Novel online detection device for water quality and conductivity

Abstract

The invention discloses a novel online detection device for water quality and conductivity. The online detection device comprises a sensor, a shield cable and a transmitter, wherein the sensor, the shield cable and the transmitter are connected in sequence. The sensor is connected with a sensor interface on the transmitter through the shield cable and transmits conductivity signals and temperature signals. The transmitter processes the conductivity signals and the temperature signals respectively and outputs water quality and temperature analog signals less than 100 mV. After the water quality and temperature analog signals are processed through an A / D (analog / digital) conversion circuit, the water quality and temperature digital signals are output to a single chip. The single chip receives the water quality and temperature digital signals, carries out temperature compensation processing and transmits the signals to an RS485 circuit. The RS485 circuit provides an external communication interface and transmits the water quality and temperature digital signals. According to the novel online detection device, the structural stability and the anti-jamming capability of the sensor are improved, the volume of the transmitter is further reduced, and the transmitter is more compact and easy to integrate and install. By digital signal output, the errors caused by secondary collection and signal conversion are radically removed; and the measurement accuracy of the device is improved.

Description

technical field [0001] The invention relates to a water quality detection device. Background technique [0002] The existing water quality conductivity on-line detection device usually consists of a conductivity sensor, a temperature sensor, a signal transmission cable, a signal amplification and transmission circuit, and a built-in or external display. The basic structure of the sensor (two-pole type) is a metal cylindrical outer electrode, which is covered with a metal inner electrode that is relatively insulated from the outer electrode, and they together form a conductance measurement circuit. The conductivity of the medium (water) between the inner and outer electrodes is measured by applying a certain voltage externally, and then the conductivity (us / cm) or resistivity (MΩ.cm) of the water is obtained through the amplification and conversion of the transmission circuit; at the same time, A thermistor is embedded in the middle of the inner electrode so that the inner e...

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Problems solved by technology

[0006] 1. The water sealing effect of the single sealing ring structure is relatively unreliable. Once water seeps into the sensor, the sensor will fail;

[0007] 2. For the sensor with high sensitivity measurement, the inner electrode is thicker, longer, and the mass is larger. The single sealing ring structure makes it difficult to locate. Even if the top is sealed with glue, the shaking of the inner electrode cannot be completely avoided, resulting in Not fixed, measurement error increases

[0008] Second, the anti-interference ability is not strong;

[0009] In particular, the signal transmission cable is easily disturbed by the external space magnetic field, and the power supply is also easily disturbed. The measurement value fluctuates due to poor EMC indicators or parameter changes of the switching power supply.

[0010] 3. The volume of the transmitter is too large, which is not conducive to highly integrated installation and use;

[0011] Most conductivity transmitters are designed in the form of instruments, that is, the transmission and display are integrated, and they are installed with panel-type openings. This structure is not conducive to the miniaturization and integrated assembly of the system, especially when multiple channels are used in the system. The problem is more prominent when measuring

[0012] 4. The signal output of the transmitter is mostly analog (4-20mA), the transmission distance is limited, and the host computer acquisition and A-D conversion process are prone to errors;

[0013] Five, the measurement accuracy is not high;

[0014] In particular, most transmitters communicate with the peripheral circuit through the single-chip microcomputer, and after two A / D and D / A conversions, the water quality temperature signal is converted from the analog quantity on the probe to the internal digital quantity, and then the internal digital quantity is converted to After the external 4-20mA analog output, it seriously affects the measurement accuracy

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