Method of using a computer to collect chemical signals directly

The present invention relates to a method of using a computer to collect chemical signals directly from a chemical sensor. This method first converts output signals received from the chemical sensor into digital signals by using a transforming circuit and an analog-to-digital converter in cooperation with a control computer program executed in the computer; transfers the digital signals to the computer and processes the digital signals in the computer in accordance with the type of the chemical sensor used.

FIELD OF THE INVENTION 
The present invention is related to a method of using a computer to collect 
chemical signals directly. 
BACKGROUND OF THE INVENTION 
There are three types of chemical sensors: chemical sensors used in 
conductometry, chemical sensors used in amperometry and chemical sensors 
used in potentiometry. For example pH electrodes, ion-selective 
electrodes, ISFET (ion-selective field effect transistors), enzyme 
electrodes, biosensors, etc. are widely used in chemical, biochemical, 
biotechnological, environmental protection and medical analyzers such as a 
pH-meter, ion analyzer, polarography, chemical analyzer, bioanalyzer, 
bioreactor, ion chromatography, flow-injection analyzer, etc. Moreover, 
Chemical sensors are used in quality control analysis, on-line analysis 
and monitor-control apparatus for chemical manufacturing processes. U.S. 
Pat. No. 4,897,128 discloses a method of controlling the ionic 
concentrations of reactants in a zinc phosphate coating sink by using 
pH-electrodes and fluorine-ion selective electrodes. 
A chemical sensor can convert a specific chemical signal (i.e. 
concentration of a certain component of a sample) or the sum of many 
chemical signals into an electronic signal such as electric potential, 
resistance, or current. However, in order for the users to understand the 
physical meanings of a chemical signal, this electronic signal still needs 
to be further processed, stored, and/or displayed by an signal processing 
equipment. For example, a pH-electrode has to be incorporated with a pH 
meter to determine the pH value of a solution. Similar requirements 
applies to the usage of a chemical analyzer, and pH monitor control 
equipment. A chemical sensor for amperometry can determine the reaction 
current in the potential static condition by relying on a potentiostat, 
and then indirectly obtain the concentration of a specific specie. Similar 
requirement applies to the usage of a chemical analyzer and a biochemical 
analyzer. A chemical sensor for conductometry can determine the 
conductivity by relying on a conductometer, and the determined 
conductivity can then be used to indicate the ending of a conductometric 
titration, or used as the standards of ionic concentrations in ion 
chromatography. Each of these kinds of signal processing equipment has a 
specific usage, and cannot be exchanged for use in another chemical 
sensor. For example, a pH-meter can not be used as a conductometer or a 
coulometer, and it also can not be extended to another use. Without a 
special design, a potentiometer cannot be extended to be used in 
potentiostatic coulometry. 
Generally speaking, conventional signal processing equipment can be divided 
into 4 categories. The first category includes the simple instruments 
which cannot be connected to a computer or a recorder. For example, 
pH-meters (types 704, 620, 588) of Metrohm, Switzerland, do not have very 
powerful functions, and do not have the ability to execute data 
communication with other instruments like chemical analyzers. 
The second type of signal processing equipment, however, cannot be 
connected with a computer externally, but is able to communicate with an 
external recorder through its analog signal output node, and, therefore, 
enhance its function. Examples are the pH-meter (PHM82) of Radiometer, 
Denmark, and the Potentio/Galvanostat and Coulomb/Amperohour Meter of 
Nichia, Japan. The functions of these signal processing equipment are 
still limited. Although an analog signal output node is available, it is 
still physically difficult to execute data communication with other 
instruments. 
The third type of signal processing equipment cannot be externally 
connected with either a computer or a recorder, but, has its own built-in 
display and printer. Examples are the modular biological fluid analyzer 
disclosed in U.S. Design Pat. No. D330,770, and a clinical chemistry 
analyzer disclosed in U.S. Design Pat. No. D332,314. These built-in 
functions clearly can not be compared with those of a computer. For 
example, the resolution of a computer monitor is better than a built-in 
display of a signal processing equipment. A computer also has superior 
data processing/storing capabilities and various accessories which can be 
mounted into the computer easily. Moreover, the analyses and data 
processing functions of this type of signal processing instruments cannot 
be extended or enhanced. 
The fourth type of signal processing equipment can be connected with a 
computer externally in order to enhance its data 
processing/storing/display ability. Examples include the voltammetry Model 
693 VA Processor from Metrohm, Switzerland; the PHM 85 pH-meter from 
Radiometer, Denmark; the Potentiostat/Galvanostat Model 273A from EG&G, 
U.S.A.; a chemical analyzer disclosed in U.S. Pat. No. 4,935,875; and the 
on-line biological inhibition/toxicity detector disclosed in U.S. Pat. No. 
5,106,511. This type of signal processing equipment contains a central 
processing unit. For example, line 17, column 5 of U.S. Pat. No. 5,106,511 
and line 45, column 6 of U.S. Pat. No. 4,935,875 state that these signal 
processing equipment use a Model 6809 microprocessor (Motorola, U.S.A.), 
ROM, RAM, timer, display or monitor, keyboard or I/O port, 
Analog-to-Digital converter (ADC), etc. (For further details, please refer 
to FIG. 1 of U.S. Pat. No. 4,935,875 and its explanation.) In addition, 
when these signal processing equipment are to be connected externally with 
computers, RS-232 or GPIB cards need to be used as the medium for data 
communication. 
In order to extend the analysis and data processing functions, the 
inventors have focused their research on the structure of the fourth type 
of signal processing equipment. The result is that except for some minor 
components such as ADC, the primary components such as CPU, ROM, RAM, 
timer, monitor, keyboard, I/O port, printer and disk drive, are all 
included in a computer. This is advantageous because the primary 
components of a computer are generally more powerful and more compatible 
to external accessories than the built-in components in the fourth type of 
signal processing equipment. Therefore, the fourth type of signal 
processing equipment may essentially be replaced by a computer. In 
addition, the minor components such as ADC can be easily purchased in the 
market. Accordingly, it is possible to use an ADC bought from the market 
to directly convert the analog signals from a chemical sensor into digital 
signals, and transfer the digital signals to a computer where they are 
processed. If this can be accomplished, the signal processing equipment 
used at the present time can be entirely replaced by a computer with 
modifications. Nowadays, some mechanical-sensors or thermal sensors are 
using the same idea of replacing signal processing equipment with 
computers and ADCs. However, this idea has not been used in chemical 
sensors. 
Based on the above analyses, the inventors used a market-purchased ADC to 
connect a chemical sensor which is used in potentiometry (e.g. a pH 
electrode) and a computer. In other words, the output signals from a 
chemical sensor were received in a series as follows: "chemical 
sensor.fwdarw.ADC.fwdarw.computer". However, the results showed that 
although a large number of data were collected, the average value of these 
data could not represent the actual value accurately because the average 
values were not consistent for several runs repeated by the same 
procedures. The deviations were large and no pattern could be found. 
After more intensive research, the inventors found out that the addition of 
a voltage follower could solve the existing problem. That is to say, if 
the connection is in a series of "chemical sensor.fwdarw.voltage 
follower.fwdarw.ADC.fwdarw.computer", the output signals of a chemical 
sensor which is used in potentiometry can be easily and accurately 
obtained. 
Furthermore, current ADCs in the market often have an additional function 
of Digital-to-Analog Conversion (DAC) at the same time. Therefore, it is 
theoretically possible to use a DAC to convert the digital signals sent by 
a computer into analog signals, and therefore use a chemical sensor to 
execute voltammetry method; or under potentiostatic conditions, to excute 
amperometry and obtain a concentration of a certain component of a sample. 
The actual experimental results showed that although the voltage output of 
the DAC was stationary, the electric potential of the working electrode 
was fluctuating. However, this problem can be solved by the addition of a 
potentiostat circuit. Similarly, a Galvanostat circuit can be used to 
solve the same problem in potentiometry under Galvanostatic conditions. 
In the conventional signal processing equipment of a the chemical sensor 
used in conductometry, a transducer has to be added to reduce the voltage 
of an alternating current source for the conductance cell. However, the 
inventors found that by executing a control program in the computer, the 
DAC can be used as an alternating current source. 
SUMMARY OF THE INVENTION 
Based on the above discoveries, the present inventors disclose a system for 
carrying out amperometry, potentiometry, conductometry, and voltammetry 
for chemical sensors of different types, which comprises a computer, an 
ADC/DAC, a voltage follower, a current-potential converter, a potentiostat 
circuit, a Galvanostat circuit and a proper computer program which can be 
executed in said computer. In other words, the invention provides a method 
and system having the combined functions of a pH meter, an amperometer, a 
conductometer, a potentiostat/Galvanostat, and a voltammetric processor, 
and thereby substantially covers all equipment which use chemical sensors 
or any extension uses of these equipment, e.g. as a conductometer used in 
ion-chromatography. In contrast, the conventional signal processing 
equipment for chemical sensors have their own specific usages that cannot 
be exchanged. For example, a pH meter can be used only as a pH meter, not 
a potentiostat, and a voltammetric processor can not be used as a 
conductometer at the same time. 
In addition, because ADC/DAC cards on the market usually have DIO (digital 
input/output) functions, and hence they can also be used as the control of 
a pump or a valve, the system described above can generally be connected 
with other accessories (if necessary) to be used as a chemical analyzer, 
bio-chemical analyzer, clinic analyzer, pH/electric potential/conductance 
automatic titration meter, ion chromatography, polarography, and a quality 
control, on-line analysis and monitor-control equipment of a chemical 
manufacturing process. 
The first objective of this invention is to provide a method of converting 
output signals of a chemical sensor into digital signals and processing 
said digital signals by using a computer. 
The second objective of this invention is to provide a system for 
collecting chemical signals from a chemical sensor, which includes a 
computer, an ADC, a transforming circuit and a proper computer program 
which can be executed in said computer. 
The third objective of this invention is to provide a system for collecting 
chemical signals from a chemical sensor, which includes a computer, 
ADC/DAC/DIO interface cards, a transforming circuit and a proper computer 
program which can be executed in the computer.

DETAILED DESCRIPTION OF THE INVENTION 
present invention is related to a method of using a computer to collect 
chemical signals directly from a chemical sensor, in which said computer 
is provided with an Analog-to-Digital converter (ADC) and said chemical 
sensor is connected to said ADC with a transforming circuit. The present 
method includes the following steps: 
converting output signals received from said chemical sensor into digital 
signals by using said transforming circuit and said ADC in cooperation 
with a control computer program executed in said computer; 
transferring said digital signals from said ADC to said computer; and 
processing said digital signals in said computer in accordance with the 
type of said chemical sensor. 
When the chemical sensor used in the present method is for potentiometry, 
said transforming circuit is a voltage follower. In addition, said 
computer may be further provided with a Digital-to-Analog converter (DAC), 
and said DAC is connected to said chemical sensor with a Galvanostat 
circuit, wherein a Galvanostatic current is received by said chemical 
sensor from said Galvanostat circuit in cooperation with said DAC and said 
control computer program executed said computer so that a potentiometry 
under Galvanostatic condition is carried out. 
When the chemical sensor used in the present invention is for amperometry, 
said transforming circuit is a current-potential converter. In addition, 
said computer may be further provided with a Digital-to-Analog converter 
(DAC), and said DAC is connected to said chemical sensor with a 
potentiostat circuit, wherein a current having a desired electric 
potential wave form or a potentiostatic current is received by said 
chemical sensor from said potentiostat circuit in cooperation with said 
DAC and said control computer program executed by said computer so that a 
voltammetry or an amperometry under potentiostatic condition are carried 
out. 
When the chemical sensor used in the present invention is for 
conductometry, said transforming circuit is a current-potential converter, 
and said computer is further provided with a Digital-to-Analog converter 
(DAC) which is connected to said chemical sensor, wherein an alternating 
current is received by said chemical sensor from said DAC in cooperation 
with said control computer program executed said computer so that a 
conductometry is carried out. 
The chemical sensor can be a sensor array. In Chapter 6 entitled 
"Multi-Component analysis in Chemical Sensing", Vol. 2 entitled "Chemical 
and Biochemical Sensors", of Sensors (edited by W. Gopel, I. Hesse and J. 
N. Zemel, and published by VCH company, Germany), a signal sensor, a 
sensor array, and the combination of both are demonstrated. The chemical 
sensors described here are general chemical sensors, including common 
biosensors, biochemical sensors, enzyme electrodes, gas sensors, etc. The 
form of these chemical sensors can be a probe, an electrochemical sensor, 
a liquid electrolyte sensor, a solid state electrochemical sensor, a field 
effect chemical sensor, a calorimetric chemical sensor, an optochemical 
sensor, a piezoelectrically chemical sensor, etc. These sensors are 
described in Chapters 1, 5, 7, 8, 9, 10, 11, 12, 13, 14 and 16, Vols. 2 
and 3 of Sensors (edited by W. Gopel, I. Hesse and J. N. Zemel, and 
published by VCH company, Germany), which can convert chemical signals 
into electronic signals. 
The voltage follower described above is a known circuit. Please refer to 
Microelectronics, Jacob Millman and Arvin Garbel, second edition, p. 445. 
This voltage follower is used in this invention to convert the high 
impedance electronic signals of the chemical sensors described above to 
medium or low impedance signals. Generally, the output electronic signals 
of a chemical sensor are high impedance electronic signals of about 
10.sup.5 -10.sup.6 Ohms. If these signals are connected with an ADC 
directly, the ADC cannot convert the analog signals into digital signals 
accurately. However, if a voltage follower is inserted between a chemical 
sensor and an ADC, the problem will be solved. 
The Galvanostat circuit is a known circuit and is described in Principles 
of Instrumental Analysis, Dougls A. Skoog, third edition, p. 49. 
Said current-potential converter is a known circuit. Please refer to 
Microelectronics, Jacob Millman and Arvin Garbel, second edition, pp. 
449-450. This current-potential converter can convert the electric current 
signals of a chemical sensor used in amperometry into voltage signals, in 
order for the ADC to convert this analog voltage signals into digital 
signals. 
The potentiostat circuit is a known circuit. Please refer to Principles of 
Instrumental Analysis, Douglas A. Skoog, p. 49. This potentiostat circuit 
can equalize the electric potential output of a DAC and the voltage of the 
working electrode of the chemical sensor. In other words, the voltage of 
the working electrode is constant. If the DAC is connected to a chemical 
sensor, the voltage output of the DAC, V, and the voltage of the working 
electrode of the chemical sensor, V.sub.1, has the following relationship: 
EQU V=V.sub.1 +V.sub.2 +IR+V.sub.3 +V.sub.4 
V.sub.1 stands for the voltage of the counter electrode, IR stands for the 
IR drop caused by current-resistance, and V.sub.3 and V.sub.4 are the 
overvoltage of the working electrode and counter electrode, respectively. 
Because V.sub.3, V.sub.4 are related to the complex kinetic polarization 
and concentration polarization, the voltage of the working electrode is 
not stable even though the DAC output voltage (V) is constant. During an 
electrochemical analysis, it is required that the voltage of the working 
electrode remains constant. Therefore, a potentiostat circuit has to be 
inserted between the DAC and the chemical sensor to solve the problem. 
Each of the voltage follower, current-potential converter, potentiostat 
circuits and/or Galvanostat circuit described above is a simple circuit. 
When necessary, they can be combined to be in one circuit board, or even 
made into a computer serial port card, or be included in an ADC interface 
card. The ADC described above is a known circuit. Some ADC interface cards 
on the market, in addition to ADC, have DAC and DIO functions in one 
interface card. For example, the PCL-718, PCL-818, PCL-812, PCL-812PG 
interface cards manufactured by Advantech Co. Ltd., Taiwan all have 16 
channels ADC, 16 DI (digital inputs), 16 DO (digital outputs) and 1-2 
channels DAC. In each of these ADC interface cards described above, the 
DAC and/or DIO channels can also be formed in a separate interface card. 
Moreover, remote sensor-to-computer interface modules such as ADAM 4000 
series manufactured by Advantech Co. Ltd., Taiwan may be used as the ADC 
of the present invention so that said output signals of said chemical 
sensor can be collected by a remote computer. 
The computer described above can be a desktop computer (a PC or a 
minicomputer), or a portable computer (notebook or laptop computer), 
preferably a desktop PC or a notebook computer. 
The control computer program can be stored as a firmware or a software 
which can be read and executed by the computer, and preferably as software 
due to software's flexibility of editing and change. 
A system for collecting chemical signals disclosed by the present invention 
comprises: 
a computer for executing a control computer program; 
one or more chemical sensors for providing output signals; 
one or more transforming circuits for transforming said output signals 
received from said one or more chemical sensors into desired electronic 
signals, one end of said one or more transforming circuits being connected 
with said one or more chemical sensors; 
one or more Analog-to-Digital Converter (ADC) interface cards for 
converting said desired electronic signals into digital signals and 
transferring said digital signal to said computer, which connects the 
other end of said one or more transforming circuit with the computer; 
in which said one or more transforming circuits are a voltage follower 
provided that said one or more chemical sensors are the chemical sensor 
used in potentiometry; and/or 
said one or more transforming circuits are a current-potential converter 
provided that said one or more chemical sensors are the chemical sensor 
used in amperometry or conductometry, 
whereby said output signals from said chemical sensor are converted into 
digital signals by using said transforming circuit and said ADC in 
cooperation with said control computer program executed in said computer, 
and said digital signals are processed in said computer in accordance with 
the type of said chemical sensor. 
When said one or more chemical sensors are the chemical sensor used in 
potentiometry, said computer is further provided with a Digital-to-Analog 
converter (DAC), and said DAC is connected to said one or more chemical 
sensors with a Galvanostat circuit so that a Galvanostatic current can be 
received by said one or more chemical sensors from said Galvanostat 
circuit in cooperation with said DAC and said control computer program 
executed in said computer, and thus a potentiometry under Galvanostatic 
condition can be carried out. 
When said one or more chemical sensors are the chemical sensor used in 
amperometry, said computer is further provided with a Digital-to-Analog 
converter (DAC), and said DAC is connected to one or more chemical sensors 
with a potentiostat circuit so that a current having a desired electric 
potential wave form or a potentiostatic current can be received by said 
one or more chemical sensors from said potentiostat circuit in cooperation 
with said DAC and said control computer program executed in said computer, 
and thus a voltammetry or an amperometry under potentiostatic condition 
can be carried out. 
When said one or more chemical sensors are the chemical sensor used in 
conductometry, said computer is further provided with a Digital-to-Analog 
converter (DAC) which is connected to said one or more chemical sensors so 
that an alternating current can be received by said one or more chemical 
sensors from said DAC in cooperation with said control computer program 
executed in said computer, and thus a conductometry can be carried out. 
The function of this system entirely depends on a control computer program 
executed by the computer. 
The computer, ADC interface card, chemical sensor, voltage follower, 
current-potential converter, potentiostat circuit and Galvanostat circuit 
contained in the system are the same as those described above in 
connection with the method of using a computer to collect chemical signals 
from a chemical sensor directly. 
The one or more ADC interface cards can be connected with the computer by 
inserting gold contacts provided on said one or more ADC interface cards 
into one or more slots provided by the computer or expanded therefrom. 
Preferably, the one or more ADC interface cards can further have 
digital-to-analog converter (DAC) and digital input/output (DIO) 
functions. 
Generally, the system described above can be connected with other 
accessories (if necessary) to be used as a chemical analyzer, bio-chemical 
analyzer, clinic analyzer, pH/electric potential/conductance automatic 
titration meter, ion chromatography, polarography, and a quality control, 
on-line analysis and monitor-control equipment of a chemical manufacturing 
process. 
To further explain this invention, several preferred embodiments will be 
described in the following text by referring to the accompanying figures. 
FIG. 1 is a block diagram which shows a system for collecting chemical 
signals from a chemical sensor according to a first preferred embodiment 
of the present invention, wherein the chemical sensor 10 are connected to 
an ADC 30 with a voltage follower 20, and said ADC 30 is connected to a 
computer 40. 
FIG. 2 is a flow chart of a control computer program to be executed in the 
computer of FIG. 1 when the chemical sensor thereof is a pH meter, in 
which the ADC/DAC is manufactured by Advantech Co. Ltd., Taiwan (model 
PCL-714). The experiment data collected are shown in the following Example 
1. 
FIG. 3 is a block diagram which shows a system for collecting chemical 
signals from a chemical sensor according to a second preferred embodiment 
of the present invention, in which 10 stands for the chemical sensor used 
in amperometry, 21 stands for a potentiostat circuit, 22 stands for a 
current-potential converter, 30 stands for an interface card, 31 stands 
for DAC in the interface card, 32 stands for ADC in the interface card, 
and 40 stands for a computer. DAC 31 gives a specific electric potential 
to the potentiostat circuit 21 to execute potentiostatic electrolysis, 
cyclic voltammetry or square wave voltammetry. The current formed in the 
chemical sensor 10 is converted into voltage signals by current-potential 
converter 22, and the voltage signals are converted to digital signals by 
ADC 32, which are then processed by the computer 40. This system can be 
used in amperometry under potentiostatic condition or voltammetry like 
polarography. 
FIG. 4 is a block diagram which shows a system for collecting chemical 
signals from a chemical sensor according to a third preferred embodiment 
of the present invention, in which the numbers 22, 30, 31, 32 and 40 
represent the same elements represented by the like numbers in FIG. 3, and 
10 represents a chemical sensor for conductometry. DAC 31 gives an 
electric potential of sine wave to the chemical sensor 10. The resultant 
current, through the current-potential converter 22 is converted to 
resistance signals, which are then measured by ADC 32. This system can be 
used in conductometry. 
EXAMPLE 1 
The system shown in FIG. 1 was used to measure pH value of an aqueous 
buffer solution prepared by mixing 1:1 (v/v) of 0.1M acetic acid solution 
and 0.1M sodium acetate solution. A pH electrode Model PHM82 purchased 
from Radiometer, Denmark, was used as the chemical sensor 10; the circuit 
shown in FIG. 6 was used as the voltage follower 20; an IBM compatible AT 
computer was used as the computer 40; a PCL-714 ADC/DAC interface card 
purchased from Advantech Co. Ltd., Taiwan was used as the ADC 30 in FIG. 
1. 174 average pH values were obtained, each of which was obtained by 
recording about 30 thousand measurements (1-2 seconds measuring time) and 
calculating the average value of the about 30 thousand measurements. The 
results are shown as follows: 
______________________________________ 
Average Appearing Accumulation of 
pH times appearing times 
______________________________________ 
4.6287 2 2 
4.6288 17 19 (2 + 7) 
4.6289 22 41 (19 + 22) 
4.6290 54 95 (41 + 54) 
4.6291 41 136 (95 + 41) 
4.6292 23 159 (136 + 23) 
4.6293 12 171 (159 + 12) 
4.6294 1 172 (471 + 1) 
4.6295 2 174 (172 + 2) 
______________________________________ 
Two curves (normal distribution and accumulation distribution) were made 
according to the above data, as shown in FIG. 5. In FIG. 5, the horizontal 
axis stands for the average pH values. The vertical line at each average 
pH value represents the number of times an average pH value appears; the * 
at each average pH value represents the accumulation of the appearing 
times of average pH values less than or equal to the average pH value. It 
can be seen from FIG. 5 that the distribution of experimental data fits 
the theoretical distribution represented by curves I and II. The standard 
deviation is 0.0002.