Single beam balances

The procedure for pure gas adsorption measurement using the installation of Figs. 3.4, 3.5 is basically the same as with two beam balances which already has been described in Sect. 2.1.1. Nevertheless some additional remarks reflecting more than 10 years of practical experience with magnetic suspension balances (MSBs) seems to be appropriate  

MSBs offered today are fairly stable against small oscillations or motions of the basement, floor, or laboratory s table where they are mounted. The same is true as far as sneezing of the experimenter is concerned. However, one is well advised to avoid any unnecessary mechanical disturbance of a MSB installation as for example pneumatic (compressed-air) hammer activities in nearby laboratories etc. 

MSBs should be cleaned from time to time as small particles, for example activated carbon or zeolite powders may be transferred from the sorbent basket to the permanent magnet. Here they can change the magnetic field permanently and by this cause systematic uncertainties or errors of measurement. Once these are detected, they may be corrected by recalibrating the zero load position of the balance, cp. Fig. 4.12. 

Electro smog as it may be caused by - undetected - wires and cables should be avoided. These electromagnetic fields, especially if enhanced by direct or nearby lightning, can seriously disturb measurements. 

It should be emphasized that MSBs today are used not only for gravimetric gas adsorption measurement but also for a still growing variety of other thermo-physical measurements of vertical forces at extreme pressures, temperatures, and chemical conditions, cp. Chap. 4 and [3.5, 3. 6, 3.26, 3.53, 3.54]. Besides, simple mechanical spring balances are still in use. They can give quick, but often only approximate data of adsorption equilibria, which however still may be useful for orientational purposes [3.1, 3.9]. 

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This chapter is organized as follows In Sect. 2 we consider pure gas adsorption measurements by both two beam and single beam balances. Section 3 is devoted to thermogravimetry. In Section 4 multicomponent gas adsorption equilibria are discussed. Finally in Sect. 5 pros and cons of gravimetry especially compared to volumetry/manometry are elucidated. A list of symbols and abbreviations used is given followed by references dted. 

The single pan, triple beam balance (Centogram) (Fig. 2.8) is operated in the following way. 

Using a single pan, triple beam balance (Centogram) or a top loading balance (if available), determine the mass of the block (3). Record the mass to the nearest 0.001 g. Calculate the density of the block (4). Repeat the measurements for a second trial. 

The single-pan electronic balance [Fig. 1 l(m)] capable of weighing to either 0.01 or 0.001 g and having a capacity of 100-250 g is very useful. Weighing is a pleasure with these balances. Although the top-loading digital balances are the easiest to use, a triple beam balance will work just as well. 

The single-pan balance is a commonly used balance in the clinical laboratory. It is most often electronically operated and self-balancing. Such a balance may be coupled directly to a computer or recording device. In the electronic singlepan balance, a load on the pan causes the beam to tilt downward. A null detector senses the position of the beam and indicates when the beam has deviated from the equilibrium point. 

A triple-beam balance with a sensitivity less than that of a typical top-loading auxiliary balance is also useful. This is a single-pan balance with three decades of masses that slide along individual calibrated scales. The precision of a triple-beam balance may be one or two orders of magnitude less than that of a top-loading instrument but is adequate for many weighing operations. This type of balance offers the advantages of simplicity, durability, and low cost. 

The background of a diffraction pattern obtained with a diffractometer may be reduced by means of a single-channel pulse-height analyzer, as mentioned in Sec. 7-9. An even better method is to use a crystal monochromator in the diffracted beam. Balanced filters present still another option. 

Fig. 18.15 Advanced methods for single particle analysis in LC ARROW chips, (a) Nanopore added to reservoir for single particle entry into LC ARROW (b) Optical dual beam particle trap based on balancing the scattering force due to counter propagating beams...

Figure 2-4 Single-pan mechanical balance. To weigh an object on the pan, we use mechanical knobs to detach removable weights until the balance beam is restored as near as possible to its original position. The remaining small deflection is read on the optical scale.

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