PWM wave based multi-channel 4-20 mA control command converting system

Abstract

The invention provides a PWM wave based multi-channel 4-20 mA control command converting system. The system includes a controller unit (1), an electric level converting unit (2), an isolation conversion unit (3), a low-pass filtering unit (4), a 4-20 mA voltage / current converting unit (5), a current signal transmission cable (6) and a load interface unit (7) connected in sequence. The system is applied as a CPU into an ARM in an embedded system widely with high performance and at a low cost, multi-channel PWM wave voltage signals of required (fixed) frequency and adjustable duty ratio are generated from multi-channel PWM waveforms of TIM<X> of the ARM and are converted to multi-channel 4-20 mA current output signals. The anti-interference capability is improved and multi-channel long-distance transmission is realized. Besides, the system is high in control precision, stable in performance and reliable in operation.

Description

technical field [0001] The invention belongs to the technical field of power electronic conversion and control, in particular to a multi-channel 4-20mA control command conversion system based on PWM waves. Background technique [0002] It is generally necessary to measure various non-electrical physical quantities (such as temperature, pressure, speed, angle, etc.) and electrical physical quantities (such as voltage, current, resistance, magnetic induction, etc.) Transmitter equipment) to convert them into analog electrical signals that are easy to transmit. The practice of industrial field operation shows that to reliably, safely and healthily transmit the above-mentioned physical quantities to the control room or display and control device hundreds of meters away, the most common method is to use 4-20mA current for transmission. The reasons are: [0003] (1) The transmitted analog quantity is not easy to be disturbed, because the amplitude of the noise voltage in the indu...

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Problems solved by technology

[0009] However, in operation practice, it is found that if no necessary measures are taken, the accuracy of the 4-20mA signal conversion circuit based on PWM waves cannot meet the control technical requirements of power electronic devices, and an external conversion module has to be used, although the accuracy has been improved. Further improvement, but the price is generally more expensive, especially with the increase of the number of channels, it not only increases the cost, but also because of the additional conversion module, it is not easy to use, the failure rate is high, and the reliability is low

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