JPS5842927Y2 - Vibrating density meter - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a vibrating density meter, which is one type of liquid density meter.

Conventional devices of this type have a standard oscillator, which calculates the difference between the standard frequency and the output frequency of the detection section, and provides this to the frequency/voltage conversion circuit, due to accuracy constraints on the frequency/voltage conversion circuit. It is configured.

However, with this conventional device, it is necessary to select a standard oscillator with an appropriate frequency depending on the measurement range.
The circuit constants of the frequency/voltage conversion circuit that was cut must be changed.

Furthermore, when trying to obtain a wide measurement range, the error in the frequency/voltage conversion circuit becomes large and the accuracy decreases considerably.

In the past, in conventional buttons, temperature compensation was performed based on the assumption that the output frequency of the detection section changes in proportion to the temperature.

For this reason, accuracy is poor. An object of the present invention is to provide a vibrating density meter that eliminates the drawbacks of the conventional devices as described above.

The present invention will be explained in detail below with reference to the drawings.

The figure is a configuration diagram showing an embodiment of the device of the present invention.

In the figure, 1 is a base, 2 is a thin-walled pipe whose one end is attached to the base cover 1, and 3 is a connecting block that connects the other ends of the pipes 2.

The mass of the block 3 is chosen to be considerably smaller than that of the base 1.

Further, the base 1 and the block 3 are provided with a passage for the liquid to be measured through the hole of the pipe 2.

Reference numeral 4 designates a temperature sensing element, such as a temperature sensing resistor, arranged in the passageway of the block 3.

5 is a magnet placed opposite to each other across the pipe 2, and 6 is a transformer.

In this transformer 6, the oscillator (1 tongue) operated by the base 1, the pipe 2, and the block 3 is used as a secondary winding.

T is a detection electrode for detecting the displacement of the pipe 2 as a capacitance change; 8 is an oscillation amplifier that supplies current to the transformer 6;
9 is a power source.

Among the above, base 1, pipe 2, block 3, magnet 5,
The transformer 6, the electrode 7 button, and the amplifier 8 form a detection section 100.

10 is a signal conversion circuit that converts the output of the temperature sensing element 4 into a frequency signal according to its magnitude; 11 is a signal conversion circuit that receives the output of the signal conversion circuit 10 and the output of the detection unit 100 (amplifier 8) as input; 12 is a counting circuit that counts the output frequency of the signal selection circuit 11, 13
is a digital arithmetic circuit which uses the output of the counting circuit 12 as its power.

This arithmetic circuit 13 has a function of sending a command signal to the signal selection circuit 1F to output which signal, and a function of sending command signals to the counting circuit 12 to reset the count value and start and stop counting. It has

The operation of the device of the present invention constructed in this manner will be described next.

When a current i flows from the amplifier 8 to the primary winding of the transformer 6, the current i flows to the vibrator, which is the secondary winding, and the pipe 2 in the magnetic field is displaced according to Fleming's left-hand rule.

This displacement is detected by a capacitance type detection electrode 7 provided close to the pipe 2, and is positively fed back to the round blade side of the amplifier 8.

As a result, ζ Eve 2 vibrates at the natural frequency of the oscillator with its center as an antinode.

Since the liquid to be measured is flowing in the pipe 2, the frequency of the A signal with frequency f is output.

Further, the signal conversion circuit 10 outputs a signal with a frequency f8 corresponding to the temperature t of the number to be measured.

−t, the frequency f of the vibrator is expressed by the following equation.

however C: constant t: length of pipe 2 ρ1: Density of pipe 2 D: Outer diameter of pipe 2 D2: Inner diameter of pipe 2 ρ: Density of fixed liquid From the upper ridge equation, ρ is expressed by the following equation.

However, according to experiments, A(t) can be approximated with sufficient accuracy by a quadratic equation instead of the linear equation 1 for the temperature t, and B(t) can theoretically be approximated by a cubic equation since it is a change in density.

That is, A(t) and B(t) can be expressed by the following equations.

A(t)=a +a t+a2t2
(5) 1 B (2 b+b t+b t+b t
(6) 0 1 2 3 where a a a: Constant 0, 1. 2 b b b b: constant 0, l, 2. 3 In the device of the present invention, the arithmetic circuit 13 operates based on the above equations (2), (5), and (6).

That is, the arithmetic circuit 13 first causes the signal selection circuit 11 to select the output of the signal conversion circuit 10, and causes the counting circuit 12 to count the frequency fs.

Next, the output of this counting circuit 12 is read and the temperature t is determined.

Furthermore, this temperature t and the preset a "'-
From a0 2゜b −b, based on equations (5) and (6), A
(t), B(t)3 is calculated.

Next, the arithmetic circuit 13 reads the frequency f using the signal selection circuit 11 and the counting circuit 12 in the case of the frequency f and A(t)$ obtained by the above calculation.
- and B(t) are substituted into equation (2), and the density ρ of the liquid to be measured is
7, and outputs a signal corresponding to ρ, or further determines the density at the reference temperature and outputs a signal corresponding to this.

Note that the configuration of the counting circuit 12 that counts the frequencies fX and f8 is such that the period 1/f 1/f is measured and the interval X,
S It may be something that directly counts fx and f8.

As explained above, the device of the present invention is constructed without using a frequency/direct voltage conversion circuit or a standard oscillator.

Therefore, even if the measurement range is wide, there is no decrease in accuracy, and the measurement range can be easily changed.

Furthermore, since temperature compensation is performed using a digital arithmetic circuit, accurate temperature compensation can be performed.

Further, a vibrating densitometer is frequently used as a densitometer because concentration and density have a fixed relationship with temperature as a parameter.

In such a case, the apparatus of the present invention is advantageous because the concentration can be easily determined from the temperature t and the density ρ using the digital calculation section.

[Brief explanation of the drawing]

The figure is a configuration diagram showing an embodiment of the device of the present invention. 100...detection section, 4...temperature sensing element,
10... Signal conversion circuit, 11... Signal selection circuit, 12... Counting circuit, 13...
・Digital calculation circuit.

Claims (1)

[Scope of utility model registration request] A detection unit that generates a frequency signal corresponding to the vibration frequency of a pipe through which a liquid to be measured flows, a temperature sensing element disposed within the detection unit to detect the temperature of the liquid to be measured, and this temperature sensing element. a signal conversion circuit that converts the output of the signal conversion circuit into a frequency signal, a signal selection circuit that receives the output of this signal conversion circuit and the output of the detection section as input, and counts the output frequency of this signal selection circuit and outputs it as a digital signal. A vibrating density meter equipped with a counting circuit and a digital calculation circuit that performs temperature compensation calculations based on the output of this counting circuit.