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Back Pressure Sense Circuit

IP.com Disclosure Number: IPCOM000083722D
Original Publication Date: 1975-Jul-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 3 page(s) / 59K

Publishing Venue

IBM

Related People

Appenzeller, HA: AUTHOR

Abstract

Ultralow pressure fluidic devices, such as amplifier valves and diaphragm actuated electrical switches which work in the range of 1/2'' to 5'' of water column, are extremely susceptible to supply pressure fluctuations, hose lengths, sense orifice diameters etc. This is especially true in a back pressure sense circuit, where an object covers an orifice and the resulting back pressure trips the fluidic device. The addition of a "venturi Tee" into the circuit makes it immune to the above conditions.

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Back Pressure Sense Circuit

Ultralow pressure fluidic devices, such as amplifier valves and diaphragm actuated electrical switches which work in the range of 1/2'' to 5'' of water column, are extremely susceptible to supply pressure fluctuations, hose lengths, sense orifice diameters etc. This is especially true in a back pressure sense circuit, where an object covers an orifice and the resulting back pressure trips the fluidic device. The addition of a "venturi Tee" into the circuit makes it immune to the above conditions.

A comparison of a standard back pressure circuit and a venturi equipped circuit is illustrated schematically in Figs. 1 and 2.

In Fig. 1, which illustrates a standard back pressure circuit, low pressure regulated air flows through a sense line and bleeds to atmosphere at the sensor orifice. When the orifice is blocked, back pressure trips a fluidic device. Supply pressure, line size and length, and orifice size must be balanced to operate the circuit properly. Any change in the supply pressure, or flexing of the sense line can accidentally trip the fluidic device.

In Fig. 2, which illustrates a venturi equipped back pressure circuit, low pressure regulated air flows through the venturi tube and continues on to the orifice where it bleeds to atmosphere. As the air flows through the venturi tube it creates a vacuum in the fluidic device. Should the supply pressure rise, the vacuum also increases thereby preventing the fluidic device from actuating. The sense line length, diameter of hose, and flexing of the hose is, therefore, no longer critical.

Fig. 3 illustrates a typical application using venturi equipped back pressure sense circuits. The device is used to raise a wafer from one level to another automatically.

In operation, a wafer 9 is placed on the pedestal 10 and he...