Instrumental causes

Quite often problems arise when instruments for normal seiwice are subjected to low temperature use. Since some metals become brittle at low temperatures, the instrument hteraUy falls apart. Elastomeric gaskets and seals contract faster with decreasing temperatures than the surrounding metal parts, and the seal often is lost. Even hermetically sealed instruments can develop pin holes or small cracks to permit ciyogenic liqmds to enter these cases with time. Warming the instrument causes the trapped hquid to vaporize, sometimes generating excessive gas pressure and failure of the case. 

Instrument cause DP meter reading is misleading due to failed... 

Operators increased pump out rate to vessel creating a vacuum and implosion. Loss of instrumentation caused a second fire elsewhere in the facility to occur. 

Loss of instrumentation cause chemical reaction upset and explosion within the reactor occurred. 

Figure 11.23—Average curves representing each of the instrumental causes of error in absorbance measurements and the global curve (4) resulting from their sum (see text).

DMSO Suitable in small quantities mode can be difficult to flush from die instrument, causing problems with negative ionisation. High viscosity and interaction with PEEK tubing... 

Temperature and salinity data are obtained with SBE 16 Seacat thermosalinometers at four depth levels (7, 12, 17, and 19.5) and cover the entire water column from the mixed surface layer to the sea bed. Additional temperature sensors are installed at 2 and 5 m depth since 2003. Intercalibrations of the instruments with a SeaBird SBE 9 CTD are carried out during regular maintenance cruises approximately every three months. The accuracy of temperature and salinity is 0.01 K and 0.02 psu, respectively. Occasionally, failures of instruments caused a partial loss of data in a few periods of time. 

Inadequate stoichiometry and poor calibration of the analytical device are interconnected problems. The kinetic model itself follows the stoichiometric rules, but an inadequate calibration of the analytical instrument causes systematic deviations. This can be illustrated with a simple example. Assume diat a bimolecular reaction, A + B P, is carried out in a liquid-phase batch reactor. The density of the reaction mixture is assumed to be constant. The reaction is started with A and B, and no P is present in the initial mixture. The concentrations are related by cp=CoA-Cj=Cob -Cb, i e. produced product, P, equals with consumed reactant. If the concentration of the component B has a calibration error, we get instead of the correct concentration cb an erroneous one, c n ncs, which does not fulfil the stoichiometric relation. If the error is large for a single component, it is easy to recognize, but the situation can be much worse calibration errors are present in several components and all of their effects are spread during nonlinear regression, in the estimation of the model parameters. This is reflected by the fact that the total mass balance is not fulfilled by the experimental data. A way to check the analytical data is to use some fonns of total balances, e.g. atom balances or total molar amounts or concentrations. For example, for the model reaction, A + B P, we have the relation ca+cb+cp -c()a+c0 -constant (again c0p=0). 

Refineiy Debutanizer The ability to condense the overiiead product was lost because of vapor blanketing in the condenser shell. Venting solved the problem. A newly installed, nitrogen-purged instrument caused the problem. Ensure adequate venting when inerts are likely to be present... 

Free induction decay, FID The analog signal induced in the receiver coil ofan NMR instrument caused bythexy component of the net magnetization. Sometimes the FID is also assumed to be the digital array of numbers corresponding to the FID S amplitude as a function of time. 

As with every technique, there are pitfalls for the unwary. It is a destructive technique, and processes other than simple desorption may occur during the heating (and cooling) stages. Surface reconstruction is thermally activated and may take place on a similar time-scale to the heating its degree of completion at the top temperature may be a function of exposure, and the structure may not revert to its pristine state on cooling. False effects due to the sample holder and other instrumental causes are well understood and easily corrected. Caveat operator ... 

Also a number of condensation polymers such as Nylon 6, polycarbonate, and polyesters were studied (see Table 10.2). These polymers usually possess broad MM distributions, the value of the ratio MJM being usually around 2. From the inspection of Table 10.2 it can be seen that MALDl underestimates both and M in the case of condensation polymers and that the ratio M IM derived from MALDl spectra of polydisperse polymers is strongly underestimated, and the MM distribution is much narrower. This evidence indicates that lighter molecules are preferentially detected in MALDI-TOF instruments, causing the underestimation of the presence of larger molecules and limiting the use of MALDl for MM and MMD determinations to "monodisperse" samples. 

The electronics for instrumentation designed flame AAS typically have long time constants (0.1-1 s) to smooth the steady-state signals obtained in this technique. However, the use of these electronics in early ETA-AAS instrumentation caused distortions of the transient ETA-AAS signals, which are typically a few seconds in width. Modem instrumentation for ETA-AAS employs time constants on the orders of milliseconds to prevent these errors. 

Stray light within instrument causes spurious readings. 

An open circuit in a thermocouple connected to a UWNR console instrument causes the temperature indication to fail ... 

Electrical installation circuits usually carry in excess of 1A and often carry hundreds of amperes. Electronic circuits operate in the milliampere or even microampere range. The test instruments used on electronic circuits must have a high impedance so that they do not damage the circuit when connected to take readings. All instruments cause some disturbance when connected into a circuit because they consume some power in order to provide the torque required to move the pointer. In power applications these small disturbances seldom give rise to obvious emors, but in electronic circuits a small disturbance can completely invalidate any readings taken. We must, therefore, choose our electronic test equipment with great care, as described in Chapter 4 of Basic Electrical Installation Work 8th Edition and shown here at Fig. 4.16. 

In this way, students were able to gain hands-on experience, and meet at first hand the limits of measurement with instrumentation, caused by some of the peculiar properties of LNG, with its foaming, spitting and Marangoni wall films. 

---