JPH03289537A - Measuring circuit - Google Patents

Abstract

PURPOSE:To make it possible to measure inputs in a broad range and to perform highly accurate measurement and to correctly grasp the tendency at the time of abnormality by setting a region whose resolution is different in one range. CONSTITUTION:A comparator 4 imparts a signal for changing a gain from alpha1 to alpha2 when a specified voltage is inputted into a variable-gain amplifier 3. When a voltage V1 which is inputted into the amplifier 3 is smaller than a constant voltage Vc which is generated in a constant-voltage diode ZD1, an output voltage V2 of the amplifier 3 has the value obtained by multiplying the voltage V1 by the gain alpha1. The voltage V2 when the voltage V1 is larger than the voltage Vc has the value obtained by adding the output of an amplifier OA6 to the output that is changed to alpha2 from the gain of an amplifier OA4. The voltage V2 undergoes A/D conversion without decreasing resolution. In this way, the inputs in the broad range can be measured without switching the range, and the highly accurate measurement and the grasping of the tendency at the time of abnormality can be correctly performed.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a measuring circuit used in water quality measuring instruments and the like.

B1 Summary of the Invention The present invention detects an input in a measurement circuit that performs detection and measurement over a wide range, and automatically changes the gain when the input is at a predetermined level. This allows for high-precision measurements and accurate understanding of trends in abnormal situations.

C0 Conventional Technology Turbidity meters, densitometers, and the like used to measure water quality utilize transmission and scattering of light, and perform arithmetic processing on received light signals to determine the quality of water. Digital technology is utilized in the calculation section of measuring instruments, and microcomputers are often used. By using a microcomputer, advanced calculations, signal processing, and various additional functions can be easily realized.

By the way, the signal obtained by the detection section is generally an analog quantity, and in the case of a turbidity meter, it is a voltage proportional to the amount of light received by the photodiode. An A/D converter is required at the connection between the analog circuit and the digital circuit, and the resolution of the detection signal is limited at this point. For example, for an 8-bit A/D converter with an input range of 0 to IOV, the resolution is I/25
6, and 39 mV per gradation.

In order to perform detection measurements over a wide range without reducing resolution, a variable gain amplifier is required. The reason is as follows.

(1) In order to transmit the analog signal from the detection section to the conversion section, it is advantageous to amplify the analog signal as much as possible to increase the S/N ratio.

(2) The input voltage range of the A/D converter is limited.

(3) A/D converters with high resolution are expensive.

(4) Digital processing of inputs with high resolution (large number of bits) is complicated accordingly.

Therefore, the turbidity meter (Meiden Jiho Bulletin No. 197, 1987)
In the No. 6r water purification plant meter), as shown in FIG. The variable gain amplifier 13 is an operational amplifier O
A, two input resistances R++, R,2, two feedback resistances R13+ R,, and an analog switch S, and by switching the input resistance and feedback resistance of the operational amplifier OA s with the analog switch S. , 4 ranges. The gain is as shown in the table below.

In this case, a determination process as shown in FIG. 9 is performed to prevent the resolution of the full scale in each range from deteriorating. However, to simplify the explanation, FIG. 9 shows two ranges of operation.

Note that the detection signal is converted into a DC signal by a filter circuit I4, a rectifier circuit, etc. after the variable gain amplifier 13, and then
It will be transmitted to the conversion section (arithmetic processing section).

D1 Problems to be Solved by the Invention The turbidity value of the output signal obtained by the measuring instrument having the above configuration is unknown unless the range signal is simultaneously received. Furthermore, when the number of ranges is increased, the number of signal lines for range signals increases.

In particular, when we look at the usage of turbidity meters, we find that, for example, in the receiving well of a water treatment plant, the normal measurement value is about 5 to 10 degrees, but it can suddenly change to about 500 degrees due to rain or other factors. There is movement. The high concentration is often temporary, but the range changes many steps and the gain changes when rising and falling. In such cases, it is difficult to grasp the situation using a recorder or the like. In addition, when the turbidity is normally low, it is necessary to measure the measurement value with high accuracy, but when there is a temporary abnormality, it is necessary to understand the degree and trend in order to make predictions and countermeasures.

Note that in order to obtain an output for a wide range of input voltages, as shown in Figure 1O, a resistor R1I is connected to one input terminal of the operational amplifier OAs, and a resistor R12 is connected to the output terminal. End and resistance R1! A transistor Q is connected between the output terminal side of the transistor Q
There is a logarithmic compression circuit in which the other input terminals of the base seven operational amplifiers OAs are respectively grounded.

However, this has the following problems.

(1) It is difficult to convert with high accuracy.

(2) It is difficult to linearize (inverse calculation) after inputting to a digital circuit.

An object of the present invention is to provide a measurement circuit that has multiple resolution regions in one range and can perform normal high-precision measurements over a wide range of inputs and accurately grasp trends in abnormal situations. .

81 Means for Solving the Problems The present invention includes a variable gain amplification circuit which mainly includes an operational amplifier and amplifies an input voltage proportional to a detected amount, and which detects the level of the input voltage and amplifies the amplification circuit when the input voltage reaches a predetermined level. It is characterized in that it includes an input level detection section that prompts the circuit to change the gain, and that one level has a plurality of regions with different resolutions.

When the level of the F1 action input voltage is detected and a gain change signal is applied to the variable gain amplifier circuit when it is at a predetermined level, the gain of the amplifier circuit is automatically changed. In other words, one range has regions with different resolutions.

Therefore, A/D conversion can be performed without lowering the resolution.

G. Examples Hereinafter, the present invention will be explained in detail based on examples shown in the drawings.

1 to 4 show an embodiment of the present invention.

In FIG. 1, l is a fort diode, 2 is a preamplifier, 3 is a variable gain amplifier, and 4 is a comparator that provides a gain change signal to the variable gain amplifier 3 at a predetermined input voltage. The relationship between the input voltage (voltage proportional to the photodetection voltage) vl and the output voltage V is as shown in FIG.

That is, in the range where the input voltage ■ is O-V, the gain G=
α3, gain G=α in the range VII-VII.

Therefore, the output voltage V, is V! when the input value vII. 1.V
When at, it becomes V□.

As shown in FIG. 3, the comparator 4 has a configuration in which a constant voltage diode ZD is connected between the (-) input terminal of the operational amplifier OA and the ground point, and (1) an input voltage vI is applied to the input terminal. ing.

The variable gain amplifier 3, as shown in FIG. 4, is composed of an operational amplifier 0At-OAe, an analog switch s1, a large number of resistors, and the like. The output stage amplifier OA t has a gain of G=1, the amplifier OA to which only the input voltage vI is applied has a gain of G-a, and the amplifier OA4 to which (V r V II) is applied has a gain of G-α.

The constant voltage V13, VH is the constant voltage diode ZD.
The constant voltage Vc generated at I is amplified by amplifiers OAs and OAe. The analog switch S is provided between the amplifiers OAs, OA, , OAs and the amplifier OAt. The switch S is an opening/closing part SI%S2,S.

have. The opening and closing operations of SI, S2, and S3 are opposite to each other, and S is turned on in the low gain region, and Sl and S3 are turned on in the high gain region.

Next, we will discuss the operation. When V, <Vc, the output Vcc of comparator 4 is "0", and the analog switch S is S
, is ON, Sl and S are OFF, and the output voltage ■,
becomes V t = V I · α1.

■When ≧Vc, the output ■CC of comparator 4 is “
l'', analog switch S is OFF, S1 is OFF.

And S3 is turned ON. Therefore, the output (V IV + + )・α of amplifier OA4 is connected to the input terminal of amplifier OA t.
.

and the output V 2 I of amplifier OA a are added together.

That is, the output voltage V is: V t = (V + V r 1) ” αt +
V t +.

Output voltage ■, can be adjusted by A/D without lowering resolution in signal processing section.
converted.

For example, if the output voltage ■ is assigned to 8 bits (256 gradations), 192 gradations are assigned to 0 to VtI, V2. ~6 on VH
Four gradations can be assigned. Converting this to an input voltage, in terms of input, it is 26 mV per gradation for O < V and < V, and 78 m for Vll ≦ V + < V r t.
The resolution is V. However, this is the case where V 1t-10V.

FIG. 5 shows another embodiment of the present invention, in which an input resistor R1 is connected to one input terminal of the operational amplifier OA 7, and the other input terminal is grounded. Further, a resistor R7 is connected between one input terminal and the output terminal, and a series circuit of a resistor R3 and a constant voltage diode ZD is connected in parallel to this resistor R7.

With such a circuit configuration, when an input voltage V is applied, the gain changes at a certain voltage, resulting in input/output characteristics (VIV2 characteristics) as shown in FIG. The gain α is R, /R,,
α is (Rt +R3)/R+・R2・R3.

FIG. 7 is a flow diagram showing a process for linearizing the output again after A/D converting the output voltage described above using the digital circuit.

In addition, although the said description was made with application to a turbidity meter and a concentration meter, it is applicable not only to these but also to other measuring instruments. In addition, in the above embodiment, low turbidity region = high accuracy (high resolution)
However, depending on the application, it can be reversed or applied to change the resolution of a specific area in the middle. There are 3 resolution setting stages.
It may be more than one stage. Furthermore, it is also possible to add it as a "wide scale Lenz" to conventional automatic range switching measuring instruments.

H1 Effects of the Invention As described above, according to the present invention, since regions with different resolutions are set within one range, it is possible to measure a wide range of inputs without having to change ranges in many stages, and high-precision measurement is possible. This makes it possible to accurately grasp trends in abnormal situations, and also enables measurement without using a high-bit A/D converter.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the measuring circuit according to the present invention, Fig. 2 is an input/output characteristic diagram of the embodiment, Fig. 3 is a circuit configuration diagram of a comparator in the embodiment, and Fig. 4 is a block diagram showing an embodiment of the measuring circuit according to the present invention. FIG. 5 is a circuit diagram showing the configuration of the variable gain amplifier in the same embodiment, FIG. 5 is a circuit diagram showing another embodiment of the present invention, FIG. 6 is an input/output characteristic diagram of another embodiment, and FIG. 7 is an A/ A flow diagram for linearization processing after D conversion, FIG. 8 is a circuit diagram showing a conventional example,
FIG. 9 is a flowchart for conventional determination processing, and FIG. 1O is a connection diagram of a logarithmic compression circuit. ■...Photodiode, 2...Preamplifier, 3...
・Variable gain amplifier, 4... comparator, OA, ~
OA? ...Operation amplifier, S...Analog switch, ZD, and ZD, ... Constant voltage diode, Vl...
・Input voltage, ■, output voltage, α, and α, ... Gain of variable gain amplifier. 2 people outside Figure 6 Figure 7 D-----One person's strength 〒 and 7-7yru A fin with two teeth □ Shoulder level yCh----Human power turned hVγ and Sokan T Gradation D2--...-Person 7UL■22I This 1st eye''315th floor 4[)2>D+>0

Claims (1)

[Claims] (1) A variable gain amplifier circuit mainly composed of an operational amplifier that amplifies an input voltage proportional to the detected amount, and an input level that detects the level of the input voltage and prompts the amplifier circuit to change the gain when the input voltage reaches a predetermined level. A measuring circuit comprising a detection section and having a plurality of regions with different resolutions in one range.