JP2000509143A - Method and apparatus for detecting the presence of a liquid on a reflective surface using modulated light - Google Patents

Abstract

SUMMARY OF THE INVENTION The present invention is a method and apparatus for detecting the application of a droplet to a transparent reaction chamber or other reflective surface in the presence of ambient light and transient movement of the chamber. . The light source (4) is modulated by the modulator (3) at a fixed or variable modulation rate to two or more discrete levels. These levels include off-levels where there is no light from the light source. Light from the light source is reflected by a light detector (5), and the light reflected by the light detector (5) is sampled at least once for each modulated light level. The difference between the modulation level and the off level represents the reflectivity of the surface or chamber. The reflectivity changes as liquid enters the chamber or is applied to the surface. This causes a detectable change between the modulation level and the off level. Ambient light simply shifts the absolute value of the level. The difference in amplitude is compared to a threshold to determine if a change in reflectivity has occurred that is sufficient to indicate the presence of liquid. If such detection is made over three or more complete modulation cycles, the presence of liquid is reported.

Description

DETAILED DESCRIPTION OF THE INVENTION     Method and apparatus for detecting the presence of a liquid on a reflective surface using modulated light Technical field   FIELD OF THE INVENTION The present invention relates generally to the field of detecting changes in reflected light in the presence of ambient light. In particular, the application of liquids to reaction chambers with reflective or highly reflective surfaces It is concerned with detecting the usage. Background art   Varying levels of light reflected from surfaces in various biomedical applications It would be highly desirable to be able to detect when it happened. This is Oberhardt ) Described in U.S. Pat. Nos. 4,849,340 and 5,110,727. Especially when it is desired to detect the application of a liquid to the reaction chamber as Useful for   Accurately measure the time between the start and end of a biochemical reaction in a reaction chamber In order to determine, it is necessary to know the exact start time of the reaction. By Overhart In a reaction of the type taught, a drop of blood or serum is placed in a chamber. Is the start time. The application of this liquid causes the refractive index or absorption of the chamber The rate changes. This changes the amplitude of the reflected light.   Conventional methods for detecting this change have an absolute value greater than a predetermined fixed threshold. It was only determined that the level of reflected light had increased or decreased. This method is Due to changes in ambient light reaching the detector and due to vibration or movement of the chamber. It is easy to generate a trigger by mistake. For example, if a flash or shadow change enters the detector , The system will falsely trigger and start timing the reaction early. Also, anti The reaction chamber is mounted on some kind of backing card, False triggers also occur when the card is slightly moved relative to the dispenser. this Yo The move is Becton Dickinso in Rutherford, NJ Vacutainer manufactured by Becton Dickinson (R) Alpha Sai at Southeastern Pennsylvania inserted DIFF-S manufactured by Alpha Scientific Before a blood dispenser such as AFE® delivers a drop of blood or serum Occurs when touching the surface of the test card.   It is very sensitive to changes in reflected light, but very insensitive to changes in ambient light, It is highly desirable to have a detection method that is insensitive to vibration and transient movement of the reflecting surface. No. Disclosure of the invention   The present invention provides for static application of droplets to a transparent reaction chamber or other reflective surface. In transient or changing ambient light conditions and with transient chamber movement Including methods and apparatus for doing so.   The light source is modulated to two or more discrete levels at a fixed or variable modulation rate. These levels include an off level at which no light is output from the light source. Light source The light is reflected from the reflective surface to a photodetector. The output of this detector is Are sampled sequentially at least once.   The sample value from the detector, which represents the off-level, is proportional to the amount of ambient light entering the system. For example. Difference between other modulation levels and off-level represents surface or chamber reflectivity . When liquid enters the chamber or is applied to the surface, a difference in refractive index or absorption The reflectance changes. This allows for on-level illumination even in the presence of large amounts of ambient light. A change occurs in the difference between the level and the off level. However, the difference is variable only with ambient light. The amplitude of all levels simply increases or decreases.   Determine if reflectivity has changed enough to indicate that liquid has been applied The difference between the amplitudes is compared to a threshold. If one or more differences have changed sufficiently, The stem reports that liquid has been detected.   Since there is a possibility of long-term drift, take the moving average of the difference, and You may make it compare with this average value instead of a value.   Also, large reflections or ambient light can cause the optical detection system to have the brightest modulation level. The present invention senses this condition and may detect one or more differences. Changes can be ignored. BRIEF DESCRIPTION OF THE FIGURES   For a more complete understanding of the invention, it is shown in more detail in the accompanying drawings, in which: Reference should be made to the examples described below by way of illustration.   FIG. 1 is a block diagram of the present invention.   FIG. 2 shows a light source, a reflective surface that is part of a reaction chamber, and a photodetector.   FIG. 3 shows the light level data from a three-state modulator sampled in the presence of ambient light. FIG.   FIG. 4 is a state diagram of an embodiment of the modulator.   FIG. 5 is a schematic diagram of an embodiment of a modulator.   FIG. 6 is a flowchart of a possible detection program.   It is to be understood that this invention is not necessarily limited to the particular embodiments illustrated. Must understand. BEST MODE FOR CARRYING OUT THE INVENTION   FIG. 1 is a block diagram of the present invention. Timer 1 is periodic at a given repetition rate Generate a strong signal. This timer 1 is well known in the field of digital technology Type 555 for generating periodic signals, or other capable of generating periodic signals Of the type described above.   A repetition rate between 400 Hz and 1200 Hz to give satisfactory results I understood. If a rate of about 833 Hz is used, the modulation rate of the present invention will be described later. It is 10 mS as shown.   Timer 1 is a programmable logic device that generates a set of control signals. Drive (PLD) state machine 2. This state machine 2 has a discrete This can be achieved by means of a trick, an integrated circuit, or other digital means. these The control signal drives a modulator 3, which is configured by a TAW. TRW Electronic Components Group )), A light source 4 similar to infrared LED, type OP290 Control. Wavelengths other than infrared can also be used. The light source is off level (light None) and at least one on-level is generated. Two on The level allows proper detection of liquid application in the presence of ambient light. Not only that, it can function with a wide dynamic range of ambient light and reflected light levels.   Light from the LED 4 is reflected from the surface in question to the photodetector. This optical test The dispenser is, for example, a PIN die manufactured by Siemens. Aether, type BP104BS. If it is sensitive to the light from the light source 4, Any photodetector can be used. The current output of the photodetector is converted to a voltage, It is amplified by a well-known transconductance amplifier in the field. This voltage The signal is supplied to an analog input of the A / D converter 7. In one embodiment of the present invention, A PIN diode is used as a photodetector. Other photodetectors known in the art, such as lasers, photodetectors, etc. Will make. By Texas Instruments Use a similar optical / frequency converter in the similar circuit to the TSL 230 being manufactured You can also.   The A / D converter is a 10- or 12-bit converter that performs conversion at a speed of 100 kHz or more. It can be composed of a heat exchanger. A / D converters are well known in the field of data acquisition technology . Manufactured by National Semiconductor hand Not only parallel units such as the ADC12062, but also Maxim Integral Manufactured by Maxim Integrated Products A series unit such as MAX186 can also be used. Use an optical / frequency converter In this case, the A / D converter can be omitted without changing the present invention.   The A / D converter is synchronized with the state machine 8 and has different modulated light levels. One conversion is performed for each. Its digital output is known in the art. A microprocessor that can be configured by any microprocessor or microcontroller It is supplied to the sensor 8. The processor 8 controls the level between the modulation level and the off level. Detect differences, evaluate off-level against the presence of ambient light, calculate moving average, To determine when liquid has been applied to the reflective surface or reaction chamber. You.   The processor 8 can be connected to a port 9 for reporting the detection of a liquid. Alternatively, Simply continue with another program (eg, timing a biochemical reaction) when the delivery occurs I do. The light source outputs a fixed light level for other applications after detection The modulator can be adjusted as follows.   Through standard input / output ports known in the art, the optical The bell can be controlled directly from the processor 8. Implementation of such an alternative In an aspect, the state machine functions are simulated by a processor program. It is. Further, the processor can control the timing and start of the A / D conversion.   FIG. 2 shows a reflection through an opening in an opaque surface 12 with a transparent cover 10. A light source 4 for generating light reaching a surface or reaction chamber 11 is shown. Light from light source 13 is reflected at the surface 11. The specular ray 14 passes through a second aperture in the opaque surface 12. Enters the photodetector 5.   FIG. 3 shows the modulated light that would appear at the output of the transconductance amplifier 6 (FIG. 1). Indicates the level of In this embodiment, one off level 15 and two on levels 1 A total of three modulation levels, 6 and 17, are used. The first on level 16 is light Represents a medium brightness condition where the source is only about half on. Second on-level 17 Represents a bright state in which the light source is almost completely on. After bright condition 17, above Is repeated indefinitely. The time for each level is between 5ms and 20ms There must be. In practice, a value of 10 ms works satisfactorily. Within the level If one is off level of the light source (no light), then any other sequence of light levels Can be used in the present invention.   When ambient light enters the system, the off-level amplitude 18 detected by the photodetector increases. Ascend. This measured off-level value is directly proportional to all ambient light entering the detector. For example. The other two levels 19 and 20 also rise, but level 19 and off level 1 8 and the difference between level 20 and off level 18 are kept approximately constant. You.   The difference is significant when liquid enters the chamber or is on a reflective surface. It changes intentionally. Levels 21, 22 and 23 are the same as levels 18, 19 and 20 Displays the detection light in the presence of the same amount of ambient light but with liquid in the chamber. are doing. The difference between level 23 and level 21 is the difference between level 20 and level 18. It can clearly be seen that it is greater than the difference between them. Difference between level 22 and level 21 Is the same as when comparing the difference between level 19 and level 18. Change in this difference Is used to detect the presence of liquid on the reflective surface. Differs depending on the type of liquid Increases or decreases as shown in FIG. 3 (not shown). Therefore, the absolute difference The value must be considered and compared to a threshold for detection.   FIG. 4 shows the state of state machine 2 (FIG. 1) that can be used to control the modulation. FIG. It is driven by the periodic output from timer 1 (FIG. 1). Week At each rising edge of the periodic signal, the state machine 24, labeled S0-S7, changes state to one. Go forward. If the periodic signal is about 833 Hz, the S0-S7 state machine 24 One cycle is completed in about 10 ms. State machine 24 is known in the art. Is a Mealy-type sequential circuit (Mealy Machine) that leaves state S7. Activate the second state machine 25 labeled F0-F3 and advance its state by one. Let Therefore, every cycle of the S0 to S7 machine 24, the F0 to F3 machine 2 5 advances one step. F0 to F3 machines 25 are S0 to S7 machines 24 Each time a complete cycle is repeated three times, one cycle is completed. Therefore, If the periodic signal from timer 1 (FIG. 1) is about 833 Hz, F0-F3 The thin 25 completes one cycle in about 30 ms.   The S0-S7 state machine 24 performs the conversion when passing through state S6 (27). Will provide the signal to the A / D converter. The S0-S7 state machine 24 converts this Moore-type sequential circuits, all of which are well-known in the digital arts, (Moor Machine) (output by state) or Mealy type sequential circuit (Mealy Machine) (Output by state transition).   F0-F3 state machine 25 can drive two control lines to modulator 3 (FIG. 1). Wear. These control lines indicate that the light source is off in state F0 (28) and state F0 (28). 1 (29), the light source is medium brightness, and in state F2 (30), the light source The brightness is large. Thus, the F0-F3 state machine 25 separates the light source. And the amount of light reaching the photodetector.   The state machine shown in FIG. 4 is merely representative of the controls needed to drive the modulator Things. This particular embodiment shows that the modulator has three brightness levels that increase sequentially. To have a state of. Other state machines and modulation schemes are included in the present invention. Any It is possible to use a number of brightness levels and arrange them in any order. all It is not necessary that all levels have the same duration. An important feature of the present invention is One of the bells is to indicate the off state of the light source. This level enters the photodetector. Provide information about the amount of ambient light   The state machine of FIG. 4, or any state machine that can control the modulator, is PLDs manufactured by Cypress Semiconductors , Type 22V10 or its equivalent. Also, S It can be composed of cleat integrated circuits or components, which are themselves micro It can also be a processor or a microcontroller.   FIG. 5 is a schematic diagram of some possible embodiments of the modulator. Control lines 37 and 38 Comes from the state machine PLD. If an off-state is required, these control lines Both go high. If medium brightness is required, one of the lines Goes high and the other goes low. If maximum brightness is required, both Line goes low. Control lines 37 and 38 are 74ACT244 integrated circuit 3 1 (74AC244 will also work well). This circuit Usually used as a bus driver, but when its control line is high, its output 3 4 has a very high impedance with respect to the ground (tri-state). If Input is low (ground) 35 and the control line is low (enabled). Output 34 will have a very low impedance to ground. But Thus, this element functions well as a ground switch.   Output line 36 connects to LP2951 manufactured by Micrel. Current control lead of a similar constant current source (pin 7). This constant current element Used to drive the light source so that the amount of current on the light source 36 determines the brightness of the light source. It is. Two resistors 32 and 33 are provided in parallel with each other and in series on line 36 I have. These resistors are connected to the output of 74ACT 244 (34). did Thus, when both enable lines 37 and 38 are high, 74ACT 244 is off. It becomes open, and no current flows through the line 36. As a result, the light source is turned off. . One of the enable lines, for example, line 37 is low and the other enable line is low. When high, only half of the 74ACT 244 is turned on, and current flows through one of the resistors ( In this example, the current flows only through the resistor 32). In this state, the brightness of the light source is halved Become. When both enable lines 37 and 38 are low, both halves of 74ACT 244 The minute is turned on and the current flows through the resistors 32 and 33 combined in parallel. In this case, the brightness of the light source increases. Thus, line 3 from the state machine 7 And 38, the state of the brightness of the light source is set. In this embodiment, , There are only three brightness states, so that any number of brightness states can be obtained. A similar modulator can be constructed. Also, departures from the spirit and scope of the present invention. Use any high quality analog switch instead of 74ACT244 without the need it can. The resistors 32 and 33 provide the required brightness level for the light source used. To be selected. Resistors 32 and 33 are typically about 100-300 ohms .   FIG. 6 shows a flowchart of a program used to detect the application of a liquid to a surface. It is a chart. For the purpose of FIG. 6, the A / D converter is a new modulated brightness level. One sample is provided for each of the bells, and there are three levels of brightness. Assume that When the program of FIG. 6 starts, the first sample arrives And then determine which level it represents. Ambient light Because any sample value can change, the program 3 samples (ie all levels) to synchronize with the data stream Must be captured. Synchronization step 39 consists of the first three (different Samples at different levels). Compare them and order them by size. From this ordering, determine when the next sample representing the off-level will arrive. This many samples are then delayed for synchronization. Control light level generation If a processor is used for synchronization, no synchronization is required.   After synchronization, the program divides the data samples into groups of three in this example. Continuously capture as The program must first be calibrated before detection takes place. (40). This is the difference between the amount of ambient light present and the level present. It means establishing a baseline. At this point, if there is no liquid on the surface You have to make an assumption. If a very large amount of ambient light is present, the program Will determine to wait to calibrate (42). If the ambient light is reasonable, The program consists of several groups of corresponding samples (samples representing the same level). Will simply average and establish a baseline. Or each level An operation will be started to determine a moving average or a moving average of the difference between the levels. This The moving average of the difference between the bells will lead to long-term drift in the system that does not represent the application of the liquid. The effect is to follow slowly. If you use a fixed average, the program Must be recalibrated from time to time to prevent false triggering from long-term drift (41).   Once a baseline or moving average has been established, the program will be incremented by three (or Continue to capture groups (by number of levels used). New complete For each group, the latest difference is used to detect large changes. Compare with in difference. Judge "hit", that is, a state where there is a large difference between both For this purpose, the absolute value itself obtained by comparing these differences is compared with a threshold value. This is the first This is performed in step 43. Three more samples were taken, and at step 44, "H Search for " If no hits were found, count hits And the program behaves as if no "hit" had occurred. (46). If a second subsequent "hit" is detected in step 44, Take three samples and check for the third "hit" in step 45 . If there is no third hit, reset the "hit" count and program Restarts the operation as if no "hit" occurred (46). Third If a subsequent "hit" is detected in step 45, a trigger is declared. This This means that liquid was detected. Report that liquid was detected or Exit the routine after declaring a trigger to perform the rest of the assay. (47).   Statistics of three consecutive "hits" eliminate random fluctuations and provide accurate fluid The probability of body detection can be increased. Long-term drift by using moving average of difference Makes it possible to set threshold values with higher sensitivity without generating false triggers. You. Three consecutive “hits” to combat fast flashes and transient chamber movements To make the system insensitive. According to the difference method, DC ambient light and 60Hz (or 50Hz) Hz) even in the presence of incandescent light, the device according to the invention is not affected by them. I can do it.   Depending on the surface, a high response may cause the photodetector to saturate at the brightest level. Has an emissivity. The present invention relates to the case where the brightness level is higher than a predetermined absolute value. Compensates for this by ignoring its brightest levels. in this case , Based on the difference between the remaining level and the off level. This state If detected, the threshold may be changed. To prevent false triggering, If only one ON level remains, the threshold is usually slightly increased. Alternatively, the brightest level may be lowered until the light comes out of the optically saturated state. This Dynamic reduction of the brightest light levels, such as Is required.   The above apparatus is merely illustrative of the application of the principles of the present invention and will be apparent to those skilled in the art. Other devices are conceivable without departing from the spirit and scope of the invention.

────────────────────────────────────────────────── ─── Continuation of front page    (81) Designated countries EP (AT, BE, CH, DE, DK, ES, FI, FR, GB, GR, IE, IT, L U, MC, NL, PT, SE), OA (BF, BJ, CF) , CG, CI, CM, GA, GN, ML, MR, NE, SN, TD, TG), AP (KE, LS, MW, SD, S Z, UG), EA (AM, AZ, BY, KG, KZ, MD , RU, TJ, TM), AL, AM, AT, AU, AZ , BB, BG, BR, BY, CA, CH, CN, CZ, DE, DK, EE, ES, FI, GB, GE, HU, I S, JP, KE, KG, KP, KR, KZ, LK, LR , LS, LT, LU, LV, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, S D, SE, SG, SI, SK, TJ, TM, TR, TT , UA, UG, US, UZ, VN (72) Inventor God Levski, Gregory, S.             United States 27615 North Carolina             Old English, Raleigh, Na             New Court 1124 (72) Inventor Buck, David, Tee.             United States 27615 North Carolina             Falcon Resta, Raleigh, Na             Vehicle 7744

Claims (1)

[Claims] 1. An apparatus for detecting the application of a liquid to a light reflecting surface in the presence of ambient light, the apparatus comprising: The reflective surface is of the type used to perform a solidification assay;   Light source,   A plurality of intensity levels, including an off-level of zero intensity, connected to the light source. Modulation means for amplitude modulating the light source for   A photodetector that generates an electrical signal proportional to the intensity of the light,   Liquid acceptable, positioned to reflect light from a light source to a photodetector A reflective surface,   It is connected to a photodetector and synchronized with the modulating means, and controls each of the intensity levels. Converting means to generate at least one intensity sample,   Measure the difference between the intensity sample representing the light level and the intensity sample representing the off level. Processing means, wherein the difference is proportional to the reflectivity of the reflective surface in the presence of ambient light Processing means,   Reporting means for reporting the presence of liquid on the reflective surface when the difference has changed by a predetermined amount. Including equipment. 2. 2. The apparatus according to claim 1, wherein said conversion means is an A / D converter. 3. 2. The device according to claim 1, wherein said converting means is an intensity / frequency converter. 4. Processing means for determining the intensity of ambient light from the intensity sample representing the off level The device according to claim 1. 5. The device according to claim 1, wherein the light source is a light emitting diode. 6. 6. The device according to claim 5, wherein the light emitting diodes emit infrared light. 7. The apparatus of claim 1, wherein said processing means is a microprocessor. 8. An apparatus for detecting the application of a liquid to a light reflecting surface in the presence of ambient light, the apparatus comprising: The reflective surface is of the type used to perform a solidification assay;   At least one on-amplitude level and one off-level that occur at a given time A light source to be modulated;   Reflective surface and light detection positioned to reflect light from a light source to a light detector Vessels,   Responds to the amplitude level from the photodetector and measures the difference between the amplitude level and the off level. Processing means for calculating the difference, the difference representing the reflectance of the reflective surface, Representing light, said processing means applying the liquid on the reflecting surface when said difference changes by a predetermined amount. A device that reports 9. Detect liquid application to reflective surfaces that is insensitive to ambient light and transient movement of reflective surfaces. A device that emits   Each level has three different levels: off level, intermediate level, and bright level. A light source for generating light that is sequentially modulated so as to be held for a predetermined period,   A light detector;   A reflective surface capable of receiving liquid, which reflects light from a light source through the reflective surface to a photodetector. A reflective surface positioned to radiate,   Connected to the photodetector and synchronized with the light source, at least for each modulation level An A / D converter that sequentially generates one sample value;   Measure the amount of ambient light from the off-level sample values, and The first difference between the sample value at the intermediate level and the sample value at the intermediate level From the second difference between the bell sample values, measure the surface reflectivity proportional to these differences. Processing means for determining   Report application of liquid on the surface when the first and second differences change by a predetermined amount And reporting means. 10. The apparatus of claim 9, wherein the processing means is a microcontroller. 11. The device according to claim 9, wherein the light source is a light emitting diode. 12. The device according to claim 9, wherein the photodetector is a PIN diode. 13. 10. The device according to claim 9, wherein the light detector is an intensity / frequency converter. 14． Apply liquids to reflective surfaces insensitive to ambient light and transient movement of reflective surfaces A method of detecting,   Modulate light source at a given time to generate discrete amplitude levels, including off levels Steps to   Light from a light source is reflected on a reflective surface that can receive liquid and is incident on a photodetector. Steps   The output of the photodetector is sampled at least once for each of the different modulation levels. Pulling,   Compare the difference between the modulation level and the off level to determine the amount of ambient light and the liquid Measuring the change in the reflectivity of the reflective surface indicating the application of the method.