Selection and Use of Electronic Density Balance - "Avoiding Pits Guide"

1、 From 'Scale' to 'Soul Scale'

When Archimedes of ancient Greece shouted "Eureka" in the bathtub, he simply put his crown into the water to measure its volume; Today, engineers placed 0.1 g of PEEK microspheres into an electronic density balance and were able to simultaneously read mass, volume, density, porosity, and even infer the pore defects after 3D printing within 30 seconds. This seemingly ordinary electronic balance is actually a "soul scale"‐ — It refers not only to weight, but also to the 'internal order' of materials.

2、 Technical Profile: Double Dance of Electromagnetic Force and Buoyancy

1. Heart: Electromagnetic Balance Sensor

Using the principle of electromagnetic force compensation, when the sample is placed on the weighing plate and the displacement sensor detects a lever offset, the servo current instantly applies a reverse force, causing the system to return to zero. There is no cutting edge or friction throughout the entire process, and the reading is stable at 0.1 mg with a repeatability error of less than 0.02%.

2. Limbs: Archimedes Basket System

Hang a stainless steel basket under the balance, first measure the mass m1 of the sample in air, and then measure its mass m2 immersed in auxiliary liquid (water/ethanol/silicone oil); =m1/(m1–m2)× ρ 0. The CPU provides density within 1 second, with a resolution of up to 0.0001 g/cm3;.

3. Brain: Temperature Drift Compensation Algorithm

The built-in Pt1000 temperature probe compensates for the drift of liquid density with temperature in real-time (0.02% change in water every 1 ℃), ensuring the reliability of the fourth decimal place.

3、 Four scenarios for 'soul check ups'

Scenario A: Pore warfare of lithium copper foil

If the porosity of 6-meter ultra-thin copper foil exceeds 0.5%, it will cause battery swelling. Engineers take 50× A 50mm copper foil is rolled into a small tube and placed in a basket. The electronic density balance completes the test in 20 seconds, and batches with porosity exceeding the standard are immediately labeled with red RFID tags and taken offline.

Scenario B: 3D printing of "invisible cracks" in titanium alloy

Ti-6Al-4V powder was atomized using argon gas, with a theoretical density of 4.43 g/cm3;; Tested 4.39 g/cm³ It indicates that the proportion of hollow powder is greater than 2%. The balance data is directly written into the EOS M290 printer, and the laser energy density is adjusted in real-time, resulting in an 18% increase in the fatigue life of printed parts.

Scenario C: The density trap behind the "weight consistency" of pills

The average weight of the same batch of amoxicillin tablets is 498 mg, but the density ranges from 1.312 to 1.335 g/cm3; Not waiting, it indicates that the filling depth of the tablet press fluctuates. Based on this, pharmaceutical companies have integrated the balance into the PAT system to achieve online feedback control, resulting in a decrease in tablet weight CV value from 2.1% to 0.6%.

Scene D: Jewelry "gold wrapped in silver" instantly appears

At the pawnshop counter, the 18K gold necklace has a nominal gold content of 75% and a measured density of 14.9 g/cm3; , below the theoretical value of 15.4 g/cm3³ The balance immediately reported "silver or tungsten core doping", saving consumers from a loss of tens of thousands of yuan on site.

4、 Selection and Use of "Avoiding Pits Guide"

1. Range and accuracy

The conventional model is 120 g/0.1 mg, and if large volume foam is tested, 3 kg/1 mg can be selected; It is recommended to choose 21 g/0.01 mg semi trace level for measuring silicon wafer micropores.

2. Liquid compatibility

Anhydrous ethanol is required for measuring magnesium alloys, while silicone oil can be used for measuring porous ceramics; The instrument needs to have a corrosion-resistant basket and a waste liquid tank.

3. Environmental traps

Airflow greater than 0.2 m/s can cause 1 mg drift; Suggest adding a windproof cover and keeping it at least 1.5 meters away from the air conditioning outlet.

4. Calibrate the rhythm

Preheat for 30 minutes after starting up daily, and use 200 g standard weight+20 ℃ pure water for two-point calibration to ensure long-term accuracy.

5、 Future: From 'single point' to 'imaging'

The "density imaging module" being tested by METTLER in Switzerland replaces the suspended basket with a 256 point array electrode. Through the conductivity density coupling algorithm, a density cloud map with a resolution of 100 μ m can be generated on a 5mm sample; Combined with AI defect recognition, a carbon fiber composite board can complete non-destructive testing at the "pore CT" level within 10 seconds in the future, with a cost only 1/50 of micro CT.

The electronic density balance incorporates Archimedes' principle into a 24 bit ADC and compresses the buoyancy error into the range of 0.1 mg. It makes a piece of metal, a drop of resin, or a pill speak, telling us whether they are dense enough, pure enough, and reliable enough. Next time, when you pick up a lightweight carbon fiber phone case or swallow a 500mg pill, perhaps you can think about it: in the laboratory, there was a "soul scale" that had a precision of 0.1mg and conducted a physical examination about the future for it.