What is force gauge?
The use of the elasticity of the metal to mark the scale to measure the size of the force is called force gauge
. The force gauge has various forms of construction, but the main part of them all is a bent and elastic steel sheet or spiral spring. When the external force so that the elastic steel or spring deforms, through the lever and another transmission mechanism to drive the pointer rotation, the pointer stops at the position on the dial, that is, the value of the external force.
Spring scale is the simplest kind of force meter
. Use the force meter to lift the object vertically, when the spring dynamometer and the object are stationary, the object is subject to the balance of forces, that is, gravity and tension are a pair of balanced forces, and the size is equal. The object to the dynamometer pull and the dynamometer to the object of the pull force and the reaction force, the size is equal. So, the reading is the gravitational force of the object being measured. According to F = k-X (Hooke's law), the force is proportional to the elongation of the spring.
Type of force gauge
Push pull gauge
A. Anchor cable force gauges
The basic principle of the anchor cable force gauge is to install a high stability and sensitivity strain string sensor or force sensor on the pressure-bearing cylinder, and it is generally believed that the mature string sensor has better zero point stability and stronger anti-interference ability than the strain gauge, while its signal output is frequency instead of voltage, and the frequency signal can be transmitted over long distances without obvious attenuation caused by changes in cable resistance and contact resistance. The signal output is frequency rather than voltage, and the frequency signal can be transmitted over long distances without significant attenuation due to cable resistance and contact resistance variations. On the other hand, despite the above advantages, only a few famous string instrument manufacturers are able to produce truly high-quality and long-term reliable string anchor force gauges due to the unique technical problems involved in the design and processing of string anchor force gauges.
The load acting on the barrel can be measured directly by the string sensors fixed on the barrel.
The use of multiple transducers can reduce or eliminate the effect of uneven or eccentric loads. To ensure reliable fixation of the transducers, spot welding or other techniques are used to securely weld the transducers to the barrel. A thermal thermometer is additionally installed in the barrel to measure the anchor cable force gauge and the ambient temperature in the field. In order to adapt to the harsh conditions of the site, an integral sealing technology is used, which ensures that the anchor cable force gauge can work properly under 2MPa water pressure.
B. Digital force gauge
Digital force meters are widely used in various industries such as pharmaceuticals, cosmetics, food, packaging, automotive, electrical, electronics, and machinery. It is an indispensable force measurement tool in product manufacturing, quality control, and research and development. There is a new type of force meter with perfect data management function, which can be connected to the computer through the USB interface, capable of fast peak measurement of 1000 times/second, and can set the upper and lower limit values to judge whether the product is qualified or not. It can also be used with a force gauge stand to obtain high-precision measurements.
Weighing items through the weight sensor mounted on the mechanism, the gravity into an analog signal of voltage or current, after amplification and filtering processing by the A/D processor into a digital signal, the digital signal by the central processing unit (CPU) computing processing, and the surrounding required functions and various interface circuitry and CPU connection applications, and finally by the display screen to a digital display.
A. Steel string type rebar dynamometer
The principle of operation is derived from the fact that the resonant frequency of a tensioned steel string vibration is proportional to the strain or tension of the string. This basic relationship can be used to measure a variety of physical quantities such as strain, load, force, pressure, temperature, and tilt. The advantage of a vibrating string sensor over a normal sensor is that the output of the sensor is a frequency rather than a voltage. The frequency can be transmitted over long cables (>2000m) without significant signal attenuation due to changes in wire resistance, water immersion, temperature fluctuations, contact resistance, or insulation changes. In addition, the unique design and manufacturing process of Kirkland's vibroseis sensors provide excellent long-term stability, especially for long-term monitoring in harsh environments.
B. Soil pressure box
The soil is composed of tiny particles and the presence of a large number of pores inside the soil gives it the two basic conditions for the presence of microfractures in the soil. It also conforms to the assumption of fracture mechanics that microfractures are inherently present in the material. Under certain stress conditions, the structural connection between soil grains gradually breaks along the weak links, and the microfractures gradually develop into macroscopic cracks, which eventually lead to fracture damage of the soil body.
According to the theory of fracture mechanics, the fracture damage of an object can be divided into the following three basic types of stresses.
a. Open type crack (type Ⅰ) that is, the positive stress and the crack surface perpendicular.
b. Slip-open crack (type II) in the case of shear on the surface of the member or specimen, if the shear stress is parallel to the surface of the crack but its direction of action is perpendicular to the crack side so that the crack is extended by relative slip between the upper and lower sides of the crack.
c. Tearing crack (Type III), shear stress, and crack surface are parallel, and the upper and lower planes of the crack are torn and expanded under the action of shear stress.
C. Pore water pressure meter
The working principle is that the pressurized water in the soil pore space is collected into the pressure chamber through the permeable stone and acts on the pressure-bearing diaphragm. The center of the diaphragm is deflected to cause the stress of the steel string to occur.
Use of force gauge
Specific use of spring dynamometer
A. Before using
a. Pull the spring. Pull the spring repeatedly (excessive force may damage the spring) to prevent it from jamming, rubbing, and colliding.
b. Understand the range. You should know what the maximum range (range) is for measuring force.
c. Identify the division values. Understand the scale of a spring dynamometer. Know how much N is represented by each big frame and the smallest frame.
d. Zero calibration. Check whether the pointer is aligned with the zero scale line, if not, you need to adjust to alignment.
B. In use
a. Do not use over the range. (Balance, measuring cylinder, and measuring cups cannot be used over the range, except for the scale)
Additional note: The use of over-range may damage the spring dynamometer, and cause plastic deformation, resulting in errors. And over-range use will lead to the measurement of the exact force, such as a 6N force, you use a range of 5N spring dynamometer measurement, and the pointer points to 5N, but actually 6N, the error.
b. When measuring the force in the same direction, let the direction of the spring axis inside the spring dynamometer with the direction of the measured force in a straight line, and the spring cannot rest on the dial.
c. The line of sight should be perpendicular to the dial.
C. After use
Adjust the spring dynamometer so that the pointer is aligned with the zero scale line.
a. If the pointer is above or below the zero-scale line, and the pointer is not adjusted to 0 at this time, an error will occur. Above the zero scales, the measured force is smaller than the actual force, and vice versa below the zero scale, the measured force is larger than the actual force.
B. If the spring dynamometer is placed on its side, the measured value will be small.
Pull force gauge
Experimental method to study the relationship between the spring elongation and the applied force
a. The principle and use of common dynamometers. The tool for measuring the size of the force is called a dynamometer, the laboratory dynamometer is a spring dynamometer. The working principle of the spring dynamometer is that within the limits of elasticity, the elongation of the spring is proportional to the amount of tension applied.
b. The measurement range of the spring dynamometer. Each spring dynamometer is marked with the maximum scale value, the maximum scale value that is the measurement range of this spring dynamometer, beyond this range, the spring dynamometer may be damaged.
Range and elastic limit
Spring elongation and tension are proportional to the law of a certain limit, that is, the force added to the spring cannot be too large, after a certain value of tension, that is, beyond the elastic limit of the spring, the spring elongation is no longer proportional to the tension, or even unable to restore the original state. The range of the spring dynamometer is the maximum value of the force allowed to be measured by the spring dynamometer.
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