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technical article
Characteristics of sensors and transmitters (4)
2011-7-26 8:38:53

变送器 的特点(四) Characteristics of sensors and transmitters (4)
 
电容式物位变送器 4. Capacitive level transmitter
Capacitive level transmitter is suitable for industrial enterprises to measure and control the production process during the production process. It is mainly used for long-range continuous measurement and indication of liquid level or powdery solid level of conductive and non-conductive media.
Capacitive liquid level transmitter is composed of capacitive sensor and electronic module circuit. It is based on two-wire 4-20mA constant current output. After conversion, it can be output in three-wire or four-wire mode. 5V, 0-5V, 0-10mA and other standard signals.
Capacitive sensors consist of insulated electrodes and a cylindrical metal container with a measuring medium.
When the material level rises, the dielectric constant of non-conductive materials is significantly smaller than the dielectric constant of air, so the capacitance changes with the height of the material.
The module circuit of the transmitter is composed of units such as reference source, pulse width modulation, conversion, constant current amplification, feedback and current limiting.
The advantages of using the pulse width modulation principle for measurement are low frequency, good RF interference to surrounding elements, good stability, good linearity, and no obvious temperature drift.
超声波变送器 5.Ultrasonic transmitter
Ultrasonic transmitters are divided into general ultrasonic transmitters (without meter heads) and integrated ultrasonic transmitters. Integrated ultrasonic transmitters are more commonly used.
The integrated ultrasonic variable updater is composed of a meter head (such as an LCD display) and a probe. This transmitter that directly outputs a 4-20 mA signal is a combination of a miniaturized sensitive component (probe) and an electronic circuit. Make it smaller, lighter and cheaper.
Ultrasonic transmitters can be used for level. Level measurement and open channel, open channel and other flow measurement, and can be used to measure distance.
 
锑电极酸度变送器 6. Antimony electrode acidity transmitter
     Antimony electrode acidity transmitter is an industrial online analysis instrument integrating PH detection, automatic cleaning, and electrical signal conversion. It is a PH value measurement system composed of antimony electrode and reference electrode.
     In the tested acidic solution, as the antimony trioxide oxide layer will be formed on the surface of the antimony electrode, a potential difference will be formed between the antimony metal surface and antimony trioxide.
     The magnitude of this potential difference depends on the concentration of antimony trioxide in Sansho, which corresponds to the moderate level of hydrogen ions in the acid solution being measured.
     If the appropriate amounts of antimony, antimony trioxide, and aqueous solutions are taken as 1, the electrode potential can be calculated using the Nernst formula.
     The solid module circuit in the antimony electrode acidity transmitter consists of two parts.
For the sake of safety in the field, the power supply uses AC 24V to power the secondary instrument. In addition to providing driving power for the cleaning motor, this power supply should also be converted into the corresponding DC voltage by the current conversion unit for use in the transmission circuit.
The second part is the measurement transmitter circuit, which sends the reference signal and PH acidity signal from the sensor to the slope adjustment and positioning adjustment circuit after being amplified, so that the internal resistance of the signal can be reduced and adjusted. The amplified PH signal and the temperature compensated signal are added to the conversion circuit, and finally a 4-20mA constant current signal corresponding to the PH value is output to the secondary meter to complete the display and control the PH value.
 
变送器 的特点 未完待续) ( Features of sensors and transmitters to be continued)