Analog Input sensor to sense rpm

gandhi

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Join Date
Aug 2010
Location
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Hello,

I have to read 10 rpm to 8000 rpm in a machine.

I tried Proximity switch but I cannot read more than 3000rpm as my plc can sense only upto 50 pulses per sec and I cannot use encoder in this machine.

Kindly suggest me any analog input type sensors, as i have unused analog input and output points in my plc.

I tried to search on the net but i am not sure which one to use it

Thanks for your help....:site:
 
Tacho?

If using gearing... can you position your proxi on a slower gear and multiply your pulses within the PLC?

What drive system are you using? More info required!

Is there an accessible parameter within your drive system which you can manipulate to suit?


.
 
Last edited:
1 minute = 60,000 milli Seconds
divided by 3000 RPM = 20 mS
the scan time of your PLC would have to be less than 10 mS for it to register that pulse rate .

60,000 divided by 8000 RPM = 7.5 mS, so your scan time would need to be under 3 mS for it to register, which is outside the range of most PLC inputs, unless they have high speed counting capable inputs.
 
Hi silva,

Actually there is a disc connected to the center shaft and on the under edge of the disc there is small bolt is welded which is sensed by the proximity switch for each pulse.

My plc input response time is 10ms as in the datasheet.
 
Bear in mind that the pulses will not have an 50/50 mark/space ratio! The pulse duration maybe very small and any counter must be able to handle 2 times that implied frequency to be able to count it.

Nick
 
Hi Manglemender,

I dont have high speed counter, is it possible if i can use any analog input sensor which can sense these kind of high speed.

For eg:

for 0 rpm = 0V and for max.10 V = 8000rpm from the sensor.
 
gandhi said:
Hi Manglemender,

I dont have high speed counter, is it possible if i can use any analog input sensor which can sense these kind of high speed.

For eg: for 0 rpm = 0V and for max.10 V = 8000rpm from the sensor.
Click to expand...

I think you need to tell us what tolerance you need on RPM output signal. If 1% that is + - 80 RPM at 8000, 10% is 800.
Depending on what you want and need a tach generator may suffice ??

Dan Bentler
 

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