Sampler Disturbance

Coring ahead with ball valve open 

Pressurized core sample (1.65 in. diameter x 34 in. long 10,000 psi working pressure) 

Core retrieval mode with sample chamber closed 

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The principal implication of these studies for the accurate measurement of strong acids in gaseous and aerosol phases is that sampling must be performed in a way that does not disturb the equilibrium significantly in the process. This necessity has led to the development of the diffusion denuder sampler (61), which measures nitric acid after its removal to the walls of a... 

Thin L-shaped probes are commonly used to measure solids concentration profile in slurry pipelines (28-33), However, serious sampling errors arise as a result of particle inertia. To illustrate the effect of particle inertia on the performance of L-shaped probes, consider the fiuid streamlines ahead (upstream) of a sampling probe located at the center of a pipe, as shown in Figure 2. The probe has zero thickness, and its axis coincides with that of the pipe. The fluid ahead of the sampler contains particles of different sizes and densities. Figure 2A shows the fluid streamlines for sampling with a velocity equal to the upstream local velocity (isokinetic sampling). Of course, the probe does not disturb the flow field ahead of the sampler, and consequently, sample solids concentration and composition equal those upstream of the probe. 

Fig. 2 The improved pneumatic lance is constructed from concentric tubes. Low-speed aeration from both tubes allows the lance to be inserted with minimum disturbance to the powder supply. Once the sampling location is reached, a high-speed flow is applied to the central tube to capture a sample below the filter or frit. (A) Construction of the pneumatic sampler (B) process used to obtain a sample from a bulk of powder.

One type of probe is a hand-held stainless-steel hollow auger, which has soil-air vent holes drilled into the shaft near the bottom and is fitted with a gas sample port near the top (Lovell, 1979). Another type of hollow probe has a straight shaft with a gas sample port at the top and soil-air vent holes at the bottom this probe is pounded into the soil by means of a captive hammer that slides up and down the shaft to either drive the probe into or remove it from the soil (Dyck, 1972 Chemical Projects Limited, Toronto, Ontario, Canada, written common., 1972 Lovell, 1979). Both the hollow auger and hollow hammer-probe are efficient dynamic soil-gas samplers in light soils. Neither sampler works well in stony or hard, compacted soils, or in soils containing layers of caliche attempts to use probes in these soils may either bend the probe or disturb the soil to the extent that the soil-gas sample is diluted by atmospheric air. Soil gas can not be sampled in wet soils with these probes. 

The usual method for obtaining samples at significant depths below the surface is to push or drive a pipe or tube into undisturbed soil at the bottom of a drill hole. Of course, this process disturbs the soil, particularly when the pipe is heavy walled. Many different kinds and sizes of samplers are used, and the most common is shown in Figure 1.1. This sampler is commonly called a split spoon. When used with the dimensions shown, and hammered into the soil by a free falling, 140 pound weight, dropping 30 inches, this is the Standard Penetration Test (see ASTM Standard D.1586,... 

Thin wall samplers are generally pushed into the soil rather than driven. Even so, they still cause disturbance mostly adjacent to the tube... 

With the help of spade, dig out the sampler and remove the sample can without disturbing the soil core contained therein. 

Because these samplers physically disturb the natural state of the marine microlayer, in vitro results obtained from collected samples could not be proven to represent films in their natural state. Despite this limitation, these studies resulted in characterisation of quasi-static film elasticities and led to parameterisations that adequately define bounds within which the marine microlayer typically ranges. By setting such bounds, these works provided constraints for laboratory experiments (e.g., Hirsa et al. 1995, McKenna 1997, Saylor 1997). At the same time, techniques for making short wave measurements in situ were developed by independent researchers (Hwang 1989, Bock and Hara 1995), and others have followed (Zhang 1995, Suoja2000). 

Consider the block diagram of a direct digital feedback control loop shown in Figure 29.9. Such loops contain both continuous- and discrete-time signals and dynamic elements. Three samplers are present to indicate the discrete-time nature of the set point j/Sp( ), control command c(z), and sampled process output y(z). The continuous signals are denoted by their Laplace transforms [i.e., y(s), Jn(s), and d(s)]. Furthermore, the continuous dynamic elements (e.g., hold, process, disturbance element) are denoted by their continuous transfer functions, H(s), Gp(s), and GAs), respectively. For the control algorithm, which is the only discrete element, we have used its discrete transfer function, D(z). 

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