JPH0352006B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a pulse sending circuit for a flowmeter that sends out a pulse signal of a frequency corresponding to the value of an electric signal sent from a flowmeter. be.

[Prior art]

Figure 1 is a block diagram of a conventional example.
The output voltage Eo from the flowmeter, which is applied to
Here, a pulse signal with a frequency corresponding to the input voltage Ei is generated and sent from the output OUT ₁ , and if necessary, the frequency is divided by the frequency divider DV, and the frequency is output from the output OUT _2. Each of these outputs OUT ₁ and OUT ₂
An electromagnetic counter or the like is connected to indicate the integrated flow rate value.

In addition, the transmission frequency change range of VFC/V/F is
If D is a constant determined by the resistance value of the resistor R _t connected to this and determined according to the characteristics of VFC/V/F, then the sending frequency f is given by the following equation.

f = Ei / R _t・D (Hz) ...(1) However, in flowmeters used for industrial measurements, etc.
The minimum value and range of change of the output voltage Eo are determined by zero adjustment and span adjustment according to the measurement range of the flow rate, and there are also models that send out a current instead of the output voltage Eo, and these electrical signals are For example, 0 to 4V or 4 to 100% of
It is set to 20mA, etc.

For this reason, the span of the electrical signal sent out from the flowmeter differs depending on the type, and it becomes necessary to consider the scalar range constant S when setting Ei in equation (1).

Note that the scalar range constant S is expressed by the following equation, where α is the coefficient.

S=Q _S /Q _P・α ...(2) Q _P : Flow rate per pulse of the sending pulse signal Q _S : Flow rate when the flow meter output is at its maximum value Therefore, Fig. 1 In this configuration, when adjusting the potentiometer RV, the scaler range constant S must be directly readable, and the potentiometer RV must be of high precision, which has the disadvantage of being expensive. will occur.

In addition, in order to improve the conversion accuracy by VFC/V/F, the output voltage Eo applied to the input IN or the current flowing thereto is increased, and
Frequency division using a frequency divider DV has also been adopted, but this requires the flow meter to have a high output, and
A frequency divider DV must be used, which has the disadvantage of being generally expensive.

[Summary of the invention]

The present invention has the purpose of fundamentally solving such drawbacks of the conventional art, and includes a VFC that receives an electrical signal as a voltage signal and sends out a pulse signal of a frequency corresponding to the voltage signal, and two terminals each connected to the VFC at one end.
four resistors whose resistance values are weighted decimally, and four resistors connected to each of the other ends of the four resistors and having decimal markings;
A switch is provided which generates a voltage signal corresponding to a pulse signal of one digit frequency by binary selection so that the combined resistance value is inversely proportional to the decimal display value. The present invention provides an extremely effective pulse sending circuit for a flowmeter in which the frequency of the pulse signal to be sent can be set to a desired value.

〔Example〕

The details of the present invention will be explained below with reference to FIG. 2 and subsequent figures showing embodiments.

Figure 2 is a block diagram that includes an electromagnetic flowmeter, and the magnetic flux generated by the excitation winding EC flows through the measurement tube.
As the fluid L flowing through the MP intersects with the magnetic flux, an electromotive force is generated according to the flow velocity of the fluid L, and this is detected by the electrodes P ₁ and P ₂ . , these detect the detection part.
DET is configured.

The detected voltages from the electrodes P ₁ and P ₂ are amplified by the amplifiers A ₁ and A ₂ of the conversion unit CNV, and the difference between both inputs is determined by the differential amplifier DA, and then the zero adjustment circuit ZAJ and the span adjustment Via circuit SAJ,
It is applied to the output circuit OC and becomes an electric signal of voltage or current, which is sent out from the output OUT _Q as an electric signal indicating the measured flow rate determined by the cross-sectional area of the measuring device MP and the flow rate of the fluid L.

Output OUT _Q has VFC/V/V via input IN.
F is connected, and if the electrical signal from the output OUT _Q is a voltage, it remains as is, and if it is a current, it is connected to a resistor.
Insert Ri to convert to voltage and convert these voltages Ei to
VFC/V/F receives and responds to the frequency f
It is designed to generate a pulse signal and send it out from the output OUT _P.

In addition, for VFC/V/F, the resistor R _t shown in Figure 1 is used.
The resistance values 8・R, 4・R,
2・R, 1・R, 80・R, 40・R, 20・R, 10・
Resistors with different resistance values depending on the binary relationship of R, 800・R, 400・R, 200・R, 100・R
R ₁ ~ _{R 4} , R ₁₁ ~ R ₁₄ , R ₁₀₁ ~ _{R 104} are provided,
One end of these is connected in common and VFC
V/F, and the other ends of these are connected to resistors R ₁ to _{R 4} , each having a resistance value of the same number of digits.
For each group of R ₁₁ to _{R 14} and R ₁₀₁ to R ₁₀₄ , fixed electrode terminals ₁ , ₂ ,
4 and 8, respectively, and to the VFC/V/F via the movable terminals C of the switching devices _S1 to _S3 .

However, as shown in FIG. 3 showing the front view of the head, the switching devices S ₁ to _{S 3} each perform rotation switching in 10 steps from "0" to "9", and the "0" on the display ”
.about.9, fixed electrode terminals 1, 2, 4, and 8 are binary selected and connected to movable electrode terminal C.

Note that the capacitor _C1 is also involved in determining the frequency like the resistor _Rt , but since it is fixed, it is included in the constant D in equation (1).

Here, if the decimal point is set as indicated by the △ mark in Figure 3A, and the input voltage Ei is given by the linear change characteristic of the measured flow rate of 1/sec, then the right side of equation (1) can be written as the following equation: By setting as shown in FIG. 3A, the setting corresponding to the display values "0" to "9" of the switching devices S ₁ to _{S 3} corresponds to the display values "0" to "9". The frequency f of the sending pulse signal is determined.

K=Ei/R・D=8……(3) ∴f=1/Σr・8……(4) Then, Σr is the resistor R ₁ ~ selected by the switch S ₁ ~ _{S 3} This is the parallel combined resistance value of _R104 .

In other words, switch S ₁ is set to "1", and S ₂ and S ₃ are set to "0".
If set to , only the resistor R ₁ is connected, and the frequency f is obtained from equation (4): f = 1/8 x 8 = 1.0 (Hz) Also, set the switch S ₁ to "3", S ₂ , S When ₃ is set to "0", R ₁ and R ₂ are connected in parallel, and from equation (4), f = (1/8 + 1/4) x 8 = 3.0 (Hz) Switch S ₁ , S ₃ If you set "0" and S ₂ to "1", only resistor R ₁₁ is connected, and from equation (4), f = 1/80 x 8 = 0.1 (Hz) Switch S ₁ , S ₂ When is set to " ₀ " and S ₃ to "1", only resistor R ₁₀₁ is connected, and similarly, f = 1/800 x 8 = 0.01 (Hz) _. If S ₃ is set to ``0'', resistors R ₁ and R ₁₁ are connected in parallel,
Similarly to the above, f = (1/8 + 1/80) x 8 = 1.1 (Hz) Also, when the switches S ₁ to _{S 3} are each set to "1", the resistors R ₁ , R ₁₁ , and R ₁₀₁ Connected in parallel, similarly, f = (1/8 + 1/80 + 1/800) x 8 = 1.11 (Hz
) Therefore, as is clear from the above example, the binary selection according to the decimal marking of the resistors R ₁ to _{R 104} by the switches S ₁ to _{S 3} causes the resistors R _{1 to}
~The parallel combined resistance value of R ₁₀₄ exhibits a binary change,
The frequency f is set to match each digit of the decimal display value "0" to "9", and based on this, the frequency f changes according to the measured flow rate.

However, rather than the unit of measurement in /sec, e.g.
The same applies when using the unit of measurement m ³ /h,
It is sufficient to set a conversion coefficient in the VFC/V/F or frequency dividing circuit.

In addition, as VFC/V/F, integrated circuit
LM331 type (National Semiconductor CO.LTD
), the rotary switch S is used as the switch S ₁ to _{S 3} .
-2010 type (manufactured by Copal Electronics KK) etc. are suitable.

In addition, due to measurement conditions or changes in the flowmeter, the change characteristics of the input voltage Ei may change to 10/sec of the measured flow rate.
When this happens, just move the decimal point marked △ as shown in Figure 3B. In case A, the flow rate per pulse is 1, while in case B,
The flow rate per pulse is 10, and the frequency f can be set accordingly.

Note that by adjusting each value of equation (4) depending on the situation, an arbitrary setting range of the frequency f can be obtained.

Therefore, the frequency f can be set in accordance with the decimal display value "0" to "9", and this setting is easy and the setting status can be read directly.
The accuracy of converting input voltage Ei to frequency f is improved,
Moreover, it is inexpensive as it does not require particularly expensive parts, and
This makes it possible to share circuits with various flowmeters.

Moreover, the resistors R ₁₁ to R ₁₄ , R ₁₀₁ to _{R 104} are R ₁ to
Compared to _R4 , resistance value errors have less influence on the parallel combined resistance value, and inexpensive ones can be used for these.

However, as VFC/V/F, it is also possible to use a device that sends not only pulse signals but also signals with other waveforms as long as it has the same function. In this case, waveform shaping is required separately. In addition to adding a circuit, etc., it is also possible to add a frequency divider to send out pulse signals in each frequency range, and the number of switchers S ₁ to _{S 3} depends on the number of digits required. It is possible to use other switches or strap terminal boards as the switching devices _S1 to _S3 , etc.
Various modifications are possible.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, a pulse sending circuit having a frequency setting function that can be directly read in decimal form can be obtained with an inexpensive configuration, and can convert the electrical output of various flowmeters into pulse signals. When transmitted, it has a remarkable effect.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional example, Fig. 2 and subsequent figures show examples of the present invention, Fig. 2 is a block diagram, and Fig. 3 is a block diagram of a conventional example.
The figure is a front view of the head of the switching device. DET...detection section, CNV...conversion section, OUT _Q ,
OUT _P ...Output, IN...Input, V/F...VFC
(voltage/frequency converter), R ₁ ~ R ₄ , R ₁₁ ~ _{R 14} ,
_R101 to _R104 ...Resistor, _S1 to _S3 ...Switcher.

Claims (1)

[Claims] 1. A pulse sending circuit that is connected to the output of a flowmeter that sends out an electrical signal within a predetermined range in accordance with a measured flow rate, and that sends out a pulse signal with a frequency corresponding to the electrical signal, comprising: a voltage/frequency converter that receives a voltage signal and sends out a pulse signal with a frequency corresponding to the voltage signal;
four resistors connected to the frequency converter and having binary weighted resistance values; connected to each of the other ends of the four resistors and having decimal markings; and a switch for generating a voltage signal corresponding to a pulse signal with a frequency of one digit by binary-selecting the resistors such that the combined resistance value thereof is inversely proportional to the decimal indicated value, 1. A pulse sending circuit for a flowmeter, characterized in that four resistors are switched by one of the switching devices to generate a pulse signal with a frequency corresponding to one digit.