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
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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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cyberbadger
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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 366 times
-CB
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cyberbadger
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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 335 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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barts
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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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Bart Smaalders http://smaalders.net/barts Menlo Park, CA
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