Capacitor level switch based on 555 time-base circuit

Abstract

The invention discloses a capacitance level switch based on a 555 time-base circuit, which comprises the 555 time-base circuit, the input end of the 555 time-base circuit is connected with a level tank body, capacitance formed by a measuring electrode and a tank body shell is in direct proportion to the height of the quantity, and the output end of the 555 time-base circuit is connected with the AD acquisition end of a main controller after passing through a pi-type filter network circuit; square waves output by the 555 time-base circuit are filtered and then transmitted to the main controller, and the main controller judges the height of the material level according to a voltage value collected by an AD end; the PWM output end of the main controller is connected with the trigger end of the 555 time-base circuit, and the output end of the 555 time-base circuit is connected with the main controller to form a closed loop; during debugging, the main controller outputs PWM with a large period to the trigger end of the 555 time-base circuit, collects the period and duty ratio of square waves output by the output end of the 555 time-base circuit under the condition that a material bin is full, and self-regulates the PWM output by the main controller to the trigger end of the 555 time-base circuit, so that the square waves output by the output end of the 555 time-base circuit reach the optimal signal-to-noise ratio of capacitance level switch measurement. According to the invention, the self-adaptive adjustment of the capacitance level switch on the measurement of materials with different dielectric constants is realized.

Description

technical field [0001] The invention relates to the technical field of material height measurement, in particular to a capacitive level switch based on a 555 time base circuit. Background technique [0002] The PWM period of the existing capacitive level switch output to the trigger terminal of the 555 time base circuit is fixed. When measuring materials with low dielectric constant, such as petrochemical products, the pulse width of the output terminal of the 555 time base circuit is too narrow, so that the signal-to-noise ratio Low, difficult to measure; when measuring materials with high dielectric constant, such as salt water products, the pulse width of the output terminal of the 555 time base circuit is too wide, so that the signal exceeds the range and cannot be measured. Therefore, in the application, it is necessary to adjust the circuit parameters for different measured materials, and the adaptability of the measuring instrument is weak. [0003] For non-conductiv...

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Problems solved by technology

[0002] The PWM period of the existing capacitive level switch output to the trigger terminal of the 555 time base circuit is fixed. When measuring materials with low dielectric constant, such as petrochemical products, the pulse width of the output terminal of the 555 time base circuit is too narrow, so that the signal-to-noise ratio Low, difficult to measure; when measuring materials with high dielectric constant, such as salt water products, the pulse width of the output terminal of the 555 time base circuit is too wide, so that the signal exceeds the range and cannot be measured

Therefore, in the application, it is necessary to adjust the circuit parameters for different measured materials, and the adaptability of the measuring instrument is weak.

[0003] For non-conductive liquids, conductive liquids, iron powder and other materials with different dielectric constants, the capacitance C changes differently. The capacitance C of non-conductive liquids changes very little, the capacitance C of conductive liquids changes greatly, and the capacitance of iron powder C varies greatly. If a fixed cycle is used to measure non-conductive liquids, the output pulse width of the 555 time base circuit is too narrow, and the measurement effect is poor. When measuring materials containing iron powder, the output pulse width of the 555 time base circuit is too wide, and even the entire The signal is high and cannot be measured

[0004] At present, the known adjustable capacitive level switch needs to manually adjust the circuit parameters and adjust the pulse period of the trigger terminal of the 555 time base circuit. For materials with different dielectric constants, the general solution is to manually adjust according to the engineer’s experience. Weak

Therefore, the existing capacitive level switches are not adaptable to materials with different dielectric constants, and cannot be adaptively adjusted for materials with different dielectric constants.

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