CN210572474U - Two-wire Hall type effective value current transmitter - Google Patents
Two-wire Hall type effective value current transmitter Download PDFInfo
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- CN210572474U CN210572474U CN201920987265.3U CN201920987265U CN210572474U CN 210572474 U CN210572474 U CN 210572474U CN 201920987265 U CN201920987265 U CN 201920987265U CN 210572474 U CN210572474 U CN 210572474U
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Abstract
The utility model discloses a two-wire Hall type effective value current transmitter, this transmitter mainly comprises C-shaped magnetic ring, Hall sensor, differential amplification circuit, effective value detection circuit, V/1 converting circuit, two-wire output circuit, bias voltage generating circuit, common mode resistance-capacitance network, the measured current passes C-shaped magnetic ring, Hall sensor installs in the C-shaped magnetic ring air gap, Hall sensor voltage output end connects to differential amplification circuit input, differential amplification circuit output end connects to effective value detection circuit input, effective value detection circuit output end connects to V/I converting circuit input, the output of bias voltage generating circuit connects to differential amplification circuit and effective value detection circuit bias voltage input, V/I converting circuit output connects to two-wire output circuit, output 4 ~ 20mA current signal through two-wire output circuit, meanwhile, the output current source and the voltage source of the V/I conversion circuit respectively supply power for the Hall sensor and each circuit link.
Description
Technical Field
The utility model relates to an electrical detection technology and automation equipment field, more specifically say, the utility model relates to a two-wire system hall formula effective value current transmitter instrument.
Background
The effective value current transmitter is widely applied to power and electric energy metering in the fields of power automation, relay protection, motor control, industrial automation and the like, and converts an effective value of alternating current or direct current of a tested main loop into a 4-20 mA standard direct current signal according to a linear relation to output and remotely transmit.
The hall sensor is the most common sensor for measuring magnetic field or current, has the advantages of high sensitivity, simple structure, small volume, wide frequency response range, long service life and the like, is suitable for measuring alternating current and direct current magnetic fields or current, and is suitable for measuring static current and dynamic current, so that the current transmitter constructed by taking the hall sensor as a sensitive element has incomparable superiority.
Most of the existing Hall type current transmitters adopt a three-wire system or four-wire system wiring mode, except a signal transmission loop, a power supply loop is required to be additionally provided for the transmitters, and the Hall type current transmitters are complex in wiring and inconvenient to maintain. For example, the 'guide rail type installation current transducer based on hall closed loop principle' with application number 201320382320.9 adopts a closed loop feedback type working principle, the working circuit structure is more complex, and a special power supply loop is needed to provide + Vc and-Vc power supplies, namely a four-wire wiring mode is needed.
However, the two-wire hall type current transmitter is simpler and more reliable in wiring mode, convenient to use and widely applied to various measurement and control systems, so that the current transmitter for developing the two-wire 4-20 mA standard signal has great technical development value and wide market demand. The two-wire Hall current transmitter with the application number of 201810424278.X adopts the output form of a two-wire 4-20 mA standard signal, but the transmitter can only be used for measuring the instantaneous value of alternating current and direct current and has no function of measuring effective value current.
The two-wire Hall type effective value current transmitter not only requires that the total current of the system work is less than 4mA, namely the whole system needs to be designed with low power consumption, but also has the function of detecting the effective value of a measurement signal, and has larger development difficulty. The utility model discloses a two-wire system hall formula effective value current transmitter's realization provides a solution.
SUMMERY OF THE UTILITY MODEL
The utility model aims to solve the technical problem that adopt hall sensor to realize the measurement of alternating current-direct current virtual value to can carry out signal transmission and system power supply through two wire system standard 4 ~ 20mA current return circuit.
In order to solve the technical problem, the utility model provides a two-wire system hall formula effective value current transmitter, its characterized in that: the transmitter mainly comprises a C-shaped magnetic ring, a Hall sensor, a differential amplifying circuit, an effective value detection circuit, a V/I conversion circuit, a two-wire output loop, a bias voltage generating circuit and a common-mode resistance-capacitance network, wherein the current I to be measured ismThe Hall sensor passes through the C-shaped magnetic ring and is arranged in an air gap of the C-shaped magnetic ring, the voltage output end of the Hall sensor is connected to the input end of a differential amplifying circuit, the output end of the differential amplifying circuit is connected to the input end of an effective value detecting circuit, the output end of the effective value detecting circuit is connected to the input end of a V/I converting circuit, the output end of a bias voltage generating circuit is connected to the bias voltage input ends of the differential amplifying circuit and the effective value detecting circuit, the output end of the V/I converting circuit is connected to a two-wire system output loop, and the constant current source output end of the V/I conversion circuit is connected to the excitation current input end of the Hall sensor, the constant voltage source output end of the V/I conversion circuit is connected to the power supply ends of the differential amplification circuit, the effective value detection circuit and the bias voltage generation circuit, and the common mode resistance-capacitance network is connected between the excitation current return end of the Hall sensor and the constant voltage source of the V/I conversion circuit and the reference ground end returned by the constant current source.
In the measuring process, the measured current I passing through the C-shaped magnetic ringmGenerating and measuring current I in magnetic ringmThe annular magnetic field with the size in direct proportion vertically penetrates through the Hall sensor, and the Hall sensor is connected with the exciting current provided by the V/I conversion circuit, so that the voltage output end of the Hall sensor outputs the current I to be measuredmThe voltage signal is amplified by the differential amplifying circuit and then input to the effective valueA detector circuit for converting the input AC signal into a current I to be detectedmThe effective value of the voltage signal is directly proportional to the effective value of the voltage signal, and the voltage signal is input to a V/I conversion circuit, the V/I conversion circuit converts the input voltage signal into a 4-20 mA current signal, the signal transmission is performed by the two-wire output loop, and the voltage signal output by the bias voltage generating circuit is input to the bias voltage input end of the differential amplifying circuit and the effective value detecting circuit to provide proper common mode bias voltage for the effective value detecting process, and the V/I conversion circuit outputs a constant current source to provide an excitation current signal for the Hall sensor, the constant current source flows out from the exciting current return end of the Hall sensor and then flows through the common-mode resistance-capacitance network to generate voltage drop, and appropriate common-mode input voltage is provided for the differential amplifying circuit, and the V/I conversion circuit outputs a constant voltage source to provide a working power supply for the differential amplifying circuit, the effective value detection circuit and the bias voltage generating circuit.
The differential amplification circuit mainly comprises a high-precision micro-power-consumption instrument amplifier AD627, the effective value detection circuit mainly comprises a precision micro-power-consumption effective value detector LTC1966, a differential voltage signal output by a Hall sensor is connected to a differential input end of the AD627, an output offset end of the AD627 is connected with a bias voltage generated by a bias voltage generating circuit, a gain adjusting potentiometer is connected between pins 1 and 8 of the AD627 and can be used for adjusting the measuring range of the transmitter, an output end of the AD627 is connected to a positive phase input end of the LTC1966, the bias voltage output by the bias voltage generating circuit is simultaneously connected to a negative phase input end and an output offset end of the LTC1966, the bias voltage provides a proper common mode working voltage for the LTC1966, and a periodic capacitor is connected between the output end and the output offset end of the LTC 1966.
The V/I conversion circuit mainly comprises a voltage/current conversion chip XTR105, which linearly converts an input voltage into 4-20 mA current for output, a direct-current voltage output by an effective value detection circuit is input to a positive phase input end of the XTR105, a voltage adjusting circuit formed by connecting 2 fixed resistors and 1 potentiometer in series is connected in the V/I conversion circuit, a potentiometer center tap is connected to a negative phase input end of the XTR105, an adjusting voltage output by the potentiometer center tap can provide a proper common mode working voltage for the XTR105 and can be used for adjusting a transmitter measurement zero point, in addition, a fixed resistor is connected to an amplification factor adjusting end of the XTR105, the resistor determines a voltage/current conversion coefficient of the XTR105, meanwhile, 2 0.8mA constant current sources are output by the XTR105, the 2 constant current sources are connected in parallel and then input to a Hall sensor to be used as an excitation current source of the Hall sensor, the chip also outputs 1 path of constant voltage source with 5.1V and 1mA capacity as the working power supply of the differential amplifying circuit, the effective value detecting circuit and the bias voltage generating circuit.
The bias voltage generating circuit is composed of a follower consisting of 2 series-connected divider resistors and a low-power-consumption operational amplifier MAX4480, wherein the 2 series-connected resistors are connected between 5.1V voltage sources generated by the V/I conversion circuit, a series point is connected to a positive phase input end of the MAX4480, a negative phase input end is connected with an output end, and 1.6V bias voltage is generated at the output end.
The differential amplifying circuit, the effective value detection circuit and the bias voltage generating circuit are extremely low in total power consumption, and the total current of the working loop in the transmitter is less than 4mA, so that two-wire system current output with 4mA as a measurement zero point can be realized.
The two-wire output loop is mainly composed of an NPN type driving triode, an overvoltage protection diode, a diode rectifier bridge, a load resistor and an external power supply, wherein the diode rectifier bridge in the loop has a reverse connection protection function, the external power supply can be connected into the two-wire output loop in any direction, 4-20 mA current signals are output and transmitted through the two-wire output loop, and meanwhile, power is supplied to the internal working loop.
The common-mode resistance-capacitance network is formed by connecting 1 potentiometer and 1 capacitor in parallel and is connected in series between an excitation current return end of the Hall sensor and a reference ground end returned by a constant voltage source and a constant current source of the V/I conversion circuit, and a 1.6mA constant current source output by the V/I conversion circuit flows through the common-mode resistance-capacitance network, so that a proper common-mode voltage can be provided for the work of the differential amplifier by adjusting the resistance value of the potentiometer, and the capacitor can filter ripples of the common-mode voltage.
The utility model discloses at least, include following beneficial effect:
(1) the Hall type instantaneous current detection device is added with an effective value detection function on the basis of Hall type instantaneous current detection, and can be used for measuring the effective values of alternating current and direct current.
(2) A two-wire wiring mode and a 4-20 mA standard current signal transmission mode are adopted, a power supply loop and a signal loop are combined into a whole to share one loop, a diode rectifier bridge stack is connected in an output loop, and two wiring terminals have no positive and negative division, so that wiring is simpler, more convenient and more reliable.
(3) The measuring output signal of the Hall sensor is processed and converted by adopting a pure analog circuit, an analog/digital conversion and digital signal processor are not needed, a complex closed loop feedback circuit is not needed, and the working circuit is simple in structure, low in cost and high in cost performance.
(4) The zero point and range adjusting potentiometer are connected in the circuit of the transmitter, and the zero point and range of measurement of the transmitter are convenient to adjust and flexible and convenient to use.
(5) The unequal potential of the Hall sensor and the offset voltage of the differential amplifier, the effective value detector and the V/I converter can be offset by zero point adjusting voltage, and the Hall sensor is excited by a constant current source, so that the temperature coefficient is greatly reduced, and the current transducer has high measurement precision.
(6) The system is connected with a bias voltage generating circuit and a common-mode resistance-capacitance network, the common-mode bias voltage of each signal conversion circuit link is appropriate, the static working point of the system is reasonable, and the measuring circuit is high in precision and good in linearity.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.
Drawings
Fig. 1 is a schematic diagram of a principle of composition of a two-wire hall-type significant value current transmitter according to the present invention.
Fig. 2 is a specific circuit diagram of the two-wire hall-type rms current transmitter of the present invention.
Detailed Description
The present invention is further described in detail below with reference to the drawings so that those skilled in the art can implement the invention with reference to the description. It will be understood that terms such as "having," "including," and "comprising," as used herein, do not preclude the presence or addition of one or more other elements or groups thereof.
In order to solve the technical problem, the utility model provides a two-wire system hall formula effective value current transmitter, as shown in FIG. 1, this transmitter mainly comprises C shape magnetic ring 1, hall sensor 2, differential amplifier circuit 3, effective value detection circuit 4, V/I converting circuit 5, two-wire system output circuit 6, bias voltage production circuit 7, common mode resistance-capacitance network 8, and current I is surveyedmThe Hall sensor 2 passes through the C-shaped magnetic ring 1, the Hall sensor 2 is arranged in an air gap of the C-shaped magnetic ring 1, the voltage output end of the Hall sensor 2 is connected to the input end of a differential amplifying circuit 3, the output end of the differential amplifying circuit 3 is connected to the input end of an effective value detecting circuit 4, the output end of the effective value detecting circuit 4 is connected to the input end of a V/I converting circuit 5, the output end of a bias voltage generating circuit 7 is connected to the bias voltage input ends of the differential amplifying circuit 3 and the effective value detecting circuit 4, the output end of the V/I converting circuit 5 is connected to a two-wire output loop 6, the constant current source output end of the V/I converting circuit 5 is connected to the exciting current input end of the Hall sensor 2, the constant voltage source output end of the V/I converting circuit 5 is connected to the, the common-mode resistance-capacitance network 8 is connected between the excitation current return end of the Hall sensor 2 and the reference ground end returned by the constant voltage source and the constant current source of the V/I conversion circuit 5.
As shown in figure 1, during the measurement process, the measured current I passing through the C-shaped magnetic ring 1mGenerating and measuring current I in magnetic ringmThe annular magnetic field with the size in direct proportion vertically penetrates through the Hall sensor 2, and the Hall sensor 2 is connected with the exciting current provided by the V/I conversion circuit 5, so that the voltage output end of the Hall sensor 2 outputs the current I to be measuredmThe voltage signal is amplified by the differential amplifier circuit 3 and then input to the effective value detector circuit 4, and the effective value detector circuit 4 converts the input ac signal into a signal proportional to the instantaneous value of the voltage signalMeasuring current ImThe voltage signal output by the bias voltage generating circuit 7 is input to the bias voltage input ends of the differential amplifying circuit 3 and the effective value detecting circuit 4 to provide an appropriate common mode bias voltage for the effective value detecting process, the V/I converting circuit 5 outputs a constant current source for providing an excitation current signal for the Hall sensor 2, the constant current source flows out from the excitation current return end of the Hall sensor 2 and then flows through the common mode resistance-capacitance network 8 to generate a voltage drop for providing an appropriate common mode input voltage for the differential amplifying circuit 3, the V/I converting circuit 5 outputs a constant voltage source for the differential amplifying circuit 3, The effective value detection circuit 4 and the bias voltage generation circuit 7 supply operating power.
As shown in FIG. 1, the C-shaped magnetic ring 1 is a Zn-Mn ferrite magnetic ring, the magnetic ring is provided with a 2mm air gap along the radial direction, the Hall sensor 2 is a TO-92 packaged linear Hall sensor HG-302C, and the sheet Hall sensor 2 is arranged in the center of the air gap of the C-shaped magnetic ring 1 in parallel. Measured current ImThe magnetic field generated by excitation in the C-shaped magnetic ring 1 passes through the air gap and vertically penetrates through the upper surface and the lower surface of the Hall sensor 2, and the air gap magnetic field intensity B and the measured current I of the magnetic fieldmProportional to the current and the Hall sensor 2 is energized with an excitation current I provided by a V/I conversion circuit 5HThe voltage output end of the Hall sensor 2 outputs and the current I to be measuredmWeak voltage signal U with proportional instantaneous valueHCan be expressed as
UH＝UH+-UH-＝kIHB (1)
In the formula, k is a hall coefficient of the hall sensor. It can be known that the output voltage U of the Hall sensorHWith the measured current ImIs in direct proportion.
As shown in fig. 2, the differential amplifying circuit 3 mainly comprises a high-precision, micro-power consumption instrumentation amplifier AD627, the effective value detecting circuit 4 mainly comprises a precision micro-power consumption effective value detector LTC1966, the differential voltage signal output by the hall sensor 2 is connected to the differential input terminal of the AD627, andthe output bias terminal of the AD627 is connected with a bias voltage U generated by a bias voltage generating circuit 7refThe gain adjustment potentiometer R is connected between the No. 1 pin and the No. 8 pin of the AD6273Then the output voltage U of the differential amplifying circuit 3DCan be expressed as
UD＝UH×(5+200/R3)+Uref(2)
In the formula, R3The resistance value of the gain adjustment potentiometer connected between pins 1 and 8 of the AD627 ranges from 0 to 1k omega, and the potentiometer can be used for adjusting the measuring range of the transmitter, namely UrefIs a bias voltage generated by the bias voltage generating circuit 7. The output terminal of the AD627 is connected to the non-inverting input terminal IN1 of the LTC1966, and the bias voltage U output from the bias voltage generating circuit 7refThe inverting input terminal 1N2 and the output bias terminal VOUT _ RTN of the LTC1966 are connected simultaneously, the bias voltage provides a proper common mode operating voltage for the LTC1966, and a 1 muF detection period capacitor C is connected between the output terminal VOUT and the output bias terminal VOUT _ RTN of the LTC1966AVEThe DC voltage U output from the effective value detection circuit 4RMSCan be expressed as
Wherein T ═ RoCAVEIs an internal output resistance R of LTC1966o85k omega and external capacitor C AVE1 μ F-determined detection period, UrefIs a bias voltage generated by the bias voltage generating circuit 7.
As shown in FIG. 2, the V/I conversion circuit 5 mainly comprises a voltage/current conversion chip XTR105, which linearly converts the input voltage into 4-20 mA current for output, and the effective value detection circuit 4 outputs a DC voltage URMSThe positive phase input VIN + of XTR105 is inputted and connected with R in V/I converting circuit 54＝2.2MΩ、R61M Ω fixed resistance and R5A voltage adjusting circuit formed by connecting 200k omega potentiometers in series, wherein the center tap of the potentiometer is connected to the inverting input terminal VIN-of the XTR105, and the adjusting voltage U output by the center tap of the potentiometeroffCan be XTR105, providing a proper common mode working voltage within the range of 1.5-1.8V, and being used for adjusting the measurement zero point of the transmitter. In addition, there is a fixed resistance R71k omega is connected to the amplification factor adjusting terminal of XTR105, the resistance determines the voltage/current conversion coefficient of XTR105, then XTR105 outputs the current I to the two-wire output loop 60Is composed of
I0＝4+40×(URMS-Uoff)/R7(4)
In the formula of URMSA direct current voltage U output from the effective value detection circuit 4offIs a potentiometer R5The adjusting voltage of the center tap output ranges from 1.5V to 1.8V, I0To output a current, R7The resistance of the gain adjustment resistor of XTR105 is 1k Ω. Meanwhile, the XTR105 outputs 2 paths of 0.8mA constant current sources, the 2 paths of constant current sources are connected in parallel and then input to the Hall sensor 2 to be used as an excitation current source of the Hall sensor 2, and the chip also outputs 1 path of constant voltage sources with the capacities of 5.1V and 1mA to be used as working power supplies of the differential amplifying circuit 3, the effective value detection circuit 4 and the bias voltage generating circuit 7.
As shown in fig. 2, the bias voltage generating circuit 7 is composed of R12.2M Ω and R2IM omega series divider resistance and low power consumption operational amplifier MAX4480, 2 series resistances are connected between 5.1V voltage source generated by V/I conversion circuit 5, series point is connected to positive phase input end of MAX4480, and negative phase input end is connected with output end, so that bias voltage U generated at output end is obtainedref1.6V, an appropriate common mode bias voltage can be provided for the effective value detection process.
The differential amplifying circuit 3, the effective value detection circuit 4 and the bias voltage generating circuit 7 are extremely low in total power consumption, and the total current of a working loop in the transmitter is less than 4mA, so that two-wire system current output with 4mA as a measurement zero point can be realized.
The two-wire output loop 6 mainly comprises an NPN type drive triode, an overvoltage protection diode, a diode rectifier bridge, a load resistor and an external power supply, wherein the diode rectifier bridge in the loop has reverse connection protection function, and the external power supply can be connected into the two-wire output loop in any directionAnd 6, outputting and transmitting a 4-20 mA current signal through the two-wire output loop 6, and simultaneously supplying power to the internal working loop. In the embodiment shown in fig. 2, the NPN-type driving transistor Q19014 is adopted to improve the current output capability of the transmitter, reduce the heat emission of the XTR105 chip, and enable the triode Q1Is connected with pin 9 of XTR105, Q1Is connected to pin 8 of XTR105, Q1The collector of (a) is connected with the No. 10 pin of the XTR105 and connected to one vertex of the diode rectifier bridge; the overvoltage protection diode D5The 36V Zener diode 1N4753 can absorb the surge current of the loop, play the role of overvoltage protection, and the overvoltage protection diode D5A capacitor C with 0.1 muF is connected in parallel at two ends3The filtering function is achieved; the diode rectifier bridge D1～D4The rectifier bridge stack is formed by 4 rectifier diodes 1N4007, and a rectifier bridge stack is formed according to the connection mode shown in the figure, so that the reverse connection of a power supply can be prevented, and the wiring direction of the power supply of the transmitter can be randomly exchanged; in addition, the +24V DC external power supply and the load resistor R are required to be accessed at the remote terminal of the transmitterLAnd forms the complete two-wire output loop 6. Under the action of +24V DC power supply potential, charge flows through an external power supply, a diode rectifier bridge, an XTR105 and a driving triode 9014 in an output loop (6) in parallel, and a load resistor RLTherefore, a current signal transmission path is formed, a 4-20 mA current signal flows through the current signal transmission path finally, and meanwhile the +24V DC external power supply supplies power to the internal working circuit through the current signal transmission path in the output circuit (6).
As shown in fig. 2, the common mode rc network 8 is composed of 1 potentiometer RCM2k Ω and 1 capacitor CCM0.1 muF, connected in parallel and connected in series between the exciting current return terminal of the Hall sensor 2 and the reference ground terminal returned by the constant voltage source and constant current source of the V/I conversion circuit 5, and the 1.6mA constant current source output by the V/I conversion circuit 5 flows through the common mode RC network 8, so that the potentiometer R can be adjustedCMThe resistance value of (A) provides a proper common mode voltage in the range of 0-3.2V for the operation of the differential amplifier, and (C)CMThe ripple of the common mode voltage can be filtered out.
Further, in embodiments, at constant voltage source VCCAnd a reference ground end GND are connected with C in parallel as shown in FIG. 21＝10μF、C2Two capacitors of 0.1 muF are used to filter out ripple waves to improve the stability of the voltage source.
While embodiments of the invention have been disclosed above, it is not intended to be limited to the applications listed in the specification and the examples. It can be applicable to various and be fit for the utility model discloses a field completely. Additional modifications will readily occur to those skilled in the art. The invention is therefore not to be limited to the specific details and illustrations shown and described herein, without departing from the general concept defined by the claims and their equivalents.
Claims (8)
1. The utility model provides a two-wire system hall formula significant value current transmitter which characterized in that: the transmitter mainly comprises a C-shaped magnetic ring (1), a Hall sensor (2), a differential amplifying circuit (3), an effective value detection circuit (4), a V/I conversion circuit (5), a two-wire system output loop (6), a bias voltage generating circuit (7) and a common mode resistance-capacitance network (8), wherein the current I to be detected is ImThe Hall sensor (2) penetrates through the C-shaped magnetic ring (1), the Hall sensor (2) is arranged in an air gap of the C-shaped magnetic ring (1), the voltage output end of the Hall sensor (2) is connected to the input end of a differential amplifying circuit (3), the output end of the differential amplifying circuit (3) is connected to the input end of an effective value detection circuit (4), the output end of the effective value detection circuit (4) is connected to the input end of a V/I conversion circuit (5), the output end of a bias voltage generating circuit (7) is connected to the bias voltage input ends of the differential amplifying circuit (3) and the effective value detection circuit (4), the output end of the V/I conversion circuit (5) is connected to a two-wire output circuit (6), the constant current source output end of the V/I conversion circuit (5) is connected to the exciting current input end of the Hall sensor (2), and the constant voltage source output end of the V/I conversion circuit (5) is connected to the differential, The power supply ends of the effective value detection circuit (4) and the bias voltage generation circuit (7), and the common-mode resistance-capacitance network (8) are connected between the exciting current return end of the Hall sensor (2) and the reference ground end returned by the constant voltage source and the constant current source of the V/I conversion circuit (5).
2. The method of claim 1The two-wire Hall type effective value current transmitter is characterized in that: in the measuring process, the measured current I passing through the C-shaped magnetic ring (1)mGenerating and measuring current I in magnetic ringmThe annular magnetic field with the size in direct proportion vertically penetrates through the Hall sensor (2), and the Hall sensor (2) is connected with an exciting current provided by the V/I conversion circuit (5), so that the voltage output end of the Hall sensor (2) outputs the current I to be measuredmThe voltage signal is amplified by a differential amplifying circuit (3) and then input into an effective value detection circuit (4), and the effective value detection circuit (4) converts the input alternating current signal into a current I to be detectedmThe voltage signal output by the bias voltage generating circuit (7) is input to a bias voltage input end of the differential amplifying circuit (3) and the effective value detection circuit (4) to provide a proper common mode bias voltage for the effective value detection process, the V/I conversion circuit (5) outputs a constant current source to provide an exciting current signal for the Hall sensor (2), the constant current source flows out from an exciting current return end of the Hall sensor (2) and then flows through a common mode resistance-capacitance network (8) to generate a voltage drop to provide a proper common mode input voltage for the differential amplifying circuit (3), and the V/I conversion circuit (5) outputs a constant voltage source to the differential amplifying circuit (3), An effective value detection circuit (4) and a bias voltage generation circuit (7) supply operating power.
3. The two-wire hall active value current transmitter of claim 1 wherein: the differential amplification circuit (3) mainly comprises a high-precision micro-power consumption instrument amplifier AD627, the effective value detection circuit (4) mainly comprises a precision micro-power consumption effective value detector LTC1966, a differential voltage signal output by the Hall sensor (2) is connected to a differential input end of the AD627, an output offset end of the AD627 is connected with a bias voltage generated by a bias voltage generating circuit (7), a gain adjusting potentiometer which can be used for adjusting the measuring range of the transmitter is connected between pins 1 and 8 of the AD627, an output end of the AD627 is connected to a positive phase input end of the LTC1966, the bias voltage output by the bias voltage generating circuit (7) is simultaneously connected to an inverted input end and an output offset end of the LTC1966, the bias voltage provides proper common mode working voltage for the LTC1966, and a detection period capacitor is connected between the output end and the output offset end of the LTC 1966.
4. The two-wire hall active value current transmitter of claim 1 wherein: the V/I conversion circuit (5) mainly comprises a voltage/current conversion chip XTR105, which linearly converts an input voltage into 4-20 mA current for output, a direct current voltage output by an effective value detection circuit (4) is input to a positive phase input end of the XTR105, a voltage adjusting circuit formed by connecting 2 fixed resistors and 1 potentiometer in series is connected in the V/I conversion circuit (5), a potentiometer center tap is connected to a negative phase input end of the XTR105, an adjusting voltage output by the potentiometer center tap can provide a proper common mode working voltage for the XTR105 and can be used for adjusting a transmitter measurement zero point, in addition, the fixed resistor is connected to an amplification factor adjusting end of the XTR105, the resistor determines a voltage/current conversion coefficient of the XTR105, meanwhile, the XTR105 outputs 2 0.8mA constant current sources, and inputs the 2 constant current sources after being connected in parallel to a Hall sensor (2), as an excitation current source of the Hall sensor (2), the chip also outputs 1 path of constant voltage source with 5.1V and 1mA capacity as the working power supply of the differential amplifying circuit (3), the effective value detection circuit (4) and the bias voltage generating circuit (7).
5. The two-wire hall active value current transmitter of claim 1 wherein: the bias voltage generating circuit (7) is composed of a follower consisting of 2 series-connected divider resistors and a low-power-consumption operational amplifier MAX4480, wherein the 2 series-connected resistors are connected between 5.1V voltage sources generated by the V/I conversion circuit (5), a series point is connected to a positive phase input end of the MAX4480, an inverse phase input end is connected with an output end, and 1.6V bias voltage is generated at the output end.
6. The two-wire hall-type active value current transmitter of claim 1, wherein: the differential amplification circuit (3), the effective value detection circuit (4) and the bias voltage generation circuit (7) are extremely low in total power consumption, and the total current of a working loop in the transmitter is less than 4mA, so that two-wire current output with 4mA as a measurement zero point can be realized.
7. The two-wire hall-type active value current transmitter of claim 1, wherein: the two-wire output loop (6) is mainly composed of an NPN type driving triode, an overvoltage protection diode, a diode rectifier bridge, a load resistor and an external power supply, the diode rectifier bridge in the loop has a reverse connection protection effect, the external power supply can be connected into the two-wire output loop (6) in any direction, and 4-20 mA current signals are output and transmitted through the two-wire output loop (6) and power is supplied to an internal working loop.
8. The two-wire hall active value current transmitter of claim 1 wherein: the common-mode resistance-capacitance network (8) is formed by connecting 1 potentiometer and 1 capacitor in parallel and is connected in series between an excitation current return end of the Hall sensor (2) and a reference ground end returned by a constant voltage source and a constant current source of the V/I conversion circuit (5), and the 1.6mA constant current source output by the V/I conversion circuit (5) flows through the common-mode resistance-capacitance network (8), so that a proper common-mode voltage can be provided for the work of the differential amplifier by adjusting the resistance value of the potentiometer, and the capacitor can filter ripples of the common-mode voltage.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110187158A (en) * | 2019-06-26 | 2019-08-30 | 南京林业大学 | A kind of two-wire system Hall-type RMS current transmitter |
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2019
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110187158A (en) * | 2019-06-26 | 2019-08-30 | 南京林业大学 | A kind of two-wire system Hall-type RMS current transmitter |
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