JPH02216915A - Multi-point measuring instrument - Google Patents

Abstract

PURPOSE:To attain the multi-point measurement at high speed and with high reliability in comparatively simple constitution and to eliminate the mutual interference between the measuring channels by providing a pulse width modulating part to output a pulse width signal via a photocoupler in accordance with the value of an analog signal. CONSTITUTION:The pulse width modulating parts 311-31n are prepared at each measuring point, and output the pulse width signals via the photocouplers 331-33n in accordance with the value of an analog signal. A multiplexer 34 consists of a semiconductor switch and outputs selectively the pulse width signals supplied from the parts 311-31n. Then an A/D converting part 35 converts the pulse width signal received from the multiplexer 34 into a digital signal. In such constitution, the mutual interference is eliminated between the measuring channels. Then the multi-point measurement is attained at high speed and with high safety and high reliability.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a multi-point measuring device, and more particularly, to improving the characteristics of a device using a feedback pulse width modulation type A/D converter. It is.

<Prior Art> One type of multi-point measurement device that selectively takes in analog signals from a plurality of measurement points and converts them into digital signals uses a feedback pulse width modulation type A/D converter.

FIG. 2 is a block diagram showing an example of such a conventional device. Each input terminal 11 to 1 corresponds to multiple measurement points
Analog input signal A ijl + ~A applied to 1
jrL% is converted into a common signal form (for example, DC voltage) by each of the converters 21 to 2TL. These converters 2. The output signals of ~21 are selectively sent to a feedback pulse width modulation type A/D converter 4 via a scanner 3 using a relay.
input and converted into a digital signal. The feedback pulse width modulation type A/D converter 4 includes an analog section 5 consisting of a pulse width modulation (PWM) section that converts an analog signal into a pulse width signal, and an A/D converter that converts the pulse width signal into a digital signal.
It is composed of a D conversion section 6 and a photocoupler (PC) 7 that optically couples them in an electrically insulated state.

FIG. 3 is a configuration explanatory diagram showing an example of such a feedback pulse width modulation type A/D converter. In Figure 3,
8 is an input terminal for the analog input signal to be converted VLrL, and an operational amplifier 10 forming an integrator I via a resistor 9.
is connected to the inverting input terminal of A capacitor 11 is connected between the inverting input terminal and the output terminal of the operational amplifier 10, and the non-inverting input terminal is connected to a common potential point. 1
2 is an operational amplifier used as a comparator,
The output terminal of the operational amplifier 10 is connected to the non-inverting input terminal, and the inverting input terminal is connected to a common potential point. An output terminal of the operational amplifier 12 is connected to a data terminal of a flip-flop 14 via a photocoupler 13. The output terminal of the flip-flop 14 is connected to one input terminal of the AND gate 15, and its output signal PWM-
is applied to the selector switch 17 via the photocoupler 16 as a switching drive signal. The anode side of the reference voltage source -Vs is connected to one fixed contact a of the changeover switch 17, the cathode side of the reference voltage source -Vs is connected to the other fixed contact a, and the movable contact is operated via the resistor 18. amplifier 10
is connected to the inverting input terminal of Reference numeral 19 denotes a count clock generation circuit that outputs a count clock CCK, and its output terminal is connected to the clock terminal of the flip-flop 14 and to the other input terminal of the AND gate 15. The output terminal of the AND gate 15 is connected to a counter (not shown). 20 is a basic clock generation circuit that outputs a basic clock CK for keeping the integration period of the integrator I constant in order to remove the influence of the commercial power frequency, etc., and its output terminal is connected to the photocoupler 21. Amplifier 22. It is connected to the inverting input terminal of the operational amplifier 3 via a capacitor 23 and a resistor 24 that cut DC components. Note that the basic clock CK and the count clock CCK are synchronized. Also, photo coupler 13.16
．． 21 is used to electrically insulate the analog section and the digital section.

In such a configuration, the comparator 12 outputs a signal PWM having a pulse width proportional to the amplitude of the analog input signal to be converted VirL. That is, by measuring the pulse width of this signal PWM, the amplitude value of the analog input signal v to be converted can be determined. Therefore, this signal PWM is used as a gate signal, and the time related to the pulse width is counted using the count clock CCK. Note that the flip roller 114 is for outputting a signal PWM synchronized with the count clock CCK.

<Problem to be solved by the invention> However, according to this conventional configuration←, since a relay with mechanical contacts is used as the scanner 3,
Problems include slow operation speed, relatively short lifetime, low reliability, and short circuits between measurement channels when multiple relays are turned on at the same time.

In addition, since the measurement channels are switched before the photocoupler, for example, when performing multi-point measurements including AC power supply voltage, if the AC power supply voltage measurement channel and other signal measurement channels are short-circuited, the AC power supply There is also the risk that the power supply voltage will flow from the voltage measurement channel to other signal measurement channels, causing a serious accident.

The present invention has focused on these points, and its purpose is to provide a highly secure multiplex system that has a relatively simple configuration, can perform highly reliable high-speed measurements, and can prevent mutual interference between measurement channels. An object of the present invention is to provide a point measuring device.

Means for Solving the Problems> The multi-point measuring device of the present invention is a multi-point measuring device that selectively takes in analog signals from a plurality of measuring points and converts them into digital signals, and includes: a multi-point measuring device that is provided at each measuring point; A multiplexer consisting of a pulse width modulation section that outputs a pulse width signal according to the magnitude of the analog signal via a photocoupler, and a semiconductor switch, and selectively outputs the pulse width signal input from each pulse width modulation section. and an A/D converter that converts the pulse width signal output from the multiplexer into a digital signal.

Effect> In the multi-point measurement device of the present invention, the pulse width modulation section provided for each measurement point is electrically isolated from the A/D conversion section by a photocoupler, and each pulse width modulation section is made of a semiconductor. Selectively common A via a multiplexer using a switch
Since it is connected to the /D conversion section, mutual interference between measurement channels can be prevented, and high-speed measurement with high safety and reliability can be realized.

<Example> Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.

In FIG. 1, each analog input signal A1 to A1n1L corresponding to a plurality of measurement points is connected to each converter 3.
1+ to 321, it is converted into a pulse width signal PWM. That is, each converter 31. ~32TL11t are provided with pulse width modulation units 321 to 321 similar to the analog unit in FIG. The pulse width signal PWM output from each pulse width modulation unit 321 to 32TL is transmitted to the photocoupler 331 to
The signal is input to the multiplexer 34 via 331.

The output signal of this multiplexer 34 is input to an A/D converter 35 similar to the digital section in FIG. on the other hand,
From this A/D converter 35, the basic tarock CK is inputted to the demultiplexer 36, and the feedback pulse width signal PWM
- is input to the demultiplexer 37. The output signal CK of the demultiplexer 36 is output from the photocouplers 381 to 3.
87L to each pulse width modulator 32. 321, and the output signal PWM- of the demultiplexer 37 is input to the photocoupler 39. ~391 to each pulse width modulator 32
1 to 321 are input. In addition, multiplexer 3
4 and demultiplexers 36 and 37 are composed of semiconductor switches, and are simultaneously driven and controlled in accordance with a control signal Sc outputted from the control section 40 so as to select the same converter.

In such a configuration, selection of measurement channels is performed by converters 31 . This is performed by switching the connection relationship between the ~31TL and the A/D converter 35. By selectively connecting the converters 311 to 311 and the A/D converter 35 using the multiplexer 34 and the demultiplexer 36, 37 in this manner, feedback pulse width modulation substantially similar to that shown in FIG. A system A/D converter will be constructed.

With this configuration, selection of the measurement channel is performed after the photocoupler that performs insulating coupling. Therefore, the signal level handled is lower than in the case of switching selection using relays as in the past, and it is possible to use relatively inexpensive semiconductor switches as the multiplexer and demultiplexer. Since the measurement channels are selected after the photocoupler in this way, mutual interference between the measurement channels can be prevented.

In particular, in multi-point measurements including AC power supply voltage measurements, even if multiple selections including AC power supply voltage measurement channels are made, the AC power supply voltage is unlikely to flow into other measurement channels, and high safety can be maintained.

Furthermore, since the measurement channels are switched using a semiconductor switch, the drawbacks inherent to mechanical switches such as relays can be overcome.

Note that in the above embodiment, the reference clock CK and the feedback signal PWM- are sent to the A/D through the demultiplexer.
Although an example has been shown in which the reference clock CK is input from the conversion section to the pulse width modulation section, the reference clock CK may be always applied, or the feedback signal PWM- may be constantly fed back by providing a feedback loop within each pulse width modulation section. You can do it like this.

<Effects of the Invention> As explained above, according to the present invention, highly reliable high-speed measurement can be performed with a relatively simple configuration, and multi-point measurement with excellent safety can be performed by preventing mutual interference between measurement channels. The device can be realized and has great practical effects.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing an example of a conventional device, and FIG. 3 is a circuit showing a specific example of a feedback pulse width modulation type A/D converter. It is a diagram. 31...Converter, 32...Pulse width modulation unit, 33°38.39...Photocoupler, 34...Multiplexer, 35...A/D conversion unit, 36.37...Demultiplexer Figure 1

Claims (1)

[Claims] In a multi-point measurement device that selectively captures analog signals from a plurality of measurement points and converts them into digital signals, a pulse width signal provided at each measurement point is provided to generate a pulse width signal according to the magnitude of the analog signal. A pulse width modulation section that outputs via a photocoupler, a multiplexer that is composed of semiconductor switches and selectively outputs the pulse width signal input from each pulse width modulation section, and a pulse width signal output from this multiplexer. A multi-point measuring device comprising: an A/D converter for converting into a digital signal.