Method for monitoring and selectively sampling a fluid flow stream

• US 5,798,699 A
• Filed: 01/06/1997
• Issued: 08/25/1998
• Est. Priority Date: 01/06/1997
• Status: Expired due to Term

• Current Assignee: Chemtrac, Inc.
• Original Assignee: Chemtrac Systems, Inc.
• Inventors: Bryant, Robert L., Veal, Charles R.
• Primary Examiner(s): Hofsass, Jeffery
• Assistant Examiner(s): LIEU, JULIE BICHNGOC
• Application Number:
  US08/779,051
• Time in Patent Office: 596 Days
• Field of Search: 340/627, 340/309.15, 250/573, 250/574, 356/37, 356/338, 356/339, 356/442
• US Class Current: 340/627
• CPC Class Codes: G01N 21/534 by measuring transmission alone, i.e. determining opacity

Abstract

An improved method and apparatus for monitoring, in real time, the quality of a flowing fluid stream and of automatically taking samples therefrom when the level of particulate matter in the flow stream exceeds an acceptable limit for a predetermined period of time. The apparatus includes a particle monitor and at least one three-way valve electronically linked via a programmable logic controller to the particle monitor. Not only is the latter an instrument for continuously measuring, on-line, numbers known as particle indices which are indicative of particulate matter concentrations in the flow stream, but also the particle monitor generates electronic signals. Both these signals and the particle index are proportional to fluctuations in the intensity of a light beam traversed by particles which are present in a portion of the flow stream during a fixed interval of time. Importantly, the particle monitor can detect relatively short-lived "spikes" in the level of 0.50 micron or larger particles which may be present in the flow stream. Utilizing this sensitivity of the particle monitor to such "spikes", the apparatus can be set to automatically take samples when excursions in the levels of particulate matter occur rather than at random intervals. As a result, the method can facilitate the diagnosis of an impending process equipment breakdown/malfunction in its early stages, while its observable effect is only an infrequent "spike".

Claims

1. A method of collecting discrete samples of a fluid flow stream, in which an intense light beam is directed towards a detector and across a portion of the flow stream, each sample of the flow stream being collected only when concentrations of particulate matter in the flow stream exceed a predetermined limiting concentration, comprising:

(a) continuously measuring, on-line, numbers know as particle indices which are indicative of particulate matter concentrations in the flow stream, each particle index being proportional to a ratio equal to fluctuations in intensity of the light beam divided by absolute intensity of the light beam, the fluctuations being caused by particles which are present in said portion of the flow stream during a fixed interval of time;

(b) measuring how long the particulate matter concentration continuously exceeds the predetermined limiting concentration;

(c) comparing each time period over which the particulate matter concentration has been greater than the limiting concentration with a preset time interval; and

(d) automatically diverting the flow stream into a sample collection container when the particulate matter concentration, as indicated by the particle index, is greater than the predetermined limiting concentration over a time period which is at least as long as the preset time interval.

2. An apparatus for collecting discrete samples of a fluid flow stream, in which an intense light beam is directed towards a detector and across a portion of the flow stream, each sample of the flow stream being collected only when concentrations of particulate matter in the flow stream exceed a predetermined limiting concentration, comprising:

(a) means for continuously measuring, on-line, numbers known as particle indices which are indicative of particulate matter concentrations in the flow stream, each particle index being proportional to a ratio equal to fluctuations in intensity of the light beam divided by absolute intensity of the light beam, the fluctuations being caused by particles which are present in said portion of the flow during a fixed interval of time; and

(b) means for automatically collecting at least one sample of the flow stream when the particulate matter concentration, as indicated by the particle index, is greater than the predetermined limiting concentration.

3. The apparatus according to claim 2 wherein the collecting means further comprises means for controlling how long a time period must elapse after the particle index exceeds the predetermined limiting concentration before said sample is taken.