0 Introduction Micro-injection pump is a commonly used in clinical and life science research, long time asked for uniform microinjection of the instrument. At present, domestic and foreign micro-injection pump is facing difficulties in accuracy and cost is relatively high. Domestic similar products using software to control the accuracy of injection, which led to poor tolerance of the instrument, and can only use a single manufacturer of syringes. The similar foreign products using potentiometer control injection accuracy, to achieve a relatively high accuracy of the potentiometer is very demanding. The sensor is a device or device capable of sensing or responding to the specified measured physical quantity and converting it into an available signal output according to certain rules. The sensor can convert the input variable into an electrical signal for detection and send various parameters to a computer System, intelligent monitoring, control, measurement system is a kind of pre-part. In recent years, sensor applications are moving in two directions, one is the development of a single-function sensor toward the integrated application of multi-purpose sensors; the other is the interface between the sensor and the microprocessor, which not only improves the measurement accuracy and reliability of the sensor but also improves Microprocessor computing accuracy, the two complement each other. At present, sensors have been widely used in various fields such as industry, agriculture, transportation, energy, space, resource development, environmental protection, natural disaster prediction, medical care and cancer diagnosis. This paper studies the application of several sensors in the measurement, selects the sensor such as the capacitive grid sensor for the design of micro-injection pump system, successfully improves the injection precision, and compatible with syringes from multiple manufacturers, enhances the function of the micro-injection pump . This article describes the use of these sensors in micro-syringe pumps. A capacitive grid sensor is a capacitive digital sensor based on variable area working principle that can measure large displacement. Compared with other digital displacement sensors such as grating and inductosyn, it has the advantages of small size, simple structure, High resolution and accuracy, fast measurement speed, low power consumption, low cost and low requirements for the use of the environment, so it occupies a very important position in the electronic measurement technology. With the development of measurement technology towards precision, high speed, automation, integration, intelligence, economy, non-contact and multi-function, capacitive grid sensors are more and more widely used. The system is mainly on the linear displacement measurement, so the use of linear capacitive sensor grid. The capacitive grid sensor is very similar in structure to the parallel-plate capacitor. It consists of a parallel set of parallel plate capacitors arranged in a grid structure. If the periodic signal changes with time, through the control of the electronic circuit, Different phase distributions are applied to the grids of the sequentially arranged grid capacitors, and the induced signals generated at any moment on the other common plate will have the same phase distribution as the excitation signals loaded at that instant. The equivalent circuit of the capacitor formed between the grid of the grid sensor and the plates of the stator grid is shown in FIG. 1, and C1 (x), C2 (x), C3 (x) On the 48 plate and the gate on the corresponding plate constitutes the capacitance, which is a function of the displacement x, assuming a small emitter plate and reflector plate completely covered when the capacitance between the two C0, each small launch When the width of the plate is w, it can be seen from the figure that when 0 ≦ x ≦ w, C 8 x = C 0 x / w C 1 x = C 2 x = C 3 x ) = C 0, C 4 (x) = C 0 (1-x / w), c5 (x) = c6 (x) = c7 (x) = 0. From this we can draw the whole range of the capacitance between the two plates with the displacement x of the law. As can be seen from Fig. 1, when x is any value, a part of the 48 plates on the moving grid always form a capacitance with "ground" (shield plate), and the corresponding input signal source is directly connected to "ground" However, in order to derive the uniform formula of φ (x) (φ (x) is the phase shift of the output signal of the sensor with respect to a certain driving signal) and continuously vary with the displacement x, the derivation does not consider These plates form capacitances to "ground," while still treating them as forming a capacitor to the grid, except that their capacitance is zero at this point. Since these capacitances are zero, the impedance is infinite. The corresponding signal source all falls on these electric capacity, similarly, have no effect on the output signal of the sensor. If the transmission voltage V1 ~ V8 applied to each of the emitter plates of the capacitive sensor is eight sinusoidal alternating voltages with the same frequency and the same amplitude but with a phase difference of π / 4 between adjacent small plates, On the voltage Vf, there is a voltage on the receiving pole Vr. Application of AC circuit theory and Kirchhoff's current law, the interpretation of the equivalent circuit in Figure l, as follows: If Vo represents the amplitude of each emitter voltage, and take 8 signals in the first phase of the signal phase as a reference value , Then: where φ0 is the phase angle of V1. By substituting these quantities and Ci (x) (i = 1, 2, ..., 8) into the above two equations, it can be seen that the output voltage of the capacitive grid sensor is a sinusoidal voltage of the same frequency as the transmitted voltage, A small range of changes, can be approximated as a constant, and the phase ahead of V1 π / 4 + φ (x). Phase displacement φ (x) can be measured with phase-detection circuit to obtain the relative displacement x, we can see capacitive grid sensor is a phase-tracking displacement sensor, the sensor is not sensitive to changes in the amplitude of the input signal, It has good anti-interference ability. Throughout the measurement system, the main function of the capacitive grid sensor is to convert the amount of mechanical displacement into the phase change of the electrical signal, which is then sent to the measurement circuit for data processing. The capacitive sensor is controlled by a precision voltage comparator TLC354 and is powered by a relay. The CPU89C52 provides the required excitation signal and receives the induced signal. The phase difference between the excitation signal and the induced signal is measured by a phase-detection type circuit. Series of changes, you can draw the length of the piston moving distance. 2 photoelectric switch In the design, in order to be compatible with a number of manufacturers of syringes, we have specifically considered the issue of measuring the diameter of the syringe. First, the choice of high-precision CCD optical sensor, but taking into account the main function to detect the diameter of the syringe, and different types of syringe diameter with a step-by-step characteristics, in order to reduce costs, we will replace it with a photoelectric switch is a Electricity sensor, which changes the intensity of light between the transmitter and receiver changes into current changes, that is, the electrical signal → optical → electrical signal conversion, in order to achieve the purpose of detection. Because the photoelectric switch output circuit and the input circuit is electrically isolated (ie, the electric edge), so it can be applied in many occasions. The working principle shown in Figure 2. In this system, we choose the type of photoelectric switch for the HY-301-05, when the locking syringe valve is lifted, respectively, referred to different heights, through the optoelectronic open obscuration and read out the diameter of the syringe. 3 pressure sensor Pressure sensor is the most commonly used in industrial practice of a sensor, and we usually use the pressure sensor is mainly the piezoelectric effect of piezoelectric sensors. At present, many types of pressure sensors, vibration cylinder, quartz Bourdon tube, piezoresistive, strain gauge and so on. The system uses a resistive pressure sensor, its working principle is to be measured non-electrical converted into resistance, measured by measuring the resistance to achieve the purpose of non-electricity. The traditional resistance strain gauge pressure sensor is a combination of a sensitive grid and a flexible sensing element, as shown in Figure 3. should