Microbalance

As a microbalance is called analytical balances, whose division at 0.001 mg, that is 1 ug or is smaller. Micro scales are commonly used for chemical analysis, such as in thermogravimetry. The weight range is usually at 3 to about 50 gram load. Specific forms of microbalances are used in basic research to measure very small masses.

Ultra-micro balances are the most accurate scales in chemical and physical laboratories. The pitch is 0.1 micrograms, and smaller. The weight range is usually only 2 to 3 grams. These scales are produced by different manufacturers.

Principle of operation

Electromagnetic force compensation

Most micro scales used in the laboratory work on the principle of electromagnetic force compensation. In this case, a reaction force is generated by a coil in a permanent magnet which corresponds to the weight of the sample to be measured on the scale pan. This counter force that equilibrium is maintained. This is accomplished by a position sensor and a control amplifier, which are necessary for maintaining the equilibrium state. About a lever system, it is possible that with a smaller counter-force, a greater force on the scales in balance can be maintained. The coil current is measured as a voltage drop across a measuring resistor and further processed and displayed by an analog- digital converter.

For several years, micro balances are built in the form of a magnetic suspension balance. The sample to be weighed is completely separated spatially from the measuring cell. The sample is located in a permanent magnet which is held by an electromagnet mounted on the scale in a free floating state. With this magnetic suspension, the coupling weight of the sample body to be measured is transmitted without contact from the measuring chamber to the microbalance. Still The measurement itself but follows the principles of electromagnetic force compensation.

Other measurement principles

There are also a variety of other weighing technologies. For example, the laser-interferometric measurement of the deformation of a quartz spring.

Until the 1980s, however, special beam balances were common, in which manually corresponding weight riders had to be set.

Resonant microbalance ( also quartz crystal microbalance )

A special design of a microbalance is the quartz crystal microbalance. The operating principle is based on the frequency change of a quartz crystal when changing its mass; the frequency can be extremely accurately measured. It is the context:

In principle, other materials such as langasite ( La3Ga5SiO14, " LGS " ) and gallium orthophosphate ( GaPO4 ) can be used in addition to quartz. With this method the masses ( 8:10 -14 g =) can be measured to less than 80 femtograms.