GB2054164A

GB2054164A - Automatic Titration Apparatus

Info

Publication number: GB2054164A
Application number: GB8020705A
Authority: GB
Original assignee: Mitsubishi Kasei Corp
Current assignee: Mitsubishi Kasei Corp
Priority date: 1979-06-25
Filing date: 1980-06-24
Publication date: 1981-02-11
Also published as: IT8049040A0; IT1129019B; FR2459975A1; DE3022639A1; NL8003526A

Abstract

An electric signal from electrode 3 corresponding to a state of a titrating system is amplified (4) and subtracted from the output of a controlled end point setter (5) and the difference signal is converted into frequency significant pulses which are applied to a pulse motor (9) driving a titration burette (10) and to a counter display unit (16). The loop gain of the system may be set by potentiometer 7, and frequency divider 11 may be used to reduce the number of pulses from converter 8 that reach the stepping motor. Reagent concentration setter 13 and multiplier 14 may be used so that the counter 16 readout is in concentration units. <IMAGE>

Description

SPECIFICATION Automatic Titration Apparatus The present invention relates to a titration apparatus, and more particularly an automatic titration apparatus in which the state of a titration system is detected electrically and a resulting electric signal is used to drive a pulse motor for operating a burette.

Among prior art methods of controlling a titration apparatus a method of manually controlling the apparatus while observing the concentration (colour of a reagent, detection electrode potential, etc.) of the titration system is known. For example, according to one known method, titration is manually controlled by ON.OFf control of a burette driving motor while observing the variation in the polarization potential of a titration system. Such a control method, however, is not only not automatic, but also can not accurately determine the end point and effect rapid control.

Accordingly, it is an object of this invention to provide a novel automatic titration apparatus that can accurately control the end point of the titration at high speeds and at high efficiencies and without passing through the end point, or hunting.

According to this invention, there is provided an automatic titration apparatus comprising a detector for electrically detecting a state of a titration system to generate an electric signal; an amplifier for amplifying the electric signal; a controlled end point setter for the titration system; a subtractor for subtracting an output of the controlled end point potential setter from an output of the amplifier; a converter for converting an output of the subtractor into an output pulse proportional thereto; a pulse motor driven by the output pulse; a titration burette driven by the pulse motor; and a counter for counting the number of the output pulses.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a block diagram showing one example of an automatic titration apparatus embodying the invention; Fig. 2 is a block diagram showing a modified embodiment of this invention, and Fig. 3 is a block diagram showing the pulse multiplier utilized in Fig. 2.

A preferred embodiment of this invention which is illustrated in Fig. 1 comprises a titration cell 1 containing a liquid to be titrated which is constantly stirred by a motor driven stirrer 2. A detection electrode 3 (for example, a pH electrode, an ion electrode or a platinum electrode) is immersed in the liquid in the titration cell 1 so as to electrically detect a state of a system to be controlled in terms of voltage or current. The detection electrode 3 is connected to the input terminal of an amplifier 4 and the output thereof is supplied to one input of a subtractor 6, the other input thereof being connected to the output terminal of an end point potential setter 5 acting as a controlled end point setter of the system being controlled. Where a state of the system is detected in terms of current it is usually converted into voltage by the amplifier 4.The subtractor 6 subtracts the output of the end point potential setter 5 from the output of the amplifier 4 and the difference, i.e., the output of the subtractor 6 is applied to a converter 8 to be converted into a pulse having a frequency proportional to the difference. The output pulse of the converter 8 is applied to a pulse motor 9 to drive the same in proportion to the number of pulses, thus driving a titration burette 10 at the end of the control operation. Since the amount of drive of the pulse motor (i.e., the amount of titration) is determined in proportion to the number of pulses supplied to the pulse motor, it is possible to know the amount of operation, (i.e., the amount of titration) of the titration burette 10 by displaying on a counter 16 the number of the output pulses from converter 8.

The titration operation with the automatic titration apparatus described above is performed in the following manner. After pouring a predetermined amount of the liquid being titrated into the titration cell 1, the titration operation is commenced. Then, an electric signal corresponding to a definite substance in the liquid, for example the concentration of hydrogen ions is supplied to the amplifier 4, and the amplified output thereof is applied to the subtractor 6 together with the output of the end point potential setter 5 which has been set with a predetermined end point potential of the titration system. The difference output of the subtractor 6 is converted into a pulse by the converter 8 to drive the pulse motor 9 and the titration burette at a speed corresponding to the variation in the state of the liquid being titrated.More particularly, at the initial stage of titration, the burette 10 is driven at a high speed, but as the titration proceeds to a point close to the end point the speed is decreased. As the output of the end point potential setter 5 becomes equal to that of the amplifier 4, the output of the subtractor 6 becomes zero to reduce the output of the pulse motor 9 to zero to stop the pulse motor 9 thus terminating the titration. The amount of titration reagent required for each titration operation can be determined by the count of the counter 1 6 which counts the number of the pulses utilized to drive the pulse motor 9 because the amount of titration per one pulse is determined by the size of the titration burette and the angle of rotation of the pulse motor.

According to a more advantageous embodiment, means for automatically correcting or compensating for the concentration and the factor of a liquid to be titrated is also provided as shown in Fig. 2 in which elements corresponding to those shown in Fig. 1 are designated by the same reference numerals. The embodiment shown in Fig. 2 is different from that shown in Fig.

1 in the following points. Thus, a potentiometer 7 is inserted between the subtractor 6 and the converter 8 for determining the loop gain of the titration system, in other words, for varying the output of the subtractor 6 when the response speed of the titration system varies or when detection is delayed. Furthermore, a frequency divider 11 is connected between the converter 8 and the pulse motor 9 for adjusting the number of pulses supplied to the pulse motor 9 thereby adjusting the amount of titration per one pulse applied to the pulse motor. It should be understood, however, that the frequency divider 11 is not always necessary.Since the amount of titration effected by the burette is determined in proportion to the number of pulses applied to the pulse motor, it is possible to read directly the corrected amount of the titration effected by the burette 10 (analyzed and measured amount in ,ug, mg or milli equivalent) by supplying the output of the converter 8 to a multiplier 14 where the output is multiplied with the output of a reagent concentration setter 1 3 and then applying the output 1 5 of the multiplier 14 to the counter 1 6.

Where the sizes and specifications of the pulse motor 9 and or the burette 10 and the ratio of frequency division are selected such that the amount of titration per one pulse of the output of the converter 8 would be 1 O~nml (where n is an integer or zero) and where the reagent concentration setter 13 is set to 1,000, the count of the counter 1 6 displays the amount of titration in a unit of 1 O-"ml.

The reagent concentration setter 13 is used for the purpose of causing the counter 1 6 to display the concentration and the factor of the reagent in terms of corrected analyzed and measured values (yg, mg, or milli-equivalent unit) so that a desired correction coefficient is set in the reagent coefficient setter 1 3 to multiply the pulse input to the multiplier 14.

The construction of one example of the multiplier 14 is shown in Fig. 3 which comprises a pulse generator 17 which produces a high frequency pulse of the order of one to 10 Mega Hz., and AND gate circuit 18, a preset counter 19, a frequency divider 20 and one shot multivibrators 21 and 22. These elements are fabricated as an integrated circuit. More particularly, the outputs of the pulse generator 17, one shot multivibrators 21 and 22, and the preset counter 1 9 are applied to the inputs of the AND gate circuit 1 8 and the output thereof is supplied to the preset counter 19 and the frequency divider 20. The output of the one shot multivibrator 21 is also supplied to the preset counter 19 and the output of the one shot multivibrator 22 is applied to the one shot multivibrator 21 and the preset counter 1 9.

In operation, a concentration (factor) of the titration reagent is set in the reagent concentration setter 13. Each time a pulse is inputted to the one shot multivibrator 22 from converter 8, the preset counter 19 is reset by the one shot output of the one shot multivibrator 22.

Then by the output of the one shot multivibrator 21 the value set in the reagent concentration setter 13 is loaded, i.e., preset in the preset counter 19 and at the same time the AND gate circuit 1 8 is enabled to apply the high frequency pulse generated by the pulse generator 1 7 to the preset counter 1 9 so that the preset counter counts down until the preset value is reduced to zero. Then by a borrow output signal of the preset counter 1 9 the AND gate circuit 18 is disabled to block the high frequency pulse.

The high frequency pulse applied to and counted by the preset counter 19 is also applied to the frequency divider to undergo a frequency division of 10-" (where n=1, 2, 3,...) and the output of the frequency divider 20 is sent to counter 1 6 also acting as a display device. The ratio of frequency division of the frequency divider 11 is selected to be equal to the unit of the least significant digit to be set in the concentration setter 1 3.

The actual titration operation with the apparatus shown in Figs. 2 and 3 is generally the same as that of the embodiment shown in Fig. 1.

It will be clear that the titration apparatus of this invention is applicable not only for measuring moisture but also for such automatic titration utilizing a liquid or gaseous titration reagent as, for example, a neutralization titration, an oxydation reduction titration, a chelete titration or a precipitation titration.

As above described according to the automatic titration apparatus of this invention a proportional control is possible in which at the commencement of the titration, the titration is made at a high speed (in a large amount) according to the concentration of the liquid to be titrated, as the end point is approached, the titration is made at a low speed (in a small amount) and at the end point the titration speed is reduced to zero, thus automatically stopping titration. This eliminates indefinite end point obtain with the prior art apparatus. In addition, when compared with an arithmetical operation control with a computor or an intermittent waiting time control, the invention makes it possible to effect titration more readily, and at higher speeds and efficiencies. Moreover, the measurement and display of the amount titrated can be made digitally with simple means in terms of volume, weight or equivalent value by merely counting the number of pulses.

Claims

1. An automatic titration apparatus comprising a detector for electrically detecting a state of a titration system to generate an electric signal; an amplifier for amplifying the electric signal; a controlled end point setter for the titration system; a subtractor for subtracting an output of the controlled end point potential setter from an output of the amplifier; a converter for converting an output of the subtractor into an output pulse proportional thereto; a pulse motor driven by the output pulse; a titration burette driven by the pulse motor; and a counter for counting the number of the output pulses.

2. An apparatus according to claim 1 wherein the counter also provides a display.

3. An apparatus according to claim 1 or 2 further comprising a multiplier connected between the converter and the counter, and a titration reagent concentration setter, the multiplier multiplying the output pulse of the converter with a concentration of a titration reagent set by the titration reagent concentration setter.

4. An apparatus according to claim 1, 2 or 3 which further comprises a potentiometer connected between the subtractor and the converter, the potentiometer acting to decrease the output of the subtractor.

5. An automatic titration apparatus substantially as herein described with reference to Figure 1 with or without reference to Figures 2 and 3 of the accompanying drawings.

5. An apparatus according to claim 3 or 4 wherein the multiplier comprises a high frequency pulse generator, and a preset counter which is preset with a set value of said reagent concentration presetter each time a pulse is generated by said high frequency pulse generator and then counts down the preset value according to the pulse.