Lengthening and shearing of the sensor cable of th

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Lengthening and shearing of the sensor cable of ultrasonic flowmeter

due to the particularity of the industrial site, the sensor cable needs to be lengthened at some ultrasonic flowmeter installation sites. In some ultrasonic flowmeter factories, the three theft gangs, especially foreign products, prohibit the extension and cutting of sensor cables. If we must adhere to the strategic drive, if we can understand the structural principle of the sensor, we can lengthen and cut the sensor cable without affecting the accuracy of measurement

the resonant frequency of piezoelectric ceramics is about 1MHz, and the ultrasonic flowmeter (water measurement) of domestic manufacturers is basically 1MHz. It is capacitive in impedance characteristics. In other words, the capacitive reactance of two sensors of a set of probes should be consistent in a strict sense, so that the measurement of static (0 point) 2.12 safety protection: it will be more accurate when it exceeds 2 ~ 10% of the maximum load. This is not difficult to analyze. If the sensor cable is cut, the two sensor cables of a set of probes should be cut into the same length to maintain the same impedance characteristics

now let's talk about the lengthening of the sensor cable. Analyze the sensor cable before discussing the extension of the sensor cable. For one sensor in a set of probes, there are roughly two-wire system and three wire system

I 2-wire sensor cables are generally coaxial cables. That is, the center line of coaxial cable is connected to the positive pole of piezoelectric ceramics, and the shielding wire of coaxial cable is connected to the negative pole of piezoelectric ceramics. The coaxial cable with the same specification can be used to lengthen the 2-wire sensor cable. The problem to be noticed is that the lengthened joint should be handled properly. The center line of the coaxial cable is best connected by welding, and the insulation with the shielding wire should be done well. For the connection of the shielding wire, the whole shielding layer at the connection should be wrapped with copper thin, and finally the external waterproof insulation should be done well

II 3-wire sensor cables are generally two-core shielded cables. That is, the two inner cores of the two core shielded cable are respectively connected to the positive and negative stages of piezoelectric ceramics. The shield wire is not connected at one end of the sensor, and it is connected to the terminal position of GND wire on the transmitter of variable LED lighting that is replacing incandescent lamp, halogen lamp and fluorescent lamp lighting system. The general mistake of lengthening the 3-wire sensor cable is to choose a multi-core shielded cable, take three of them to connect the original 3-wire sensor cables respectively, and connect the selected three wires to the corresponding transmitter location. According to the above analysis, such an extended cable has no continuation of the shielding layer, loses the protection of the shielding, and is easily disturbed by the external environment, which is manifested in crash, unstable value, frequent restart and other phenomena. The correct method is to select a two-core shielded cable, take two of the inner cores and connect them to the two inner cores of the original 3-wire sensor cable (the two non ground wires), and then connect the shielded wire to the ground wire of the 3-wire sensor cable. The connection method can refer to the above two-wire sensor cable lengthening connection method, do a good job of shielding wire (wrap the entire shielding layer at the connection with copper thin), and finally do a good job of external waterproof insulation

finally, no matter the lengthening or cutting of sensor cables, the length of two sensor cables of a set of probes should be consistent

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