What Is a Force Transducer?
Force sensor A device that converts the magnitude of a force into an associated electrical signal. Force is the direct cause of changes in material motion. The force sensor can detect mechanical quantities such as tension, tension, pressure, weight, torque, internal stress and strain. Specific devices include metal strain gauges, pressure sensors, etc., which have become indispensable core components in power equipment, engineering machinery, various types of work machines and industrial automation systems. [1]
- Chinese name
- Force sensor
- Foreign name
- force sensor
- Category
- Electronic component
- Make up
- Three parts
- Main classification
- Strain tube
- Force sensor A device that converts the magnitude of a force into an associated electrical signal. Force is the direct cause of changes in material motion. The force sensor can detect mechanical quantities such as tension, tension, pressure, weight, torque, internal stress and strain. Specific devices include metal strain gauges and pressure sensors, which have become indispensable core components in power equipment, engineering machinery, various types of work machines and industrial automation systems. [1]
- The force sensor is mainly composed of three parts:
- 1 --- force-sensitive components (ie elastomers, common materials are aluminum alloy, alloy steel and stainless steel).
- 2 --- Conversion element (the most common is a resistance strain gauge).
- 3--circuit part (usually enameled wire, pcb board, etc.).
- Force can produce a variety of physical effects. Many different principles and processes can be used to design and manufacture force sensors for different needs. The force sensors mainly include: (1) the measured force causes the elastic body (such as a spring, a beam, a bellows, a diaphragm, etc.) to generate a corresponding displacement, and a force signal is obtained through the displacement measurement. (2) The elastic member and the strain gauge together constitute a sensor, and the strain gauge is firmly adhered to the surface of the member. The elastic member is deformed when subjected to force, which changes the resistance value of the strain gauge (when the strain occurs, the geometry and resistivity of the strain gauge changes, resulting in a change in resistance value), and a force signal is obtained through resistance measurement. Strain gauges can be made of metal foil or semiconductor materials. (3) Use piezoelectric effect to measure force. The piezoelectric crystal converts the force directly into a potential difference placed on the electrodes on both sides of the crystal. (4) Force causes the natural frequency of the mechanical resonance system to change, and information about the force is obtained through frequency measurement. (5) Through the balance of the electromagnetic force and the force to be measured, the force information is obtained from the relevant electromagnetic parameters during the balance. [1]
The main categories of force sensors
Force sensor strain tube
- Quartz Force Sensor
- Two or four strain gauges are affixed to the cylinder wall, half of which is stuck to the solid part as a temperature compensation gauge, and the other half is used as a measurement strain gauge. When there is no pressure, the four strain gauges form a balanced full-bridge circuit. When pressure is applied to the internal cavity, the cylinder becomes a "waist-drum", causing the bridge to lose balance and output a voltage that has a certain relationship with the pressure. This sensor can also use a piston to convert the measured pressure into a force to be transmitted to a strain cylinder or through a vertical chain-shaped diaphragm to transmit the measured pressure. The strain tube pressure sensor has a simple structure, convenient manufacturing and strong applicability, and is widely used in the dynamic pressure measurement of rockets, artillery shells and artillery.
Force sensor diaphragm
- Its elastic sensitive element is a round metal flat diaphragm fixed around. When the diaphragm is deformed under pressure, both the radial strain and the tangential strain at the center reach a positive maximum, while the radial strain at the edge reaches a negative maximum, and the tangential strain is zero. Therefore, two strain gauges are often attached to the positive and negative maximum strains respectively, and connected to a half-bridge circuit of adjacent bridge arms to obtain greater sensitivity and temperature compensation. The use of circular foil strain gages (see resistance strain gages) maximizes the strain effect of the diaphragm. The non-linearity of this sensor is significant. The latest product of the diaphragm pressure sensor is the integration of the role of the elastic sensor and the strain gauge in the single-crystal silicon diaphragm, that is, the integrated circuit process is used to diffuse the single-crystal silicon diaphragm to make the resistance bar, and the peripheral fixed structure Into a solid-state pressure sensor (see Piezoresistive sensors).
Force sensor strain beam
- When measuring small pressures, a fixed beam or an equal-strength beam can be used. One method is to use a diaphragm to convert pressure into force and then transmit it to the strain beam through a force transmission rod. In Figure 3, the maximum strain of the fixed beam at both ends is at the two ends and the midpoint of the beam, and the strain gauges are attached to these places. There are other forms of this structure, such as suspension beams and diaphragms or bellows.
Force sensor combination
- In the combined strain pressure sensor, the elastic sensitive element can be divided into a sensing element and an elastic strain element. The sensing element converts pressure into force and transmits it to the most sensitive part of the elastic strain element, and the strain gauge is attached to the maximum strain of the elastic strain element. In fact, the more complicated strain tube type and strain beam type belong to this type. Sensing elements include diaphragms, capsules, bellows, Bourdon tubes, etc. Elastic strain elements include cantilever beams, fixed beams, beams, ring beams, and thin-walled tubes. They can be combined into multiple types according to different needs. Strain pressure sensors are mainly used to measure the dynamic or static pressure of flowing media, such as the pressure of gas or liquid at the inlet and outlet of power pipeline equipment, and the pressure of internal combustion engine pipelines.
- Force Sensors Improve Force Sensor Accuracy-Compensation
- Temperature will cause the strain signals (resistances) of the four strain gauges to change in the same direction and degree.
- Force sensor compensation
- The remaining small residual errors can be corrected by special nickel metal connected to the Wheatstone bridge.
- In addition, strain gages require temperature-sensitivity compensation (TCS). As the temperature changes, the E-modulus of the material will decrease, resulting in strain. In addition, the sensitivity of the strain gauge depends on temperature. Compensation of resistance under high temperature conditions will produce greater voltage drop. This will reduce the output signal of the Wheatstone bridge.
- Under load, the linearity error will also change. This can be done by optimizing the material and structure of the elastomer and selecting precise measurement points.
- A summary of the compensation methods is shown in the figure. In addition to the TKzero and TCS described above, linearity and sensitivity can also be compensated by adjusting.
Application field of force sensor
- The choice of load cell form mainly depends on the type and installation space of the load, ensuring proper installation and safe and reliable weighing. On the other hand, the manufacturer's recommendations must be considered. For the sensor manufacturer, it generally specifies the force of the sensor. Situation, performance index, installation form, structure form, material of elastomer, etc.
For example, aluminum cantilever sensors are suitable for electronic pricing scales, platform scales, case scales, etc .; steel cantilever sensors are suitable for electronic belt scales, sorting scales, etc .; steel bridge sensors are suitable for track scales, automobile scales, etc. Load cells are suitable for truck scales, dynamic track scales, large tonnage hopper scales, etc.
Load cells are mainly used in various electronic scales, industrial control fields, online control, safety overload alarms, material testing machines and other fields. Such as electronic truck scales, electronic platform scales, electronic forklifts, dynamic axle load scales, electronic hook scales, electronic pricing scales, electronic steel scales, electronic track scales, hopper scales, batching scales, canned scales, etc.
How to replace a force sensor
- During the actual use of the load cell, it sometimes encounters overload, impact, etc., causing plastic deformation of the sensor and affecting the accuracy of the measurement. In severe cases, it can also cause the sensor to be damaged and cannot be used normally. At this time, the sensor needs to be replaced. What should we do now? What else do I need to pay attention to when replacing? The following experts share this issue with you.
The premise that the load cell can be replaced is that the axis of the applied force coincides with the axis of the force of the sensor. This is the first point.
As the rated load increases, the microvolt / dividing signal output by the load cell decreases, rather than the output signal increases as the rated load increases. This is often overlooked. Therefore, when replacing the sensor, use the sensor with the same load as possible. If you want to replace the slightly larger load, you must pay attention to whether the scale of the weighing scale of the electronic scale is adjustable: If it is an old display instrument that is not adjustable, the microvolt / division signal will be output because it is replaced by a sensor with a larger load. It becomes small and cannot be output or displayed at full scale. The dial adjustment cannot achieve the purpose and cannot be used. If it is a load cell with adjustable range and replaced with a larger load sensor, you can set the range and debug according to the instructions. use. At the same time, it should be noted that if the rated load of the sensor is too large, the output microvolt / dividing signal is too small, it is easy to reduce the sensitivity of the scale.
For electromechanical combined scales with S-shaped sensors installed in the second force transmission link, it should be noted that the length of the link after re-installing the sensor is the same as the original link length. On the other hand, it is necessary to ensure that the first force transmission lever is horizontal and the linkage is perpendicular to the first force transmission lever at a 90 degree angle. If there is a deviation, it will directly affect the accuracy and sensitivity of the scale. If the length of the link is too long, the phenomenon of "large scale" will appear; if it is too short, the phenomenon of "small scale" will appear. At this time, it should also be noted that the link must be in a free hanging state, and must not be rubbed with other objects, so as not to affect the sensitivity of the scale.
In the debugging of the electromechanical combined scale after the sensor is replaced, the instruction of the weighing display instrument should be performed on the basis of the accurate adjustment of the mechanical scale.
Whether it is an electronic scale or an electromechanical combined scale, after the sensor is replaced, it must be qualified before being used.
The above solutions are effective for S-shaped sensors in addition to general load cells. The situation that the load cell needs to be replaced is often encountered during use. As long as the above operation is performed, even if the sensor is replaced, it will not affect the measurement.