WO2000054045A1

WO2000054045A1 - Chemical sensor systems

Info

Publication number: WO2000054045A1
Application number: PCT/GB2000/000809
Authority: WO
Inventors: Andrew Pike
Original assignee: Marconi Applied Technologies Ltd
Current assignee: Teledyne UK Ltd
Priority date: 1999-03-05
Filing date: 2000-03-06
Publication date: 2000-09-14
Anticipated expiration: 2001-09-05
Also published as: GB9905051D0; AU2928600A; EP1159608A1; GB2348009A; GB0005358D0; JP2004506174A

Abstract

In a chemical sensor system, samples are taken at multiple locations and then processed at a single processor module to give at or on line monitoring of a product or process.

Description

Chemical Sensor Systems

This invention relates to chemical sensor systems, and more particularly for at- or on¬

line monitoring of a product or process.

Chemical sensor array systems for sensing in the liquid, gas or vapour phase,

including as a sub-class those arrays sometimes referred to as electronic noses as they operate

using odour analysis, have been successfully employed in laboratory instruments for the measurement of headspace volatiles. Typical applications include quality control of raw

materials and final product, new product development and correlation with sensory panel

data. Those instruments developed to date have primarily aimed at laboratory use.

In applications where substances are being handled or modified during manufacture or

processing, there are typically several stages during the process where there is a requirement

for assessment of quality, authenticity and/or compositional property of a substance.

Chemical sensor array systems (SAT) may be used in assessing these characteristics.

The present invention seeks to provide a chemical sensor system which is particularly suitable for at-line or on-line monitoring.

According to the invention, there is provided a chemical sensor system for at or online monitoring of a product or process comprising: sampling means arranged to acquire

samples of a substance to be sensed from a plurality of different locations in the product or

process line; sensor means including an array of sensors arranged to sense the samples; and processing means for deriving information from the output of the sensor means concerning

the substance or substances to be sensed.

As used in this specification, "at-line" means that a monitoring instrument is located

next to the detection point of interest, from which a sample may be introduced either

manually or by automated means. Analysis of the product or process is achieved from a

discrete sample or batched samples. The term "on-line" is defined to mean that there is a physical connection between the monitoring system and the detection point, which allows the

product or process to be monitored by discrete samples, batched samples or continuously with

automated sampling. "In-line" systems are a subset of on-line systems.

By using the invention, it is possible to analyse samples of substances from different

locations in a product or process line and to assess them together within the process system as

a whole or to assess samples individually. This would, for instance, provide a means of

monitoring at several stages during a production process. The substance sampled at a

plurality of different locations may be nominally the same substance or it could be another

substance introduced, modified or generated during a production process. More than one

substance may be sensed at a single location to give a more complete characterisation of the

manufacturing or process line.

The advantage of using monitoring technology in an at-line or on-line configuration is

that it enables 'point of use' or in-situ measurement of a sample which in turn allows real¬

time monitoring of a product or process. A process to be monitored may involve one or more

physical or chemical procedures used in the treatment, conversion or manufacture of an intermediate or final product. In a manufacturing environment at- or in-line monitoring

allows rapid corrective action to be taken if there has been a deviation from normal or

acceptable performance or quality in product or process. The delay in taking a sample for

remote off-line analysis in a laboratory-based instrument is often unacceptable. At and on¬

line monitoring is therefore preferable in many areas of industry and also in environments

where the system is monitoring for hazardous conditions e.g. fire or generation of toxic

vapours.

The sampling means may be incorporated as part of the sensor means, with sensors of the sensor means being placed at a detection point of interest. The sampling means might

alternatively be discrete from the sensor means. Examples of the sample means are

arrangements using at least one of the following techniques to acquire a sample: portable;

liquid headspace; liquid sparge; sample vaporisation; a probe; solid head space; direct insertion of an array of liquid phase chemical sensors into the sample or sample stream; gas

line and ambient monitoring. For a particular system, it is necessary to select a sample

handling technique appropriate to the substance to sensed.

A sample handling apparatus extracting a sample from a liquid head space is suitable

for monitoring ambient volatiles above a liquid sample. Liquid sparge comprises flushing a

liquid sample with inert gas to release volatiles. A probe may comprise, for example, a

flexible tube and pump to acquire a sample. In a solid head space, ambient volatiles are

monitored above a solid sample. A gas line might be used in which a sample is drawn off

from a gas stream, this being particularly suitable for processes involving fermentation. A sample handling module may use an ambient technique such as passive monitoring of the local environment, for example, for fire detection. Other techniques may be appropriate for

other applications. Where a sample is to be monitored in the liquid phase a sensor array may

be inserted into the sample or sample stream.

The sample handling means may be such as to acquire a sample without operator

intervention to give an automated procedure, and samples may be taken at discrete time

intervals which are fixed or variable, or continuously. Also, switching between discrete,

batched and continuous sampling may take place depending on the particular time in a

production process, location from which the sample is taken or for some other reason.

In one system, the sampling apparatus includes means to introduce a calibration or

reference sample. Alternatively, this may be provided at the sensor means. This allows

calibration or checking of the sensor array performance.

The distributed chemical sensor system may provide information concerning the

operation of a production line or a process which can then be used in a control feedback

system, in which data generated by the system is fed back to determine the settings of control

hardware, for example, in a System Control and Data Acquisition (SCAD A) system.

Feedback may also be provided to the monitoring system itself, for example, to adjust sensor

settings or sampling frequency.

In one embodiment of the invention, the sensor means comprises a plurality of sensor

arrays located at respective different locations. This minimizes the path to be taken between

the sampling means and sensor means, where these are separately housed, as each sensor array module may be located at the detection point at which the sample is acquired.

In a chemical sensor, a change in a physical property, such as a change in electrical

conductivity, is produced in response to a gas or vapour being sensed. Many different sensor

technologies are available for use in the sensor means. Advantageously, the sensor means

includes a sensor array using at least one of the following types of sensor technology: mass

sensitive sensor; electronic conductance or capacitance sensors; field effect sensors;

calorimetric sensors; electrochemical sensors (for example, amperometric, potentiometric or

conductimetric sensors); optochemical or photometric sensors; and biosensors. In fact any

sensor which produces a useful output corresponding to a change in characteristic when a

chemical is sensed may be suitable. Mass sensitive sensors may be for example those using

bulk acoustic wave or surface acoustic wave techniques. Electronic conductance and

capacitance sensors may be for example chemo-resistors based on conducting polymer or metal oxide semiconductor materials. Calorimetric sensors may for example be pellistors.

Electrochemical sensors are for example potentiometric cells. Infra red and fibre optic based

techniques may be used in optochemical or photometric sensors. Biosensor and

electrochemical sensors may be particularly suitable for liquid phase sensing.

A system in accordance with the invention may include a sensor array having sensors

of one technology type only. In that case, the sensor environment can be specifically tailored

for use with sensors of that type. In alternative arrangements, the sensor array includes

sensors of a combination of different technology types. This gives increased sensitivity and/or discrimination in some cases, the particular combination being tailored to the

substance to be sensed. Several sensor arrays of differing technology types or different combinations of technology types may be included in a system.

The processing means may be arranged to simultaneously accept information relating

to samples acquired from respective different locations or to obtain such information

sequentially. The information obtained from the samples taken at different points may

individually be used to give an assessment of the state of the product or process on-line or they may be used in combination. Thus, the processing means may classify substances at

individual locations or classify the status of the line as a whole.

Preferably, the processing means uses pattern recognition to characterise the

substance. The pattern recognition technique used in the processing module may use at least

one of the following: a statistical method (for example, principal component analysis (PCA),

or multiple discriminant analysis (MDA)); fuzzy logic; an artificial neural network; and a

proprietary classifier algorithm. The technique or techniques adopted depend on the substance to be sensed and the use made by the system of information acquired via the

monitoring procedure.

Some ways in which the invention may be performed are now described by way of

example with reference to the accompany drawings in which:

Figure 1 schematically illustrates a chemical sensor system in accordance with the

present invention; and Figures 2, 3 and 4 relate to another chemical sensor system in accordance with the

invention.

With reference to Figure 1, a chemical sensor array system is used to monitor a

product manufactured by a process including several processing steps. In this case it is

wished to monitor the composition of a substance at various points in the processing method

to assess the effectiveness of the process line. The monitoring system includes a sampler 1 at

a first point A at which a sample of the substance is extracted using an appropriate sampling technique. In this case, a sample is taken at fixed timing intervals. The container in which

the sample is housed is connected via a pipe to a sensor array module 2 in such a way that

volatiles existing in the headspace above the solid sample are transferred over sensors of the

array. The output of the sensors is determined by their response to the volatiles to which they

are exposed. In this case, the sensor array module 2 combines a plurality of different sensor

technologies providing a set of signal outputs characteristic of the substance of the sample. A

central processor 3 accesses the outputs of the sensor array module 2 via a fixed link 4 to

provide a series of data points characteristic of the sample being sent. Pre-processing occurs

in the central processor 3 to place the acquired data in a form suitable for pattern recognition

techniques to be applied thereto.

A second sampler 5 is arranged to take samples downstream of location A at a second

location B at which stage it is expected that the substance being processed has been modified.

A sample is taken by the sample handling means 5 in a way appropriate to the form of the

substance and the most appropriate types of sensor technology to detect changes in its

physical or chemical characteristics. The sample is presented to a second sensor array module 6 which is located locally to the sample handling means 5. The second sensor array module 6

produces a set of responses characteristic of the composition of the substance being sampled.

These are also accessed by the central processor 3. Additional samples may be taken at other

points of detection in the process line. These points of detection may be down-stream of the

first one or could be at locations A and B but arranged to take samples of different

substances.

The central processor 3 is arranged to apply a suitable pattern recognition technique to

the data required from the second sensor array module 6. The processor 3 then assesses the

data derived from each sensor array module in turn to characterise the substance sampled at

the point of detection associated with that sensor array module. In addition, the central processor 3 provides an overview of the production line as a whole to characterise the entire

process system.

The information which results from the processing stage is then applied by a link 7 to

a user interface 8, which in this case takes the form of a visual display from which an operator

may view the performance of the system. In addition, the user interface 8 permits the

operator to input control data, for example, to vary the frequency at which samples are taken,

control characteristics of sensors in the sensor array modules 2 or 6 or to implement different

functions of the central processor 3. Other changes to the monitoring system may be arranged

to be implemented or automatically via the central processor 3. For example, if the central

processor 3 detects rapid changes in characteristics of a set of samples, it may send control

signals to the sample means to increase the rate at which samples are taken. The central processor 3 is also linked via line 9 to a manufacture control system 10

which utilises the information acquired from the monitoring system to adjust the parameters

of the process line in dependence on any detected variations from the sample composition

from the desired characteristics.

The central processor 3 may be set up so that it is able to acquire data communicated

from either a single sensor array module or from several and place them into a form which is

suitable for further processing. A pattern recognition technique may be applied to each sensor array module in turn or to a plurality of sensor array modules simultaneously.

Another system in accordance with the invention is illustrated in Figure 2. This

system is used in the monitoring of waste water from a chemical plant. Samples are taken at

three locations XA, XB and XC via samplers 11, 12 and 13 each of which is associated with

its own sensor module 14, 15 and 16. The outputs of the sensor modules 14, 15 and 16 are

connected via a bus arrangement 17 to a processing module 18. A user interface 19 is

integrated into the same enclosure 20 as the processing module 18. A schematic diagram of

the enclosure 20 is illustrated in Figure 3.

The processor elements of the module 18 comprise a single board computer (SBC) 21

and a hard-drive 22 to provide additional memory. The user interface includes a flat panel

display 23 and a keypad 24 that are mounted on the front of the enclosure 20. The software to

acquire and control the system is run on a DOS operating system installed on the Single Board Computer 21. The setup and operation of the system is menu driven via the software,

visible on the display 23. Buttons on the keypad 24 are used to select menu items. The SBC 21 is connected to sensor modules 14, 15 and 16 via an asynchronous RS 485 multi-drop

serial data link. A power supply unit (psu) 25 is also included in enclosure 20.

One of the sensor modules 14 is illustrated in Figure 4 and includes means for

transmitting and receiving data and control signals from the processor module 18. It contains

an array 26 of chemical sensors which is in a temperature controlled housing 27 that allows

samples to pass over the sensors. In some sensor modules the flow and relative humidity

(RH) are also measured. Other parameters relating to sensor operation are also controlled. All

the sensor and control hardware 30 require interface electronics 28 to make them compatible

with the input/outputs of a microcomputer 29. The microcomputer 29 acquires sensor data

and transmits the data over the RS 485 connection to the processor 18 via a driver IC 31. The

RS 485 driver IC 31 is required to interface the signals over the data communications bus 17

to the microcomputer 29 . Data is collected, processed and transmitted to the processor

module 18. The other sensor modules 15 and 16 are similarly configured.

Both the microcomputer 29 in the sensor module 14 and the SBC 21 in the processor

18 adhere to the same interface protocol. In this instance, the data link is 19,200 baud, and the

data mode is 8 data bits, 1 stop bit, even parity. This can be reconfigured for different

applications.

The SBC 21 will communicate with a sensor module 14, 15 or 16 via a number of

commands e.g. idle mode, acquire data, cleanup mode, diagnostics. Other commands relating

to changing the setup of the sensor module may also be sent. A sensor module may send a

reply to the SBC 21 to inform that the message has been received and understood. Each sensor module has a unique identifying number that is used by the SBC to identify the recipient of a

command. Since the RS 485 bus is multi-drop, a number of units can be connected to the

same pair of wires. Normally, communication will be with one sensor module at a time, bui

certain commands can be sent to all sensor modules at once by use of a global identifier.

When data is transmitted from the sensor module to the SBC, data relating to the identity of

the sensor module is attached. In one mode of operation each sensor module is polled in turn

by the processor module to avoid message collision.

An application that can benefit from this invention is a process plant that has its effluent monitored in order that its chemical composition does not exceed levels set by

environmental agencies. At these sites there are typically multiple sources of effluent, which

are connected together to form a single drain off site. A sensor module can be installed at each

of the sources of effluent using a suitable sampling technique. By collecting the entire

chemical sensor data at the processor unit across the data link, it provides a profile of the

quality of effluent water across the whole site. This information can be used to control the

diversion of polluted water into temporary storage to prevent chemical content levels being

exceeded off the site.

Other applications include processes where batches are blended to attain a final product of uniform quality.

Claims

1. A chemical sensor system for at- or on-line monitoring of a product or process comprising:

sampling means arranged to acquire samples of at least one substance to be sensed from a

plurality of different locations in the product or process line; sensor means including an array

of sensors arranged to sense the samples; and processing means for deriving information from

the output of the sensor means concerning the substance or substances to be sensed.

2. A system as claimed in claim 1 wherein locations at which the samples are taken are remote from one another.

3. A system as claimed in claim 1 or 2 wherein locations at which the samples are taken are

local to one another.

4. A system as claimed in claim 1, 2 or 3 wherein the sensor means comprises a plurality of

sensor arrays located at respective different locations.

5. A system as claimed in claim 4 wherein the sensor arrays are housed in separate modules.

6. A systems as claimed in any preceding claim wherein sampling means and sensor means

are housed in a common module.

7. A system as claimed in any preceding claim wherein the processing means is arranged to acquire simultaneously information relating to samples acquired from respective different

locations.

8. A system as claimed in any of claims 1 to 6 wherein the processing means is arranged to

acquire sequentially information relating to samples acquired from respective different

locations.

9. A system as claimed in any preceding claim wherein processing means is arranged to apply pattern recognition to data relating to the samples.

10. A system as claimed in any preceding claim and including a user interface.

11. A system as claimed in any preceding claim and including means for deriving signals to

control the product or process line in dependence on the samples sensed.

12. A system as claimed in any preceding claim and including means for controlling the

sampling means and/or sensor means in dependence on information derived from the samples

sensed.

13. A system as claimed in any preceding claim wherein the processing means provides

control signals to the sensor means.

14. A system as claimed in any preceding claim wherein the sensor means comprises at least

one sensor array module which includes sample handling capability.

15. A system as claimed in any preceding claim wherein the sensor means includes at least

one of the following types of sensor technology: mass sensitive sensors; electronic

conductance or capacitance sensors; field effect sensors; calorimetric sensors; electrochemical

sensors; optochemical or photometric sensors; and biosensors.

16. A system as claimed in any preceding claim wherein the sensor means includes sensors of only one sensor technology type.

17. A system as claimed in any of claims 1 to 15 wherein the sensor means includes sensors

of a combination of different technology types.

18. A system as claimed in any preceding claim wherein the sampling means uses at least one

of the following techniques to acquire a sample: portable; liquid headspace; liquid sparge;

sample vaporisation; a probe; solid head space; direct insertion of an array of liquid phase

chemical sensors into the sample or sample stream; gas line and ambient monitoring.

19. A system as claimed in any preceding claim and including a bus connecting a plurality of

sensor arrays to the processing means.

20. A system as claimed in any preceding claim wherein the processing means is connected to

the sensor means via an asynchronous multi-drop serial data link.

21. A system as claimed in any preceding claim wherein the processing means is arranged to

poll in turn sensor arrays included in the sensor means.

22. A system as claimed in any preceding claim wherein the processing means includes a

single board computer, a hard drive and a user interface display.

23. A system as claimed in any preceding claim and including a relative humidity sensor.

24. A system as claimed in any preceding claim and wherein data transmitted from a sensor

array includes an identification number identifying that array.

25. A system as claimed in any preceding claim in which samples of effluent from a chemical

processing plant are monitored at different locations.

26. A chemical sensor system for at- or on-line monitoring of a product or process

substantially as illustrated in and described with reference to the accompanying drawing.