Temperature Compensated Level Measuring Unit and Level Meter in Radio Frequency Admittance Level Meter

Abstract

The invention discloses a material level measurement unit based on temperature compensation in a radio frequency admittance material level meter and the material level meter. The material level measurement unit comprises a first measurement electrode, a second measurement electrode and a measurement circuit electrically connected to the first and second measurement electrodes; the lower ends of the first and second measurement electrodes are inserted into a material container the material level of which is to be measured, and the upper ends of the first and second measurement electrodes are electrically connected to the measurement circuit; the measurement circuit comprises a first frequency selection network, a second frequency selection network, a third frequency selection network, a temperature compensation circuit, an excitation signal generation circuit, a pi / 4 phase shift narrow pulse generation circuit and an acquisition circuit of pi / 4 phase point amplitude signals; the excitation signal generation circuit generates sine wave excitation signals S1, and the pi / 4 phase shift narrow pulse generation circuit is electrically connected to an output end of the excitation signal generating circuit and used for receiving the excitation signals S1; the pi / 4 phase shift narrow pulse generation circuit is also electrically connected to the acquisition circuit of the pi / 4 phase point amplitude signals, and the acquisition circuit is used for receiving narrow pulse signals S4 and outputting pi / 4 phase point amplitude signals S5.

Description

technical field [0001] The invention relates to the field of level measurement, in particular to a temperature-compensated level measurement unit in a radio frequency admittance level meter based on a T-shaped frequency-selective network to assist value acquisition to eliminate the influence of material hanging. Background technique [0002] The current contact level meter (level switch) is widely used in the field of industrial production, with various principles and varieties. Among them, level detection devices such as tuning fork level meters, capacitive level meters, radar level meters, and mechanical level meters account for the vast majority of the market share. However, these current contact level meters still have defects in industrial production. When the material to be measured is attached to the surface of the measuring electrode, it will bring errors to the measurement, and cannot be used reliably in the measurement environment for a long time. An important fac...

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Problems solved by technology

[0004] 1. The MCU performs zero point detection, takes the position between 3π / 4 and 7π / 4 for chopper integration, and controls the signal through the photoelectric switch; this method has more value points and the operation is more complicated

[0005] 2. Use a combination of capacitors and resistors to shift the signal phase by π / 4; although this method is simple in circuit, the measurement results are poor. When the material level changes, the capacitance value to be measured changes, causing the phase shift to change accordingly. The error will be larger

[0006] 3. Use the MCU to calculate the impedance and capacitive reactance of the capacitive sensor, and use the principle of radio frequency admittance to invert the capacitive reactance of the material to obtain the actual capacitance value; this method is complex to calculate, and there are large unknown errors in the data

[0009] 1. Density elimination method: eliminate the error caused by the density change of the measured medium due to temperature changes. The density elimination method is to measure the density change by adding a circuit for measuring the density of the medium to correct the density change to the measurement error. influence; however, this method cannot eliminate the influence of the circuit itself on the measurement results due to temperature changes;

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