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Low SOLVENT Flow Rate Measuring

IP.com Disclosure Number: IPCOM000039690D
Original Publication Date: 1987-Jul-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 34K

Publishing Venue

IBM

Related People

Ask, RG: AUTHOR [+4]

Abstract

A very sensitive flow rate indicator is used to measure low flow rates (less than 20 ml/min) for automatic control of solvent rates in the wash process that is used in the production of particulate disks. This indicator consists of a "T" in the solvent line prior to solvent dispense. A vertical tube (transparent or translucent) is connected to the solvent system at the "T" and is open to the atmosphere at the top. The solvent rises in the vertical tube until the head in the column reaches an equilibrium with the back pressure of the solvent line. Since the back pressure is linearly related to the flow rate and also to the height in the vertical column, the height in the tube is an indication of the solvent flow rate.

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Low SOLVENT Flow Rate Measuring

A very sensitive flow rate indicator is used to measure low flow rates (less than 20 ml/min) for automatic control of solvent rates in the wash process that is used in the production of particulate disks. This indicator consists of a "T" in the solvent line prior to solvent dispense. A vertical tube (transparent or translucent) is connected to the solvent system at the "T" and is open to the atmosphere at the top. The solvent rises in the vertical tube until the head in the column reaches an equilibrium with the back pressure of the solvent line. Since the back pressure is linearly related to the flow rate and also to the height in the vertical column, the height in the tube is an indication of the solvent flow rate. Optical sensors are used to set high and low control limits on the flow rate and they are monitored automatically by the machine control software. A separate valve closes in order to trap solvent in the column when the solvent flow is not on. This makes the response almost instantaneous when the solvent flow is turned on. The solvent flow system is useful for any processing application which utilizes a low flow rate liquid and requires an automated flow sensing system. The system consists of the following items (see the WASH SOLVENT DIAGRAM): - A pressurized solvent solution storage tank 1.

- A valve 2 which is computer controlled and turns

the solution flow on and off.

- A manually-controlled needle valve 3 for precise

adjustment of the solvent flow rate.

- A "T" fitting 4 which divides the solvent flow

into the vertical column 6 and into the solvent

dispensing pipe 9.

- Another computer-controlled valve 5 between the

"T" fitting 4 and the clear flow sensing column 6.

This valve traps the solvent in the column when

the solvent is off, greatly reducing the response

time for equilibrium when the solvent is turned

on.

- A clear glass or plastic sensing tube 6 which

holds the static column of solvent. It is mounted

vertically above valve 5 and is open to the

atmosphere at the top. The height may be 1-2

feet, or possibly higher for some applications.

- Two optical sensors 7 which are used to detect

situations when the flow rate is out of control

(too high or too low). These sensors are mounted

directly on the sensing tube 6 above and below the

desired operating point and are monitored by the

computer.

- A solvent-dispensing pipe 9 with a series of small

holes for even distribution of the solvent onto a

wipe cloth. The pipe used for the wash operation

is about 12 cm long, with the orifices spaced

1

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about 1 cm apart. The equilibrium height of the solvent in the...