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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).
高级
2 days
说明
1
1
Mount the four load cells
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.
此步骤所需材料：
称重传感器4 个
秤的底板和顶板1 base and top plate
机螺钉8 cell screws所需工具：
丝锥板牙套装
螺丝刀套装
未知尺寸2
2
Wire one bridge and the readout
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.
此步骤所需材料：
运算放大器集成电路1 amplifier
模数转换器1 个
段码液晶屏1 个
电池1 as the circuit needs
连接导线1 as needed
焊锡丝1 a little所需工具：
电烙铁3
3
Fit the top plate on hard rubber pads
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.
此步骤所需材料：
硬橡胶棒1 four pads
双组分环氧胶1 a little所需工具：
钢锯4
4
Fit the feet
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.
此步骤所需材料：
硬橡胶棒1 four feet双组分环氧胶1 a little所需工具：
钢锯5
5
Set the overload stops
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.
此步骤所需材料：
机螺钉8 overload screws双组分环氧胶1 a little所需工具：
校准砝码组螺丝刀套装材料
11- 4 个占位符
- 1 base and top plate占位符
- 8 overload screws占位符
- 1 amplifier占位符
- 1 个占位符
- 1 个占位符
- 1 as the circuit needs占位符
- 1 as needed占位符
- 1 a little占位符
- 1 four feet占位符
- 3 a little占位符
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