What factors affect the measurement accuracy of the conductivity analyzer
Conductivity is the ability of a substance to transmit electric current and is the reciprocal of resistivity. In liquids, the reciprocal of resistance - conductance is often used to measure the size of its conductivity. Water conductivity is an important indicator of water quality. It reflects the level of electrolytes present in the water. Depending on the concentration of the electrolyte in the aqueous solution, the degree of conductivity of the solution is also different. The solubility of an electrolyte in a solution is analyzed by measuring the conductivity of the solution. This is the basic analysis method of conductivity meter. The measurement principle of the conductivity analyzer: In order to avoid electrode polarization, the meter generates a highly stable sine wave signal and applies it to the electrode. The current flowing through the electrode is proportional to the conductivity of the solution to be measured. The meter transfers the current from a high-impedance operational amplifier After being converted into a voltage signal, the potential signal reflecting the conductivity is obtained after program-controlled signal amplification, phase-sensitive detection and filtering; the microprocessor alternately samples the temperature signal and the conductivity signal through switching, and after calculation and temperature compensation, the obtained The conductivity value of the measured solution at 25°C and the temperature value at that time. The conductivity analyzer mainly has four parts that are easily damaged and affected by the test: power supply part, bridge part, oscillator and indicator part. At the same time, these three main components are also key positions used during testing. Their quality is directly related to the results of the test. So their maintenance is very important. We will introduce these three parts separately. Firstly, we will introduce the power supply part of the conductivity analyzer when the low-voltage AC power supply fails, if the indicator light and each filament are not on. We should check in the order of power input, transformer primary, transformer secondary low voltage, etc. during inspection. The high-voltage DC power supply can light up the indicator light and each filament, but the electric eye tube does not emit green light, and the replacement of a new electric eye tube does not work, the problem may occur in the high-voltage DC power supply part. When testing with a conductivity analyzer, it is found that the high-cycle gear of the conductivity analyzer cannot measure the accurate balance point. At this time, we can determine that its fault is: the fault of the oscillator and the cathode output device. We can first Replace the oscillating tube and the cathode output tube. If the problem still cannot be solved at that time, we need to measure the voltage and wiring of each pole of the two tubes. At the same time, we can also use an oscilloscope to track and check each signal point. In this way, the problem can be found. First check the electrode system in the bridge, replace or repair the electrode system. If it cannot be measured, the following method can be used to continue checking. Reading button part. Sometimes the sliding wire resistance inside the reading button is not in good contact, you can use a clean silk cloth to wipe the contact point to make good contact everywhere. The magnification button part is mostly due to misalignment of the internal band switch or poor contact. You can use cotton to absorb a small amount of absolute ethanol or trichloroethylene to clean it and reset it. Capacitance problem. Sometimes the edge of the light band of the indicator is blurred, you can adjust the capacitor of the bridge arm to make it clear. I have introduced to you the problem of the power supply, the problem of the bridge and the troubleshooting of the oscillator, and then I will introduce to you the fault of the indicator. Let’s first determine where the problem of the bridge occurs: If the edge of the indicator light band is still blurred after adjusting the capacitance of the bridge circuit, you can replace the electric eye tube. The green fluorescent band of the former moves in a fan shape, and the latter moves up and down. And the wiring is different. When the indicator of the conductivity analyzer is not sensitive, you can replace the amplifying tube and the electric eye tube at this time. If it is still insensitive, you need to check the voltage and wiring of each pole, and the anode of the amplifying tube.