Field device

Abstract

A field device includes a detected signal converter configured to convert a detected signal of a sensor into a predetermined voltage and then to output the voltage, an amplifier configured to amplify an output signal of the detected signal converter, and a switching power supply as an internal driving power supply of the field device.

Claims

1. A field device comprising: a detected signal converter configured to convert a detected signal of a sensor into a predetermined voltage and then to output the voltage; an amplifier configured to amplify an output signal of the detected signal converter; and a noise filter, wherein the detected signal converter is configured to set a primary-side voltage of the noise filter as a reference voltage.

2. A field device comprising: a detected signal converter configured to convert a detected signal of a sensor into a predetermined voltage and then to output the voltage; an amplifier configured to amplify an output signal of the detected signal converter; a switching power supply as an internal driving power supply of the field device; and a noise filter, wherein the amplifier is configured to set a primary-side voltage of the noise filter as a reference voltage.

3. The field device according to claim 1, wherein the field device is a pressure transmitter.

4. The field device according to claim 2, wherein the field device is a pressure transmitter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a block diagram showing a voltage output type transmitter according to an embodiment of the present invention.

(2) FIG. 2 is a block diagram showing a voltage output type transmitter according to another embodiment of the present invention.

(3) FIG. 3 is a block diagram showing a voltage output type transmitter according to further another embodiment of the present invention.

(4) FIG. 4 is a block diagram showing an example of a related-art voltage output type transmitter.

DETAILED DESCRIPTION

(5) The present invention will be now described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing a voltage output type transmitter according to an embodiment of the present invention, wherein the same parts as those in FIG. 4 are designated by the same reference numerals. As the voltage output type transmitter, a pressure transmitter having a pressure sensor is used, for example. In FIG. 1, a switching power supply 9 is provided instead of the linear regulated power supply 6 used as a power supply for supplying a driving voltage to each internal part of the device in the circuit configuration of FIG. 4.

(6) A subtractor 10 is connected to a D/A converter 3 and an amplifier 4. An output terminal of the D/A converter 3 is connected to one input terminal of the subtractor 10. A connection point P between a noise filter 5 on a ground wiring G, a voltmeter 8 and a minus terminal of a DC power supply 7 is connected to the other input terminal thereof.

(7) In this configuration, the switching power supply 9 is operated so that an operation current I is decreased when a primary-side power supply voltage is high and the operation current I is increased when the power supply voltage is low. Namely, the switching power supply is operated so that power consumption is kept substantially constant even if the primary-side power supply voltage is varied.

(8) Because the operation current I is varied depending on the power supply voltage by using the switching power supply 9, it seems that an input impedance to a transmitter is lower as compared to the related-art example shown in FIG. 4.

(9) As a result, a noise N is intruded from the exterior to flow as a noise current I.sub.N in the ground wiring G, so that the operation current I is changed to generate an error voltage E.sub.error.

(10) However, according to the circuit configuration of FIG. 1, the error voltage E.sub.error is subtracted from the output voltage of the D/A converter 3 by the subtractor 10, so that an influence of the error voltage E.sub.error is compensated and a correct voltage in which the influence of the error voltage E.sub.error is compensated is outputted to the voltmeter 8.

(11) Because the switching power supply 9 is mounted as an internal driving power supply of a voltage output type field device, which is configured to convert an detected signal of a sensor 1 into a predetermined voltage and then to output the voltage, the field device can be operated with a lower power consumption as compared to the related-art configuration shown in FIG. 4, even if a voltage of the DC power supply 7 is high.

(12) Also, by providing the subtractor 10 serving to correct the influence of the error voltage E.sub.error, the correct output voltage can be obtained even if the noise filter 5 is employed.

(13) In the related art, from the point of view that a sufficient noise rejection performance cannot be ensured, the switching power supply has never been mounted as the internal driving power supply of the voltage output type field device, but this can be realized owing to the circuit configuration as in the present invention.

(14) FIG. 2 is a block diagram showing a voltage output type transmitter according to another embodiment of the present invention, wherein the same parts as those in FIG. 1 are designated by the same reference numerals. Differences between FIGS. 1 and 2 are in that a primary-side voltage of the noise filter 5 is used as a reference voltage. More specifically, the subtractor 10 in FIG. 1 is not required in FIG. 2 and also the connection point P between the noise filter 5 on the ground wiring G, the voltmeter 8 and the minus terminal of the DC power supply 7 is connected as a reference voltage of the D/A converter 3 and the amplifier 4.

(15) According to the configuration of FIG. 2, the reference voltage of the amplifier 4 is not influenced by the error voltage E.sub.error, and like the configuration of the FIG. 1, a correct voltage which is not influenced by the error voltage E.sub.error is outputted to the voltmeter 8.

(16) In addition, according to the configuration of FIG. 2, the subtractor 10 of FIG. 1 is not required, thereby obtaining the effect of reducing the number of parts as compared to the configuration of FIG. 1.

(17) FIG. 3 is a block diagram showing a voltage output type transmitter according to further another embodiment of the present invention, wherein the same parts as those in FIG. 1 are designated by the same reference numerals. Differences between FIGS. 1 and 3 are in that the subtractor 10 in FIG. 1 is not required in FIG. 3 and also the error voltage E.sub.error at the connection point P between the noise filter 5 on the ground wiring G, the voltmeter 8 and the minus terminal of the DC power supply 7 is converted into a digital signal by an A/D converter 11 and then fed back to a measurement control unit 2.

(18) The measurement control unit 2 performs the calculation of subtracting a value of the error voltage E.sub.error, which is fed back as the digital signal through the A/D converter 11, from a set value of the D/A converter 3.

(19) According to the configuration of FIG. 3, a voltage output transmitter in which noise rejection performance and output accuracy are compatible with each other can be realized like the configurations of FIGS. 1 and 2.

(20) Also, although in each of the foregoing embodiments, the voltage output type transmitter as the field device is described by way of example, the field device is not limited to the transmitter, and for example, may be a flow meter.

(21) As described above, according to the present invention, a field device having a lower power consumption and a higher noise rejection performance can be realized.