Comparison of rpm with the reference rpm

[simonpedro]

Hi, I'm trying to copy a circuit (I seen that just for a while), have a rotor with a captor that generates a pulse at every turn.

A potenciometer controls the reference rpm, so if the rpm are stable (arround the reference rpm) nothing happens, but if the rpm go up, a signal is generated (an light turns on, a big one, an 11Watts 12Volts lamp). If the rpm go down, another light turn on.

That works fine, they can regulate the rpm emergency areas with the potenciometer.

To do that, I think they convert to tension the pulses from de captor with an lm2907 or something and then compare the output with the potenciometer output through a couple of operational amplifiers, or an lm339 may be.

But I'm not very good in that (neither english xd, I really bad in fact), how can I do that? is good idea do that with an lm2917 and lm339? will that can manage the 11watts lamps?

Sorry for my english.

Thanks

 

[Reloadron]

Yes, you can use a Frequency to Voltage converter like the LM2907/LM2917 Frequency to Voltage Converter. Using a speed sensor that provides pulses or a frequency that frequency is converted to a voltage. The voltage is proportional to a shaft RPM for example. That voltage can then be fed to a Voltage Comparator circuit using a LM339 or other similar comparator as can be seen here. If you scroll down the comparator linked page you will see a configuration called a "Window Comparator" or a "Voltage Window Detector Circuit". When the voltage is outside the window, and indication can be provided signaling either a high or low shaft speed (RPM).

Ron

 

[simonpedro]

Ok, thanks. Now I'm thinking that, if I want to establish the value of rpm reference through a button, and when you press the button, an SCR or something is activated and the value of the tension on the output of the LM2907 is stored in an ... an what?
I can't think how to do that, any idea?

 

[Reloadron]

I don't understand what you are asking? A motor has a rotating shaft, the shaft has a speed sensor connected to it. The speed sensor will output a number of pulses per revolution. This all depends on the sensor and how it picks up the speed. For example the shaft may have a gear with 60 teeth so 60 pulses equals 1 revolution of the shaft. So if my frequency is 60 Hz for example my rotational speed is 1 revolution in one second or 60 RPM. The frequency is passed to a F/V (Frequency to Voltage) converter where a voltage proportional to frequency is output. That voltage can then be run into a window comparator to determine if the shaft rotational speed is within certain limits. There is no SCR involved.

Ron

 

[simonpedro]

I'll try to be more specific, sorry but I can't speak english very well, I'm latin american.
Everything you say is correct, I have a F/V and compare the output with the output of an potenciometer through an window comparator.

Now, I want to remove the potenciometer, and compare the F/V output with an previous status. I mean, I stablish the reference tension through an button, when I push the button, the tension on the F/V output is stored in something and then starts to compare the F/V output with the new reference tension.

I thing in an SCR to maintain the circuit charged o something, but I don't know how to store an specific tension value.

 

[unclejed613]

you need a Sample/Hold circuit.... look here https://images.search.yahoo.com/search/images?_adv_prop=image&fr=yfp-t-701&va=sample/hold+schematic

do a google search for "sample/hold schematics"

 

[atferrari]

It seems that Simón Pedro needs some RAM to store data from last reading to compare with the fresh one which in turn would be stored in RAM...

Es así?

 

[ericgibbs]

hi Simon,
I would suggest a PIC [ microcontroller ] would be a good option for this project rather than a frequency to voltage converter.

The PIC would read on its ADC pin the setting of the reference potentiometer and store it in its memory, the PIC would also count the pulses from the rotor and compare the count with the reference count.
It would also control the Low and High speed lights.

If you cannot write a program for a PIC, it would be a good idea to contact a local hobbyist who could help.