Pressure switch characteristics

This particular pressure switch is a mechanical switch that works by connecting a bourdon tube to a lever switch. The bourdon tube is a slender 

The switch used here is an excellent switch, however we would have preferred a tighter dead band of about 2 psi, or possibly a variable dead band for more flexibility. However, many switches with variable dead bands contain mercury, which we wanted to avoid. Plus, we wanted a snap action switch, and they were only available with a fixed dead band version. 

This particular brand is hermetically sealed, which was an important consideration because of the switch s proximity to the tank. Also, the snap action switches in this model were potted (sealed). This in itself does not provide an appropriate level of safety, but since the system uses a low current, low voltage signal, we considered the switch to be adequate for our needs and safety concerns. Of course we cannot advise the use of such equipment. Any switches used in a system must meet the standards of your area AHJ. 

This switch has a removable plastic see-through cover, which allows observation of the switch, and yet protects the mechanism. We drilled a few holes at the top of the switch case to vent any hydrogen that might accumulate. We had to be careful not to disturb the bourdon tube with the drill bit, as that would compromise the integrity of the tube. 

The most appropriate switch for this application would be the Mercoid switch DSH-7341 -153-23E. This is the same as the Mercoid switch DS-7341-153-23E except that it comes with an explosion-proof housing. With the addition of the explosion-proof housing, the switch costs almost twice as much. 

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A change of the atmosphere has a remarkable effect on the switching characteristic. For devices with an oxide interlayer the removal of oxygen leads to a reversible loss of bistability. After testing them in ambient atmosphere to confirm their bistability, devices were placed into a vacuum recipient, which was evacuated to a pressure of 10 mbar. Subsequently, the I- V characteristic was taken in vacuo. No switching was observed. The oxide interlayer devices showed a nearly ohmic characteristic with currents comparable to the high conducting state. 

Thermal Dispersion. Thermal dispersion level switches are used on appHcations where multiple shifts inhquid characteristics are present. The unit is responsive only to a change in the thermal conductivity of the Hquid and ignores shifts in specific gravity, dielectric, density, temperature, and pressure. Units are used for alarm signal however, pump control maybe obtained using two units with a latching relay. 

The soft-switch technology uses a so-called quantum tunneling composite (QTC). This composite has a remarkable characteristic that enables it to be an isolator in its normal condition and to change into a metal-like conductor when pressure is being exercised on it77. 

The most distinctive characteristics of NTP as a chemical process will be its capability to induce various chemical reactions at atmospheric pressure and room temperature. These moderate operation conditions enable a rapid start-up of the NTP process by turning on a switch, and vice versa. Since the NTPs use oxygen and water vapor to produce reactive radicals (for example OH, 0( D). 0( P). N, etc.). O3, and excited molecules (Nj ) for the chemical reactions, additional chemicals for oxidants are not necessary. Chemical reactions involving free radicals terminate in short time (usually less than 10 seconds). In most cases the influence of gas residence time on the gas removal efficiency is negligible. This rapid reaction also enables us to make the system compact. One of the important features of NTP is its flexibility in combining NTP with other technology, which is the main topic in this chapter. 

E = 24.5P + 6.7(P/fieff) kV/cm where Rgff is 0.115P for spherical electrodes and 0.23R for cylindrical electrodes and P is pressure in atmospheres. To increase the high-voltage characteristics of a switch other dielectrics can be used (Table 18.9). 

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