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31  Topics / Science and Measurement / Re: Volume Meassurement (Dry Method) on: May 05, 2014, 10:26:55 pm
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Most all the same considerations are needed. In both cases we have temerature, pressure, flow and volume.
I just did not know about this procedures you are mentioning and its really interesting to know about them. I'll make some time and check the links. Thanks.
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Re: The compressibility factor (Z) of air - the curve is similar to the deviations you have found. It would only take some simple mathematics or use values from a look up table to correct for this.
I did not know about that either and that was the reason for my question. On the other hand, neither the graph nor the compensation is required to find the volume. That's why I did not put much effort on solving that. Thanks for that info also. (another subject to study)
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Approximating 3 decimal digits might be enough for the display, but its how the numbers are determined that can influence the effective precision in the results. Certain equations can have a precision reducing effect.
That is absolutely true; but I'm not approximating until the results are send to the display. All calculations are done with the floats without any approximations. On the other hand, none of the results shown are used to calculate the volume with the only exception of the TC which is measured by Arduino and I did not placed any approximations in the Arduino code. In the Processing code, there aren't any approximations in calculating the volume either and its just a simple linear equation linking the TC and the volume as explained above. That's why such repeatability is obtained, which is way better than solving the exponential equation as there would be more measured variables involved, each of them contributing with errors to the results. If you try to solve the exponential equation with the values shown, there will be significant errors not corresponding to the volumes shown, because I did not do it that way.  I realized that was a tough proposition. You can find the equation I used though, by simply plotting the Volumes vs. TCs values shown in Excel, (insert graph, add trend line-show equation in the options). I left the other values there because I wanted to calculate the Standard Deviations for them and observe "behavior" of those variables and also to help explain the method. Same as with the Graph; but none of that is really necessary. The screen is probably saturated with information an operator does not need and will just create confusion; but I need it for now, while I get this right.
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From your link to the sensor, its pressure range is 1 psi to 150 psi (60 mbar to 10 bar) (69 hPa to 10,342 hPa). The datasheet notes High resolution (min. 0.03 %FSS), so this represents 3.1 hPa resolution.
1psi-150psi is the possible Full Scale Span (FSS) of the sensors in that Series (SSC). In other words, in that particular Series you can find sensors with FSS inside that range; but there are many different ones in there with different FSS and not all of them are 150psi FSS. The FSS for the one I'm using is 250mbar (250MG in the part number) and I believe (could be wrong though) from the table in page 2, that its resolution is 0.03% of its FSS, in this case = 0.075 mbar and not 3.1 hPa.
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I'm not sure how you have pre-conditioned the signal levels into the 10-bit ADC. Perhaps resolution could be improved as follows. If ADC code 0 represents the lowest pressure you'll ever measure, say 40 hPa, and ADC code 1023 represents the highest pressure you'll ever measure, say 140 hpa, then the resolution becomes only 0.09765625 hPa per step. You may only need an op-amp or 2 to achieve this.
Perhaps there is another way. The sensor does not provide that output. It is a linear analog sensor providing a voltage output already amplified from certain value above 0V to a little less than 5V (I don't remember exactly; but its in the datasheet somewhere) therefore the range is not 1023 different steps in the ADC as it looks; but less. That output corresponds to Pr values from 0 mbar (referenced to the Atmosphere as it is a gauge sensor and not absolute) to its FSS in this case 250mbar. That's why I chose it, as it requires no additional electronics, just power and ready to go. On the other hand it is a high quality device (check the recommended applications in the datasheet)
Cont...
32  International / Proyectos / Re: Medicion de Volumen (Metodo Seco) on: May 05, 2014, 05:51:10 pm
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RECURSOS: Yo le agregaría Motivación/Frustración, probado el concepto que te motiva a querer seguir inviertiendo en este proyecto? Cual seria tu meta a largo plazo ?
Bueno, motivaciones muchas, como por ejemplo, completar algo que comence y que parece marchar bien. Mi motivacion principal es, que llegue a utilizarse de alguna forma, en alguna aplicacion practica real; pero para eso hay que seguir invirtiendo en esto. Frustraciones ninguna. En realidad todo va saliendo bien y los esfuerzos parecen no haber sido en vano.

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Estas en USA? puedes porbar con crowdfunding en kikstarter u otro similar, pero primero necesitas visibilidad...

Bueno en realidad no se que decirte sobre esto. No tengo intenciones de crear una compania o algo similar. Eso requiere invertir mucho tiempo en la parte administrativa  dejando muy poco tiempo para lo que me gusta en realidad, que es trabajar en este tipo de Proyectos. La visibilidad se consigue pienso, haciendo cosas y con resultados concretos, de lo contrario, no creen mucho en las posibilidades que uno pueda tener, particularmente por aca.
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TEAM: Esto es crucial!
Eso es muy muy bueno; pero crear un "team" aqui, cuesta "mucho money". Hay que pagarle a los miembros del team.

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IDIOMA: Yo en este punto no negocio más
Aunque adoro mi idioma, el Ingles ademas de ser el idioma del pais donde vivo, es tambien el idioma mas utilizado en cuestiones tecnicas.
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lo que voy a hacer lo voy a hacer en mi idioma smiley-grin
De seguro eso limita  tu "visibilidad" smiley-mr-green. Es bueno utilizar lo que tanto esfuerzo te costo aprender, no?.

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En fin en que te parece que te puedo ayudar? Como hacer electronica desed el barro? Sesiones de Coaching?
Me gustaria ciertamente; pero despues de mas de 25 anos haciendo eso, como que ya me aburre un poco y no me motiva mas. Ahora estoy enfocado en algo que me gusta mas,  que es el software. Necesitas coaching en eso?

Muy interesantes tus opiniones.

Gracias.
33  International / Proyectos / Re: Medicion de Volumen (Metodo Seco) on: May 05, 2014, 08:51:46 am
Gracias por tus comentarios (simpaticos, por cierto). Sinceramente, estoy muy muy interesado en compartir este Proyecto con ustedes y me es mucho mejor y facil expresar las ideas en nuestro idioma, aunque me es dificil levar simultaneamente el mismo post en el forum en Ingles y aqui. Alla me hacen algunas preguntas y aqui otras o las mismas. Si quieres, tambien puedes seguir el topico alla (http://forum.arduino.cc/index.php?topic=235122.0) y quizas eso te aclare algunas dudas que entiendo puedes tener, particularmente sin haber visto el "cacharro" smiley-grin (me gusta esa palabra, porque describe muy bien lo que en realidad es smiley-eek-blue). Si pienso mostrarlo, si.
Si, estoy utilizando un LM35DZ como planteas y muchas de las cosas que me sugieres y agradezco mucho, ya las probe de alguna forma. Llevo bastante tiempo "cocinando"  este Proyecto.
Estos son los sensors que estoy utilizando:
-For Pressure Honeywell SSCDRNN250MGAA5 datasheet (http://sensing.honeywell.com/index.php/ci_id/44282/la_id/1/document/1/re_id/0)
-For temp LM35DZ (http://www.ti.com/lit/ds/symlink/lm35.pdf)
Con respecto a la temperatura, pienso que es mas facil encontrar la ecuacion que relaciona el volumen a implementar un sistema de control de la misma. Eso permitiria simplemente cancelar el efecto en el software sin muchas dificultades extras. Para poder hacerlo, sin embargo, tengo que resolver primero el problema de las fugas, pues este anade mucha incertidumbre a las mediciones, que no me dejan distinguir que parte de las variaciones observadas corresponde al efecto de la temperatura y cual a las fugas. Observaciones preliminares sugieren que hay una relacion aproximadamente lineal; pero hay que encontrar los factores de la ecuacion y=mx+b (si es el caso) con precision para poder utilizarla en la compensacion. Eso require de mediciones precisas. Quizas la dependencia real, sea ligeramente no lineal debido a muchos otros factores, pero aun no se con exactitud.
Hasto ahora los resultados obtenidos indican que el metodo es valido; pero honestamente no puedo continuar con esto solo, pues para resolver el problema de las fugas y la compensacion con temp se necesita de recursos de los cuales no dispongo y acceso a patrones de calibracion y otras facilidades que se van fuera de mi alcance.
Aunque pueden seguir el topico alla tambien, siempre tatare de responder cualquier pregunta que puedan tener ustedes aqui.
Gracias
34  Topics / Science and Measurement / Re: Volume Meassurement (Dry Method) on: May 05, 2014, 06:42:20 am
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Perhaps the compressibility factor (Z) of air is playing a role here.

Perhaps, yes. This could also be influencing. I've been thinking maybe its a combination of factors, some of which I have no idea about.

It is important to mention that Relative Humidity and Atmospheric Pr are not being measured at this time and RH in particular, could be influencing the results also. That is pending.

I think, the results so far prove this is possible and the method is valid, however fine tuning is required. To be honest, I can't continue from this point on with this by myself, as it is a matter of resources to build the container(s) and perform precise measurements and adjustments with precise standards I don't have access to. Perhaps, someone here has access to these things or maybe a University or Institution is willing to help with this as a research Project with real practical applications. Any help or suggestions will be much appreciated.

Thank you so much.
35  Topics / Science and Measurement / Re: Volume Meassurement (Dry Method) on: May 05, 2014, 12:29:42 am
First of all, thanks for your interesting comments.
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I do see some similarities when comparing this with the testing of diaphragm gas meters by using a bell prover
I’m trying to measure the volume of the object not the gas. I have no idea about these tests you are mentioning or the diaphragm gas meters; but I will search as it seems to be very interesting. If you have a link to a website, please post it.
 
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In both cases here, measuring temperature and pressure with high precision and accuracy is important.
That's very true. My intention so far was just to test if this could work, high accuracy is not the goal yet. These are just preliminary tests and results. I'm using some good enough sensors (I guess) for this trial; but perhaps in a future stage of this, I will need to use better ones. I didn't want to go for expensive ones without making sure it could be done, find out practical problems and details by testing, writing the code and making a prototype.
I'm using:
-For Pressure Honeywell SSCDRNN250MGAA5 datasheet (http://sensing.honeywell.com/index.php/ci_id/44282/la_id/1/document/1/re_id/0)
-For temp LM35DZ (http://www.ti.com/lit/ds/symlink/lm35.pdf)
I chose this sensors mainly because of the simplicity of use and also because they are linear and should not introduce much problems other than constant errors which could be canceled by adding or subtracting a correction factor (if present). I placed means in the code for that. There could be small calibration issues and errors added as I don’t have precise standards to check; but they will be systematic and possible to cancel. I’m more interested in "behavior" of the physical variables at this point than their exact values. Later on it all needs precise adjustment and you are right about that.

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However, I think there is a problem with precision ... it could be mathematical, poor matching of sensor range to ADC range, or perhaps higher ADC resolution is required.
That I don’t see very well; but I’ll check your suggestions carefully.
-I’m rounding the results just for display on the screen; but calculations are done without rounding with full floats before displaying the results. I’ll check anyway, there maybe some cases where its not. I though approximating 3 decimal digits was enough for display for now.
The AD conversion I’m using which includes averaging among other things, is resolving more than the 1024 normal steps the Arduino ADC can resolve (using it). I’ve been working on achieving this for a while now (you can check some of my previous Projects). That creates the 0.05hPa steps in the 0-250mbar range which will otherwise won’t be possible to achieve and constitute a very good observation from you which I haven’t noticed. Anyhow, the jumps and their differences in both cases (Start Pr and Pr@TC)  are more because of other factors, I think. The fact that Arduino takes time to read the values and the code takes time to find the thresholds as there are other things that need to be done also (communication, etc). As example, deflation starts by time 20 000 milliseconds after the inflation is stopped at 150hPa (that’s what I set it for). Inflation is stopped by finding when the Pr surpasses that threshold and there is a small error involved there. Since time elapsed is the trigger, perhaps the resolution in the differentiation of time originated by the loop duration is creating the impression of the 0.25hPa. The loop duration is not fixed though, it depends on what needs to be done and that could be another factor. The 0.25hPa jumps you have observed, could be just this particular test. I have to observe if that repeats in others. On the other hand, Arduino finds the TC by looking for the Pr to drop to 36.7% of the initial value, then sends the value to the computer (the TC which is what I’m after and the Start Pr recorded). This is a true threshold comparison, different than the time elapsed triggering and the recording of the Start Pr and perhaps the reason for the diffrences in the resolutions you have observed in both cases (This could be more precise; but I don’t know???).

This is something I might need to try to improve as it adds uncertainty to the results; but honestly, I don’t think this is a major influential factor. The leaks and temp issues are, I guess. It will be good to be able to quantify how much uncertainty they add though, as you pointed out.

Also, much of the info such as Start Pr, Pr at TC is there as I placed all that from the very beginning of  the Project trying to solve the exponential equation as you thought. They are still there in case any calculations are needed; but in reality I’m not using them in the calculations or solving the exponential equation to find the volume. To do that, I needed to precisely know the flow restrictor value I used, which is a constant in the equation. The restrictor is just an obstruction I placed inside the bleeding hose, which value I don’t know. I tried to calculate that and was difficult, so I opted for another more simple method. Since the container volume is a constant, the flow restrictor is a constant (assuming no leaks) and from the equivalences for a given volume there should be a Time “Constant” regardless of the initial Pr (as the TC concept suggests) the only factor affecting the TC (TC=R*C) is (C) the Volume of  the container (affected by the volume of the object). In other words, the volume the air occupies. So I set up tests using fairly equal batteries as standards for which I measured the volume and presumed each of them equal. Ran the test with 0, 1, 2, 3, 4 and 5 batteries inside the container (each test 10 times) and then plotted expected Object Volume (determined by the batteries) vs. average TC measured in Excel, with the data being logged automatically. From there, I got an equation which relates  Object Volume  vs. TC which is fairly linear as expected.
Since the TC is the only factor I really need to have precisely measured, I concentrated on that and did not place much emphasis on the rest of the values (not needed). That’s probably why, you may have observed some precision problems; but they may not be affecting the results. Calculating the volume this way, gives much better results and accuracy than solving the exponential equation. This way any other factors influencing are contained in the equation by means of the TC. If the TC measurement is affected by anything constant (I'm aware of or not), the effect is present in the equation and effectively canceled. If trying to solve the exponential equation no other factor will be cancelled, unless I know about it and added it somehow to the calculations, if I can do that (probably not). Of course, all this procedure must be repeated precisely using a container and pneumatic system with zero leaks, real volume standards and at precise temperature. The repeatability should be improved considerably when all that and temp compensation are added. That’s why I think this is apparently working fine. I’m consistently obtaining excellent repeatability, like the one shown, given the container is not opened and temp. does not changes substantially (stays within about 1 Celsius). As you can see, I still have to work more on this to get there. Now is when $$$ is required.
Thanks.
36  International / Proyectos / Re: Medicion de Volumen (Metodo Seco) on: May 04, 2014, 05:45:32 pm
Hola:
Esta es una foto de la pantalla despues de realizer una de las ultimas pruebas. Como se puede observar, el metodo y el sistema construidos parecen funcionar como se esperaba de acuerdo a las equivalencies asumidas. La repetibilidad de las mediciones es bastante buena, mientras no se abra el envase, lo que provoca que cambien las fugas por la tapa o la temperatura cambie sustancialmente. Las fugas de aire al presurizar el envase y las variaciones que introducen los cambios de temperature son los 2 problemas principals en los que aun tengo que trabajar mas; pero no creo que afecten la validez del metodo y pienso que pueden ser resueltos. Una vez que logre eliminar el problema de las fugas, sera mas facil encontrar la relacion entre los cambios de temperatura y volumen medido. El problema radica en que el volume de aire que entra al envase para alcanzar la presion deseada depende de la temperature y esto afecta los resultados.
Les agradezco cualquier idea o comentario.
Gracias.
37  Topics / Science and Measurement / Re: Volume Meassurement (Dry Method) on: May 04, 2014, 08:07:43 am
This is a screen picture after one of my latest tests. The repeatability looks really good while the container is kept sealed and temp does not changes substantially. I definitely has to seek professional help to solve the container leaks problem; but that costs real $$$ and not just my personal time on this. Please beware I'm still working on this; but anyhow if you have any ideas, let me know.
38  International / Proyectos / Re: Proyecto luz pulsada -dudas- on: May 03, 2014, 05:10:05 pm
Puedes estudiar los temas "voltaje rms" y "modulacion de ancho de pulso" para que comprendas mejor.
Este video quizas te ayude a observar lo que sucede y como varian la senal y el voltaje medido, al variar el ciclo util con modulacion de ancho de pulso. Es importante que notes, que el voltaje pico de la senal (en tu caso 5V, en el video 10V) no varia al cambiar el ciclo util (excepto cuando es 0% el ciclo util y no hay pulsos, por supuesto)
https://www.youtube.com/watch?v=271qPIFaC2E
39  Topics / Science and Measurement / Re: Volume Meassurement (Dry Method) on: May 02, 2014, 07:16:40 pm
I've been thinking on the 2 containers method you suggested and seems very feasible too; but perhaps, I will have the same 2 problems again: containers leak and temp dependency of the amount of air entering the first container (the one with the object) and it will basically be the same thing; but I really don't know either??. So far, the results I've obtained with one container, apparently indicate the method is working; but I still have to solve these two problems, that I think  are the reasons for (greater) inaccuracies, which only appear, once I open the container or the temp changes substantially. The results repeat, when temp is about the same and leaks are about the same, which I can observe by repeating the test over and over without opening the container.
Thanks.
40  International / Proyectos / Re: Medicion de Volumen (Metodo Seco) on: May 02, 2014, 04:44:13 pm
El "cacharro", lo tengo hecho; pero no creo que sea lo importante. Es solo un prototipo para probar el concepto.
Si observas el diagrama es basicamente eso con un Arduino controlando el sistema y la computadora comandandolo todo y visualizando los resultados en la pantalla. Aun estoy trabajando en este Proyecto.
41  Topics / Science and Measurement / Re: Volume Meassurement (Dry Method) on: May 02, 2014, 03:46:39 pm
Yes, making the container leak free has been really difficult. The main problem is the leaks change every time it is opened to place the sample inside. However, once the container is sealed and the test repeated, it looks the repeatability of the results is good (if temp does not changes significantly). I already checked a local machine shop with a proposed container to be built; but since my goal for now is to find if the method could be used, I have been delaying that.
The fixed amount of air looks a good assertion; but I'm using the air pressure drop in the vessel as an indirect method of finding the volume. The initial pressure from which deflation occurs is measured on every test. The time it takes to reach 36.7% of the initial value is recorded and the volume calculated. I have changed the initial pressure at which the container is filled and the time to reach 36.7% of the new initial Pr. appears to be about the same.
Another problem affecting the results is temp drift. The air volume required to reach the required initial Pr changes at different temps, and that affects the calculated volume. This is possible to solve (I think) and I have been trying to find the relationship between the measured volume and temp, (by also measuring the temp); but that has proven to be really difficult.
I don't know much about fluids dynamics either; but I wanted to test if this method could work.
I'm still working on this.


42  Topics / Science and Measurement / Re: Something like an ARDULAB, please! on: May 01, 2014, 06:48:05 am
This posts may help you:
http://forum.arduino.cc/index.php?topic=226510.0
http://forum.arduino.cc//index.php?topic=188610.msg1396951#msg1396951


43  Topics / Science and Measurement / Re: Functions Generator on: April 30, 2014, 11:33:52 am
Thank you. While under pressure  people tend to make mistakes. At the end of the day, I think its still good to share these Projects here, even without code, as we all benefit with ideas. I have also posted some codes here before.
44  Topics / Science and Measurement / Re: Functions Generator on: April 30, 2014, 09:34:43 am
The truth of the matter is that these are codes I'm building for fun and they are probably full of inefficiencies, making them unsuitable for sale or anything like that.
45  International / Proyectos / Re: Medicion de Volumen (Metodo Seco) on: April 30, 2014, 08:08:47 am
Todavia tengo que trabajar mas en este Proyecto.
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