Planimeter

Sorting through the dust and debris of the workshop, I uncovered again a planimeter, sitting in its box, nicely tucked up. I last used it probably 50 years ago to calculate the acreage of a piece of land.

Its a BOWEN & Co (America) model No1100 and the box is impressed U.S.C.E

Lovely bit of kit, plenty on the internet which probably don't sell, but what does one do with them these days ??

Bob

Store it in the Nuclear Bunker … for use after the great ElectroMagneticPulse bricks all the modern stuff.

MichaelG.

Mine was new around 1980. Relegated to the loft donkeys years ago but too nice to bin. Unfortunately the box liner foam has collapsed so a serious clean is needed.

Clive

The only time I used one of them was during a naval architecture course. We used it whilst making hull drawings to work out the area of each of the stations along the length of the hull. You could then work out the displacement and all the other performance coefficients. We didn't actually need to do it like that but they wanted us to do it old school so we understood what we were doing.

The surveyors had them in the survey office at the collieries. Used them for working out the areas of coal that had been worked for royalty purposes and damage claims etc.

I used one just once at college as part of our course but would never need to use one in anger.

Les

I used one 50 years ago for calculating whirling speed of steam turbines. I'm struggling to remember the theory!

There was I thinking that all the steam engine builders here worked out the IHP of their models by fitting an indicator, and using a planimeter to measure the area of the plot on the card to work out the mean effective pressure. Isn’t it something like IHP = PmALE/33000?

My experience is similar to Buffer. I was a Draftsman at the Admiralty in the mid 70s. The task involved calculating the volume of spaces on a ship. The one that I was loaned from the store, was an English one (maybe Moore and Wright, but I 'm not sure), first purchased and calibrated on 1936. There were several inspection stamps suggesting that is was looked at every five to ten years. The instructions were excellent, however because the task involved lots of repetition calculations, I ended up not using the planimeter.

No doubt its in a Museum now, complete with my notes!!

cheers

Bill

Wow that brings back memories doing all that stuff in Technical College in the 1970's !

Hi All,

Have had quite a few of these lovely instruments over the years.

VERY limited market and they really don't make much when selling, we no longer buy them on their own.

Cheers, Martin

I wonder if any of the various steam-engine preservation / rebuilding groups use Indicators and Planimeter

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The formula is HP= n[PLAN / 33000] where

P is Mean Effective Pressure in p.s.i. acting on the piston from lead to release ,

L = Stroke in feet,

A = Piston Area in square inches,

N = number of Strokes per minute (rpm X 2 for double-acting).

The denominator turns the top line product, in foot-pounds/minute, to Horsepower.

That 'n' is a fraction <1, or percentage, called the 'Diagram Factor', and is a rather empirical allowance for internal losses very hard or impossible to quantify. The letter was conventionally not an 'n' but a Greek character whose name I don't know, looking a bit like an 'n'. I think on a well-designed engine the Diagram Factor could be up around 0.8, even 0.9.

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I can think of uses for planimeters in geographical work. Nature does not make areas of land, water bodies and the like to neat geometrical shapes. Nor, I very much doubt, really to those Fractals that were all suddenly so sexy to sum-smiths in the 1980s!

I knew I had used one as part of my engineering degree, but was struggling to remember what for - that was it, though: The lab had a large, single cylinder horizontal gas engine with an indicator fitted and we used the planimeter to measue the area of the indicator trace when analysing its performance.

Never used one since!

When I recovered the drawings for the diesel engine at work when it was scrapped, with permission (so I could build a model of it in the future), there was an indicator and a planimeter in one of the cupboards. The engine was built in 1960-61 and used in the laboartories' building, that used to be the engine test house up until 2000 for peak load generation and blackout protection. It made a profit of £80,000 per year through the '90s...

Same as Andyg, our college had a single cylinder gas engine which produced an indicator diagram and we were tasked in working out the indicated horsepower with the planimeter. I often wonder what happened to that lovely engine.

Not sure how readily any of them would adapt to Indicator Diagrams, but there are several ‘Planimeter’ iOS Apps available.

MichaelG.