Ground choke

Recommendation 10 (see Figure 11-19) The location where a ground choke is typically inserted (and shouldn t be ) is shown in Figure 11-19. 

The MARS-S is constituted of a multimode cavity very close to domestic oven with safety precautions (15 mL vessels up to 0.5 L round-bottomed flasks, magnetic stirring, temperature control). The magnitude of microwave power available is 300 W. The optical temperature sensor is immersed in the reaction vessel for quick response up to 250 °C. A ceiling mounted is available in order to make connection with a conventional reflux system located outside the cavity or to ensure addition of reactants. These ports are provided with a ground choke to prevent microwave leakage. It is also possible to use a turntable for small vessels with volumes close to 0.1 mL to 15 mL vessels (120 positions for 15 mL vessels). Pressure vessels are available (33 bar monitored, 20 controlled). 

A ground choke should be avoided at all costs. Think of what it can do if we put this in Figure 11-4, say on the wire connecting the PCB to the power inlet. See the following discussion. 

We ask — is it really a good idea to place a small inductor (e.g. a bead or small toroid with a few turns) somewhere in the earth connection Suppose we place it on the wire connecting the ac inlet to the enclosure (or PCB to inlet). This is then called a ground choke or earth choke. It is commonly found on low-power evaluation boards (from vendors promoting their clever IC solutions), but rarely seen on a commercial power supply. 

Fig. 14-5 Circuit diagram for a higher resistance dc decoupling devices. (KE) insulated cable end seal, (E) grounding installation, (1) resistance ( 100 mQ), (2) grounding side bar or short-circuit-resistant grounding switch, (3) breakdown fuse, (4) capacitors (ca. 60 F), (5) choke.

An operator had to drain water from a 1,200-m spherical storage vessel nearly full of propane (Figure 8-1). He opened valves A and B. When traces of oil showed that the draining was nearly complete, he shut A and then cracked it to complete the draining. No flow came. He opened A fully. The choke—presumably hydrate, a compound of water and a light hydrocarbon with a melting point above 0°C—cleared suddenly, and the operator and two other men were splashed with liquid. The handle came off valve A, and they could not get it back on. Valve B was frozen and could not be moved. Access was poor because the drain valves were immediately below the tank, which was only 1.4 m above the ground. 

Williams, Kenneth E. Detailed Facts About Choking Agent Phosgene (CG). Aberdeen Proving Ground, MD United States Army Center for Health Promotion and Preventive Medicine, 1996. 

Dufton column. A plain tube, into which fits closely (preferably ground to fit) a solid glass spiral wound round a central rod. It tends to choke at temperatures above 100 unless it is lagged (Dufton J Soc Chem Ind (London) 38 45T 1919). 

Liquid-velocity correlations are generally based on one of two concepts, and it is not always clear which one is the basis of a given correlation. One concept relies on the principle that vapour should not be entrained to the tray below. The other is grounded on the phenomenon of downcomer-inlet-choking caused by the inability of the low-density froth... 

Fountains are designed to stand upon the ground, either upon a flat base or upon a pointed wooden stick. They are choked slightly more than gerbs, and have heavier, stronger cases to withstand the greater pressures which eject the fire to greater distances. 

The combination of the above factors has rendered the nanocrystalline solution competitive, not only with amorphous Co-based alloys, but also with classical crystalline alloys and ferrites. The consequence is a steadily increasing level of applications in magnetic cores for ground fault interrupters, common mode chokes and high frequency transformers. Fig. 14 shows some typical examples. The worldwide production rate meanwhile approaches an estimated 1000 tons/year, and the trend is increasing. The only drawback of the nanocrystalline material appears to be the embrittlement that occurs upon crystallization, which requires final shape annealing and, thus, restricts application mainly to toroidally wound cores. 

---