Hey All!

I seem to have gotten myself in a bit too deep on a project here. I've deployed Logos before but always for digital I/O, this time needing an analog output. I have two photo eyes that are mounted to a 120T wheel to read RPM, these are inputs I3 and I4. I also have I1 as an override input. AQ1 is a 0-10V output, the range for the output device is 0-1.4V=0-100%.

What I am trying to do is measure RPM as a high speed counter input and ramp my analog output accordingly. AQ1 should always sit at 25% when RPM is reading less than 50RPM and ramps to 100% at 200RPM. Once RPM exceeds 100RPM, AQ1 should sit at its last highest value for 45 seconds as a cool down then return to 25%. I1 is simply a override that sets AQ1 to 100%. I should also mention that I3 and I4 should average between the two and if one sensor is reading off from the other sensor it should failover to the sensor that is reading the higher value.

If anyone is willing to take this on I am happy to compensate you for your time and we can chat in further detail about what is required if anything needs clarification.

Thanks!!

Hello AutoGen,

It is easy to see from the text that you have gotten a little too entangled in your project. It may also be due to the translation that it is difficult to follow. So I have a few questions in advance:

How many pulses are generated by the photocell per revolution ?

Is the second photocell only intended as a fail-safe (redundancy) ?

When and by what is the override triggered ?

Should AQ1 continuously follow its value of the input speed ?

"As soon as the speed exceeds 100 rpm, AQ1 should remain at its last maximum value for 45 seconds" ???? If the speed exceeds 100 rpm, it cannot be its last maximum value ? Please describe more clearly.

What output device (0-1.4V) are you talking about ? The voltage range for such a control signal is highly unusual. But if you connect a load to the analog output of the Logo, that is not possible. You would risk destroying the output module. A regulator with a 0-10V control input must be connected in between.

And by the way, this is not a service provider but a forum. We are all here to share ideas and help each other.We do this of our own free will and not to make money!

Regards Ella_68

 Thank You Ella! Apologies for any confusion.

The photocell is mounted on a 120T wheel, so 120 pulses/revolution.

This is probably best answered with a bit more info on the application. We are creating a rolling road simulation while cars are being load tested on a stationary load bank. Since some vehicles are front wheel drive, some are rear wheel drive and some are all wheel drive, we mounted photo cells on both a front and rear load cell. So, when an all wheel drive car is being tested the sensors should average, a front wheel drive car will render the rear sensor useless etc...

The override is a simple toggle switch for the operator to use when they want to run the fan at full speed for whatever reason.

AQ1 should continuously follow the value of the input speed with the exception of the 25% dead band under 50RPM.

Sorry for the confusion, a bit more application specific detail might make more sense. AQ1 will be an ECM fan. The idea is that the fan will ramp linear to the input RPM reaching a maximum speed at 200RPM. However any time the input speed exceeds 100RPM,  I am trying to have the fan maintain its last highest speed even if the input RPM decreases for a period of 45 seconds. This will serve the purpose of cooling down the car after the run.

The output device is an ECM fan, it is a 0-10V input however has been setup to operate via a potentiometer previously. I have not looked into the possibility of reprogramming the fan controller but I have tested controlling it with set values from the LOGO successfully.

I appreciate the help and hopefully I can get some knowledge on analog programming out of this! Please let me know if anything else needs to be clarified.

Thanks!

Ella_68

Hello AutoGen,

It is easy to see from the text that you have gotten a little too entangled in your project. It may also be due to the translation that it is difficult to follow. So I have a few questions in advance:

How many pulses are generated by the photocell per revolution ?

Is the second photocell only intended as a fail-safe (redundancy) ?

When and by what is the override triggered ?

Should AQ1 continuously follow its value of the input speed ?

"As soon as the speed exceeds 100 rpm, AQ1 should remain at its last maximum value for 45 seconds" ???? If the speed exceeds 100 rpm, it cannot be its last maximum value ? Please describe more clearly.

What output device (0-1.4V) are you talking about ? The voltage range for such a control signal is highly unusual. But if you connect a load to the analog output of the Logo, that is not possible. You would risk destroying the output module. A regulator with a 0-10V control input must be connected in between.

And by the way, this is not a service provider but a forum. We are all here to share ideas and help each other.We do this of our own free will and not to make money!

Regards Ella_68

OK, we can do something with this description .

But first we use the calculator and convert the revolution values ​​into pulse frequencies. This is then easier to process in the program.

The first switching threshold is 50 rpm * 120 pulses/rev = 50 / 60 rps * 120 pulses/rev = 0.8333 rps * 120 pulses/rev = 100 Hz.

The second switching threshold is 100 rpm * 120 pulses/rev = 100 / 60 rps * 120 pulses/rev = 1.666 rps * 120 pulses/rev = 200 Hz

The third switching threshold is 200 rpm * 120 pulses/rev = 200 / 60 rps * 120 pulses/rev = 3,333 rps * 120 pulses/rev = 400 Hz

Let's first compare the pulse frequencies. The higher value should always be the reference frequency. You can achieve this with a comparator (B003) and a muxer (B006).

Next comes a similar circuit for the minimum speed (B007 / B008).

The following part is a bit trickier.When the switching threshold is undershot, a drop-out delay is triggered via the negative edge of the NAND, which holds the value for another 45s (B010, B011, B012 and B014). To protect the fan, I have added an analog filter at the end of the chain (B015).

Last but not least, there is the conversion from the frequency to the analog output voltage of 0-10 V (B016).

Attached is a small program for description. Perhaps you can use parts of it.

Greetings Ella_68

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