JPH02232523A - Flow-rate measuring apparatus - Google Patents

Abstract

PURPOSE:To decrease errors due to temperature change and to make it possible to use this apparatus in all environments by correcting an electric signal which is sent from a differential pressure transmitting device by the temperature of a heat reserving case which is obtained from an ambient temperature detector. CONSTITUTION:A differential pressure transmitting device 3 is contained in a heat reserving case 2. An ambient temperature detector 11 is provided in the vicinity of the differential pressure transmitting device 3. The obtained temperature signal is sent into an electronic computer 5 through a process input/output device 4 by the same way as a differential pressure signal. The electronic computer 5 corrects the error in the differential pressure signal from the inputted temperature signal. In this way, the flow-rate measuring apparatuses can be provided under various environments, and errors in flow rates can be decreased by the temperature correction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a flow rate measuring device that inputs data obtained from a flow rate sensor and corrects errors.

(Prior art) Figure 4 shows the conventional configuration of a differential pressure flow rate measuring device using an orifice plate with a differential pressure transmitter placed in a constant temperature bath. The differential pressure type flow measuring device using an orifice plate is configured to reduce the pressure P8 on the outlet side by attaching the orifice plate 2 to the piping 1, and the pressure P2 is transmitted to the differential pressure transmitter 3 along with the pressure P1 on the inlet side. Sent to. In the differential pressure transmitter 3, the differential pressure between the received pressures P, , P, is converted into an electrical signal and sent to the electronic computer 5 via the process input/output device n4. This differential pressure transmitter 3 is placed in a constant temperature bath 8 equipped with a fan 6 and a heater 7, and the temperature is kept constant to reduce fluctuations due to temperature changes. The instantaneous value of the electric signal sent to the electronic computer 5 is read at regular intervals by the input scanning means 9, and the calculation means 10 performs calculations with corrections to determine the flow rate. Next, the conventional correction calculation method will be explained with reference to the block diagram in Fig. 5. In addition, during circulation, F is the flow rate, Q is the flow rate according to the flow rate equation, and Δ
Pya^ is the differential pressure signal from the measuring device, ΔP is the differential pressure after unit conversion, ΔP' is the differential pressure after instrumental error correction, ΔPT is the maximum converted differential pressure in the measuring device, Io is the signal zero point output of the measuring device value, I1oa is the signal 100% output value of the measuring device, ΔP
max is the design maximum differential pressure, F Ilax is the design maximum flow rate,
■D is the specific volume due to design temperature and pressure. Tf is the temperature of the fluid, Pf is the pressure of the fluid, E is the coefficient of linear expansion of the nozzle material, T
represents the thermal expansion correction reference temperature. First, the differential pressure signal ΔP■A received by the calculation means IO is converted into an actual differential pressure by unit conversion means 201 (m
A-nmH, O) is performed to find ΔP. However, since this ΔP includes the error of the differential pressure transmission itself, the instrumental error correction means 202 performs instrumental error correction.
Comparator 203 determines ΔP'. Here, the differential pressure signal ΔP′ to which the instrumental error correction has been added is the design maximum differential pressure ΔPmax, and the instrumental error correction obtained from ΔP is f
If (ΔP) (%), it can be found by . The flow rate calculation means 204 calculates the flow rate Q using the flow rate equation from ΔP'. Next, the compression correction means 205 performs a compression correction on the flow rate Q based on the compressibility of the fluid, and the expansion correction means 206 performs an expansion correction on the thermal expansion of the nozzle to determine the flow rate F. Correction based on the compressibility of the fluid is performed by setting the temperature of the fluid to Tf and the pressure of the fluid to Pf. If the corrected flow rate is Q', then The above formula (7) VSC (Tf, Pf) is the temperature Tf and pressure Pf
Correction by nozzle thermal expansion, which is a function for determining the specific volume in
)" Valve Q (1+2E・(Tf-T))...
It is found by (3). In this way, conventionally, the flow rate value was determined by performing the above correction under the condition that the temperature was kept constant in a constant temperature bath. (Issue 1i that the invention is trying to solve!) However, even though the temperature is maintained in a constant temperature bath, the ambient temperature fluctuates depending on the surrounding environment, resulting in errors. Furthermore, since the thermostatic chamber is equipped with a heater and a fan, it becomes large and requires a power source, which poses the problem that it can only be used under certain conditions. Therefore, an object of the present invention is to provide a flow rate measuring device that reduces errors caused by temperature changes and can be used in any environment. [Structure of the Invention] (Means for Solving the Problems) The present invention stores a differential pressure transmitter in a heat insulation box, and measures the temperature by providing an ambient temperature detector near the differential pressure transmitter. The correction is added to the conventional calculation formula. (Function) As a result, the flow rate measuring device can be installed in various environments, and the error in the measured flow rate can be reduced by temperature correction.

(Example) Figure 1 shows a flow rate measuring nail according to an actual example of the present invention.
In the figure, the same functional parts as in Figure 4 are given the same numbers, and the explanation will be omitted since it is redundant. The differential pressure transmitter 3 is housed in a heat insulating box 4, and an ambient temperature sensor 11 in the vicinity of the differential pressure transmitter 3 is installed to measure the temperature, and the obtained temperature signal is input into the process in the same way as the differential pressure signal. It is sent to the electronic computer 6 via the output device 5. The electronic computer 6 performs error correction on the differential pressure signal using the sent temperature signal. Next, the temperature correction method according to the present invention will be explained. A differential pressure transmitter has temperature characteristics as shown in Figure 2, and there is a zero point error Co resulting from zero point movement (A) due to temperature, and a span error Cs resulting from span fluctuation (B). , can be expressed as follows. Determine these errors through experiments and create a table like the one below. However, i=1~n As a zero point error display formula, Co= a +bt −<4
> As a span error display formula, Cs==:C+dt −・−
(s), using the least squares method with reference to Table 1 above, (Leave below) Here, the output value of the differential pressure transmitter at t ('C) is It,
If the true output value that does not include the error at t ("C) is , then the following holds true, and solving this for ko gives 100+Cs. Figure 3 shows a calculation block diagram with temperature correction. In addition, in the figure, the same reference numerals as in FIG. 5 indicate the same functional parts.
301 is a temperature correction means, ΔP'llA is a differential pressure signal after correction based on the temperature of the insulation box, and as described above, CO represents a signal zero point error due to the temperature of the insulation box, and Cs represents a signal span error due to the temperature of the insulation box. ．．゛The error due to the temperature of the insulation box is
Since it is included in the differential pressure signal 8Pa^, it is necessary to correct ΔPm^. Therefore, the temperature correction means 301
Temperature correction is performed based on the above equation (1l), and the differential pressure signal ΔP'llA after correction based on the temperature of the insulation box becomes 100+Cs. After finding the temperature correction value ΔP's^, the fifth
The flow rate F can be found using the same method as explained in the figure. Note that the zero point error Co and span error Cs in the above equations are obtained from experimental data, but the validity of the experimental data can be verified under pure steady-state constant conditions (no sudden temperature changes). Flow rate measurement can be performed simply by storing the differential pressure transmitter in a heat insulating box without a heater or fan. This not only makes the flow meter itself more compact, but also
Flow rate can be measured without being affected by the surrounding environment of the measurement location, and errors can be reduced. In the above embodiment, a flow rate measuring device using an orifice plate has been described, but it is of course possible to use a flow rate measuring device using a Pencherry Bitot tube or the like. [Effects of the Invention] As described above, according to the present invention, the flow rate to be measured can be accurately measured, and since it is not necessarily necessary to use a high-temperature bath, the device can be made more compact, and it is possible to A flow rate measuring device that can be installed even under environmental conditions can be obtained.

[Brief Description of the Drawings] Fig. 1 is a configuration diagram of a flow rate measuring device using an orifice plate showing one embodiment of the present invention, Fig. 2 is a temperature characteristic diagram of a differential pressure transmitter, and Fig. 3 is a diagram showing the temperature characteristics of a differential pressure transmitter. Flow rate calculation block diagram in Figure 1,
Figure 4 is a configuration diagram of a conventional flow rate measuring device using an orifice plate, and Figure 5 is a block diagram for calculating the flow rate in Figure 4. 4...Heat insulation box, 5...Process input/output device, 11...Nearby atmosphere temperature detector. (7317) Representative Patent Attorney Noriyuki Chika (8)
869) Representative Patent Attorney Disciple Ken Maru Diagram Diagram

Claims (1)

[Claims] A differential pressure transmitter is housed in a heat insulation box that detects the differential pressure of the fluid flowing in the piping, converts it into an electrical signal, and transmits it. Differential pressure transmission is performed based on the electrical signal sent from the differential pressure transmitter. An ambient temperature detector disposed near the differential pressure transmitter; A flow rate measuring device comprising: a correction means for correcting the electrical signal sent from the differential pressure transmitter based on the heat insulation box temperature obtained from the ambient temperature detector.