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Electronic Analytical Balance: a Coil Current in Place of Weights (Akers et al., 1977)
The equal-arm balance with its weights replaced by electricity. The pan sits on a coil in the gap of a permanent magnet. A load pushes it down; capacitor rings sense the smallest movement, and a servo drives just enough current through the coil to lift it back to its rest position. That current is the weight.
Result: a balance that reads the weight in grams or ounces on a digital display, with no weights to handle, and tare by its circuit.
Source: C. B. Akers and others (Arbor Laboratories), US Patent 4,034,819 (1977). Unknown: the resolution, capacity, magnet type, materials and sizes; the circuits are given as blocks only. Picture: patent drawing.
高级
2 weeks
说明
1
1
Build the magnet circuit
Build the magnet circuit
Stack permanent magnets into a column with a soft iron core. Enclose them in an annular outer housing with end caps, shaped so the field crosses a narrow annular air gap at a constriction. Keep the whole structure symmetrical about its vertical axis. Mount it on a support plate fixed to an upright, such as a housing panel on a base. Not given: the magnet type, materials and sizes.
此步骤所需材料：
小磁铁1 column
铁棒1 soft iron core
未知金属1 housing and end caps
未知材料1 support plate, panel, base所需工具：
螺丝刀套装
未知尺寸2
2
Hang the coil in the gap
Hang the coil in the gap
Wind the coil tightly round the middle of a light bobbin that surrounds the core, the coil sitting in the air gap. Tabs at both ends of the bobbin pass out through holes in the end caps to suspension frames. Hang the frames from thin springy cantilevers fixed to the upright, so the bobbin can only move a short way straight up and down. Keep the bobbin and its suspension as light as possible. Put the weighing pan on top. Ours: enamelled wire.
此步骤所需材料：
漆包铜线1 coil未知材料1 bobbin, frames, cantilevers
秤盘1 个所需工具：
未知尺寸3
3
Fit the capacitor rings
Fit the capacitor rings
Mount four capacitor rings inside the outer housing, two above and two below the air gap, facing matching rings on the bobbin. Cross-connect them so a tilt of the bobbin cancels out and only up-and-down movement shows. Connect them to a signal generator: as the bobbin moves, one set's capacitance rises and the other's falls, and the difference becomes the control voltage.
此步骤所需材料：
未知金属1 rings
集成电路1 sensing circuit
连接导线1 个
焊锡丝1 a little所需工具：
电烙铁4
4
Close the servo loop and read the current
Close the servo loop and read the current
Feed the control voltage to a d.c. servo that drives current through the coil, through a flexible lead, until the bobbin is back at its rest position. Pass that current through a large stable resistor, a thermal resistor that corrects for temperature and a calibration potentiometer: the voltage across them stands for the weight. A separate circuit (comparators, saw-tooth generator, oscillator and counter) turns it into a count read out as grams or ounces. Tare is ordinary circuit logic. Ours: a segment LCD; check with calibration weights.
此步骤所需材料：
集成电路1 servo and counting circuits
电阻2 stable resistor, thermal resistor
电位器1 calibration
段码液晶屏1 display焊锡丝1 a little所需工具：
电烙铁
校准砝码组材料
12- 1 column占位符
- 1 soft iron core占位符
- 1 rings占位符
- 1 bobbin, frames, cantilevers占位符
- 1 coil占位符
- 1 个占位符
- 1 servo and counting circuits占位符
- 1 个占位符
- 2 a little占位符
- 2 stable resistor, thermal resistor占位符
- 占位符
- 1 display占位符
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