Copper shield

The electrical connections to the heater and thermometer were made with NbTi wires. These wires (025 xm) were connected at the ends by tiny crimped Cu tubes (2 mg). At the copper frame upper ends of the NbTi wires a four lead connection was adopted. The frame, surrounded by a copper shield, was in thermal contact with the mixing chamber of a dilution refrigerator. 

Inner cryostat wall Liquid nitrogen coolant Copper shield wire... 

Figure 6 22. High-pressure DTA apparatus of KubaMa and Schneider (75). (u) a. r = coolers. b, n = pyrophillite insulating disk c = heating block d = high-pressure vessel e. m — copper seals f, I = Zr02 blocks g = copper shield h = calorimeter block i = thermocouple k = corundum capillary o = fastening screw p = support c] = in- and outlet of refrigerant. (/ )(i) Open Pt/Ir well In) closed teflon well with brass holder lh = steel-sheathed thermocouple).

Both guard and measuring vessels have inside copper shields which serve as temperature equalizers to prevent thermal stratification of the liquid at low heat fluxes and as a radiation shield if the liquid level is low in the guard vessel. 

Less critical measurements in everyday laboratory or industrial work are made with the unsaturated Weston cell in which no crystals of CdS048/3H20 are used and the saturated CdS04 solution is replaced by a lower-concentration solution (saturated at 4°C). The OCV of this cell is 1.0192 0.0002 V, that is, its reproducibility is lower. As the solution concentration does not vary with temperature, in contrast to the saturated Weston cell, the temperature coefficient of the unsaturated cell is very small (about 1 pV/°C) and the cell does not require careful thermostating. The unsaturated cells are placed into plastic cases with copper shields to provide for temperature equilibrium at both electrodes. 

Sometimes, a flashing of nickel is used over an aluminum or copper shield to provide abrasion protection to scratches and normal abuse. The flashing may be of the order of 1 /um. Nickel does not compromise the aluminum or copper shielding. It simply adds to the overall shielding effectiveness. 

Corrosion of copper shielding conforms to the mechanism of uniform corrosion. It is inherently resistant to differential aeration and only uniform corrosion of exposed areas occurs. 

Grouadeil copper shielding Fig. 2. Twin-plane ECT sensor. 

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