Grating sensor uses moire fringes formed by grating to convert angular displacement into photoelectric signal (Figure 2). There are two gratings, one is a fixed grating, and the other is a moving grating installed on the dial shaft. The measured object added to the bearing platform makes the dial shaft rotate through the force transfer lever system, which drives the moving grating to rotate and makes the moire fringe move with it. Using photocell, conversion circuit and display instrument, the number of moire fringes that have been moved can be calculated, and the rotation angle of grating can be measured, so as to determine and read the mass of the measured object.
The code wheel (symbol board) of the code wheel sensor (Figure 3) is transparent glass installed on the dial shaft, on which there are black and white codes coded according to a certain coding method. When the measured object on the bearing platform rotates the dial shaft through the force transmission lever, the code wheel also rotates at a certain angle. The photocell will receive the optical signal through the code wheel and convert it into an electrical signal, then it will be digitally processed by the circuit, and finally the number representing the measured quality will be displayed on the display. Photoelectric sensors used to be mainly used in electromechanical combined scales. Its working principle is to use the proportional relationship between the oscillation frequency f of the capacitive oscillation circuit and the plate spacing d (Figure 6). There are two polar plates, one is fixed and the other is movable. When the test object is loaded on the bearing platform, the leaf spring flexes, the distance between the two plates changes, and the oscillation frequency of the circuit also changes. By measuring the change of frequency, the mass of the measured object on the bearing table can be obtained. Capacitive sensor has low power consumption and low cost, and its accuracy is 1/200 ~ 1/500.
Main advantages
Resistance, inductance and capacitance are three passive components in electronic technology. Capacitive sensor is a sensor that converts the change of measurement into the change of capacitance, which is essentially a capacitor with variable parameters.
Capacitive sensors have the following advantages:
(1) High impedance, low power consumption and low input energy.
(2) Large changes can be obtained, so it has high signal-to-noise ratio and system stability.
(3) The dynamic response is fast, and the working frequency can reach several megahertz. In thick B contact measurement, the measured object can be a conductor or a semiconductor.
(4) The structure is simple, the adaptability is strong, it can work in harsh environments such as high and low temperature and strong radiation, and it is widely used.
With the development of electronic technology and computer technology, the disadvantages of capacitance sensor, such as easy interference and distributed capacitance, have been overcome continuously, and capacitive grating displacement sensor and integrated capacitance sensor have appeared. Therefore, it is widely used in non-electric quantity measurement and automatic detection, and can measure parameters such as pressure, displacement, rotation speed, acceleration, A-degree, thickness, liquid level, humidity, vibration and component content. Capacitive sensor has a good development prospect.
Main Disadvantages Disadvantages 1: High output impedance and poor load capacity.
Disadvantage 2: Nonlinear output characteristics
Disadvantage 3: After the parasitic capacitance affects the stress of the large elastic element, its natural vibration frequency is directly proportional to the square root of the stress. By measuring the change of natural frequency, we can find out the force that the measured object acts on the elastic element, and then find out its mass. There are two kinds of vibration sensors: vibrating wire sensor and tuning fork sensor.
The elastic element of vibrating wire sensor is string. When the measured object is added to the bearing platform, the intersection point of the V-shaped chord is pulled down, the tension of the left chord increases, and the tension of the right chord decreases. The natural frequencies of the two strings vary differently. Find out the frequency difference between the two strings, and you can find out the mass of the measured object. The vibrating wire sensor has high precision, which can reach11000 ~110000, and the weighing range is100g to several hundred kilograms, but it has complex structure, great processing difficulty and high cost.
The elastic element of the tuning fork sensor is a tuning fork. A piezoelectric element is fixed at the end of the tuning fork. The piezoelectric element oscillates at the natural frequency of the tuning fork, and the oscillation frequency can be measured. When the measured object is placed on the bearing platform, the natural frequency of the tuning fork increases due to the direction of tension, and the degree of increase is proportional to the square root of the acting force. By measuring the change of natural frequency, the force of the weight on the tuning fork can be obtained, and then the mass of the weight can be obtained. The tuning fork sensor has low power consumption, the measurement accuracy is as high as110000 ~1/200000, and the weighing range is 500 g ~ 10 kg. As shown in figure 10, the rotor is installed in the inner frame and rotates stably around the X axis with an angular velocity ω. The inner frame is connected with the outer frame through a bearing and can rotate obliquely around the horizontal axis Y, and the outer frame is connected with the engine base through a universal coupling and can rotate around the vertical axis Z. When no external force acts, the rotor shaft (X axis) remains horizontal. When an external force (P/2) acts on one end of the rotor shaft, it tilts and rotates around the vertical axis Z (precession). Precession angular velocity ω is proportional to external force P/2. By measuring ω by detecting the frequency, the magnitude of external force can be calculated, and then the mass of the measured object that produces this external force can be calculated.
Gyroscope sensor has the advantages of fast response time (5 seconds), no hysteresis, good temperature characteristics (3ppm), little influence by vibration and high frequency measurement accuracy, so it can obtain high resolution (1100000) and high measurement accuracy (1/30000 ~/kloc-0). 1. Definition
Digital weighing sensor is an electromechanical conversion device that converts gravity into electrical signals. Mainly refers to a new type of sensor which integrates resistance strain weighing sensor, electronic amplifier (AMC), analog-to-digital conversion technology (ADC) and microprocessor (MCU).
2. Functions and applications
The development of digital weighing sensor and digital measuring instrument technology has gradually become the new favorite in the field of weighing technology, and its advantages such as simple and efficient debugging and strong field adaptability are emerging in this field.
3. s-type definition
As shown in the figure, the S-type weighing sensor is one of the most common sensors, which is mainly used to measure the tension and pressure between solids. It is also commonly called tension and pressure sensor. Because it looks like an S-shape, it is also called an S-shaped load cell. The sensor is made of alloy steel, protected by adhesive seal, convenient to install and use, and suitable for electronic weighing systems such as hanging scales, batching scales and mechanical scales.