SSR into the mix and put the output from the SSR into a dig input like I have already explained.  Given you are in Aus, have a look at this.  I have used them very successfully when I have had to read from a very low level LED driver into a 24v dig in.  I think it would work ok, but no guarantees!

 

http://www.jaycar.com.au/Electromechanical-Components/Relays-%26-Accessories/Solid-State/PCB-Mount-Solid-State-DIL-Relay/p/SY4090

 

If you can afford it, I would still go with a dedicated industrial 24v inductive.  Will probably save you headaches & $s in the future due to the innate durability, and then the extra $ are well worth it.

 

cheers,

 

Ausman

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Hi, 

 

Thanks all for your reply. Appreciate your help. I will try with a proximity sensor 24 V to read in a high speed input, and after that I have to play with the logic and maths. 

 

Cheers, 

Marius

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Coming back. 

 

I am able to read the number of rotations of the vent. Now, I am struggling to calculate the speed of the vent. I tried to have a look in the examples, webinars and here on forum, but I could not find anything useful. 

 

Do you guys, have any idea on how to put the number of rotations in a time frame in order to calculate the rpm (rotations per minute) ? Probably is something simple, but I can not find a way at this moment. 

 

Cheers, 

Marius

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I would use a drum (personally I prefer drums for repetitive, sequential tasks over timers but timers work fine as well), to trigger two memory bits, one to read the start count, one to read the end count both into MI.

 

Then do the maths every 60 seconds, or 15 seconds, depending on the update interval.

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Hi Cantcliff, 

 

Thanks for reply. The way you are saying sounds very simple, but for a newbie (like me) is not :) 

 

I have a Counter (C1) which shows me the number of rotations of the vent. My issue is that I am not sure on how to use the Visilogic ladder in order to take the value of the counter (C1) at every 60 seconds and to put it in a math formula that will calculate the number of rotations / 60 seconds. 

 

After that it will be easy to calculate the wind speed using the following formula:

Wind Speed = L*RPM

L(circle length)=3,1416*D(circle diameter)

 

Please be patient as I am pretty new in the Visilogic ladder programming and a lot of my questions could look naive. 

 

Appreciate any reply at my issue. 

 

Cheers, 

Marius

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My humble opinion, and dont know if it will work, guess it depends on your speed, however I would have used the high speed input and set it to be a counter

 

https://www.dropbox.com/s/143r3ysv24kbzy4/Capture.JPG?dl=0

 

I couldnt work out how to add a screen shot, sorry

 

 

this will calculate out the frequency automatically in pulses per second, multiply that frequency (in my case MI3) x 60 for pulses per minute

anyway thats my 2 cents

 

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Hi Dave, 

 

Thanks for your reply. Your solution it worked for me. 

- I connected the sensor to a high speed input,

- I configured the high speed input as Frequency measurement 1000 ms

- I used a MI to read the pulses from the high speed input

- I calculated the wind speed (in km/h) using the following formula:

Number of pulses per rotation = 21

Lenght of circle = 0.125664 m 

Wind Speed = 0.125664*(((MI (PulsesPerSecond) *3600)/21) 

 

Thanks all for help. 

Marius

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