KR100389252B1 - Method and apparatus for detecting liquid presence on a reflecting surface using modulated light - Google Patents

Abstract

The present invention relates to a method and apparatus for detecting the application of liquid droplets into a transparent reaction chamber or other reflective surface in the presence of ambient light and transient motion of the chamber. will be. The light source 4 is modulated by the modulator 3 to two or more discrete levels of fixed or variable modulation rates. These levels include off levels when there is no light from the light source. Light from the light source is reflected into the photo detector 5 and sampled at least once for each modulated light level. The difference between the modulated level and the off level indicates the amount of reflectance of the surface or chamber. The reflectance changes as liquid enters the chamber or is applied to the surface. This causes a detectable change between the modulated level and the off level. Ambient light only shifts the absolute level. The amplitude difference is compared against a threshold to determine if the reflectance has changed sufficiently to indicate the presence of the liquid. If such detection appears for three or more complete modulation cycles, liquid is reported to be present.

Description

METHOD AND APPARATUS FOR DETECTING LIQUID PRESENCE ON A REFLECTING SURFACE USING MODULATED LIGHT}

In many biomedical applications, it is highly desirable to be able to detect when the level of reflected light from a surface has changed. This is particularly useful when it is necessary to detect the application of a liquid to a reaction chamber, such as the chamber described by Oberhardt in US Pat. Nos. 4,849,340 and 5,110,727.

In order to accurately measure the time interval between the start and end points of the biomedical reaction in the reaction chamber, the initial time of the reaction must be known. In the various types of reactions described by Oberhardt, the start time is when a drop of blood or serum is placed in the chamber. The application of this liquid causes the chamber to have different refractive indices or absorptivity. In either case, the reflected light beam will change in amplitude.

Conventional methods for detecting such changes have only investigated the increase or decrease of the reflected light level whose absolute value is greater than a predetermined fixed threshold. These methods are very sensitive to the change in ambient light reaching the detector and false triggering due to vibration or movement of the chamber. For example, changes in the flash or shadow entering the detector can cause a pseudo trigger of the system to trigger premature response timing. A pseudo trigger can also occur when the reaction chamber is mounted on a kind of support card and when the card is slightly moved relative to the light source or detector. This operation was performed by a blood dispenser, such as DIFF-SAFE (R) from Alpha Scientific Corporation in southeastern Pennsylvania, attached to Vacutainer (R) manufactured by Becton Dickinson, Rutherford, NJ, to deliver a drop of blood or serous fluid. This may occur if the surface of the test card is contacted prior to dispense.

It is highly desirable to have a detection method that is very insensitive to changes in reflected light but very insensitive to changes in ambient light and insensitive to vibrations or transient motion of the reflecting surface.

FIELD OF THE INVENTION The present invention relates to the field of detecting changes in reflected light in the presence of ambient light, in particular in a reaction chamber having a reflecting surface or having a highly reflecting surface. It relates to the field of detecting the application of a liquid to a chamber using modulated light.

DETAILED DESCRIPTION For a more complete understanding of the present invention, embodiments are exemplified with reference to the accompanying drawings and other examples of the present invention will be described in detail below.

1 is a block diagram of the present invention.

2 shows a light source, a reflective surface that is part of the reaction chamber, and a photo detector.

3 is a timing diagram for sampled light levels from a three-state modulator in the presence of ambient light.

4 is a state diagram for an embodiment of a modulator.

5 is a schematic diagram of an embodiment of a modulator.

6 is a flow chart of a possible detection program.

It is to be understood that the invention is not necessarily limited to the specific embodiments illustrated herein.

The present invention includes methods and apparatus for detecting the application of liquid drops into a transparent reaction chamber or other reflective surface in the presence of static or changing ambient light conditions and instantaneous movement of the chamber.

The light source is modulated into two or more discrete level states with a fixed or variable modulation rate. These levels include off levels with no light emitted from the light source. Light from the light source is reflected from the reflecting surface to the photo detector. The output of this detector is sampled at least once in sequence for each modulation level.

The sample value from the detector indicating the off level is proportional to the amount of ambient light entering the system. The difference between the other modulation levels and the off level is indicative of the amount of reflectivity of the surface or chamber. When liquid enters the chamber or is applied to the surface, the reflectance changes due to the difference in refractive index or the difference in absorption. This causes the difference between the on level and the off level to change even when the ambient light is large. Ambient light alone, however, will not cause this difference to change, it merely shifts the amplitude of all levels up and down.

The amplitude difference is compared against the threshold to determine if the reflectance has changed sufficiently to indicate that liquid has been applied. If one or more of the differences have changed sufficiently, the system will report that the liquid has been detected.

Running averages may keep the difference because there may be a long term possibility of drift, and changes in the difference may be compared against these averages rather than some initial absolute value.

In addition, since large reflections or ambients may lead the light detection system to the saturation of the brightest modulation level, the present invention can detect such a condition and ignore changes in one or more differences. Can be.

1 is a block diagram of the present invention. The timer 1 generates a periodic signal at any predetermined repetition rate. This timer 1 is for generating a periodic signal using a type 555 known in the digital art, or any type of unstable oscillator capable of generating a periodic signal.

Repetition rates between 400 Hz and 1200 Hz proved satisfactory. When a repetition rate of approximately 833 Hz is used, the modulation rate of the present invention is 10 mS as described later.

The timer 1 drives a programmable logic device state machine (2) that generates a set of control signals. This state machine can be realized in discrete logic by integrated circuits or by any other digital method. These control signals drive a modulator 3 that controls a light source 4 similar to the OP290 type infrared LED manufactured by TRW Electronic Components Group (ECG). Other wavelengths beyond infrared can be used. The light source may be driven to generate an off level (no light) and at least one on level. In the presence of ambient light it has been found that providing two on-levels is not only suitable for detecting application of liquid, but also available for the operation of a wide dynamic range of ambient and reflected light levels.

Light from the LED 4 is reflected back from the surface to a light detector such as a PIN diode of type BP104BS manufactured by Siemens. Any photo detector that reacts to light from the light source 4 can be used. The current output of the photo detector is converted into a voltage and amplified by a known transconductance amplifier. This voltage signal is supplied to the analog input of the A / D converter 7. Although one embodiment of the present invention uses a PIN diode as a photo detector, any of the known photo detectors, including photomultiplers, linear arrays or photo detectors, will operate. An optical-frequency converter similar to the TSL230 manufactured by Texas Instruments may be used in a similar circuit.

The A / D converter may be a 10 or 12 bit converter that converts at a rate of 100 kHz or faster. A / D converters are known in the data acquisition art. Parallel units such as the ADC12062 manufactured by National Semiconductor, as well as serial units such as the MAX186 manufactured by Maxim Integrated Products, can be used. If an optical-frequency converter is used, the A / D converter can be omitted without changing the present invention.

The A / D converter converts once for each different modulated light level in synchronization with the state machine 8. The digital output is supplied to a processor 8 which can be any known microprocessor or microcontroller. The processor 8 executes a program that takes the difference between the modulation level and the off level, evaluates the off level during the presence of ambient light, calculates a moving average, and compares the difference against the threshold when the liquid is reflected Or is applied to the reaction chamber.

The processor 8 may be connected to a port 9 that reports the detection of a liquid or may only continue another program (such as the timing of a biomedical reaction) when a determination is made. After detection, the modulator can be adjusted to cause the light source to output a fixed light level for other applications.

It is possible to control the light level of the modulator directly from the processor 8 via known standard input / output ports. In an alternative embodiment the function of the state machine is simulated in the program of the processor. The processor may control the timing and initiation of the A / D conversion.

FIG. 2 shows a light source 4 for generating light which is sent to the reaction chamber 11 or the reflecting surface on which the transparent cover 10 is mounted through the aperture of the opaque surface 12. Light from the light source 13 is reflected at the surface 11. Specular reflecte-d rays 14 enter the photodetector 5 through a second opening in the opaque surface 12.

3 shows the levels of modulated light, which levels appear at the output of transconductance amplifier 6 (FIG. 1). In this embodiment three modulation levels are used, one off level 15 and two on levels 16 and 17. The first level 16 represents a medium bright state where the light source is approximately half on. The second on level 17 represents a brightness state in which the light sources are almost all on. After brightness state 17, the sequence is repeated indefinitely. The time for each level should be between 5mS and 20mS, with a true 10mS working satisfactorily. Any other sequence of light levels can be used in the present invention while one of the levels is the off level (no light) of the light source.

When ambient light enters the system, the off level as detected by the photo detector is shifted up to amplitude 18. The value of this measured off level is directly proportional to all ambient light entering the detector. The other two levels 19 and 20 are also shifted up, but the difference between level 19 and off level 18 and the difference between level 20 and off level 18 remain approximately approximately-constant.

The difference varies significantly when liquid enters the chamber or is present on the reflective surface. Levels 21, 22, and 23 represent signals detected in the presence of the same amount of ambient light at levels 18, 29, and 20 but with liquid in the chamber. It can be clearly seen that the difference between levels 23 and 21 is greater than the difference between levels 20 and 18. The foregoing also holds for the difference between level 22 and level 21 compared to the difference between level 19 and level 18. This change in difference is used to detect the presence of liquid on the reflective surface. In addition to the various types of liquids, the difference may increase or decrease as shown in FIG. 3 (not shown). Therefore, the absolute value of the difference must be taken into account and compared with the threshold for detection.

4 is a state diagram of the state machine 2 of FIG. 1 that may be used to control modulation. The state machine is driven by the periodic output of the timer 1 (FIG. 1). At each rising edge of the periodic signal, state machine 24, denoted S0 to S7, emits one state. If the periodic signal is approximately 833 Hz, then the S0-S7 state machine 24 causes one complete cycle to be approximately 10 mS. State machine 24 is, to some extent, a known Mealy Machine and actually remains in state S7, causing second state machine 25, denoted F0-F3, to advance one state. Thus, during every cycle of the S0-S7 state machine 25, the F0-F3 machine 25 goes one step further. F0-F3 machine 25 forms one complete cycle every three completion cycles of S0-S7 machine 24. Thus, the F0-F3 machine 25 completes in a cycle of approximately 30mS if the periodic signal from the timer 1 (Fig. 1) is approximately 833 Hz.

The S0-S7 state machine may signal the A / D converter to convert as it passes state S6 27. The state machine can output this transform command signal to either the Moore Machine (output with state) or the Mealy Machine (output with state transition), both of which are known in digital technology.

State machine F0-F3 25 drives two control lines to modulator 3 (FIG. 1). These control lines have the light source off in state F0 28; In state F1 29 the light source is medium brightness and in state F2 30 the light source is full brightness. State machine F0-F3 25 controls the amount of light leaving the light source and the amount of light reaching the photo detector.

The state machine shown in FIG. 4 merely indicates the type of controller required to drive the modulator. This particular example allows the modulator to have three brightness states that occur in the order of increasing brightness. Other state machines and modulation schemes are included in the present invention. Any number of brightness levels can be used and these levels can be arranged in any order. All of these levels need not be at the same duration. An important feature of the present invention is that one of the levels represents the off state of the light source. It is at this level that provides information about the amount of ambient light entering the photo detector.

The state machine or any state machine shown in FIG. 4 capable of controlling the modulator can be programmed to a PLD of type 22V10 or equivalent manufactured by Cypress Semiconductors. The state machine may also be manufactured in discrete integrated circuits or components, or may itself be a microprocessor or microcontroller.

5 is a schematic diagram of a possible embodiment of a portion of a modulator. Control lines 37 and 38 come from the state machine PLD. These control lines are all high when an off state is required. If a medium brightness state is desired, one of the lines is high and the other is low. If full brightness is desired, both lines are low. Control lines 37 and 38 are connected to integrated circuit 74ACT244 31 (also 74AC244 also operates). This circuit is typically used as a bus driver, but when its control line is high its output 34 exhibits a very high impedance (three phase) to ground. If the input is low (grounded) 35, the control line is low (enabled) and its output 34 exhibits a very low impedance to ground. Thus, these devices perform well as grounding switches.

Output line 36 is a current control lead of a constant current source similar to LP2951 manufactured by Micrel (pin 7). This constant current element is used to drive the light source in such a way that the amount of current on line 36 determines the brightness of the light source. The two resistors 32 and 33 lie in parallel with each other but in line with line 36. These resistors are connected to the output of 74ACT244 34. Thus, when the two enable lines 37 and 38 are in a high state, 74ACT244 is open so that no current flows in line 36 at all. This appears to be off for the light source. When one of the enable lines, such as line 37, is low and the other enable line is high, only half of 74ACT244 is on, and current flows through only one resistor (32 in this embodiment). In this state, the light source is half the brightness. When both lines 37 and 38 are low, the 74ACT244 half is also on so that current flows through the parallel combination of resistors 32 and 33. The light source here is high brightness. Control lines 37 and 38 from the state machine set the state of the brightness of the light source. There are only three brightness states in this embodiment, but other similar modulators may be configured that allow for significant brightness states. In addition, analogue switches of significant quality without departing from the spirit and scope of the present invention may replace 74ACT244. Resistors 32 and 33 are selected and used to achieve the desired brightness level with the light source. These resistances are typically between 100 and 300 ohms.

6 is a flow chart of a program used to detect the application of a liquid to a surface. The purpose of FIG. 6 is to provide one sample for each newly modulated brightness level by the A / D converter, where three brightness levels are present. When the program shown in Fig. 6 starts, the transducer must wait for the first sample to come in and then determine which level this level represents. Since ambient light can change any sample value, the program must take three samples (or all levels) to synchronize with the incoming data stream. Synchronization step 39 takes the first three samples (different levels) coming. The step compares the samples and orders them according to size. From this ordering, the step determines when the next sample representing the off level is approaching and then delays these several samples to synchronize in turn. If the processor is used to control the generation of light levels, no synchronization is necessary.

After synchronization, the program continuously takes data samples in three groups for this example. The program must first adjust (step 40) before detection can occur. This means setting the difference between the baseline of the amount of ambient light encountered and the levels encountered. It is assumed at this point that no liquid is present on the surface. If there is a maximum amount of ambient light, the program may determine whether to wait for adjustment (step 42). If ambient light is appropriate, the program may simply set a baseline by averaging a few groups of similar samples (samples representing the same level), or start a moving average of each level or a moving average of the differences between levels. Moving averages for the differences have the advantage of being able to slowly track any long term drift of the system that does not indicate the application of liquid. If a fixed average is used, the program must be readjusted from time to time to prevent pseudo triggers from long term drift (step 41).

Once a baseline or moving average is established, the program will continue to take groups of three samples (or the number of levels used). With each new complete group, the newest difference is compared to the moving average difference or baseline difference to detect any major change. The absolute value of this comparison to the difference itself is compared to the threshold to determine the "hit" or state, in which case both differences have major changes. Step 43 is first performed. Three or more samples are taken and again a "hit" is investigated in step 44. If no "hit" is found, the "hit" count is reset and the program acts as if no "hit" has occurred at all (step 46). If a second sequential “hit” is detected in step 44, three or more samples are taken and the third “hit” is checked in step 45. If there is no third hit at all, the count is reset and the program resumes as if no hits occurred at all (step 46). The trigger that is meant to be declared. The routine is present if it reports to the routine that a trigger has been declared or if it performs part of an assay (step 47).

Statistics for three "hits" in a row eliminate the random variation, increasing the likelihood of accurate liquid detection. The use of a moving average for the differences allows a more sensitive threshold setting without pseudo triggering from long term drift. Three hits in the row method make the system insensitive to high speed flash and instantaneous movement of the chamber. The method for the difference establishes the invention in the presence of DC ambient light and 60 Hz (or 50 Hz) incandescent lamps.

Some surfaces have considerably higher reflectivity, which may result in the light detector being at the brightest level of saturation. If saturation is greater than some predetermined absolute value, the present invention can compensate for this by ignoring the brightest levels. In this case detection occurs at the difference between the remaining level and the off level. The threshold may change if such a condition is detected. The threshold is usually slightly increased to prevent pseudo triggers only if there is only one remaining in the level. Alternatively, the brightest level may be reduced in amplitude until this level deviates from the light saturation level. This dynamic reduction in the brightest light level is within the scope of the present invention and requires an additional circuit.

The arrangements described above are merely intended to illustrate the application of the principles of the invention, and those skilled in the art will understand that other devices may be devised without departing from the spirit and scope of the invention.

Claims (14)

An apparatus for detecting the application of a liquid to a light reflecting surface of the type used to perform coagulation assays in the presence of ambient light, A light source; Modulation means coupled to the light source to generate a plurality of intensity levels comprising one off level having no intensity by amplitude modulating the light source; A photo detector for generating an electrical signal in proportion to light intensity; A liquid acceptable reflecting surface positioned to reflect light from the light source into the photo detector; Conversion means coupled to the photo detector and synchronized with the modulation means to generate at least one luminance sample for each of the luminance levels; Processing to calculate differences between the intensity samples representing the light level and the luminance samples representing the off level, the difference being proportional to the reflectance of the reflecting surface in the presence of ambient light Processing means; Reporting means for reporting the presence of liquid on the reflecting surface when the difference is varied by a predetermined amount Detection apparatus comprising a. The detection apparatus according to claim 1, wherein the conversion means is an A / D converter. 2. A detection device according to claim 1, wherein said conversion means is an intensity to frequency converter. The detection apparatus according to claim 1, wherein said processing means determines the luminous intensity of ambient light from a luminous intensity sample representing said off level. The detection apparatus of claim 1, wherein the light source is a light emitting diode. The detection device of claim 5, wherein the light emitting diode emits infrared light. The detection apparatus according to claim 1, wherein said processing means is a microprocessor. An apparatus for detecting the application of a liquid to a light reflecting surface of the type used to perform a coagulant analysis in the presence of ambient light, A light source modulated with at least one on amplitude level and one off level, the levels occurring at a predetermined time; A reflecting surface and optical detector positioned to reflect light from the light source into the photo detector; Processing means responsive to an amplitude level from the photo detector for calculating a difference between the on amplitude level and the off level, the difference representing a reflectance of the reflective surface and the off level representing ambient light; And when said difference varies by a predetermined amount, said processing means reports application of liquid to said reflective surface. A device for detecting the application of a liquid to a reflective surface that is insensitive to instantaneous movement of ambient light and the reflective surface, A light source for generating light modulated in sequence to three different levels: off level, mid range level, brightness level, each level being maintained for a predetermined period of time; A photo detector; A liquid acceptable reflective surface positioned to reflect light from the light source from the surface to the photo detector; An A / D converter coupled to the photo detector and synchronous with the light source to sequentially generate one sample value for each modulated level; A processor for determining a surface reflectance from a light amount of ambient light from the off level sample value, and a first difference between a sample value of the brightness level and a sample value of the off level and a second difference between the mid range level and the off level Means, wherein the surface reflectance is proportional to the differences; Reporting means for reporting the application of liquid to the surface when the first and second differences vary by a predetermined amount Detection apparatus comprising a. 10. The apparatus of claim 9, wherein said processor means is a microcontroller. 10. The detection apparatus of claim 9, wherein the light source is a light emitting diode. 10. The detection apparatus of claim 9, wherein the photo detector is a PIN diode. 10. The detection apparatus of claim 9, wherein the light detector is a light intensity-frequency converter. A method of detecting the application of a liquid to a reflective surface insensitive to instantaneous movement of ambient light and the reflective surface, Modulating the light source at a predetermined time to generate discrete amplitude levels in which one level becomes an off level; Reflecting light from the light source on a liquid acceptable reflective surface into a photo detector; Sampling the output of the photo detector at least once for each different modulation level; Comparing the difference between the modulated levels having the off level to determine a change in the amount of ambient light and the reflectance of the reflective surface that may indicate the application of liquid to the reflective surface Detection method comprising a.