Experimental Instrumentation

[fredrosse]

OK, so what and where does one purchase the equipment between the transducers and the laptop, and how is this hooked up? You guys are writing in a language that seems "Greek" to me.

[DetroiTug]

Fred, Have a look at the Arduino programmable controller. Very inexpensive and flexible. The code is dumped from the computer to the controller and then it is stand alone. It could be used permanently for the programmed task.

Regarding the number of pulses per revolution. I got into this years ago when helping develop Mach3 CNC Mill and lathe control. They wanted to use one pulse per spindle revolution on the lathe for doing threading. I suggested it wouldn't work because as the tool entered the work, the RPM would drop and with only one pulse per revolution, it would take a few threads for the Z axis to get in sync with correct helix. I was wrong (the effect in this application is of little consequence), they went with one pulse per revolution and it works fine. Turns out there is enough inertia from the chuck (Flywheel) that it takes several rotations for RPM to fluctuate over time. Enough rotations that the controller can adjust to it.

For piston position, I'd have a look at a linear encoder (glass scale).

-Ron

[Oilking]

An earlier engineer had the "Portland" rigged with pressure transducers on each end of both cylinders. The piston position was provided by a string connected to the crosshead that was wound on wheel connected to a rotation transmitter. A spring from a recoil starter maintained tension on the string and rewound on the return stroke. Four simultaneous graphs were produced, one for each end of a cylinder, and looked like an EKG with a series of spikes showing admission tapering off to exhaust and then again admission. Not like the traditional indicator pattern, but the information was there once you got your mind around what you were looking at. The engine room also started to look like some one wired for and EKG. This engine has a nine foot stroke with a max speed of 16 RPM.

Hope all had a good Christmas and best wishes for the New Year!

Dave

[DetroiTug]

The "rotation transmitter" was more than likely a rotary encoder. Yes, a small cable wound around a flat drum can turn those, but they aren't very accurate driven that way. The cable will creep over time and get out of position. A small nylon rack gear would work to accurately turn a rotary encoder.

-Ron

[Oilking]

Ron,
On a small engine a rack to drive the encoder may be a better route with a spring device to keep the pinion loaded in a constant direction.

On the "Portland" the wheel driving the encoder had a flat grove about 3/8 inch wide and was likely 3.82 inches in diameter so one revolution was one foot. The string was light braided line that I think has a stainless sire core. This may have been subject to creep over time, but I believe there was some way to do a zero on the computer each time an observation was done.
There are two Crosby indicators on board that we are thinking about hooking up some day. The creep that may exist in the string driven encoder pales when I think of all the rigging it will take to reduce 9 feet of stroke to around 4 inches to drive the indicator drum?

Dave

[Oilking]

Ron,
On a small engine a rack to drive the encoder may be a better route with a spring device to keep the pinion loaded in a constant direction.

On the "Portland" the wheel driving the encoder had a flat grove about 3/8 inch wide and was likely 3.82 inches in diameter so one revolution was one foot. The string was light braided line that I think has a stainless sire core. This may have been subject to creep over time, but I believe there was some way to do a zero on the computer each time an observation was done.
There are two Crosby indicators on board that we are thinking about hooking up some day. The creep that may exist in the string driven encoder pales when I think of all the rigging it will take to reduce 9 feet of stroke to around 4 inches to drive the indicator drum?

Dave

[Oilking]

Ron,
On a small engine a rack to drive the encoder may be a better route with a spring device to keep the pinion loaded in a constant direction.

On the "Portland" the wheel driving the encoder had a flat grove about 3/8 inch wide and was likely 3.82 inches in diameter so one revolution was one foot. The string was light braided line that I think has a stainless sire core. This may have been subject to creep over time, but I believe there was some way to do a zero on the computer each time an observation was done.
There are two Crosby indicators on board that we are thinking about hooking up some day. The creep that may exist in the string driven encoder pales when I think of all the rigging it will take to reduce 9 feet of stroke to around 4 inches to drive the indicator drum?

Dave

[Oilking]

Ron,
On a small engine a rack to drive the encoder may be a better route with a spring device to keep the pinion loaded in a constant direction.

On the "Portland" the wheel driving the encoder had a flat grove about 3/8 inch wide and was likely 3.82 inches in diameter so one revolution was one foot. The string was light braided line that I think has a stainless sire core. This may have been subject to creep over time, but I believe there was some way to do a zero on the computer each time an observation was done.
There are two Crosby indicators on board that we are thinking about hooking up some day. The creep that may exist in the string driven encoder pales when I think of all the rigging it will take to reduce 9 feet of stroke to around 4 inches to drive the indicator drum?

Dave

[Oilking]

Ron,
On a small engine a rack to drive the encoder may be a better route with a spring device to keep the pinion loaded in a constant direction.

On the "Portland" the wheel driving the encoder had a flat grove about 3/8 inch wide and was likely 3.82 inches in diameter so one revolution was one foot. The string was light braided line that I think has a stainless sire core. This may have been subject to creep over time, but I believe there was some way to do a zero on the computer each time an observation was done.
There are two Crosby indicators on board that we are thinking about hooking up some day. The creep that may exist in the string driven encoder pales when I think of all the rigging it will take to reduce 9 feet of stroke to around 4 inches to drive the indicator drum?

Dave

[Oilking]

Sorry about that. It didn't go the first click so I clicked second time. Must have clicked more than twice!

Dave