Conductivity, electrical calibration standards

Electrical resistivities can be measured on split cores by a half-automated logging system (Berg-mann 1996). It measures the resistivity (R ) and temperature (T) by a small probe which is manually inserted into the upper few millimeters of the sediment. The resistivity (R, ) of the interstitial pore water is simultaneously calculated from a calibration curve which defines the temperature-conductivity relation of standard sea water (35%o salinity) by a fourth power law (Siedler and Peters 1986). 

The concentration of ionic constituents measured by electrical conductivity typically uses a dual-electrode probe [21] submerged in the chemical solution. Temperature compensation is important so that the reported conductivity values are consistently adjusted to a standard reference temperature. Conductivity meters/probes are calibrated with the National Institute of Standards and Technology traceable calibration standards in the conductivity range of the measurement suited for the conductivity of the chemical measured. 

However, salinity values are easily obtained with a salinometer (which measures electrical conductivity and is appropriately calibrated with standard solutions and adjusted to account for T effects). The salinity of seawater increases if the loss of H2O (evaporation, formation of ice) exceeds the atmospheric input (rain plus rivers), and diminishes near deltas and lagoons. Salinity and temperature concur antithetically to define the density of seawater. The surface temperature of the sea reflects primarily the latitude and season of sampling. The vertical thermal profile defines three zones surface (10-100 m), where T is practically constant thermoclinal (100-1000 m), where T diminishes regularly with depth and abyssal... 

Peak positions in an XPS spectrum are likely to be affected by spectrometer conditions and the sample surface. Before XPS peak identification, we often need to calibrate the binding energy. Calibration is particularly important for samples with poor electrical conductivity. Calibration can be done with an internal standard that has a peak that shows little or no chemical shift, for example, elemental Si. The most common method is use of the C Is peak at 285 eV from carbon adsorbed on the sample surface. The carbon from organic debris (as C—H or C-C) in air is found on all samples exposed to the environment. The peaks of core level binding energies as listed in Table 7.1 are sufficiently unique for element identification. 

The specific conductance (L or K) or conductivity of a solution is always obtained by measuring the resistance (R) of the solution taken in a suitable container of known dimensions called conductivity cell, the cell constant of which has been determined by calibration with a solution of accurately known conductivity e g. a standard KCl solution. The instrument used for electrical conductivity measurement is known as conductivity bridge. A typical system consists of an alternating current (A.C.) Wheatstone bridge, a primary element of conductivity cell and a null balance indicator (as in solubridge ) or an electronic eye as in the conductivity meter. 

Electronic moisture meters usually operate on a dielectric principle and/or kernel surface conductance with compensation for sample temperature and density. Thus, electronic moisture meters measure electrical properties that are calibrated to oven moisture measurements. The typical air-oven reference methods used for whole soybeans are the AOCS Method Ac 2-41, ASABE Standard S352.2, and AACC Method 44-15a. 

We have carried out a series of measurements with water suspensions of PSL spheres seeded with TFA. The spheres were supplied by Duke Scientific as calibrated size standards with nominal diameters as shown in Table I, and with an unknown standard deviation. The table shows also the electrical conductivity of the corresponding solutions as well as the ratio between dmin from equation 3 and the nominal sphere diameter. All the solutions were electrosprayed into CO2 because the high surface tension of water requires large voltages for the cone-jet to set in, which tends to produce electrical breakdown when the gas is air (26, 19), The aerosol is sampled from the spray region and passed through the DMA. This instrument operates in such a way that the exiting aerosol is carried in dry air, and its selected mobility corresponds neaiiy to that in air rather than in CO2. 

Determination of the heat meter calibration constant was made using standard samples whose conductivity at higher temperatures was accurately known from guarded hot-plate measurements. For calibration an electrically heated plate was used instead of the cold plate thus the heat meter temperature was maintained near ambient at all times. 

Electric conductivity provides highly useful information on the association of surfactants in solution. The conductivity is measured in a thermostated cell calibrated with a standard KCl solution. Polarization is avoided by using alternating current or applying short pulses of opposing polarity. The conductance data are related to the surfactant concentration by one of the following graphic presentations ... 

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