Linear accuracy is an important index to describe the static characteristics of displacement sensor. On the premise that the measured input is in a stable state, the maximum deviation between the sensor output calibration curve and the fitting line and the percentage of full scale output (linearity is also known as nonlinear error). The smaller the linearity is, the better the linearity of the displacement sensor is and the higher the measurement accuracy is. In order to meet the increasing demand of high-precision measurement and control of automatic equipment servo control system, if the processing technology of in-situ displacement sensor is improved to improve its measurement accuracy and stability, it has also become the target of manufacturers.

The linear displacement sensor based on potentiometer principle is a kind of displacement sensor widely used in automation equipment at home and abroad. The sensor is mainly composed of brush and carbon film plate. The sensor is connected to the measurement and control system by the principle of resistance voltage division, and outputs DC voltage signal. Potentiometer principle linear displacement sensor has the advantages of simple and firm mechanical structure, less affected by temperature, humidity and electromagnetic field, high resolution, low cost, convenient installation and use. The sensor is a contact structure design, absolute position measurement type displacement sensor.

The linear accuracy of linear displacement sensor based on potentiometer principle has nothing to do with the total resistance of sensor, but mainly depends on the resistance uniformity of sensor resistance plate (i.e. linearity). Theoretically speaking, with the increase of ambient temperature, the activity of electrons in the resistance body increases, which will cause the resistance of the sensor to rise. In view of the fact that the influence of temperature rise on the resistance value of the carbon film plate of the sensor is almost the same, the temperature change will not affect the linearity of the signal output of the linear displacement sensor. When the humidity is not saturated, the resistance of the sensor will increase gradually until the humidity value of the sensor increases. Under the action of external electric field and heat, the water molecular film adsorbed by carbon film is broken down or desorbed, and the resistance value of resistance plate can be gradually reduced until it returns to the original state.
 
However, the influence of contact resistance and asymmetric resistance cannot be avoided in the design, assembly and application of linear displacement sensor. For example: resistance change caused by welding process between brush and carbon film plate; contact resistance change between sensor brush and carbon film plate. Therefore, the linear displacement sensor is used for a long time, and the brush and carbon film plate gradually wear, which can cause the sensor resistance value linearity to decline slowly, and then affect the sensor output signal linearity. This phenomenon is more obvious when it is affected by the change of temperature and humidity.
 
In order to improve the linear accuracy of linear displacement sensor, the manufacturer adopts precision engraving to improve the linear degree of resistance value of resistor body (in the early stage, manual engraving is mainly used, but now automatic engraving is mostly used). Welding and assembly process should be standardized as far as possible to reduce the influence of human factors on sensor quality. The brush is usually made of silver palladium alloy and other precious metals. It has good conductivity, thermal conductivity, low and stable contact resistance, high wear resistance, welding resistance and certain mechanical strength. It can reduce the wear of brush and damage to carbon film plate in the process of using displacement sensor. Carbon film board is a mixture of resin and colloidal graphite, which is milled for a long time in strict proportion. Then, it is prepared on the polyimide copper clad laminate insulation substrate by spraying, molding, printing or depositing, and is prepared by drying and polymerization. In order to make the performance of carbon film board stable, but also through the electrical, thermal aging process. The carbon film board substrate should choose the skeleton material with smooth surface, good matching with carbon film material, high and low temperature resistance, good insulation and good mechanical processing performance. The installation and use of the sensor should be standardized to minimize the impact on the performance of the sensor (for example, attention should be paid to the neutral installation of the pull rod type linear displacement sensor. If the deviation is too large, the measurement accuracy and service life of the sensor can be greatly reduced; the sensor can be installed horizontally or vertically. When installing horizontally, the mounting bracket should be slid into the slot, and the fixing screws should be installed downward to prevent In order to prevent the abrasion of the sensor from adhering between the brush and the carbon film plate, increase the contact resistance of the sensor; take appropriate damping measures in vibration or impact situations to reduce the wear of the sensor brush and carbon film plate, etc.). For some special occasions, such as harsh water and oil environment or outdoor use, waterproof linear displacement sensor should be given priority to reduce the impact of external environment on the performance and service life of the sensor.