RU2253841C1 - Normalizing transformer - Google Patents

Abstract

FIELD: measurement technology.

SUBSTANCE: transformer has current forming cascade of 0-5mA and input signal forming unit. Current forming cascade 0-5mA is supplied through 4-20mA current forming cascade. Output of input signal forming unit is connected with input of 0-5mA forming cascade and with input of 4-20mA forming cascade through common point. Secondary equipment with different input signals can be connected to the same normalizing transformer.

EFFECT: improved efficiency of operation.

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Description

The invention relates to the field of measurement technology and can be used to create measuring transducers of physical quantities into a standard current of 0 ... 5 and 4 ... 20 mA, namely normalizing transducers, temperature sensors with current output, pressure sensors, etc. d. These converters are intended for use in regulatory systems and process control in industry and energy.

Normalizing measuring transducers are designed to convert the output signal of the primary converters and the output signal of the alternating current of the measuring devices into a unified DC signal.

There are two standards for the output current of normalizing converters: 0 ... 5 mA and 4 ... 20 mA.

Known normalizing converters [1] having an output signal of 0 ... 5 mA, which consist of primary converters made according to a statically self-compensating circuit, and connected by a three-wire circuit (figure 3). The disadvantage of such converters is the lack of the ability to connect them to secondary equipment with another standard input signal 4 ... 20 mA.

Known normalizing converters [2] having an output signal of 4 ... 20 mA and connected in a two-wire circuit (figure 2). The disadvantage of such converters is the lack of the ability to connect them to secondary equipment with another standard input signal 0 ... 5 mA.

Another disadvantage of the known standardizing converters is the impossibility of simultaneously connecting secondary devices with an output signal of 0 ... 5 mA and 4 ... 20 mA.

The technical result obtained from the implementation of the invention is the ability to connect to the same normalizing converter of secondary equipment with both an input signal of 4 ... 20 mA and an input signal of 0 ... 5 mA. It is also possible to connect two secondary measuring instruments to one transducer: one with an output signal of 4 ... 20 mA, and the second with an input signal of 0 ... 5 mA.

This technical result is achieved due to the fact that in the known normalizing converter comprising an input signal generating unit proportional to the measured physical quantity electrically interconnected and a current generating stage 4 ... 20 mA, according to the invention, an additional current generating stage 0 is included in it ... 5 mA, the power of which is provided through the 4 ... 20 mA current generating stage, while the output of the input signal generating unit is connected to the 0 ... 5 mA current generating stage and the generating stage current 4 ... 20 mA through their common point.

Figure 1 shows a circuit diagram for a normalizing converter with unified output signals 0 ... 5 and 4 ... 20 mA, figure 2 is a circuit diagram for a normalizing converter with an output of 4 ... 20 mA, in figure 3 - a schematic diagram for a normalizing converter with an output of 0 ... 5 mA, figure 4 is an embodiment of the device, the operation diagram of the device AIR-20.

The device of the normalizing converter with unified output signals 0 ... 5 and 4 ... 20 mA contains a power supply 1, the positive voltage output of which is connected in series with the first load resistor 2, cascade 4 of the formation of current 4 ... 20 mA and block 6 formation of the input signal. In addition, the normalizing converter comprises a sensor signal converter 7, the output of which is connected to the input signal generating unit 6. Also, the normalizing converter contains a second load resistor 3 and a current generation stage 5 ... 5 mA connected in series 5, the power of which is supplied through a 4 ... 20 mA current generation stage, with a second load resistor 3 connected to the positive voltage output of the power supply unit 1, and the free end of the current generating stage 5 0 ... 5 mA to the common point of the input signal generating unit 6 and the 4 ... 20 mA current generating stage 4, and the output of the input signal generating unit 6 is connected to the current generating stage 5 ... 5 mA and ka cad 4 of the formation of current 4 ... 20 mA through their common point, while the second output of the block 6 of the formation of the input signal, the output of the cascade 5 of the formation of current 0 ... 5 mA, the output of the cascade 4 of the formation of current 4 ... 20 mA are connected to negative voltage output of power supply unit 1.

As an example of a specific application, we can cite the operation of the Pressure Transducer measuring AIR-20 (Fig. 4), manufactured by the Elemer Scientific-Production Enterprise.

AIR-20 consists of a strain gauge and an electronic device. The pressure medium is fed into the strain gage chamber and deforms its membrane, which leads to a change in the electrical resistance of the strain gages located on it. An electronic device converts the magnitude of the change in resistance of the strain gages into unified current output signals. The electronic device includes a voltage stabilizer, an ADC, a microcontroller, a reprogrammable read-only memory (EPROM), converters of the PWM signal of the controller into an output current of 4 ... 20 mA and 0 ... 5 mA. The voltage stabilizer provides power to the electronic circuitry of the device from the line of the current loop 4 ... 20 mA voltage + 5V and + 3.7V. The ADC converts the analog signal of the strain gauge to a code supplied to the control microcontroller. The microcontroller, together with the ROM, converts the ADC code into a PWM signal, into an ASCI code for transmitting the latter via the RS 232 interface, and forms an algorithm for the operation of all nodes of the device. The PWM signal converter provides an analog signal for controlling transistor current sources that generate an output signal in the range from 3.5 to 22.5 mA and a 0 ... 5 mA signal.

Sources of information

1. Preobrazhensky V.P. “Thermotechnical measurements and devices”. M .: “Energy”, 1978, p. 341-346.

2. RF patent No. 2082954, MKI G 01 L 9/04, BI No. 18, 1997.

Claims (1)

A normalizing converter with 0-5 and 4-20 mA output signals, comprising a 4-20 mA current generating stage electrically connected to each other and an input signal generating unit proportional to the measured physical quantity, characterized in that a 0- current generating stage is additionally introduced into it 5 mA, the electric power of which is carried out through the 4-20 mA current generating stage, while the output of the input signal generating unit is connected to the input of the 0-5 mA current generating stage and the input of the 4-20 mA current generating stage their common point.

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