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Bathroom Scale: Four Flat Load Cells Between Two Plates (Angel, 1991)

أنشأه

Penny

2. نوفمبر 2026

Bathroom Scale: Four Flat Load Cells Between Two Plates (Angel, 1991)

A floor scale only as thick as two plates. Four flat load cells sit in the corners between a base and a top plate; their strain gauges are wired into one bridge, so the signal is the sum of the four loads wherever you stand. Result: a low digital bathroom scale reading in pounds or kilograms. The patent gives under 0.05 % non-linearity, hysteresis and non-repeatability, and under 0.1 % error from off-centre loads; its feet let it stand on thick carpet. Source: S. Angel, US Patent 4,993,506 (1991). Unknown: the plate material and size, the maximum load, and the circuit. Ours: ebonite for the hard rubber, epoxy, the amplifier and display parts. Picture: patent drawing (Fig. 5).

متقدم

2 days

التعليمات

Mount the four load cells

Put one load cell in each corner of the rigid base plate. Screw each one down to small flat raised pads on the plate. Place the pads away from the edge of the cell's beam, so that fixing the cell does not change its sensitivity. Under each cell, tap two holes through the base for the overload screws. Not given: the plate material and size.

المواد لهذه الخطوة:

خلية حمل4 قطع

قاعدة الميزان وصفيحته العلوية1 base and top plate

براغي آلية8 cell screws

الأدوات المطلوبة:

طقم أدوات قطع اللولب

طقم مفكات

أبعاد غير معروفة

Wire one bridge and the readout

Each cell's two gauges are half a Wheatstone bridge. Join the four halves into one full bridge, one half at each corner, so the bridge gives a signal in step with the sum of the four loads. The signal is amplified, turned into numbers by an analog-to-digital converter, worked into pounds or kilograms and shown on a display. Put the electronics and batteries in the space between the plates. Not given: the circuit. Ours: an op-amp and a segment LCD.

المواد لهذه الخطوة:

دارة مكبّر عمليات متكاملة1 amplifier

محول تناظري رقمي1 قطعة

شاشة بلورات سائلة مقطعية1 قطعة

بطارية1 as the circuit needs

سلك توصيل1 as needed

سلك لحام1 a little

الأدوات المطلوبة:

كاوية لحام

Fit the top plate on hard rubber pads

Glue four flat round pads of a rigid but slightly yielding material, such as hard rubber, under the top plate. Give each pad small round studs that snap into the two load holes of its cell, so the weight goes in at the centres of those holes. The pads soften impacts when something is dropped on the scale and take up sideways forces as the top plate bends. The snaps let the top plate be pulled off for repairs. Ours: ebonite and epoxy.

المواد لهذه الخطوة:

قضيب إيبونيت1 four pads

إيبوكسي ثنائي المكوّن1 a little

الأدوات المطلوبة:

منشار حديد

Fit the feet

Under the base, below each cell, fix a shallow foot of flexible material such as hard rubber, rounded underneath. Put its lowest point exactly below the centre of the cell's beam: the floor then pushes up at the beam's centre without bending it, and the scale works on thick carpet or uneven floors. Ours: ebonite.

المواد لهذه الخطوة:

قضيب إيبونيت1 four feet

إيبوكسي ثنائي المكوّن1 a little

الأدوات المطلوبة:

منشار حديد

Set the overload stops

Load the scale to its maximum capacity. Turn the short screws in from below until they just touch the arms of each cell's loading element, then lock them with adhesive. Any heavier load now rests on the screws instead of bending the cells further. Not given: the maximum capacity. Ours: calibration weights and epoxy.

المواد لهذه الخطوة:

براغي آلية8 overload screws

إيبوكسي ثنائي المكوّن1 a little

الأدوات المطلوبة: