Improvements in Planimeters, and Appliances to be employed therewith.
Year: 1895

page_text: Date of Application, 13th Feb., 1895-Accepted, 20th July, 1895
COMPLETE SPECIFICATION.
Improvements in Planimeters, and Appliances to be employed
therewith.
I, EDWARD JONES WILLIS, Mechanical Engineer, of No. 211 East Franklin
Street, Richmond, Virginia, United States of America, do hereby declare the
nature of this invention and in what manner the same is to be performed to be
particularly described and ascertained in and by the following statement :-
My invention relates to planimeters, such as are used for measuring areas, and
consists in improvements in the construction of such planimeters, and in appliances
whereby the mean effective pressure, and horse-power of a steam engine, can be
read from an indicator diagram, without requiring calculation.
I shall describe my invention referring to the accompanying drawings.
Fig. 1 is a plan showing a planimeter embodying my improvements.
Fig. 2 is a vertical section on the line X-X of Fig. 1.
Fig. 3 shows the rectilineally guiding arrangement.
Fig. 4 is a plan of an appliance used in determining horse power.
Fig. 5 is a detail section showing the form of the points used on it.
Fig. 6 is a plan of a modified form of the appliance.
Fig. 7 shows another modification.
Fig. 7 is a part of the arms in Fig. 7 showing the opposite sides.
Fig. 8 shows the adjustable points for Fig. 7.
Fig. 9 is a section of a modification of the interchangeable scale.
Fig. 10 shews part of a table of constants.
Fig. 11 is a plan of a pivotted arm that may be employed instead of the straight
guide of Fig. 1.
1 is one end of the frame of the instrument having a hole through it to receive
the tracer bar 2 which is fixed by a set screw 3 at any required point.
From the end frame 1 projects a spindle 6, at right angles with bar 2. Upon
this spindle is mounted the measuring wheel 6, which can turn freely and travel
along the spindle 6. The periphery of the wheel has a thin edge not sufficiently
keen to cut, but sharp enough to shew co-incidence with graduations of the
scales 8 of which there may be many graduated to suit the different springs with
which the indicator diagrams are taken, or to suit various units of measurement.
Several of these scales may be formed on a polygonal bar 8 or on a cylinder as
shewn in Fig. 9, mounted to revolve upon an axis 9 parallel to the spindle 6, so that
any of the scales can be brought to face the wheel 6°. The axis 9 of the scale bar,
is supported in a bar 10 which is attached to the end of the spindle 6 and to a
bar 10, projecting from the frame 1.
The frame 1 may be pivotted on the one end of a fulcrum bar 12ª Fig. 11 which
at it other end has a pivot pin to enter the paper, or it may have its pivot 5
arranged to slide in a straight guide 12 fixed by pins 13 or it might be by tacks or
drawing pins. A guide groove 14 is formed in or upon the strip, either by slotting
it or by attaching parallel ribs 15 to it. Above the tracer point 4 and the guide
point 5 and axial with them are the setting points 16.
When the instrument is used to determine the mean effective pressure of an
indicator diagram, the scale used is such as to correspond with the spring used in
taking the diagram. The setting points 16 are then set to a distance apart equal
to that of the atmospheric line of the card, or in other words, to the length of the
diagram and the tracer bar 2, is then fixed by the set screw 3; the wheel 6" is set

page_text: 13
at zero on the attached scale, and the guide point 5 is placed in the channel 14, of
the guide strip 12. The tracer point 4 is then caused to follow the diagram and
when it arrives at the point of departure, the wheel, which should remain at all
times in surface contact with the paper, or card, stands at a point of the scale
which indicates the mean effective pressure. This follows from the consideration
that if A represents the area of a diagram, M the movement of the measuring
wheel along the spindle 6, and L the length between the points 16 to which the
tracer bar is set, (which is the length of the diagram) then AM x L, and the
mean effective pressure, which may be written m. e. p, is ✓ or multiplying by
(m. e. p.) L; but, as A = M × L, obviously m. e. p. = M.
L, A =
A
Thus the mean effective pressure is equal to the number of degrees of the scale
over which the wheel moves, reckoned in pounds per square inch, the scale, as for
instance that for a 40 lb. spring, having 40 graduations to the inch, and so for
other springs.
As the horse power of an engine is equal to the mean effective pressure
multiplied by a constant involving cylinder area, stroke and speed, if. the card
length be divided by this constant and if the points 16 be set at a distance apart
equal to the quotient, the horse power can be read directly from the attached scale,
which is selected to correspond with the spring used in taking the diagram. The
horse power is the mean effective pressure multiplied by the constant which is the
card length divided by the distance of the points 16. For example in an engine
having a cylinder 12 in. diameter, stroke 18 in. and making 150 revolutions per
1 ft. x 12 x *7854 × 150
minute, the constant is
= 77 nearly. If the diagram is
4.24
-77
4.24 ins. long, then =
guide points 16.
33,000
5.5 ins. is the proper distance between the tracer and
ап
To avoid necessity for calculation and ensure accuracy, I have devised
appliance to a planimeter of the kind described, consisting of two graduated arms 17
and 18 jointed together and provided with points, either fixed, or adjustable, at
equal distances from the joint. The arms may extend beyond the joint as indicated
by dotted lines. in Fig. 4.
This appliance is used to set the points 16-16 to a distance equal to the quotient
of the card length, divided by the engine constant, thus rendering the instrument
capable of shewing the horse power on the scale without any calculation. To
facilitate this, tables may accompany the appliance giving the diameters of
cylinders, strokes and revolutions per minute for various engines, and indicating
the points upon the graduated arms 17 and 18 to which the points 16 of the
planimeter should he set. Each table gives the reciprocal of the engine constant.
The adjustment is made as follows. The arms 17 and 18 are opened apart till
their points 19 register with the ends of the atmospheric line of the diagram, the
points 16 of the planimeter are then set to the graduations on the arms 17 and 18
corresponding to the particular case. If for instance the table were:—
Distan
14

page_text: Now, using the appliance as shewn in Figs. 4 and 6 for a diagram taken with a
fifty pound spring, from an engine having a 10 in: cylinder and a stroke. 11 in.
making 210 revolutions per minute the points 16 of the planimeter would be set to
the graduations 218 on the arms 17 and 18, these having previously been adjusted
by setting. these points 19 a distance apart equal to the length of the atmospheric
line of the diagram. The fifty pound scale being attached to the planimeter, and the
diagram being followed by the tracing point, the horse power can be read directly
from the scale.
1.027
If the points 19 are adjustable on the arms as indicated by dotted lines Fig. 4
and shewn in Figure 7, a table is employed like that shewn in Figure 10. In this
case the points 19 are set on the arms to graduations corresponding to the
revolutions per minute. They are then set to the length of the atmospheric line of
the diagram and the points 16-16 of the planimeter are set to graduations on the
arms given in the table Figure 10. If the diagram were from an engine having a
9 in. cylinder and 12 in. stroke at 200 revolutions, the points 19, Figure 7, are
first set to 200 on each arm. Then the arms are opened to set the points 19 to the
ends of the atmospheric line. The number in the table Figure 10 for this engine
being 465, the points 16 of the planimeter are set to the graduations 465 on the
arms 17 and 18. Thus in going over the diagram the planimeter, having the scale-
corresponding with the indicator spring, the horse power can be read direct from
the scale.
The scale on the extensions dotted in Figure 4 is preferably the same as the
scale on the arms 17, 18 but if a different scale is used, the tables would have to be
suited to it. If for instance the scale on the dotted arms Figure 4 is twice as fine
as that on the arms 17, 18, the figures of the tables would have to be halved.
By employing adjustable points 19, set to speed, the extent of the tables is
reduced. The arms 17, 18 may be graduated on both sides, the one side coarsely
for large engines and slow speeds as illustrated in Figure 7, (these graduations
being about 16 to the inch and suitable for speeds under 200), and the other side-
finely graduated as illustrated in Figure 74 for small engines and high speeds,
(these graduations being about 60 to the inch and suitable for speeds above 200).
The appliance described may be used with any planimeter measuring mean effective
pressure, but, unless different scales are employed according to any invention, the
instrument will give correct readings for only one spring, and corrections will have
to be made in other cases.
Having thus particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I would have it understood
that I make no general claim to a planimeter of the kind which has already been
described by me in the Specification of a United States Patent dated
November 13, 1894, No. 529008, and that I do not claim anything set forth in that
Specification, but what I claim is :-
1. In combination with the planimeter constructed as herein described, a fixed
rectilineal guide in which the pivot of the planimeter moves, substantially as
described.
2. In combination with the spindle of the measuring wheel, a bar of polygonal
or other suitable form, having several scales on its sides mounted on an axis
parallel with the spindle, substantially as and for the purposes described.
3. For adjusting the tracer bar of a planimeter, an appliance consisting of a pair
of graduated arms jointed together and provided with points separable more or less
by opening or closing the arms, substantially as and for the purposes described.
4. The modification of the appliance above referred to wherein the graduated
arms bave points adjustable upon them, substantially as and for the purposes
described.
5. The combination with a planimeter, an appliance consisting of two graduated
jointed arms having points adapted to be adjusted at a distance proportional to the
length or atmospheric line of an indicator diagram, and a table of reciprocals of the-

page_text: constants of various engines to determine the adjustment of the tracer bar of the
planimeter, substantially as and for the purposes described.
Dated this 13th day of February 1895.
ABEL & IMRAY,
Agents for the Applicant.