CA1087247A - Electrostatic charge measurement - Google Patents
Electrostatic charge measurementInfo
- Publication number
- CA1087247A CA1087247A CA294,624A CA294624A CA1087247A CA 1087247 A CA1087247 A CA 1087247A CA 294624 A CA294624 A CA 294624A CA 1087247 A CA1087247 A CA 1087247A
- Authority
- CA
- Canada
- Prior art keywords
- chamber
- pipeline
- charge
- stream
- flow
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/60—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrostatic variables, e.g. electrographic flaw testing
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R29/00—Arrangements for measuring or indicating electric quantities not covered by groups G01R19/00 - G01R27/00
- G01R29/24—Arrangements for measuring quantities of charge
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Pipeline Systems (AREA)
Abstract
ABSTRACT
In apparatus for continuously monitoring the electrostatic charge transport rate or the charge density in a stream of insulating material flowing through a pipeline, a charge collection chamber and a volumetric flowmeter are connected into the pipeline. The chamber is electrically isolated from the pipeline and connected to earth through an electrometer.
The chamber is constructed to ensure turbulent flow within the chamber, the cross-sectional area being enlarged in relation to the pipeline to produce a substantial reduction in linear flow rate. When calibrated for a particular material, such as a hydrocarbon fuel, a value for charge density is derived from measurements of the flow rate and of the current measured between chamber and earth.
In apparatus for continuously monitoring the electrostatic charge transport rate or the charge density in a stream of insulating material flowing through a pipeline, a charge collection chamber and a volumetric flowmeter are connected into the pipeline. The chamber is electrically isolated from the pipeline and connected to earth through an electrometer.
The chamber is constructed to ensure turbulent flow within the chamber, the cross-sectional area being enlarged in relation to the pipeline to produce a substantial reduction in linear flow rate. When calibrated for a particular material, such as a hydrocarbon fuel, a value for charge density is derived from measurements of the flow rate and of the current measured between chamber and earth.
Description
~087Z47 This invention relates to the measurement of electrostatic charge and is of particular application to the monitoring of charge density in a stream of insulating material flowing through a pipeline.
The generation and transport of electrostatic charge by insulating material flowing through a conveyor system is a general hazard but one of particular concern in the handling of volatile hydrocarbon fuels. It is important to be able to monitor charge density so that known methods of neutralising the charge may be put into effect. In considering the possible means of measurement, however, the imprecision of the term 'insulating' when used in this context must be borne in mind.
Thus, a form of monitoring apparatus may be envisaged which is suitable for materials from which only a negligible quantity of charge is released to the wall of a test chamber during the period of measurement. Such materials have a long relaxation time. Other materials such as some kinds of liquid fuel, for which on the basis of conventional conductivity mea#urements a long relaxation time would also be predicted, in fact demonstrate comparatively rapid relaxation. It is an object of the invention to provide apparatus suitable for measurement on materials of the latter kind.
According to the invention an apparatus for continuously monitoring the electrostatic charge transport rate in a stream of insulating material flowing through a pipeline comprises a chamber ::
,, .
q~
. - . . : .
, ,: ' ~ ' ' having an electrically isolnted condllctive wall, the chamber having inlet and outlet means for connecting the chamber into the pipeline, means for connecting the conductive wall to earth potential, and means for measuring the flow of current in the earth connecting means, the chamber being of enlarged cross-sectional area relative to the pipeline for which the inlet means is designed such that the linear flow rate of the material is caused to be substantially reduced when the stream enters the chamber and providing a form of transition between the inlet and chamber cross-sections such that the ensuing pe ~m i ~tc61~
flow is ~ed to be turbulent, the arrangement being such that the value of the current is a measure of the charge transport rate.
The relationship between the measured value of current and the charge density can be derived for each material from a knowledge of the volumetric flow rate.
Preferably the chamber is substantially enclosed by an electrostatic shield'having provision for connection to earth.
The chamber may be generally cylindrical in form having a diameter in the range of ratios from ~ to ~ i with respect to the diameter of the inlet means. The square root ~otation is used to emphasise the cross-sectional area relationship.
Preferably the length of the chamber is so selected in relation to the characteristics of the stream to be monitored that in operation the residence time of an element of the stream within , ~ ~
', ' the chamber is appreciably less than the relaxation time constant of the material.
It is apparent from the li-terature of research into the electrical properties of for example liquid fuels flowing in pipes thatcomplexand incompletely understood relationships govern the exchange of charge between an insulating fluid and the containing wall. The present invention is based on the recognition that a test chamber may be specified such that the value of charge density in the insulating material may be reliably derived from a predetermined relationship between the value of charge density and the observed rate of flow of charge to the wall.
It is not necessary to consider in detail the various mechanisms which are believed to be involved in the gain and loss of charge by a moving fluid in contact with the conducting but electrically isolated wall of a pipe.
Such mechanisms result generally in a net gain of charge by the fluid, the rate of gain being termed the ~streaming current'. Since the effect of surface contact is important if not predominant in determining the charge mechanisms the fluid bulk can only be considered electrically homogeneous if the flow is turbulent but this condition can reasonably be assumed for high delivery rate pipelines. If the streaming current in a very long pipe is denoted by i1' the linear . .
,: ' ~. .' ; ~
1~87247 velocity of the stream by u and the diameter of the pipe by d the generally agreed relationship is expressed by i1 = k.u d The exponents a and b are each greater than unity and may themselves depend on the values of u and d, but precise values are irrelevant to the present discussion and we may assume a _ b = 2, 90 that i1 = k.u d ......................... (1) ' The flowing fluid therefore continues to accumulate charge in each region where streaming current enters the flow and at any point along the length of the pipe the cumulative charge den~ity may be denoted by dq. The rate of accumulation may be non-uniform since obsta:cles such as filters in the pipe are prolific ~ources of charge. (The term 'streaming current' is sometimes used to refer to the product of dqx volumetric flow rate but in this specification the product is designated 'charge transport rate'.) The progress of discharge is also complex when a volume of stationary fluid~ having a charge density dq , is exposed to a conductive wall which is maintained at earth potential, Con~idered as a dielectric the fluid would be expected to show an exponential decay of charge density dependent on the ratio Or the conductivity and relati-e per~ittivity. ~or high-purity , ., , 11)87247 fuels this ratio would yield a very long time sonstant. In practice processes such as ion recombination may operate to reduce the time constant to values in the order of one second.
The rate of decay may no longer be strictly exponential but it is convenient to allot a time constant (or relaxation time) T in the conventional sense. Thus after the elapse of a time t, the charge density d~t is given by the expression:
dqt = dqO.e i ........................ (2) Relaxation must similarly be taken into account when the generation of streaming current 1 in a ~hort length of pipe at earth potential is considered. Equation (1) is then modified to give:
i = k.u2.d2.(1 _ e -t/T) ( ) where t is now the time of flow through the pipe.
The application of equations (2) and (3) to the determination of charge density in a test chamber will be demonstrated but an embodiment of the invention will first be described with reference to the accompanying drawings in whi~ch:
Figure 1 represents a fuel delivery pipeline in which is installed a monitoring apparatus in accordance with the invention, and Figure 2 represents schematically the apparatus of Figure 1 with additionally means for neutralising charge in the pipeline.
Referring to Figure 1 a generally cylindrical metallic test chamber 10 is provided at one end with an inlet coupling 12 for a pipeline 14 and at the other end with a similar outlet coupling 16.
.
1087Z~7 Each coupling 12, 16 i9 mounted in an insulating bush 18 80 that the chamber 10 remains electrically isolated when it is connected into the pipeline 14. An electrostatic screen 20 i~ also mounted from the bushes 18 coaxially with and almost completely enclosing the chamber 10 but electrically isolated from the chamber 10and from the pipeline 14. The screen Z0 is ~rovided with an earthing connector 22 and the chamber 10 carries a terminal 24 which is accessible for electrical connection through a hole in the wall of the screen 20. The chamber 10 is designed for use with a plpeline 14 of specified diameter, the couplings 12, 16 being of similar diameter to the pipeline 14 and the chamber 10 having a diameter over the greater part of its length which is three times the diameter of the pipeline 14. The tran~ition between the diameter of the coupling 12 and the maximum diameter of the chamber 10 is made abruptly as indicated by the form of shaulder 25 for which the preferred internal angle exceeds 60 and any stre4mlining of the profile should be avoided. There will be implicit in the specification of the test chamber 10 for use with a particular diameter of pipeline~ an expectation of a specific range of flow rates. From this information the length of the chamber 10 is preferably calculated so that the residence time for an element of fluid entering the chamber 10 at the mean flow rate is appreciably less than the relaxation time for the fluid.
A flowmeter 26 of any conventional form is installed in the pipeline ~; 25 so that the volumetric flow rate can be determined at the time of t ~' , `.
,~
~t ~ ::
:~
. , :.
each charge measurement. In Figure 1 flowmeter 26 is shown downstream of chamber 10 but an upstream position is equally suitable.
In carrying out the measurement an alectrometer 28 is connected between the terminal 24 and earth and fluid i8 allowed to flow through the chamber 10 for a period sufficiently long to enable the charge distribution to stabilise. The value of current indicated by the electrometer 28 and the rate of flow are then recorded. For purposes of standardisation it is necessary to have obtained at least one direct measurement of charge density by conventional means for the same fluid together with the corresponding value of current indicated by the electrometer 28.
Measurements made on different occasions will not be validly comparable if it is possible for air to be trapped in chamber 10.
In order to exclude this possibility it is desirable therefore that chamber 10 should be mounted vertically with the inlet at the lower end.
With reference to Figure 2 one example of a control system is shown schematically in which a pipeline installation 14 includes, in the manner of Figure 1, a test chamber 10 with electrostatic screen 20, electrometer 28 and volumetric flow meter 26. Pipeline 14 also passes through a charge neutraliser 30 located upstream of the chamber 10. Neutraliser 30 operates in a known way in respon~e to the ou1:put from a controller 32 to neutralise the charge content of ', . .:
: ~
, .,, : - :
- .
10~7247 the stream as measured at each instant. Controller 32 receives, by means of any necessary transducing or ampli~ying elements, signals which represent the value of current flowing through electrometer 28 and the rate of flow recorded by meter 26. Controller 32 includes means for deriving from the two input signals an ~utput signal to determine the degree of neutralisation required to compensate for the total charge content or to reduce it to a safe level.
Experimental observation has provided evidence of the relationship between the value of charge density in the pipeline and the value of current indicated by electrometer 28 for a medium-conductivity fuel which is in accord with the following analysis:
.
10872~7 It will be apparent from the earlier discus~ion that a relaxation current i collected by the chamber 10 i9 drawn from the charge accumulated by the fluid before entry to the chamber 10 but i8 diminished by any new component of streaming currentl which may be generated in the passage of the fluid through the chamber 10.
If the volume flow rate is denoted by v' and the charge density of fluid entering the chamber 10 by dq , then i = (v'.dq - i ).
By substitution from equations (2) and (3) and by introducing the respective values u1 and d1 for the linear flow rate in the chamber 10 and the diameter of the chamber 10:
i = (vl.dq - k.u1 .d1 ) (1 - e / ).
It will be seen that, subject to the exponential decrement, since the value of u1 is dependent on 1/d12, the value of i can be made to correspond almost directly to charge density by making the diameter d1 large. It isthought that the measurement i9 best made by selecting the length of the chamber 10 so that the residence time of an element of fluid within the chamber is appreciably less than the relaxation time constant of the fluid. The effect of each element of fluid is then sensed only during the initial stage of the relaxation curve when the rate of discharge is highest.
Consideration of the factors which determine the value l has shown theoretically that the measurement proposed represents the cumulative charge density by a sample which will generally be small and will depend on the ratio t/T, and that the flow continues with the initial charge diminished by that amount.
:; :
! ~ ~
10~7Z~7 The test procedure may be summarised as follows:
.~
(1) For calibration purposes establish the relationship between main stream charge density and collector current for the fluid concerned.
The generation and transport of electrostatic charge by insulating material flowing through a conveyor system is a general hazard but one of particular concern in the handling of volatile hydrocarbon fuels. It is important to be able to monitor charge density so that known methods of neutralising the charge may be put into effect. In considering the possible means of measurement, however, the imprecision of the term 'insulating' when used in this context must be borne in mind.
Thus, a form of monitoring apparatus may be envisaged which is suitable for materials from which only a negligible quantity of charge is released to the wall of a test chamber during the period of measurement. Such materials have a long relaxation time. Other materials such as some kinds of liquid fuel, for which on the basis of conventional conductivity mea#urements a long relaxation time would also be predicted, in fact demonstrate comparatively rapid relaxation. It is an object of the invention to provide apparatus suitable for measurement on materials of the latter kind.
According to the invention an apparatus for continuously monitoring the electrostatic charge transport rate in a stream of insulating material flowing through a pipeline comprises a chamber ::
,, .
q~
. - . . : .
, ,: ' ~ ' ' having an electrically isolnted condllctive wall, the chamber having inlet and outlet means for connecting the chamber into the pipeline, means for connecting the conductive wall to earth potential, and means for measuring the flow of current in the earth connecting means, the chamber being of enlarged cross-sectional area relative to the pipeline for which the inlet means is designed such that the linear flow rate of the material is caused to be substantially reduced when the stream enters the chamber and providing a form of transition between the inlet and chamber cross-sections such that the ensuing pe ~m i ~tc61~
flow is ~ed to be turbulent, the arrangement being such that the value of the current is a measure of the charge transport rate.
The relationship between the measured value of current and the charge density can be derived for each material from a knowledge of the volumetric flow rate.
Preferably the chamber is substantially enclosed by an electrostatic shield'having provision for connection to earth.
The chamber may be generally cylindrical in form having a diameter in the range of ratios from ~ to ~ i with respect to the diameter of the inlet means. The square root ~otation is used to emphasise the cross-sectional area relationship.
Preferably the length of the chamber is so selected in relation to the characteristics of the stream to be monitored that in operation the residence time of an element of the stream within , ~ ~
', ' the chamber is appreciably less than the relaxation time constant of the material.
It is apparent from the li-terature of research into the electrical properties of for example liquid fuels flowing in pipes thatcomplexand incompletely understood relationships govern the exchange of charge between an insulating fluid and the containing wall. The present invention is based on the recognition that a test chamber may be specified such that the value of charge density in the insulating material may be reliably derived from a predetermined relationship between the value of charge density and the observed rate of flow of charge to the wall.
It is not necessary to consider in detail the various mechanisms which are believed to be involved in the gain and loss of charge by a moving fluid in contact with the conducting but electrically isolated wall of a pipe.
Such mechanisms result generally in a net gain of charge by the fluid, the rate of gain being termed the ~streaming current'. Since the effect of surface contact is important if not predominant in determining the charge mechanisms the fluid bulk can only be considered electrically homogeneous if the flow is turbulent but this condition can reasonably be assumed for high delivery rate pipelines. If the streaming current in a very long pipe is denoted by i1' the linear . .
,: ' ~. .' ; ~
1~87247 velocity of the stream by u and the diameter of the pipe by d the generally agreed relationship is expressed by i1 = k.u d The exponents a and b are each greater than unity and may themselves depend on the values of u and d, but precise values are irrelevant to the present discussion and we may assume a _ b = 2, 90 that i1 = k.u d ......................... (1) ' The flowing fluid therefore continues to accumulate charge in each region where streaming current enters the flow and at any point along the length of the pipe the cumulative charge den~ity may be denoted by dq. The rate of accumulation may be non-uniform since obsta:cles such as filters in the pipe are prolific ~ources of charge. (The term 'streaming current' is sometimes used to refer to the product of dqx volumetric flow rate but in this specification the product is designated 'charge transport rate'.) The progress of discharge is also complex when a volume of stationary fluid~ having a charge density dq , is exposed to a conductive wall which is maintained at earth potential, Con~idered as a dielectric the fluid would be expected to show an exponential decay of charge density dependent on the ratio Or the conductivity and relati-e per~ittivity. ~or high-purity , ., , 11)87247 fuels this ratio would yield a very long time sonstant. In practice processes such as ion recombination may operate to reduce the time constant to values in the order of one second.
The rate of decay may no longer be strictly exponential but it is convenient to allot a time constant (or relaxation time) T in the conventional sense. Thus after the elapse of a time t, the charge density d~t is given by the expression:
dqt = dqO.e i ........................ (2) Relaxation must similarly be taken into account when the generation of streaming current 1 in a ~hort length of pipe at earth potential is considered. Equation (1) is then modified to give:
i = k.u2.d2.(1 _ e -t/T) ( ) where t is now the time of flow through the pipe.
The application of equations (2) and (3) to the determination of charge density in a test chamber will be demonstrated but an embodiment of the invention will first be described with reference to the accompanying drawings in whi~ch:
Figure 1 represents a fuel delivery pipeline in which is installed a monitoring apparatus in accordance with the invention, and Figure 2 represents schematically the apparatus of Figure 1 with additionally means for neutralising charge in the pipeline.
Referring to Figure 1 a generally cylindrical metallic test chamber 10 is provided at one end with an inlet coupling 12 for a pipeline 14 and at the other end with a similar outlet coupling 16.
.
1087Z~7 Each coupling 12, 16 i9 mounted in an insulating bush 18 80 that the chamber 10 remains electrically isolated when it is connected into the pipeline 14. An electrostatic screen 20 i~ also mounted from the bushes 18 coaxially with and almost completely enclosing the chamber 10 but electrically isolated from the chamber 10and from the pipeline 14. The screen Z0 is ~rovided with an earthing connector 22 and the chamber 10 carries a terminal 24 which is accessible for electrical connection through a hole in the wall of the screen 20. The chamber 10 is designed for use with a plpeline 14 of specified diameter, the couplings 12, 16 being of similar diameter to the pipeline 14 and the chamber 10 having a diameter over the greater part of its length which is three times the diameter of the pipeline 14. The tran~ition between the diameter of the coupling 12 and the maximum diameter of the chamber 10 is made abruptly as indicated by the form of shaulder 25 for which the preferred internal angle exceeds 60 and any stre4mlining of the profile should be avoided. There will be implicit in the specification of the test chamber 10 for use with a particular diameter of pipeline~ an expectation of a specific range of flow rates. From this information the length of the chamber 10 is preferably calculated so that the residence time for an element of fluid entering the chamber 10 at the mean flow rate is appreciably less than the relaxation time for the fluid.
A flowmeter 26 of any conventional form is installed in the pipeline ~; 25 so that the volumetric flow rate can be determined at the time of t ~' , `.
,~
~t ~ ::
:~
. , :.
each charge measurement. In Figure 1 flowmeter 26 is shown downstream of chamber 10 but an upstream position is equally suitable.
In carrying out the measurement an alectrometer 28 is connected between the terminal 24 and earth and fluid i8 allowed to flow through the chamber 10 for a period sufficiently long to enable the charge distribution to stabilise. The value of current indicated by the electrometer 28 and the rate of flow are then recorded. For purposes of standardisation it is necessary to have obtained at least one direct measurement of charge density by conventional means for the same fluid together with the corresponding value of current indicated by the electrometer 28.
Measurements made on different occasions will not be validly comparable if it is possible for air to be trapped in chamber 10.
In order to exclude this possibility it is desirable therefore that chamber 10 should be mounted vertically with the inlet at the lower end.
With reference to Figure 2 one example of a control system is shown schematically in which a pipeline installation 14 includes, in the manner of Figure 1, a test chamber 10 with electrostatic screen 20, electrometer 28 and volumetric flow meter 26. Pipeline 14 also passes through a charge neutraliser 30 located upstream of the chamber 10. Neutraliser 30 operates in a known way in respon~e to the ou1:put from a controller 32 to neutralise the charge content of ', . .:
: ~
, .,, : - :
- .
10~7247 the stream as measured at each instant. Controller 32 receives, by means of any necessary transducing or ampli~ying elements, signals which represent the value of current flowing through electrometer 28 and the rate of flow recorded by meter 26. Controller 32 includes means for deriving from the two input signals an ~utput signal to determine the degree of neutralisation required to compensate for the total charge content or to reduce it to a safe level.
Experimental observation has provided evidence of the relationship between the value of charge density in the pipeline and the value of current indicated by electrometer 28 for a medium-conductivity fuel which is in accord with the following analysis:
.
10872~7 It will be apparent from the earlier discus~ion that a relaxation current i collected by the chamber 10 i9 drawn from the charge accumulated by the fluid before entry to the chamber 10 but i8 diminished by any new component of streaming currentl which may be generated in the passage of the fluid through the chamber 10.
If the volume flow rate is denoted by v' and the charge density of fluid entering the chamber 10 by dq , then i = (v'.dq - i ).
By substitution from equations (2) and (3) and by introducing the respective values u1 and d1 for the linear flow rate in the chamber 10 and the diameter of the chamber 10:
i = (vl.dq - k.u1 .d1 ) (1 - e / ).
It will be seen that, subject to the exponential decrement, since the value of u1 is dependent on 1/d12, the value of i can be made to correspond almost directly to charge density by making the diameter d1 large. It isthought that the measurement i9 best made by selecting the length of the chamber 10 so that the residence time of an element of fluid within the chamber is appreciably less than the relaxation time constant of the fluid. The effect of each element of fluid is then sensed only during the initial stage of the relaxation curve when the rate of discharge is highest.
Consideration of the factors which determine the value l has shown theoretically that the measurement proposed represents the cumulative charge density by a sample which will generally be small and will depend on the ratio t/T, and that the flow continues with the initial charge diminished by that amount.
:; :
! ~ ~
10~7Z~7 The test procedure may be summarised as follows:
.~
(1) For calibration purposes establish the relationship between main stream charge density and collector current for the fluid concerned.
(2) Confirm that the inflow and outflow charge densities are not significantly different. The t/T relationship must then be satisfactory whether the effective value of T
is known or not
is known or not
(3) Measure the volumetric rate of flow
(4) Measure collector current. Derive charge density or charge transport rate from (1) and (3).
It will be appreciated that in the test structure described, the diameter d1 of the test chamber i9 envisaged as being significantly enlarged in relation to the diameter d of the pipelineS
the consequent reduction in the generation of streaming current to a fraction d /d1 of that in the pipe combined with the turbulent flow conditions enables a valid measurement of charge density to be made. It is thought that while some degree of advantage will be obtained for any diameter ratio d1/d which is greater than unity, this will be small for ratios appreciably belo ~ and will not be usefully enhanced for ratios~significantly greater than ~
Similarly the length of the test chamber may advantageously be such that the value of t ]ies below 0.5T although the standardisation procedure will of course accommodate other values.
., . ~ ~ .
~,'," .
.. . . .
Economy in the installation required for refuelling demands the use of the smallest pipeline at the highe~t possible flow rate which is con~idered electrically safe. There is nonetheless an inherent risk and the use of a test meter of the kind and in the manner described enables the fuel charge density or the charge transport rate to be monitored continuously under the control of an unskilled observer to provide warning of danger. The value of the monitored parameter may of course provide an input to an automatic warning system or the automatic operation of a charge neutralisation process or other appropriate proced~re may ' be arranged. The use of a cl~osed,loop i9 indicated in Figure 2; alternatively a neutraliser located downstream of the test position may be u~ed as an open loop control.
, ' ' ' t, . . ' j: ~ ' ' ~ ' ' . :.
' .
It will be appreciated that in the test structure described, the diameter d1 of the test chamber i9 envisaged as being significantly enlarged in relation to the diameter d of the pipelineS
the consequent reduction in the generation of streaming current to a fraction d /d1 of that in the pipe combined with the turbulent flow conditions enables a valid measurement of charge density to be made. It is thought that while some degree of advantage will be obtained for any diameter ratio d1/d which is greater than unity, this will be small for ratios appreciably belo ~ and will not be usefully enhanced for ratios~significantly greater than ~
Similarly the length of the test chamber may advantageously be such that the value of t ]ies below 0.5T although the standardisation procedure will of course accommodate other values.
., . ~ ~ .
~,'," .
.. . . .
Economy in the installation required for refuelling demands the use of the smallest pipeline at the highe~t possible flow rate which is con~idered electrically safe. There is nonetheless an inherent risk and the use of a test meter of the kind and in the manner described enables the fuel charge density or the charge transport rate to be monitored continuously under the control of an unskilled observer to provide warning of danger. The value of the monitored parameter may of course provide an input to an automatic warning system or the automatic operation of a charge neutralisation process or other appropriate proced~re may ' be arranged. The use of a cl~osed,loop i9 indicated in Figure 2; alternatively a neutraliser located downstream of the test position may be u~ed as an open loop control.
, ' ' ' t, . . ' j: ~ ' ' ~ ' ' . :.
' .
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Apparatus for continuously monitoring the electrostatic charge transport rate in a stream of insulating material flowing through a pipeline, comprising: a charge collection chamber having an electrically conductive wall; inlet and outlet means for connecting said chamber into a pipeline to enable continuous flow of said material therethrough, including means to maintain said chamber in electrical isolation from said pipeline, at least part of the length of said chamber being of enlarged cross-sectional area relative to the pipeline for which said inlet means is designed and said chamber having a transition portion between said input means and said enlarged cross-sectional area which is effective to permit turbulence in the ensuing flow and the length of the chamber being predetermined in relation to the characteristics of the stream to be monitored such that in operation the residence time of an element of the stream within the chamber is appreciably less than the relaxation time constant of the material; and means for connect-ing said conductive wall to earth potential; and means for measuring the flow of current in the earth connecting means.
2. Apparatus according to claim 1 in which the chamber is substantial-ly enclosed by an electrostatic shield having earth connection means.
3. Apparatus according to claim 1 or claim 2 in which the chamber is of generally cylindrical form having an internal diameter in the range of ratios from to with respect to the internal diameter of the inlet means.
4. Apparatus according to claim 1 or 2 including volumetric flow metering means for deriving a value of flow rate in the pipeline to enable a value for charge density in the stream to be derived from the charge transport rate.
5. Apparatus according to claim 1 or 2 having means responsive to the value of charge transport rate or of charge density to control the operation of charge neutralisation means for the treatment of the material in the pipe-line.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB74277A GB1587908A (en) | 1977-01-10 | 1977-01-10 | Electrostatic charge measurement |
| GB00742/77 | 1977-01-10 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1087247A true CA1087247A (en) | 1980-10-07 |
Family
ID=9709735
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA294,624A Expired CA1087247A (en) | 1977-01-10 | 1978-01-09 | Electrostatic charge measurement |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA1087247A (en) |
| DE (1) | DE2800157A1 (en) |
| GB (1) | GB1587908A (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4249131A (en) * | 1979-04-11 | 1981-02-03 | The United States Of America As Represented By The Secretary Of Commerce | Method and apparatus for measuring electrostatic charge density |
| US6905654B2 (en) | 2000-10-06 | 2005-06-14 | Univation Technologies, Llc | Method and apparatus for reducing static charges during polymerization of olefin polymers |
| US6548610B2 (en) | 2000-10-06 | 2003-04-15 | Univation Technologies, Llc | Method and apparatus for reducing static charges during polymerization of olefin polymers |
| US20050232995A1 (en) | 2002-07-29 | 2005-10-20 | Yam Nyomi V | Methods and dosage forms for controlled delivery of paliperidone and risperidone |
| CN1303428C (en) * | 2003-05-10 | 2007-03-07 | 江苏东强股份有限公司 | Powder electrostatic monitor |
| RU2537191C2 (en) * | 2013-04-18 | 2014-12-27 | Открытое акционерное общество "Лётно-исследовательский институт имени М.М. Громова" | Spark-safe filling of aircraft fuel tanks at pressure |
-
1977
- 1977-01-10 GB GB74277A patent/GB1587908A/en not_active Expired
-
1978
- 1978-01-03 DE DE19782800157 patent/DE2800157A1/en not_active Withdrawn
- 1978-01-09 CA CA294,624A patent/CA1087247A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE2800157A1 (en) | 1978-07-20 |
| GB1587908A (en) | 1981-04-15 |
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