Microbalance
As microbalance is known analytical balances whose pitch is 0.001 mg , i.e., 1 ug or less, is located. Microbalances are usually used for chemical analyzes, such as in thermogravimetry . The weighing range is usually from 3 to about 50 grams load. Special forms of microbalances are used in basic research to measure the smallest masses.
Ultramicrobalances are the most accurate balances in chemical and physical laboratories. The division is 0.1 µg and smaller. The weighing range is usually only 2 to 3 grams.
Working principle
Electromagnetic force compensation
Most of the microbalances used in laboratories work on the principle of electromagnetic force compensation. A counterforce is generated by a coil in a permanent magnet , which corresponds to the load of the sample to be measured on the weighing pan. With this counterforce the balance is kept. This is done by a position sensor and a control amplifier, which are necessary to maintain the state of equilibrium. A lever system enables a larger force to be kept in equilibrium with a smaller counterforce. The coil current is measured as a voltage drop across a measuring resistor and processed and displayed by an analog-digital converter .
For several years now, microbalances in the form of magnetic levitation scales have also been built. The sample to be weighed is spatially completely separated from the measuring cell. The sample is located on a permanent magnet, which is held in a floating state by an electromagnet attached to the balance . With this magnetic levitation coupling, the weight of the specimen to be measured is transferred without contact from the measuring room to the microbalance. The measurement itself still follows the principles of electromagnetic force compensation.
Further measuring principles
There are also a number of other weighing principles, such as laser interferometric measurement of the deformation of a quartz glass spring.
Until the 1980s, on the other hand, special beam scales were common in which appropriate weight tabs had to be set manually.
Resonant microbalance (also quartz microbalance)
A special design of a microbalance is the quartz microbalance . The functional principle is based on the frequency change of a quartz crystal when its mass changes; the frequency can be measured extremely accurately. It is the context :
In principle, besides quartz, other materials such as langasite (La 3 Ga 5 SiO 14 , “LGS”) and gallium orthophosphate (GaPO 4 ) can also be used. With this method, masses of less than 80 femtograms (= 8 · 10 −14 g) can be measured.
Individual evidence
- ↑ Functionality of the electromagnetic force compensation , in technology differentiation - the successful strategy of Sartorius AG , p. 11 (PDF; 1.1 MB)
- ↑ Sartorius AG: Weighing Room ( Memento of the original from March 4, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 967 kB), No. 5
- ↑ chemlin.de Biosensor detects the smallest particles ( Memento of the original from March 4, 2016 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. , dated September 4, 2006
literature
- E. Bankmann: The ultramicrogravimetric determination of technetium and rhenium with the aid of the quartz thread ultramicrobalance. In: Journal of Analytical Chemistry. 223, 1966 pp. 63-64.
- H. Mayer, K. Behrndt: A new microbalance made of quartz for working in the highest vacuum. In: Journal of Physics A Hadrons and Nuclei. 147, 1957, pp. 499-506.
- H. Asbury et al .: A simple robust ultramicrobalance. In: Microchimica Acta . 44, 1956, pp. 598-618.
- HR Jenemann: The history of damping on laboratory scales. In: Reports on the history of science . 20, 2006, pp. 235-251.