digital steam engine indicator

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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Re: digital steam engine indicator

Post by Steam Captain » Thu Jul 29, 2021 10:18 pm

Yes, Fredrosse, those type of pressure transducers would do the trick. The china ones unfortunately work only if you reduce the sample rate per rotation and run the engine slowly. 100 samples per rotation for 600rpm is VERY optimistic for the china sensors. 600rpm means 10rps - with 100 samples per rotations -> every 1ms one sample. The china sensor datasheets speak of 2ms delay... I did get results, but I had to reduce the amount of samples per rotation AND the engine speed, but I think 100 samples per rotation is the absolute minimum for a reasonably detailed pv-diagram.

Cyberbadger: Try to run the engine very slowly with an intact sensor. If the slower the engine runs, the lower the pressure graph goes, it could indicate the sensor lags too much to follow the real pressure when the engine is running faster (or that you have VERY narrow steam passages, but I can't imagine that.) The vacuum showing makes sense to me, since the engine still runs out for a second or so when you shut off the steam. Thus the engine still moves due to inertia, creating a vacuum - no matter how short

I've been fiddling with this for a long time now and I strongly believe the only sensors for high steam engine revolutions and professionally clear read-outs will only be possible with spark plug sensors, which can be very hard to come by on their own. But they at least provide for a price range a dedicated hobbyist can go for. Until now I only found sensor glow plugs for 75 bucks apiece. Way cheaper than anything else I found, but I'm in contact with Kistler. I've contacted half the universe and it seems to be a real challenge, but I'm shyly optimistic
the arduino version steam engine indicator: https://app.box.com/s/b2i0z3gw6ny3rcfdet5xjg8ubrfu799i - app version coming soon
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cyberbadger
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Re: digital steam engine indicator

Post by cyberbadger » Wed Aug 18, 2021 11:19 pm

cyberbadger wrote:
Sat Jul 24, 2021 10:34 pm
Well it was only a $20 sensor. I think I'm going to order one these for $30 that says its rated for steam and comes with its own thermal management solution:
https://www.amazon.com/Akozon-Pressure- ... s9dHJ1ZQ==
I added a 4 channel 16bit Analog to Digital chip, https://www.adafruit.com/product/1085 or https://www.amazon.com/ACEIRMC-Converte ... 844&sr=8-3

A 24V boost supply that I can run off of a 9Volt battery to power the transducers.
https://www.amazon.com/Aceirmc-Current- ... 22&sr=8-29

2 of the Akozon pressure transducers listed above that are 0-1.6Mpa(0-232psi), output 4-20mA current loop.

A 250 ohm resistor added in series in the 4-20mA current loop, one for each transducer. The Analog to Digital chip reads the voltage drop across these resistors.

One of these transducers will go on the boiler, and one on the fore cylinder #1.

I have tried it on compressed air and the data looks good. I should get a chance to try it on Nyitra in the coming week under steam.

-CB

P.S. I have tried to trim the code down to make the arduino code reasonably fast. However, with the arduino I only seem to be able to capture 2 pressures at about 60Hz. In theory this 16bit A->D is supposed to be able to get up to 800 samples/sec. My limitation may be writing to the SD card.
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Re: digital steam engine indicator

Post by cyberbadger » Mon Aug 23, 2021 7:47 pm

Got one capture running the engine slow with the new $30 sensors and circuitry.

At this time my sample rate is 50hz. The bottleneck is not the A->D itself, it is supposed to be able to acquire at 800hz.

I looks pretty clear to me, but at higher engine speeds 50hz won't cut it.

In the graph that represents 10 seconds, you can see that the engine rpm is near 60rpm,
Nyitra-Toledo-1-Aug-20-2021-long.png
Nyitra-Toledo-1-Aug-20-2021-short.png
Nyitra-Toledo-1-Aug-20-2021-short.png (61.37 KiB) Viewed 2015 times
-CB
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Re: digital steam engine indicator

Post by cyberbadger » Tue Aug 24, 2021 12:23 am

Nyitra-Boiler-Aug-20-2021.png
Nyitra-Boiler-Aug-20-2021.png (37.21 KiB) Viewed 1984 times
This graph shows 27minutes, this is the second sensor that is recording the boiler pressure. I am partially doing this to confirm that the engine cylinder pressure never exceeds the boiler pressure.

Around 52,644 samples I ran the injector and added 2-3 gallons to the boiler.

You can see that the colder water cooled the boiler and it took it a few minutes to really heat that water up before the pressure started really climbing again.

-CB

P.S. You can see the two sensors in this short clip below. The one is high on the boiler next to a whistle with a yellow-red apollo ball valve to isolate it and it has a corrugated black wire sleeve protecting the sensor wire coming down to the deck. The other sensor is on top of the engine.

Getting Underway, closing cylinder petcocks:
https://www.youtube.com/watch?v=CnMhyBk2N4M
Last edited by cyberbadger on Tue Aug 24, 2021 4:07 am, edited 1 time in total.
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Re: digital steam engine indicator

Post by barts » Tue Aug 24, 2021 12:39 am

Nice - looks like your data is coming together. It would make you analysis easier to trigger sampling off a 500 count encoder so you'd get samples every 1/500th of a revolution.

As I mentioned before, if you sample at 50hz, don't forget to low pass filter w/ a cut-off at 25 hz (actually better off at 20 Hz).

You can construct a suitable LP filter w/ a op amp. Here's one; the data sheet has a suitable circuit and it only needs a single-ended supply: https://www.sparkfun.com/products/15946

Sparkfun is a dangerous place; lots of cool electronics stuff to build.

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Re: digital steam engine indicator

Post by Steam Captain » Tue Nov 09, 2021 5:45 pm

This does look nice already.
I've been tinkering with a python software to output the data from the arduino. This is an impression of what to expect:

Image

The graph was created by feeding it data from the arduino. Unfortunately, I have no workshop right now, but I let the arduino simulate data to look roughly like a pV-graph.

Note: The data is updated in a 1 Hertz rate for readability. But this can be altered. The pV-diagram obtains the data from the arduino and uses the much faster computer (or phone - Wes, I haven't forgotten about your idea) to calculate everything and draw the graph. The arduino is just not the right platform to have a reasonable display with an easy readability. The 2 points on the graph are the extreme points: the max and min pressure. I found it neat to have another way of seeing the pressure inside the engine as the supposedly precise pressure transducer is already used for the contraption anyways.

I'd like to hear input. Do you like what you see? What about the color scheme? I just used it for contrast and didn't sink too much brain into it, but it ends up looking professional, even scientific. What do you like about it? What would you do different? What would you want to add? There is already something like a "start window" before you go to this graph window, where the indiced power, momentary rpm and max pressure is displayed life in a big, easily readable format to make it easy to grab information by a brief glance while steering the boat:

Image

The diagnostics button would lead to the window with the pV diagram. I should have posted it before the other picture, because it is what you'll see first.
I know it looks very basic, but there's hundreds of lines of code behind it and I only learned python for this steam engine indicator project, which was a challenge on itself. But I hope you still like where this is going.
the arduino version steam engine indicator: https://app.box.com/s/b2i0z3gw6ny3rcfdet5xjg8ubrfu799i - app version coming soon
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Re: digital steam engine indicator

Post by TahoeSteam » Thu Nov 11, 2021 1:03 pm

I'm really impressed with the work you're doing. I bought some of those wireless Bluetooth pressure transducers a while back but haven't gotten around to utilizing them. :/

Maybe a feature where one could transpose the graph from the top of the cylinder over the graph from the bottom of the cylinder?

This way one could easily see the difference and make necessary valve adjustments so get even power from both sides of the stroke.
~Wesley Harcourt~
Check out the steamboat and steamSHIP videos on my YouTube page: https://www.youtube.com/c/wesleyharcourtsteamandmore
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Re: digital steam engine indicator

Post by cyberbadger » Sat Nov 13, 2021 5:45 pm

Steam Captain wrote:
Tue Nov 09, 2021 5:45 pm
I know it looks very basic, but there's hundreds of lines of code behind it and I only learned python for this steam engine indicator project, which was a challenge on itself. But I hope you still like where this is going.
I think it looks great.

For my purposes, I am usually way too busy onboard my boat. I would prefer to look at the data at the end of the day on a computer.

I know it's just test data but 100 bar, that would be quite an engine! On my boat I run upto just under 14bar and some think that's high. Practical steam railway locomotives usually are only operating up to 17-20bar. Reciprocating steam engines at 100bar has been tried, but shown to be a bad idea. It's so violent at those pressures that everything needs to be mechanically super reinforced, even then the engines really just want to tear themselves apart.

100 bar is really into the realm of steam tubines, but you'd need a different kind of steam indicator for a steam turbine.

-CB
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Re: digital steam engine indicator

Post by Steam Captain » Sun Nov 21, 2021 9:37 pm

The story behind the 100 bar on the screen: It was originally all in psi and inches and I took the screen photos when I was halfway through into converting everything into metric units. So, the pressure units were still in psi, but the unit name already in bar. And in fact, the program is written in a way that it can process any pressure value. It automatically adjusts to the given data range, which is a neat python matplotlib standard feature.
the arduino version steam engine indicator: https://app.box.com/s/b2i0z3gw6ny3rcfdet5xjg8ubrfu799i - app version coming soon
Excuse my occasional long response time. It's caused by the side effects from ptsd.
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cyberbadger
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Re: digital steam engine indicator

Post by cyberbadger » Tue Nov 23, 2021 7:27 pm

One idea for a display - any device that can be programmed and has I2C or QWIC can be hooked up to one of these 4 character hex-segment displays that sparkfun sells for less then $10:

They can be daisy chained if you want more characters:

Green
https://www.sparkfun.com/products/18566
White
https://www.sparkfun.com/products/18565
Red
https://www.sparkfun.com/products/16916
Blue
https://www.sparkfun.com/products/16917
Purple
https://www.sparkfun.com/products/16918
Pink
https://www.sparkfun.com/products/16919

Alternatively, you could get a tiny super fast servo and put it inside an antique analog pressure gauge...

-CB
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