DE822613C - Two-armed lever scale - Google Patents

Description

(WiGBL p. 175)

ISSUED NOVEMBER 26, 1951

p 50422 IXb j 42f D

Two-armed lever scale

For scales whose measuring range extends over a larger number of decimals, but also for other lever balances, which are used for measurements of different accuracy, is the possibility a simple and safe sensitivity adjustment desirable. Often one also wishes to be independent of the absolute value of the to be determined Masses a relative accuracy of the result that remains in the order of magnitude. In such cases the sensitivity of the instrument should be adapted to the measuring range or the applied load, that the same percentage reading accuracy is achieved in each case.

The invention relates to a two-armed lever balance in which the load is balanced by moving a counterweight on the one, as a notch ruler o. The like. Trained arm of the balance beam and its Use as a tilt lever · takes place and aims to increase the sensitivity of the balance to the various Adapt measuring ranges and within each measuring range a constant percentage To ensure reading accuracy.

According to the invention, this goal is achieved in a balance of the type mentioned above all in that that the notch ruler extends vertically below the pivot point of the beam when the balance is unloaded lying, arranged at such a distance from the pivot point from parallel or such inclined to that of the pivot point and the load application point going, with unloaded scales horizontally extending plane that either with parallel arrangement, the sensitivity of the balance to the size of the counterweight and thus the is adapted to different measuring ranges or at

inclined arrangement a constant percentage reading accuracy within each measuring area is achieved.

The invention is illustrated by way of example in the drawings.

Fig. I to 3 show schematically the balance with the notch ruler according to the invention in a parallel arrangement, Fig. 4 and 5 the scales with the inclined arrangement of the notch ruler.

The balance beam has the shape indicated in the schematic illustrations. The central axis is at point D, below point C, from which the weight arm starts. Let the load W ₁ to be weighed be attached to A and the counterweight W ₂ to B shifted.

_{The torque W 1} I ₁ resulting from this load is _{largely compensated for by a counterweight W 8} that can be displaced on a notch ruler or a similar device, the rest is read as an inclined part on the scale SK. In the design according to Fig. 1 to 3, the notch ruler runs parallel to the connecting line DA and is at a distance of a _{0 from it} . The center of gravity of the beam alone without the counterweight is at S, the distance from the pivot point D. The upper limit of the measuring range of the balance is determined by the expression for a given lever arm length I _1.

'1

I ₂ max defines the length of the notch ruler.

So in order to change the measuring range of the balance up or down, W ₂ must be replaced accordingly. The essence of the present invention is that with the exchange of the counterweight w _2, the sensitivity of the balance is changed in a manner to be determined by the construction of the device, as follows from the following.

To the sensitivity of the one drawn in fig To find the balance beam, the following considerations are made:

i. The bar plays in on zero, i. H. it lies horizontally in case

1 i e i

2. If a small additional weight μ is placed on the load side, the beam may assume the position shown in Fig. 2. It rotated through the angle Δφ. The equilibrium condition is in this case

(W ₁ -f μ) I ₁ cos Δφ = »» "· s · sin Δφ

+ W ₂ (Z, cos Δφ + a ₀ sin Δφ)

m ₀ means the beam mass, the other variables are known from the explanations above. The evaluation of the expressions in brackets of this equation gives

W ₁ Z ₁ cos Δφ + μ I ₁ cos Δφ = W ₀ ■ s · sin Δφ
-f · Wg l _% cos Δφ -f · W ₂ α ₀ sin Δφ II i

tn _x = I ₂

Since according to requirement I ₁
this equation to itself

μ I ₁ cos Δφ - (w ₀ s + W ₂ O ₀ ) sin Δφ
or tg Δφ I ₁ Δφ

φ
is, simplified

(w ₀

1H ₂ U ₀ )

for the case of small angles Δφ.

It is well known that the sensitivity of a scale is understood to mean the expression

E =

Δφ

ie the angle of inclination Δφ of the bar expressed in radians for the unit of excess weight. In our case it results

E =

s + W ₂ a ₀

If you take special care that s = ο, you leave the center of gravity of the beam with the fulcrum coincide, the simple formula results

I ₁

m, ■ a _n

E · Wo = -— = const.

It follows from this that the product of sensitivity and counterweight m ₂ is a constant, the value of which depends solely on the design data of the beam. With a small counterweight m ₂ , that is to say with a small measuring range, a greater sensitivity is automatically established and, conversely, with a larger counterweight W _2, a lower sensitivity. Both are inversely proportional to each other, so the balance gives the same percentage reading accuracy for each measuring range, which can be set to the desired value by suitable selection of the construction data of the bar.

Of course, it is possible to extend the measuring range of the balance beyond the previously discussed possibility by a second, optionally displaceable counterweight m ₃ attached to the rear extension of the connecting line DA . In this case, however, the sensitivity of the balance remains unchanged (Fig. 3).

With the arrangement explained above, the sensitivity of the balance remains constant within each measuring range, since for given lengths a ₀ and I _{1 it} only depends on the mass of the counterweight W _2. If a constant percentage reading accuracy is also desired within a measuring range, this can be achieved with the arrangement sketched in FIGS. 4 and 5. It differs from the one discussed above in that the notch ruler no longer runs parallel to the connecting line DA , but is inclined to it at a given angle α. The equilibrium conditions for this bar are:

1. In a horizontal position (Fig. 4)

I ₁ · W ₁ = I ₂ · cos α · W ₂ .

2. After adding a small overweight at W ₁ and rotating the bar by the angle Δ φ (Fig. 5) (W ₁ + μ) I ₁ cos Δφ = W ₂ Ui ^{cos a cos} Δφ

+ Ci ₀ sin Δφ + I ₂ sin α sin Δφ].

The evaluation of this equation taking into account i. results

μ I ₁ cos Δφ = m ₂ (a ₀ + I ₂ sin α) sin Δφ
or after the introduction of

Δφ

T?

E =

m ₂ (a ₀ + I ₂ sin α)

If one now forms the expression E · W ₁ , the result is

E ■ m, =

I ₂ cos α
α ₀ + I ₂ sin α

The meaning of this equation is easiest to recognize for the special case a ₀ = o, which then results in

EM ₁ = ctg α = const.

In this case, the product E · W ₁ and thus also the percentage reading accuracy within each measuring range is constant. A beam constructed in this way would have the same load-related, ie percentage reading accuracy in all cases, regardless of its load. It is possible to calibrate the scale in percent or per mille of the load.

Claims (4)

PATENT CLAIMS: i. Two-armed lever balance, in which the load is balanced by moving a counterweight on one arm of the balance beam designed as a notched ruler or the like and using it as a tilting lever], characterized in that the notched ruler extends from a point perpendicular to the pivot point when the balance is unloaded ( D) of the beam lying at such a distance from the pivot point (D) arranged point (C) parallel or so inclined to the plane passing through the pivot point (D) and the load application point (A) and extending horizontally when the scales are not loaded, that either with a parallel arrangement the sensitivity of the balance is adapted to the size of the counterweight (m ₂ ) and thus the different measuring ranges or with an inclined arrangement a constant percentage reading accuracy is achieved within each measuring range. 2. Scales according to claim 1, characterized in that the center of gravity (5) of the beam is placed in the axis of rotation (D) , whereby a sensitivity that is inversely proportional to the counterweight (w ₂ ) of the notch ruler and thus its measuring range is set. 3. Scales according to claim 1 and 2, characterized in that in addition to the counterweight (m ₂ ) of the notch ruler, a second counterweight (m ₃ ) is arranged, but which goes through the pivot point (D) and load application point (A) , acts on the horizontal plane when the balance is unloaded and thereby changes the measuring range without changing the sensitivity of the balance. 4. A balance according to claim 1 to 3, characterized in that the setting of the reading accuracy is done except by changing the distance between the axis of rotation (D) and the load application point (A) from each other by changing the notch ruler distance from the horizontal plane passing through this when the balance is unloaded . 1 sheet of drawings 3 2417 11:51