JPH0523369B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an instrumental error correction device for a flowmeter that corrects the instrumental error of a flowmeter in accordance with changes in the temperature of a fluid to be measured.

BACKGROUND TECHNOLOGY When the temperature of the fluid to be measured is not constant and changes during measurement, the fluid to be measured expands in volume due to the rise in temperature, causing an error in the flow rate measured by the flow meter. It is necessary to correct the instrumental error of the flow meter. For this reason, as shown in FIG. 3, in the conventional instrument error correction device for a flowmeter, when the temperature of the fluid to be measured is not constant and changes during measurement, the temperature of the fluid to be measured passing through the flowmeter 1 is measured. a temperature detection unit 2; a coefficient calculation unit 3 that receives a temperature signal of the fluid to be measured from the temperature detection unit 2 and calculates a coefficient correction value according to the volumetric expansion of the fluid to be measured caused by the temperature difference from the reference temperature; It was generally composed of a coefficient multiplier 4 that multiplies the flow measurement signal output from the flow meter 1 by a coefficient correction value from a coefficient calculation section 3 and outputs a corrected flow correction signal.

Problems to be Solved by the Invention However, the instrument error correction device for a flowmeter having the above configuration, for example, when the temperature of the fluid to be measured rises,
Although this method corrects the instrumental error of the flowmeter 1 according to the temperature of the fluid, it has the disadvantage that the housing 1a of the flowmeter 1 expands as the temperature of the fluid increases, resulting in an error in the measured flow rate. Ta.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an instrumental error correction device for a flowmeter that eliminates the above-mentioned drawbacks.

Means and Effects for Solving Problems The present invention provides a reference temperature setting unit that sets the temperature of the housing of a flowmeter that outputs a flow rate measurement signal q according to the flow rate as a reference temperature t ₀ , and the reference temperature t _{0 .} a meter constant setting section that sets a meter constant M ₀ at , and a change in the meter constant M ₀ according to a temperature difference t - t ₀ between a temperature t that is a temperature change of Δt from the reference temperature t ₀ and the reference temperature t ₀ . a constant setting section for a constant k that determines a rate; a linear expansion coefficient setting section that sets a linear expansion coefficient α of the housing; the reference temperature setting section; the meter constant setting section;
Reference temperature t ₀ , meter constant M ₀ , constant k, linear expansion coefficient α and 1/Mt=1/{1−kα set in the constant setting section and the linear expansion coefficient setting section
(t−t ₀ )}M ₀ , a coefficient calculation unit that calculates a coefficient correction value Mt at the time of flow rate measurement from a temperature signal t from a temperature detection unit provided in the housing; a fluid volumetric expansion coefficient calculation unit that receives the temperature signal t and outputs a coefficient correction value A corresponding to the volumetric expansion of the fluid caused by the temperature difference t− _t0 from the reference temperature _t0 ; a coefficient multiplication unit that multiplies the reciprocal 1/Mt of the coefficient correction value Mt and the coefficient correction value A from the fluid volume expansion coefficient calculation unit; This is to correct.

Embodiment FIG. 1 shows an embodiment of an instrumental error correction device for a flowmeter. In FIG. 1, the flowmeter instrumental error correction device 5 includes a reference temperature setting section 6, a linear expansion coefficient setting section 7, a meter constant setting section 8 at the reference temperature, a constant k setting section 9, a coefficient calculation section 10, and a coefficient multiplication section. It is roughly composed of the section 11.

Here, for example, if the flowmeter 1 is a vortex flowmeter, the meter constant M necessary to correct the flow rate measurement signal q output from the flowmeter 1 with a constant specific to the flowmeter 1.
is generally determined by an actual flow test at room temperature. The flow rate measurement signal q from the flowmeter 1 is multiplied by 1/M, which is the reciprocal of this meter constant M and is a coefficient correction value, and the flow rate measurement signal is corrected to q/M.

Further, the relationship between the meter constant M when measuring the flow rate of high-temperature fluid with the flowmeter 1 and the amount of change ΔM in the meter constant M when the temperature of the housing 1a changes by Δt can be expressed by the following equation.

ΔM/M=-kαΔt... k is a constant specific to the flowmeter determined by design specifications such as the ratio of the inner diameter of the housing 1a to the width dimension of the vortex generating column (restriction ratio). Furthermore, although the meter constant M changes with changes in temperature, it does not change uniformly, so the rate of change of the meter constant M in response to the temperature difference from the reference temperature is determined by the constant k. Further, α is a coefficient of linear expansion depending on the materials of the housing 1a and the vortex generating column.

Furthermore, housing 1 when conducting an actual flow test
The temperature _t0 of a is the reference temperature, and the meter constant determined by the actual flow test is _M0 , and the housing 1a
The meter constant Mt at a temperature t that has changed by Δt from the reference temperature t ₀ can be determined by the following equation.

Mt={1-kα(t- _t0 )} _M0 ... Therefore, the coefficient correction value of the flow rate measurement signal is 1/
Mt can be found using the following formula.

1/Mt=1/{1-kα(t- _t0 )} _M0 ... That is, the flow meter instrumental error correction device 5 calculates based on the formula, and the coefficient multiplier 11 corrects the flow rate measurement signal. It is something.

In FIG. 1, a reference temperature setting section 6 sets the temperature t ₀ of the housing 1a of the flow meter 1 as the reference temperature when the meter constant M ₀ of the flow meter 1 is determined by an actual flow test. The linear expansion coefficient setting section 7 sets the linear expansion coefficient α according to the material of the housing 1a. The meter constant setting section 8 sets the meter constant M ₀ determined by the actual flow test when the housing 1a is at the reference temperature t ₀ . The constant k setting unit 9 sets a constant k that determines the rate of change of the meter constant Mt according to the temperature difference t−t ₀ from the reference temperature t ₀ .

Reference numeral 12 denotes a temperature detection section, which is provided inside the housing 1a so as to measure the internal temperature of the housing 1a and the temperature of the fluid to be measured.

The coefficient calculating section 10 sets the reference temperature by each setting section of the reference temperature setting section 6, linear expansion coefficient setting section 7, meter constant setting section 8 at reference temperature _t0 , and constant k setting section 9.
t ₀ , linear expansion coefficient α, meter constant at reference temperature t ₀
Once M ₀ and the constant k are set, a coefficient correction value 1/Mt at the time of flow rate measurement corresponding to expansion or contraction of the housing 1a is calculated based on the output of the temperature signal t from the temperature detection section 12. The coefficient multiplier 11 calculates the coefficient correction value 1/Mt at the time of flow measurement calculated by the coefficient calculation part 10 and the coefficient correction value A calculated by the fluid volume expansion coefficient calculation part 3 based on the temperature signal from the temperature detection part 12. and 1/Mt and A as coefficient correction values to the flow rate measurement signal q from the flowmeter 1.
The coefficient-corrected flow rate correction signal q・
Outputs (1/Mt)・A.

Therefore, when measuring high-temperature fluid, the housing 1a of the flowmeter 1 expands, but the coefficient correction value 1/Mt obtained based on the formula and the coefficient correction value A that corrects the volumetric expansion of the fluid are Flow rate measurement signal q
The flow rate measurement signal due to the expansion of the housing 1a accompanied by the temperature change of the fluid is corrected by multiplying this to eliminate measurement errors and correct the instrumental error of the flow meter 1.

Here, when measuring the flow rate, the flow meter instrumental error correction device 5
executes the processing shown in FIG. In Fig. 2, flowmeter 1 measures the flow rate of the fluid to be measured, and outputs a flow rate measurement signal q.
(step 21), the reference temperature setting section 6
Read the reference temperature t ₀ set by (step 22). Next, the linear expansion coefficient α set by the linear expansion coefficient setting section 7, the meter constant M ₀ at the reference temperature t ₀ set by the meter constant setting section 8, and the constant set by the constant k setting section 9 k sequentially (steps 23 to 25). When the set value of each setting section is read, the coefficient calculation section 10 causes the temperature detection section 1 to
A coefficient correction value 1/Mt is calculated according to the temperature signal t of the housing 1a outputted from step 2 (step 26). Further, the fluid volumetric expansion coefficient calculating section 3 calculates a coefficient correction value A for the fluid volumetric expansion corresponding to the temperature of the fluid (step 27).

Next, the coefficient multiplier 11 multiplies the flow rate measurement signal q by the coefficient correction value 1/Mt and A (step 28) to obtain a flow rate signal whose coefficient has been accurately corrected according to the temperature change of the fluid and the housing 1a. Output (step 29) and return to step 21.

In the above description, a vortex flowmeter is used as the flowmeter, but the present invention is not limited to this, and can of course be applied to, for example, a positive displacement flowmeter or a turbine flowmeter. Additionally, if the pressure of the fluid to be measured fluctuates, the pressure of the fluid may be measured and the coefficient correction value of the pressure correction device that corrects the flow rate control signal according to the pressure fluctuation may be output to the coefficient multiplier. .

In the above explanation, the coefficient calculation unit calculates the coefficient correction value 1/Mt, and the coefficient multiplication unit multiplies the flow rate measurement signal q by the coefficient correction value 1/Mt to correct it.
Not limited to this, for example, in the coefficient calculation section, the meter constant
Mt may be calculated, and the meter constant Mt may be reciprocated by the coefficient multiplier and the flow rate measurement signal q may be multiplied by the coefficient correction value 1/Mt.

Effects of the Invention As described above, the instrument error correction device for a flowmeter according to the present invention applies the temperature difference t−t ₀ of the flowmeter housing calculated by the coefficient calculation unit to the flow rate measurement signal q output from the flowmeter. In order to multiply the corresponding coefficient correction value 1/Mt and the coefficient correction value A according to the volume expansion of the fluid output from the fluid volume expansion coefficient calculating section, the flow rate of the flowmeter is Changes in meter constants during flow measurement due to expansion or contraction of the housing can be automatically corrected, so even if the temperature of the measured fluid changes significantly, the flow measurement signal can be corrected to eliminate the effects of expansion or contraction of the housing. output a highly accurate flow rate signal.
By correcting the flow rate measurement signal together with the coefficient correction value due to the volumetric expansion of the fluid, it has the advantage of being able to correct the instrumental error of the flowmeter so as to output an extremely accurate flow velocity or flow rate measurement signal.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram for explaining an embodiment of an instrumental error correction device for a flowmeter according to the present invention, and FIG. 2 is a flowchart for explaining the processing executed by the device shown in FIG. 1. FIG. 3 is a schematic configuration diagram for explaining a conventional instrumental error correction device for a flowmeter. 1...Flowmeter, 1a...Housing, 2, 12
... Temperature detector, 3, 10 ... Coefficient calculation section, 4 ...
... Coefficient multiplier, 5 ... Instrumental error correction device for flowmeter, 6
...Reference temperature setting section, 7... Linear expansion coefficient setting section,
8...Meter constant setting section, 9...Constant k setting section,
11... Coefficient multiplier.

Claims (1)

[Claims] 1. A reference temperature setting section that sets the temperature of the housing of the flowmeter that outputs the flow rate measurement signal q according to the flow rate as a reference temperature _t0 , and a meter constant _M0 at the reference temperature _t0 . A meter constant setting section to be set, and a constant k that determines the rate of _{change of the meter constant M0 according to the temperature difference t-t0 between} the temperature t which is a temperature change of Δt from the reference temperature _t0 and the reference temperature _t0 . a setting section; a linear expansion coefficient setting section for setting the linear expansion coefficient α of the housing; the reference temperature setting section; the meter constant setting section;
Reference temperature t ₀ , meter constant M ₀ , constant k, linear expansion coefficient α and 1/Mt=1/{1−kα set in the constant setting section and the linear expansion coefficient setting section
(t−t ₀ )}M ₀ , a coefficient calculation unit that calculates a coefficient correction value Mt at the time of flow rate measurement from a temperature signal t from a temperature detection unit provided in the housing; a fluid volumetric expansion coefficient calculation unit that receives the temperature signal t and outputs a coefficient correction value A corresponding to the volumetric expansion of the fluid caused by the temperature difference t− _t0 from the reference temperature _t0 ; An instrumental error correction device for a flowmeter, comprising: a coefficient multiplication section that multiplies the reciprocal 1/Mt of the coefficient correction value Mt and a coefficient correction value A from the fluid volume expansion coefficient calculation section.