Experimental Instrumentation

[russkey]

Does anybody have experience with electronic measurement of engine and boiler conditions? Things like temperature and RPM should be easy enough, but what about pressure? Most pressure sensors I've ever used would collapse before they ever reached 100˚C. I would imagine no digital sensor would survive the heat either, but there must be some sort of analog measurement method. I'm looking to characterize the conditions within a prototype engine, especially to see how those conditions change with use over the course of days and months. Any thoughts?

[farmerden]

http://www.ogdenmfg.com/pdf/tech21.pdf
It would appear that if one knows the pressure than the temperature is already known as it is in a constant with the pressure according to this graph anyway .So if you have a constant operating pressure you will know the temperature without using a gauge. At 120 psi the temp would be 350F. Saturated steam tables should be printed in every book about steam so they shouldn't be hard to find. Looking back at your question you want an electronic pressure gauge rather than a pressure activated gauge? I remember when trucks tryed out digital gauges-they were terrible.We had become so conditioned to the position of the needle in the guage always being in a normal operating place that when the gauge read say 2100 RPM on a digital readout you had to actually think about what that meant,not just look at the position of the tach needle.I guess I wasn't the only guy having trouble cause they dropped them.Sorry for the ramble and thru all that I don't think I answered your question anyway Den

[fredrosse]

A pressure gauge pigtail is used to protect the pressure gauge from the effect of hot pressure media such as steam. The siphon allows condensate to form and be collected inside the pigtail portion of the siphon, preventing the hot media from coming in direct contact with the pressure instrument. The pigtail siphon is normally used for vertical applications.

You can buy them as shown, or make your own from a few elbow fittings.

[russkey]

Well, the goal here is to measure the conditions within the cylinder of a prototype engine, so the sensor, whatever it is, would need to respond fairly quickly to changes. Temperature measuring devices tend to have a bit of a lag, so I'm not sure that would be ideal. On a similar note, does the water cushion inside the siphon cause a similar "low pass filter" effect on the readings? The end goal is to obtain a PV diagram for the engine, and to see how it changes over time, if at all (it is a rotary engine, so there is some concern about seal wear; I don't think its a problem, but I do feel that it would be best to have quantitative support for my gut feelings).

[artemis]

Start by using Google.
Type "electronic pressure and temperature sensors".
You'll be amazed at the listings. There are digital and dial readouts.
You'll also find software that will "massage" that info into the results you're looking for.
"Let your fingers do the walking" - not mine

[russkey]

No doubt google has catalogued quite a bit of information regarding this and other fun topics. In fact, there is a large number of transducers to be found at digikey and newark. I posted the question on this particular forum because I wanted to know about sensors that the steam engine community, especially the small scale steam, has to say on the matter. Sensors abound, as does the software to analyze the collected data (and I have no problem with writing a bit of code myself), but personal experience is harder to come by.

Thanks,
Al

[mtnman]

My sensors consist of a 100 year old MARSH steam pressure gauge and a knowledge of how to bank a coal fire.

[87gn@tahoe]

I think there were/are some members of the SBA working on a digitized engine indicator

[87gn@tahoe]

Your rotary engine, is this something like a Wankel, but with steam or another of design?

[russkey]

It is a design based on the Tverskoy engine. I haven't had a chance to boot into Windows, but as soon as I do, I'll make some diagrams from the SolidWorks files. By SBA you mean the folks over here: http://www.steamboat.org.uk/ ?