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Re: digital steam engine indicator

Posted: Mon Nov 21, 2016 5:43 pm
by cyberbadger
fredrosse wrote:These issues are already addressed in this forum thread, April of this year. See previous posts..
I'm not seeing an example of an actual sensor that you can buy that would be appropriate in this forum thread - no links.

If the one I just posted is not appropriate, I am looking for an example of one.

Good point on the snubber.

-CB

Re: digital steam engine indicator

Posted: Sun Feb 03, 2019 5:31 pm
by Ramón
Digging up this interesting, yet unfinished thread, a spontaneous idea came in my mind. For me, an old-scool indicator would be enough, but maybe someone is still interested to one day put one together.
There seemed to be some confusion if the crank rotation or the piston movement is better suited for an indicator. Only the piston movement will provide for an accurate indicator diagram. Nothing else. No crank rotation, no nothing. Only the exclusively linear motion of the piston/piston rod/cross head can provide for this. Though someone loving to program could de-distort an indicator diagram tapped from the crankshaft with some written program by using the individual stroke and connecting rod length as a variable.

Another solution I was wondering about:
Couldn't a laser distance sensor be used to tap the linear movement off the cross head - maybe with a small piece of metal attached to the side of the cross head. That way, the con rod wouldn't be in the way. I think the pressure tapping was already solved. There are loads of different digital pressure gauges on the market. From the technical point of view, there is no stepping stone left. Only the programming front would have to be cleared to spit out some graphs on a computer or independent steampunk display.

Re: digital steam engine indicator

Posted: Wed Mar 06, 2019 1:17 pm
by Ramón
I was originally not so much into this indicator and just had an idea to give, but I found myself caught by it. Now, I am communicating on some arduino forums for its realizability. I actually found a way to messure the piston position. There are linear position sensors for cnc mills and lathes. These sensors are more than suitably accurate and can handle speeds of up to a couple of m/s. I think I will try to throw one together. I am having the specs of my engine in mind (3300 rpm max), but I am trying to realize it in a way, that it can be used by everyone. But I need to exchange ideas with the arduino pros first to find a way, because I am not able to program at all.

But I was thinking of an output in the form of a p-V-diagram and an automatic calculation of the average pressure/internal power.

Re: digital steam engine indicator

Posted: Fri Mar 08, 2019 5:04 am
by TahoeSteam
I know I would love to have one. Especially something mated with a user-friendly (read near-luddite) graphing software.

Re: digital steam engine indicator

Posted: Fri Mar 08, 2019 5:27 pm
by marinesteam
There is no reason that a rotary encoder couldn't be used as the piston location measuring device. It could be done the same way as mechanical indicators with a string and spring return. with the dynamic issues attendant with this kind of mechanical linkage. Measuring the rotational location of the crank would also work. There would need to be some math involved with the crank throw, connecting rod length would need to be inputs and some way to set the timing to the actual crank position would be needed too. This could be easy as a push button to "zero" the position when the crank is stationary and at TDC or BDC. Laser distance sensor would also work but might be costy with the speed and accuracy needed. A view unobstructed and in-line to the axis of motion of the target would also be required. Linear transducer would probably be my last choice. Mounting would be difficult and many have translation speed limits more because of mechanical limitations. A rotary encoder would be easy to mount given access to the free end of the crankshaft. The rest is just programming.

Cheers

Ken

Re: digital steam engine indicator

Posted: Tue Mar 12, 2019 3:30 pm
by Ramón
Your considerations made me look deeper into the rotary encoder and it looks very well. I was more inclined to a linear solution to reduce the programming, but maybe I could try the rotary solution. It both has pro's and con's. A linear sensor could automatically determine the piston stroke and doesn't need an angle-piston-travel-conversion, yet, It'd need some method of attaching to the crosshead. On the other hand, the incremental rotary encoder needs this calculations. But what makes me interested in those rotary encoders is their specs. I found a cheap incremental encoder being capable of working up untol 5000 rpm (probably only interesting for me) and still being able of delivering 600 signals for each rotation (much more than needed by the way. 100 signals would aready create a very, very smooth graph - maybe even just 50.).

Now, I ordered the arduino and I just need a working computer:)

Re: digital steam engine indicator

Posted: Thu Mar 14, 2019 7:28 pm
by Ramón
TahoeSteam wrote:
Fri Mar 08, 2019 5:04 am
I know I would love to have one. Especially something mated with a user-friendly (read near-luddite) graphing software.
Well, we are sitting in the same boat there:) I ALWAYS wanted to evade IT stuff. Now, am sitting next to an arduino:)

Re: digital steam engine indicator

Posted: Fri Mar 29, 2019 4:17 pm
by wsmcycle
I see there has been much interesting discussion of the indicator proposal. I did not think of the difficulty of establishing the piston position and therefore the volume. I thought a rotary encoder would be fine. Even though the math would be rather simple to execute, it would have to happen fast. Perhaps just store the information and process it later. I did however want to see the graph "LIVE" or rather the salient determinants from the graph, mainly Horsepower and efficiency. So that adjustments to the engine would lend a direct readout of the resulting PV diagram.
Perhaps a simplified method would be to attach to the flywheel reflective-adhesive dots to trigger an infrared detector and capture the (Pressure, volume) points. This would have to include a special dot for a start reference. Simply, two dots very closely spaced for the reference signal. something more durable than adhesive reflection material will probably be thought of (such as magnetics), or a hall affect sensor.

Re: digital steam engine indicator

Posted: Fri Mar 29, 2019 7:37 pm
by Mike Rometer
Crankshaft rotation/postion sensing is nothing new or difficult on motor vehicles. The usual method is a magnetic reluctor. If it can be done for 1000s of rpm 100s shouldn't be too hard.

Re: digital steam engine indicator

Posted: Fri Mar 29, 2019 8:48 pm
by wsmcycle
Mike, please give a brief explanation of a magnetic reluctor. I don'know that term. My thinking was to apply something that would not require access or contact to the crank shaft. (remote sensing)