The Study On Digital Signal Processor And Gear Pump Of Uroflowmeter Calibration Device

Research BackgroundUrine flow rate is urine volume discharged by urethra per unit of time with a unit of ml per second. Urine flow rate measurement is one of the most widely used urology tests for dysfunction disease, and the application of screening value is of great important, the Chinese medical association uropoiesis surgical department branch recommended it as a necessary method to examine the disease of BPH (Benign Prostatic Hyperplasia), it often used for patients with urinary tract obstruction as preliminary detection, and has an important clinical value.Urine flow rate measurement equipment is uroflowmeter, it is still lack of specification or test standard associated with uroflowmeter calibration at home and abroad, its calibration operation relies mainly on the device’s own calibration procedure, but when there is deviation with the device sensor itself, the credibility of the calibration could not reach the requirements of calibration, which lead to hidden trouble on uroflowmeter in clinical application. International association of urinary control of the technical specification for urine dynamics (good urodynamic practices, GUP) as well as our country the urine dynamics test guide (2010 edition) "(hereinafter referred to as guide) are required once a week of calibration for uroflowmeter, but the recommended approach is relatively rough, only use beaker test simulation method for correction, which only can rough estimate the reliability of the equipment, it has a biggish error in calibration method and do not give the detailed operational details.When uroflowmeter detection error is large, it can affect the doctor’s judge for patients with urinary storage and micturition symptoms, which will affect the decision of the clinical diagnosis and treatment of formulation, which lead to severe clinical effects, therefore science calibration on uroflowmeter is an important guarantee to obtain accurate urine dynamics results, and carrying on corresponding uroflowmeter calibration study is particularly urgent and importantResearch ObjectiveThe purpose of this research is to develop a calibration device which to calibrate uroflowmeters and detail the calibration process, so we can determine the uroflowmeter application quality through effective technical regulations, and make sure the uroflowmeter calibration based on professional measuring instruments and on the basis of quantitative detection, and also make the calibration process accurate and reliable, provides a new method for uroflowmeter calibration.Research ProjectThe approach of this research is as follows:first, according to the human body urination design a flow curve, make sure the curve contains key information such as the maximum urinary flow rate, urine output, and other urinary flow curve information; second, make uroflowmeter calibration device output a water flow in the form of the curve accurately; Finally, input the output of flow calibration device to uroflowmeter, after uroflowmeter measuring, comparing the difference between the output of urine flow rate curve and the input curve, thereby the uroflowmeter calibrated.Content and ProcessAccording to the analysis of urinary flow rate curve and combined with urine flow rate measuring range recommended by the guide, set the urine flow rate calibration range at 9-50 ml/s. At the same time guide points out that the highest resolution urine flow rate is 0.5 ml/s, urine flow rate of the maximum measured value is 50 ml/s, so the error of calibration device should be less than 1%.As the liquid volume pump out by every circle of the gear pump is fixed, so the output flow rate is proportional to the speed, due to the characteristics of gear pump, we employ an E-motor to drive gear pump to obtain different water flow. Under the control of the DSP, the motor driven by high accuracy voltage output by DA, by changing the motor speed can change gear pump output flow, so it can output high precision and stable flow of water according to the set speed.Using DSP as its core, the calibration device is mainly composed by speed control module, flow produce module, data transmission module and power module.Under the control of the DSP, the speed control module output a high precise voltage to the flow produce module according to the form of objective urine flow rate curve, then the gear pump drive water running, in order to produce the target water flow in the form of urine flow rate curve. The feedback pulse signal of motor directly put into processor’s 10 pin, then after calculation and analysis sent to the PC via a serial port. DSP communicate with external DA converter through the SPI, and the UART for data transmission with PC.Our microprocessor is TI company’s DSP and ARM dual-core microprocessor OMAPL138, it mainly control DA converter to output a high-precision voltage, and the communication between DSP and PC via means of serial ports, as well as calculate the feedback pulse simultaneously, it meets the data acquisition accuracy, the efficiency of the transmission and processing power requirements of the calibration system. The flow produce module selects the Italian Fluid-o-Tech company’s all-in-one FG213 gear pumps, the liquid volume pump by every rev of the gear pump is the same, which is 0.9 ml per/rev. When the control voltage is 0.3-5 v, the speed range is 300-5000 RPM (Revolution Per Minute RPM), and the corresponding flow rate is 4.5～52.5 ml/s in theory, which meet 9-50 ml/s of urine flow rate calibration scope, at the same time it can output 0 to 5V DC voltage pulse signal in feedback for the DSP to calculate the real-time speed of the motor. The digital analog converter in this design adopted AD company’s AD5060, its reference voltage provided by the benchmark source chip ADR444BRZ, which can output precise voltage range in 0-4.096 V, it meets the requirement of the control voltage’s range from 0.3 V to 3.5 V, and make the urine flow rate resolution of the output less than 0.5 ml/s.The software of calibration device includes the pulse acquisition module, DAC voltage output module, calculation analysis module and serial interface communication module. The DAC voltage output module output control voltage to the motor according to the preset curve, and then gear pump come into operation, at the same time the pulse acquisition module collected the motor feedback pulse into DSP’s 10 pin, processing module used to calculate the corresponding value of flow rate and integral value, finally processed data send to PC by serial interface communication module for the comparison of experimental results.Testing Experiment(1) First of all, as a calibration tool, urinary flow rate meter calibration device should generate a stable flow in the same condition; Secondly when repeat the test there should no significant difference of the results; Finally by changing the conditions, the system can produce different rate of flow. With DSP as the core, by DA converter, the all-in one gear pump and other machine components constitute a flow test system, we verified the ability of this system in three aspects:stability, repeated precision, and different rate of water flow produced by the system, thus analyzed the feasibility of our scheme.(2)On the basis of the urine dynamics test operation guide (2010 edition) and related document, we designed a flow rate curve complying with the human micturition process. According to the key information of the urinary flow rate curve contains, with the help of MATLAB, we fitting out the urinary flow rate target curve according to the relationship between urinary flow rate and time. Based on this curve, we obtained the voltage curve that DA converter needed, then compare the difference between DAC curve in theory and that actually output.(3) DA converter output the control voltage curve to all-in-one gear pump, after processing the data received by the serial port, use MATLAB to draw the practical and theoretical urine flow rate curve, calculate the maximum urinary flow rates, urine flow volumes and the deviations with the theoretical value respectively. Repeat each condition of test more than 5 times, and then analyze the experimental results.(4) Using this calibration device in two urine flow rate meter- LABORIE and MMS for clinical trials, in each trial, we calibrated linear and curve calibrations.Linear calibration means at a given voltage, the calibration device will output stable water flow to the urinary flow rate meter,and then the water flow will be measured, observe the output flow rate curves and compare their similarity, also to determine the accuracy of indexes such as the time of total flow, flow rate and the average flow rate. Curve calibration refers to measuring urine flow rate meter according to the design curve, testing if the output of urine flow rate curve is in accordance with the expected change rule, and the accuracy of indexes such as maximum urinary flow rate, urine output, and other indicators.Testing Results and Discussion(1)By testing experiments, the calibration system build on the research plan can produce stable, high repeat precision and different rate of water flow, system error is less than 1%, and can be use in calibrate clinical urine flow rate with the scope of 9～ 50 ml/s, this indicate that the test system is feasible when used to construct the urine flow rate meter calibration device.(2)Comparing the actual output voltage curve of DA converter observed by an oscilloscope with the theory voltage output curve fitting by MATLAB, we find the output voltage curve shape of DA converter in practical and in theoretical is consistent, curves are equal in duration, peak voltage, the time reach to highest point voltage, so the theory of the DAC output voltage curve is consistent with the actual output voltage curve.(3)The experimental results shows that the trend in both actual output flow rate curve and theoretical curve is consistent, after many repeated measurement, the actual maximum urinary flow rate and urine flow volume are all close to the theoretical value, the maximum error of maximum urinary flow rate is 0.40%, that of urine flow volume is 0.90%, both of them less than 1% error range. That shows our curve designed reasonably and calibration device can output stably flow rate of required form. Use that water flow as the input of the urine flow rate meter, and compared the input and output curves of the urine flow rate meter, thus the urine flow rate meter is calibrated.(4) The experiment results showed that, as a result of the calibration device outlet placement、height impact to urine flow rate meter weighing system and urine flow rate meter need some time to detected urine flow, and also other factors, the urinary flow time, peak time and the average flow rate cannot controlled, the errors are very big. But the calibration method of the design process of simulating human urine can detect urinary flow rate change rule, and calibrate the most reference value of urine flow rate curve of maximum urinary flow rate and urine output, that shows calibration method and the device has reached the design requirements. By measuring and judge urine flow rate meter maximum urinary flow rate and urine output error range, we can know LABORIE urine flow rate meter in out of control condition, MMS urine flow rate meter performance good. This shows that we can determine urinary flow rate meter application quality through effective technical basis, and our system is stable and reliable.Summarization and OutlookFirst of all, the system integration is not high enough, its volume is huge and hard to move.In particular the gear pump, to prevent the vibration impact on the calibration experiment in the process of operation, the motor is fixed in a thick piece of wood, makes the whole calibration device is not easy to move, the portability of the device needs to be improved. Secondly, due to the limitation of time and experimental conditions, device calibration experiment only involves in weighing type urinary flow rate meter, in the subsequent experiments should widen the scope of the experiment and improve applicability of the device. Thirdly, the design of the calibration device used PC, data analysis adopted the way of MATLAB, it is a bit too heavy, so the embedded system can be directly used in way to do this in the subsequent development, so as to improve the applicability of the device. Fourthly, without any processing, the flow data output by gear pump of calibration device may be interfered by pulsation phenomenon, the result of the experiment may also be influenced, so in late research should regulated the calibration device outlet.