SOLUTION LOADING ANALYZER

Abstract: A portable, battery powered instrument for measuring the amount of material dissolved in a liquid solution employs electro-optic technology based on the Beer-Lambert Law. A sample probe (14) is inserted in a solution to be measured. The results of the measurement are displayed on a display (22). The displayed results are frozen for a predetermined period of time at the expiration of which, the power is turned off to conserve battery power.

Description: SOLUTION LOADING ANALYZER DESCRIPTION BACKGROUND OF THE INVENTION Field of the Invention The present invention generally relates to chemical analysis instruments and, more particularly, to a portable, battery powered ' instrument for measuring the amount of material dissolved in a liquid solution. Description of the Prior Art Determination of the amount of material dissolved in a liquid is typically a difficult problem. Visual estimation is inaccurate at best and totally wrong at worst. Laboratory determination is inconvenient, time consuming and expensive. However, the penalty for having too much or too little material in a solution can be serious. The printed circuit board industry, for example, has need to measure the amount of photoresist dissolved in developer or stripper baths. Many other industrial solutions such as used in plating, chemical milling, paper making, waste water monitoring, etc., require frequent monitoring by measurement. In the past, this has been done by taking samples of the solution and submitting the samples to a laboratory for analysis using, for example, a spect ophotometer . Spectrophotometers are expensive, precision instruments and do not provide the quick and easy results often demanded in a production environment. SUMMARY OF THE INVENTION It is therefore an object of the subject invention to provide an instrument capable of the direct measurement of the amount of material dissolved in a solution. It is another object of the invention to provide a portable, battery powered instrument which can be used in a production environment for making direct readings of the amount of material dissolved in a solution. According to the present invention, these objects are attained by a rugged and portable, battery powered instrument which employs electro- optic technology to measure the amount of material dissolved in a liquid solution. A ruggedized sample probe is inserted in a solution to be measured. The results of the measurement are displayed on a large readout, such as a liquid crystal display (LCD) . A feature of the invention is that it can be precalibrated to measure several different liquids. In a preferred embodiment, the precalibration feature supports three liquids. Calibration is simple and requires no special training. The operating principles of the instrument are based on the Beer-Lambert Law which states that the optical absorbance of a solution is proportional to the concentration of the material dissolved in it. A light of selected wavelength is passed through the solution to be analyzed. A photodetector senses the amount of light passing through the solution, and electronic circuitry performs the necessary computations to calculate optical absorbance and associated concentration. BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects, aspects and advantages of the invention will be better appreciated from the following detailed description of a preferred embodiment of the invention with reference to the drawings, in which: Figure 1 is a pictorial illustration of the solution loading analyzer according to a preferred embodiment of the invention; and Figure 2 is a block and schematic diagram of the electronic circuitry of the solution loading analyzer shown in Figure 1. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION Referring now to the drawings, and more particularly to Figure 1, there is shown a preferred embodiment of the solution loading analyzer according to the invention comprising a a case or housing 10 with a carrying handle 12 and an attached probe 14. The probe is composed of a probe head 16, a handle 18 and a cable 20 connected between the handle 18 and the housing 10. The preferred construction of the probe head 16 and handle 18 is of polypropylene with VYCOR optical windows and silicone rubber window seals. The entire probe 14, including the cable 20, can survive complete immersion in most caustic industrial solutions for short periods. The probe 14 is also mechanically rugged and can generally survive being dropped on a hard surface. The housing 10 has on one face thereof a digital display 22, which in the preferred embodiment is a liquid crystal display (LCD) . On the top of the housing 10 adjacent one end of handle 12 is a push button switch 24, while adjacent the other end of the handle 12 is a rotary switch 26. On one side of the housing 10 is an access panel 28 which may be opened to reveal screw driver adjustments for potentiomenters used to precalibrate the instrument. In operation, the probe 14 is held in the operator's right hand and inserted into the solution to be measured. Testing is initiated by depressing push button switch 24. This may be done with the thumb of the left hand which grasps the handle 12. The measurement is made automatically and the result is displayed in digital form on display 22, in appropriate units such as ft^- mil/gal, gram-moles/liter, % loaded, etc. Three separate calibration settings are available by means of rotary switch 26 so that up to three different solutions may be measured with a single instrument. The operating principles are based on the Beer-Lambert Law which, by convention, is expressed by the following equation: logiθ( I / I o) = -εcx, where I is the intensity of the light through the sample, I 0 is the intensity of the incident light, ε is a proportionality constant, c is the concentration of material in solution, and x is the thickness of the absorber. Absorption is described quantitatively as the log of the ratio of measured light to incident light as expressed in the following equation: A = -log(I/I 0 ) = +εcx. In the subject invention, light of selected wavelength is passed through the solution which fills a gap 30 in the probe head 16. A photodetector senses the amount of light passing through the solution, and electronic circuitry, shown in Figure 2, within the housing 10 compares the transmitted value of light with the incident value. Analog circuitry performs the necessary computations to calculate the optical absorbance and associated concentration. The result is converted to a digital form and displayed in appropriate units on display 22. Calibration is simple. During calibration, the sample probe 14 is inserted in a solution which contains no dissolved material. The solution does not have to be visually clear. A ZERO potentiometer is adjusted to provide a zero reading on the display 22. The probe 14 is then inserted in a solution of known concentration. A corresponding SPAN potentiometer is adjusted to provide the value of the known concentration on the digital display 22. This procedure is repeated for each different solution which, for the preferred embodiment, is three different solutions. As mentioned, the instrument is battery powered. A feature of the preferred embodiment is that the display 22 is activated with a "LO BAT" indication when battery charge is less than 10% of full charge. A charger can be attached to the instrument for charging the batteries and providing a visual indication of charging status. However, the circuitry is designed to automatically turn off after a predetermined period of time in order to prevent undue battery drain. More specifically, when the push button switch 24 is depressed, a period of five seconds elapses before the measurement is frozen on the display 22. This is announced with a beep from a built-in speaker. After thirty seconds has elapsed, the power to the circuitry is automatically turned off unless the switch 24 is depressed during this period. Turning now to Figure 2, the dotted line 32 represents the probe head 16. It contains an ultraviolet fluorscent light source 34 connected via cable 20 to a power supply 36. In the preferred embodiment, the light source 34 and power supply 36 are models BF959 and BF12V, respectively, manufactured by JKL Components Corp. of Pacoima, California. The probe head also contains photodetectors 38 and 40 which are provided with ultraviolet filters (not shown) so as to be responsive to only preselected wavelengths of light from light source 34. The photodetectors 38 and 40 may be SD100-13-13-022 devices manufactured by Silicon Detector Corp. of Newbury Park, California. Photodetector 38 receives the light which is transmitted through the sample solution, while photodetector 40 measures the incident light from light source 34. The photodetectos 38 and 40 are connected across the input terminals of respective operational amplifiers 42 and 44. Both of these amplifiers have capacitive negative feedback provided by capacitors 43 and 45, respectively, as well as resistive negative feedback to provide the desired transfer function for amplification of the signals from photodetectors 38 and 40. The resistive feedback for amplifier 42 is provided by a resistor 46 and potentiomenter 47; however, the resistive feedback for amplifier 44 is provided by a resistor 48 connected by a switch 49 to one of three potentiomenters 50, 51 and 52. These potentiometers are used for the ZERO adjustment calibration of the instrument as described above. The outputs of the operational amplifiers 42 and 44 are connected to inputs of a real-time analog computational unit (ACU) 53. This is an AD538 integrated circuit (IC) device manufactured by Analog Devices, Inc., as described in their "Data Acquisition Databook Update and Selection Guide 1986". This device is a real-time computational circuit which provides precision analog multiplication, division and exponeniation. Programming of the device is by pin strapping. As used in the preferred embodiment of the invention, the output voltage V 0 is proportional to ~ ~ -ogχo (\ ~ z/ ~~ x ) t where V z is the voltage of the signal output by amplifier 42 and V x is the voltage of the signal output by amplifier 44. The output of ACU 53 is connected to the input of operational amplifier 54 having both capacitive and resistive negative feedback. The capacitive feedback is provided by capacitor 56, while the resistive feedback is selectable by switch 26 to be either potentiometer/resistor combinations 59/60, 61/62 or 63/64. The SPAN potentiomenters 59, 61 and 63 are used to calibrate the instrument for any of three different solutions as previously described. The output of the operational amplifier 54 is supplied to the input of analog-to-digital (A/D) converter 66 which has a display/hold feature. The preferred embodiment of the invention uses an ICL7116 IC manufactured by Intersil Corp. This A/D converter 66 is specially designed to drive an LCD display 68 and contains not only an analog-to- digital converter for converting the analog voltage output of operational amplifier 54 to a digital value, but also the seven-segment decoder/drivers required to drive the display 68. Power to the circuitry is supplied by a battery 70 which is rechargable via a recharger (not shown) that is connected to the battery by means of a jack 72. The positive terminal of battery 70 is connected to the emitter of NPN transistor 74 and also through primary winding of transformer 76 to the d.c. input terminal of power supply 36. A pair of one-shots 78 and 80 are activated by pressing the push button switch 22. The first of these one-shots 78 has a thirty second time out period during which time transistor 74 is biased into conduction to supply battery voltage to series connected voltage regulators 82 and 84 supplying, respectively, regulated positive and negative voltages to the circuitry. At the end of the thirty second time out period, the transistor 74 reverts to its nonconducting state turning off the power to voltage regulators 82 and 84. The second one-shot 80 is powered from the collector of NPN transistor 74 and turns off after a five second delay. In doing so, the gate voltage to field effect transistor (FET) 86 is turned off so that the light source 34 is therefore energized only for a five second duration at the beginning of the thirty second time out period of one-shot 78. The output of one-shot 80 is also connected to one input of an exclusive OR gate 88, connected as an inverter, which actuates the hold feature of A/D converter 66. This causes the display to be frozen after five seconds, thus facilitating easy reading of the measurement. This is announced to the user by a beep produced by a speaker 90 which is connected to amplifier 92. The input of amplifier 92 is connected to an RC differentiator circuit 94 which produces a pulse output from the output of one-shot 80. Connected across the battery and to the test output of A/D converter 66 is a low voltage sensing circuit 96. This circuit may be an ICL8212 IC manufactured by Intersil Corp., for example. If the battery charge falls below 10% of full charge, circuit 96 forces the output of display 68 to display a "LO BAT" indication, and the instrument can not be used until the battery is recharged. While the invention has been described in terms of preferred embodiment, those skilled in the art will appreciate that the invention can be practiced with modification within the spirit and scope of the appended claims.

Claims: CLAIMS Having thus described our invention, what we claim as novel and desire to secure by Letters Patent is as follows: 1. A portable, battery powered solution loading analyzer for measuring the amount of material in a liquid solution comprising: probe means for insertion into a solution, said probe means including light source means for generating light radiation and first and second photodetector means for receiving, respectively, light transmitted through the solution and incident light from said light source means; computation means connected to receive signals respectively from said first and second photodetector means for computing the negative logarithm of the ratio of said signals and generating an output signal; and display means connected to said computation means and responsive to said output signal for displaying a value proportional to said output signal. 2. The portable, battery powered solution loading analyzer recited in claim 1 further comprising control means for supplying battery power to said probe means, said computation means and said display means for a first predetermined period of time, turning off power to said probe means and freezing a display on said display means after a second predetermined period of time shorter in duration than said first predetermined period of time and then turning off power at the expiration of said first predetermined period of time. 3. The portable, battery powered solution loading analyzer recited in claim 2 wherein said control means comprises first and second one shots activated simultaneously, said first one shot having a delay period equal to said first predetermined period of time, and said second one shot having a delay period equal to said second predetermined period of time. 4. The portable, battery powered solution loading analyzer recited in claim 2 further comprising audible means activated by said control means at the expiration of said second predetermined period of time for sounding an indication that a measurement may be read from said display means. 5. The portable, battery powered solution loading analyzer recited in claim 2 further comprising. selectable gain means connected between said computation means and said display means for permitting the selection of a plurality of precalibrated corresponding to a plurality of different solutions. 6. The portable, battery powered solution loading analyzer recited in claim 5 further comprising first and second amplifier means connected, respectively, between said first and second photodetector means and said computation means for amplifying the signals generated by said first and second photodetector means, said first and second amplifier means including calibration means for providing a zero adjustment of the analyzer for each of said selectable gains. 7. The portable, battery powered solution loading analyzer recited in claim 6 wherein said selectable gain means includes calibration means for providing a span adjustment for each of said selectable gains.

Inventors: CASACIA EDWARD A, MAY JOE T, CASACIA, EDWARD, A., MAY, JOE, T.
Applicants: ELECTRONIC INSTRUMENTATION AND, ELECTRONIC INSTRUMENTATION AND TECHNOLOGY, INC.
Application year: 1988
Main classification: G01N21
IPC codes: G01J1, G01N21