In the turbine flowmeter calibration interference isolating circuit design application

Speed of turbine flowmeter is a kind of flow meter, which makes use of the rotating angular velocity in the fluid in the impeller and the fluid flow rate is proportional to the relationship, by measuring the rotating speed of the impeller to reflect the size of the volume flow through a pipe. Turbine flowmeter by the turbine flow sensor and flow display instrument ( ) flow totalizer. especially Composition, which can realize the instantaneous flow and cumulative flow measurement. 1. The working principle of turbine flow sensor of turbine flow sensor principle diagram is shown in figure 1. Put a turbine, in the center of the pipe ends is supported by bearings. When fluid through a pipe, turbine blades, on the turbine driving moment, make the turbine to overcome the friction moment and fluid resistance torque and rotation. Within a certain flow range, for a certain amount of fluid viscosity, the rotation of the turbine angular velocity is proportional to the fluid velocity. As a result, the fluid velocity can be obtained through the rotation of the turbine angular velocity, which can calculate the fluid flow through a pipe. Turbine rotating angular velocity is through the sensing coil to detect in a casing. When the turbine blade cutting lines of magnetic force produced by casing * magnets, it could cause sensing coil in the magnetic flux changes. Sensing coil to detect the signals of magnetic flux cycles for preamplifier, the signal amplification, plastic, is proportional to the velocity of the pulse signal, into the unit conversion and flow integrating circuit and display the accumulated flow value; This authorization together with your completed also send a pulse signal to one frequency conversion circuit, current pulse letter to convert analog electrical flow, which indicates the instantaneous flow values. Figure 2 overall principle block diagram for the turbine flowmeter. 2. 2 the turbine flow sensor calibration and real problem. 1 turbine flow sensor calibration method water flow standard device for liquid turbine flow sensor calibration, the accuracy of the device is 0. Level 1. Figure 3 for the turbine flow sensor calibration. When the fluid flows through the turbine sensor, the impeller rotation inside the sensor, pulse converter converts the rotation of the impeller to electrical impulses, pulse counter for verification equipment. Synchronize with commutator device of pulse counter, it will only record the commutator fluid in the number of pulses into work again. In the verification process is completed, read the pulse number and pulse counter work again the actual volume of each check point values obtained the instrument coefficient of each test. JGC198 - according to procedures 94 speed meter verification regulation, each inspection fixed-point test three times and, in turn, it is concluded that all offices shall have to calculate the instrument coefficient of flow point average instrument coefficient, thus it is concluded that the flow sensor in certain flow within the scope of the average coefficient of instrument. 2. 2 calibration problems existing in the process of normal work, the high-speed rotating impeller turbine flow sensor, pulse converter in order to effectively capture each blade rotation, its internal sensing coil and high sensitivity done of the preamplifier, vulnerable to interference and generate additional interference pulse electromagnetic field around, in one pulse with normal pulse superposition transmitted pulse counter, which affects the measurement accuracy. So when installing a turbine flow sensor, well grounded, but in the actual test, only to do ground handling often cannot achieve the purpose of eliminating interference, the main reason is that near the prover, tend to have high power electric equipment, such as water pump motor, fan, electronic ballast of fluorescent lamp, etc. , will be released due to interference of electromagnetic wave, especially now generally adopts frequency converter drive the fluid pump on the fluid source voltage regulator, voltage regulator with the higher harmonic caused by frequency converter power source of pollution is quite serious, such as turbine meter high sensitivity of the equipment will be disturbed. Turbine flow sensor if disturbed, in the process of verification test results generally has the following characteristics: one is the instrument coefficient is bigger than normal, this is because the superposition of the thousands of interference pulse in a calibration pulse counter receives the pulse count a lot more than normal; Another characteristic is poor repeatability, tends to zero. Level 5 of the turbine flow sensor, check out the repetitive reached 2% or more, this is due to the interference of randomness, every thousand scrambling degree is different; There is a poor linearity within range. Table 1 for the verification of a model for LWG80 turbine flow sensor, in the case of interference in mishan. 2. Three measures can be seen from table 1, as a result of the existence of thousands of interference makes verification data migration happens, caused the calibration error. According to the analysis and experiments show that the entry of jamming signal, mainly because the power of the pulse converter is provided by verification device of dc regulated power supply, voltage pulse signal transmitted directly to the pulse counter, the grid of high harmonics in one pass by dc regulated power supply in pulse converter, thus normal pulse series. In addition, pulse converters and cables between pulse counter, also inevitably induction to interference signal. Such interference measures to eliminate a disconnect between pulse converter and prover direct electrical connection, using electrical isolation of the signal transmitted pulse signal transmission mode, can effectively isolate interference pulse to enter. Another use of optocoupler isolation circuit as shown in figure 4, the optical coupler parts is used to isolate the pulse counter with pulse converter, no electrical connection between them, pulse converter by independent isolated power supply, ensure the normal work and normal pulse signal to drive optocoupler, make its can smoothly through the isolation circuit; And 'into the interference signal on load capacity is very low, and mainly is the common mode signal, can't drive optocoupler and quarantined, effectively eliminate the interference.

Beijing Sincerity Automatic Equipment Co., Ltd in the right situation can streamline the entire process, enabling your team to deliver higher quality work in a shorter amount of time.

For more information please see our site at Sincerity Flow Meter. Don't be hesitate to contact us!

Simultaneously being able to offer not only the product but also the service, gives the customer a quality 'one-stop-shop' service.