Principle and Common Fault Analysis of SN-697B Radioimmuno γ Counter

1 Instrument principle

The dual probe radioimmuno gamma counter is a device used for medical sample measurement. It is a kind of nuclear instrument field, a high-tech industry produced by nuclear science combined with electronic technology, computer technology and other fields of technology. It is a knowledge.

Intensive, technology-intensive, widely used and cost-effective industries. The development and equipment level of nuclear instruments reflect the level of national productivity to a certain extent, along with the deepening of China's reform and opening up and the development of the socialist market economy. This industry will be more fully developed, and the research on nuclear instruments has gradually evolved from the original specialization and modularization to the direction of industrialization and integration. In recent years, the bioactive compound microassay technology has entered a new era of radioimmunoassay from the era of chemical measurement, because of its high sensitivity. It has strong specificity, low blood volume, good repeatability, accuracy and reliability. It has become an indispensable equipment for basic medical clinical diagnosis. The intelligent dual-probe radioimmunoassay counter meets the needs of biochemistry, endocrinology, pharmacology, immunology, molecular biology, microbiology, and clinical medicine. Instrument principle as a block diagram:

The machine uses upper double tube measurement. The speed is twice as fast as a single tube, and the dual probe automatic efficiency correction is used. The whole machine consists of four parts: probe, sample drive, main engine and auxiliary machine. The probe includes a lead chamber, a scintillation crystal, a photomultiplier tube, and a preamplifier.

The sample transfer section consists of an input control device, a sample drive, and a motor. The input control device consists of five infrared light control sensors, which respectively act to advance the sample into position, the sample horizontal direction step control, the lift motor upper position, the lower position

Control, sample advance and retreat control. The sample transmission section is composed of four motors and their power and motor drive circuits. These motors act on forward, backward, horizontal and lift, respectively. The main part includes signal processing circuit, microcomputer interface, high voltage and low voltage

source. The microcomputer consists of the following:

(1) controlling the information acquisition process and storing the acquired data;

(2) Perform efficiency correction on the two probes;

(3) Calculating the acquired data;

(4) output the result to the experimenter;

(5) Control the movement of the sample to be measured to enter and exit the measurement chamber. Auxiliary part

Including experimental project storage, isotope selection, three isotopes are provided: ¹²⁵ I, ⁵⁷ Co, ⁵¹ Cr. Get keyboard information. It consists of the following features:

(1) Display the measured data in real time on the LCD:

(2) providing an experimental operator to edit experimental parameters;

(3) selecting the isotope of the experiment to be performed;

(4) Switch between single probe and double probe.

The machine also has a stable spectrum system. Because the fluctuation of the isotope radiation-proof substance affects the accuracy of the measurement, after the steady-spectrum technique is adopted, the adjustment of the high voltage by the computer enables the measurement of the maximum energy value of the sample, which greatly improves the value. The correctness of the measurement makes the linearity of the standard curve optimal. And the efficiency calibration system is used to keep the two probes consistent. The instrument uses a hardware timing device. It uses a 100K crystal oscillator to perform two l0 divisions in the timer and feeds the count timing for 1000Hz. When recording 1000 pulses, it is one second. According to the time determined by the system, it is judged whether the time measurement is over. Send the count results to the computer. The program uses Intel 8051 assembly language encoding, which accounts for 54K and 15K respectively.

2 instrument common fault analysis

The instrument will inevitably fail during use. The common faults and analysis of the instrument are listed below:

2.1 Electrical and control parts failure:

(1) After the power is turned on, the power indicator does not light up: 1 the power cord is not in good contact; 2 the fuse is bad; 3 the low voltage power supply is faulty; 4 the connection between the single chip and the keyboard is poor; 5 the power supply part of the keyboard board (7805) is bad; The display is broken.

(2) Booting does not work: 1 The internal connector of the instrument is not in good contact; 2 The low voltage power supply and the motor power supply are not normal; 3 The sensor potential is abnormal; 4 The motor control board is faulty; 5 The single chip board is faulty.

(3) Press START after power on to not measure: 1 panel key failure; 2 keyboard board failure; 3 single-chip and keyboard and interface failure; 4 motor and motor interface failure.

(4) There is no tube when there is a tube: 1 sensor s4 fault; 2 motor speed is wrong; 3 timing frequency is wrong.

(5) The sample holder cannot be retracted: sensor S5 is faulty.

2.2 Measurement section:

(1) No counting: 1 measurement circuit board failure or poor contact; 2 no output of high voltage parts; 3 damage of high voltage parts; 4 bad contact of high voltage output cable; 5 +12V of high voltage parts is not normal; 6 probe failure: photoelectric multiplication The tube is damaged, the front output DC level is abnormal (should be 6~7V), the anode output coupling capacitor in the front part is bad; 7 the voltage dividing resistor for the photomultiplier tube is open; 8 12V on the front part or signal cable line contact Not good; 9 MCU counts partial failure or bad contact.

(2) The counting is not normal: 1 high voltage out of control; 2 measuring room pollution; 3 measuring circuit board failure; 4 single chip circuit board failure (timing frequency is not normal).

(3) The background is high: 1 radioactive contamination; 2 NaI crystal aging yellow; 3 measuring circuit board failure.

(4) The counting is unstable: 1 the high voltage output is unstable; 2 the amplification board is faulty; 3 the threshold and the line width voltage are unstable; the timing frequency is unstable in the 4 single-chip circuit.

(5) - Poor probe efficiency consistency: Efficiency correction can be performed again.

2.3 Mechanical part:

(1) Lifting rod top sample holder: The sensor s2 positioning is not adjusted. Remedy: Adjust the horizontal positioning plate and tighten the compression screw.

(2) The top of the sample tube is at the entrance of the probe: the lifting guide column is caught by the protective sleeve and cannot be reset. The test tube cannot be guided because the protective suit is deformed. Handling: Re-adjust the NaI crystal hole and the lead chamber hole concentricity when the probe is assembled, so that the protective cover

No resistance when in place (to prevent deformation of the protective cover).

(3) The lifting motor is not running smoothly: the resistance of the lifting rod is too large. Handling: Clean the lifting slide and add a proper amount of sewing machine oil (4 to 5 drops).

(4) The sample rack has a large cycle and does not enter the measurement room: the s1 baffle is not reset except for the sensor sl', s2 electrical failure. Processing: Check the s1 baffle and adjust it.

(5) The sample holder cannot be retracted, and it collides with s5: Except for the sensor s5 electrical failure, the S5 baffle is not reset. Handling: Check the S5 baffle and adjust.

(6) Sample leakage test: In addition to the sensor S4, S6 electrical failure, the sample bottle height is not enough. Treatment: The height of the vial should be ≥ 60mm.

(7) Booting can not be opened: in addition to electrical reasons. The resistance of the lifting chute is too large. Disposal: Clean the lifting chute and add appropriate amount of sewing machine oil (4-5 drops).

(Medical equipment information LIU Zhen, Chen Longquan)