JPS61137017A - Mental capacity built-in type thermal flow amount detector - Google Patents

Abstract

PURPOSE:To keep high accuracy over a wide characteristic range, by providing an operational processing part for operating the feedback current supply electric energy to the heat generation element in a feedback current supply control loop and outputting a current supply signal matched with the characteristic of a flowing fluid. CONSTITUTION:An operational processing part 8 constituted of a microprocessor takes in the digital signal output of an A/D converter part 7 and operates the feedback current supply electric energy to a heat generation element 1a corre sponding to the temp. of a flowing fluid to output a feedback current supply control signal. the temp. TH of the heat generation element 1a and the temp. TC of a temp. compensation element 2a are taken in the operational processing part 8. PID control is performed in the operational processing part 8 so as th keep TH-TC always constant.

Description

[Detailed Description of the Invention] [Industrial Application Field] This BA is based on the flow velocity,
The present invention relates to a thermal flow rate detection device that detects the flow rate t of a flowing fluid such as a flow rate.

[Conventional technology]

A conventional device of this type is shown in FIG. In the figure, ■ is a heating element made of platinum wire wound on a ceramic bobbin, 2 is a temperature compensation element made of almost the same shape and material as heating element 1, and 3 is the heating element construction and temperature compensation. Element 2: a differential amplification section that detects the difference in electrical resistance, that is, the amount of difference corresponding to the temperature difference, and amplifies it to a predetermined size;
Reference numeral 4 denotes a power supply control section that controls the amount of feedback power supplied to the heating element 1 in accordance with the output of the differential amplification section 3. Note that 5 is a resistor, and 6 is a linear drive which will be described later.

Next, the operation of the heat-sensitive flow rate detection device having the above configuration will be explained. As described above, thin platinum wire is used as a temperature-sensitive material for the heating element 1. The reasons for using platinum are that it is a material commonly used as a temperature standard, that it has excellent linearity in resistance vs. temperature characteristics, and that it is a chemically stable material. This is because the aim is to reduce the thermal time constant and to obtain a certain resistance value cheaply with a small amount of material.The incandescent thin wire is wound on a ceramic mesh and the surface is coated with a lath to provide a protective layer. Similarly, the temperature compensation element 2 has the same resistance value and temperature characteristics.

The resistance value of platinum can be approximated by Rel'l = Ro + α (TTo) with respect to temperature T, where the resistance value at room temperature is 't Ro and the temperature coefficient of resistance is α. The differential amplification unit 3 has a temperature difference of 1.5 m, where RH is the electrical resistance of the heating element 1, Rc is the electrical resistance of the temperature compensation element 2, and Rx is the resistance for producing a temperature difference sound. 1+C+-Rii(Tl)・f
The output of unc (RH) and (i + Cz・(Re E)
+ Rx) ) ・It works to amplify the output of func (RH) so that this difference becomes 0, and C1 and 02
is adjusted so that #de is approximately equal, so Rx=RH
(1) The relationship 5α° (TH-Tc) in −Re holds true. Then, depending on the output of the differential amplification section 3, the heating element 1
power supply control unit 4 that controls the amount of feed back power supply;
This realizes constant temperature difference drive in which the difference between the temperature TH of the heating element 1 and the temperature Tc of the temperature compensation element 2 is kept constant.

This constant temperature difference drive is based on analog signal processing that uses three basic elements: an operational amplifier that constitutes a common-mode amplifier, an operational amplifier that constitutes a differential amplifier, and a transoster that is a current amplifier. In this signal processing circuit, CI and C! Precise resistance adjustment is performed to ensure that the circuit constants of the two are equal, and this is an important part that determines the accuracy of automotive detectors that are used over a wide temperature range. 5 p as resistance
Although products with high accuracy of prr/°C are used, they do not fully satisfy the temperature range H-40°C to +130°C required for automobiles.

The basic operating principle of the flow rate detection device is based on the principle of a known hot wire anemometer, and the power supplied to the heating element 11 is set to Pin,
If the amount of heat transfer between the heating element 1 and the fluid is Pout, then in a state of thermal equilibrium, Pin == Pout =h-A
s·ΔT holds true. Here, h is the heat transfer coefficient between the heating element 1 and the fluid, As is the surface area of the heating element 1, and ΔT is the temperature difference between the heating element 1 and the fluid. Generally °Reynolds number Re
However, under laminar flow conditions of 1<Re<2000, the heat transfer a
h can be approximated with respect to the flow velocity V by h=a+b−v.

Here a, t) are constants. The electric power Pin to be supplied to the heating element 1 is as follows: where the resistance of the heating element 1 is R11, the current is Is, and the voltage is Va, then Pin = I'm - Rs ==
V! 12/R11, so in the constant temperature difference drive method where R8 is constant, Va = (As ・Δ
The relational expression T-Ra(a+b-voos,,0.!S) is obtained, which is a non-linear relationship in which the output voltage depends on the 14th power of the flow velocity.Therefore, when a linear relationship with respect to the flow velocity is required As shown in FIG. 3, a linearizer 6 composed of a microprocessor was attached externally to perform correction and obtain a linear relationship.

[Problem that the invention seeks to solve]

Conventional thermal flow rate detection devices are configured as described above, so precise resistance adjustment is required to ensure high accuracy in the detection device, and high accuracy and reliability can be achieved over a wide operating temperature range. Either it was difficult to obtain, or the detection characteristics are non-linear, so an external linear drive is required.
There were problems such as high cost.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a heat-sensitive flow rate detection device with built-in intelligence that has high accuracy over a wide temperature range and is highly reliable.

[Means for solving problems]

The heat-sensitive flow rate detection device with built-in intelligence according to the present invention includes an A/D converter, a D/A converter, and a feed-back power supply amount of the heat-generating element in the feed-back power supply control loop of the heat-generating element. It is equipped with an arithmetic processing section that performs arithmetic operations and outputs a feed/back supply 1iE control signal according to the flow rate range and temperature of the flowing fluid.

[Effect]

The heat-sensitive flow rate detection device with built-in intelligence of the present invention performs nonlinear correction on a control signal determined by a PID control algorithm using a table lookup method in a microprocessor according to the flow velocity range of the flowing fluid, and then The flow rate signal is then re-corrected according to the output of the compensation element.

〔Example〕

FIG. 1 shows the configuration of a heat-sensitive flow rate detection device with built-in intelligence according to an embodiment of the present invention. In the figure, 1a is a heating element made of a temperature-sensitive material such as platinum, and 2a is a temperature compensation element made of a temperature-sensitive material such as platinum or a thermistor for directly or indirectly detecting the temperature of a flowing fluid.

7 is an A/D that converts analog voltage values corresponding to the resistance values of the heating element 1a and temperature compensation element 2a into digital signals.
A converter 8 is a digital signal output of the A/D converter 7, calculates the amount of feed back power supplied to the heating element 1 according to the temperature of the flowing fluid, and generates a feed back power supply control signal. 9 is a D/A converter that converts the feed back supply of this arithmetic processing unit 8 into a control signal into an analog signal; 4
Reference numeral a denotes a power supply control section that controls the amount of feedback power supplied to the heating element 1a according to the output of the D/A conversion section 9.

In the heat-sensitive flow rate detection device with built-in intelligence configured as described above, the temperature TH of the heating element 1a and the temperature Tc of the temperature compensation element 2a are determined by the resistance value RHs Rc of the pixel element momentarily, A
It is converted into a digital signal by the /D converter 7 and sent to the arithmetic processor 8.
It will be taken into account. In this arithmetic processing unit 8, TH-'r is always
The microprocessor uses the known P so that c is constant.
ID control), the constant temperature difference drive of the present invention is realized. On the other hand, the approximate formula for heat transfer coefficient h = a + b・
7 is a rough approximate equation known as King's equation,
In reality, it is necessary to make corrections depending on the specific shape of the heating element 1a and the boundary conditions around the heating element 1a, and the upstream velocity dependence of the experimental formula varies from 0.3 to 0 depending on the range of the Ray true e number of the flowing fluid. It changes greatly up to the 8th power. Furthermore, the Prandtl number Pr, kinematic viscosity coefficient ν, and heat conduction ``4k, which determine the properties of the flowing fluid, change depending on the temperature of the flowing fluid, so under conditions where the operating temperature range is wide such as in automobiles, the In this example, the control signal determined by the PID control O7 algorithm is subjected to nonlinear correction using a table lookup method within the microprocessor according to the flow velocity range of the flowing fluid, and then the temperature Since the flow rate signal is re-corrected according to the output of the compensating element 2aO, high accuracy can be maintained over a wide flow rate range and temperature range.

FIG. 3 is a flowchart showing the control operation of this embodiment, and 10 is a power-on reset process, in which the power is turned on.
Immediately after, initial value settings for each coefficient etc. and RAM are cleared. 1
1 is a quantity corresponding to the resistance value of the heating element 1a and the temperature compensating element 2a, and 12 is an input process to be input into the memory of the microprocessor via the A/D converter 7, and 12 is various calculations for constant temperature difference drive. and an output process 13 for outputting the result of the arithmetic process 12 as a feedback to the heating element 1a via the D/A converter 9.

In arithmetic processing 12, the output #&element 1all? : If ΔVN+1 is the control deviation to be packed, then ΔVN+1 =
VN+1- VN= KIVN'+ Km(VN'-
VN-'1) + Ka E VN', and by converting this control amount VN+1 into D/A conversion in the output processing 13 and feeding it back to the heating element 1a, the desired constant temperature difference drive is achieved. Realized.

Here, K, , K, , K are proportional coefficients, V
N+1 is the next control operation amount, vN is the previous control operation amount,
V' represents an amount corresponding to the temperature difference between the heating element 1a and the temperature compensating element 2a, N represents the current value, and N-1 represents the previous value.

In addition, in the above embodiment, an example was shown in which the A/Dfi converter 7 and the D/A converter 9 were provided outside the arithmetic processing unit 8.
A microprocessor having a built-in /D converter 7 or a D/A converter may be used, and in this case, the same effects as in the above embodiment can be achieved with a compact and inexpensive configuration.

〔Effect of the invention〕

As described above, according to the heat-sensitive flow rate detection device with built-in intelligence of the present invention, the feed back supply to the power generating element in the feed back power supply control loop is 1! The structure is equipped with a calculation processing unit that calculates the amount of electric power and outputs a feed back power supply control signal according to the flow rate range and temperature of the flowing fluid, so it can maintain a high P'II degree over a wide flow rate range and temperature range. There is an effect that a thermal flow rate detection device having the following can be obtained at low cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a thermal flow rate detection device with built-in intelligence according to an embodiment of the present invention, FIG. 2 is a flowchart showing its control operation, and FIG. 3 is the configuration of a conventional thermal flow rate detection device. FIG. 1a... Heat generating collector, 2a... Temperature compensation element, 4a...
...Kit system t part 1, 7...AID conversion part, 8...
Arithmetic processing unit, 9...D/A conversion unit. Agent Masuo Oiwa Diagram 2 procedural amendment (voluntary) l, Indication of the case Patent application No. 1982-259742 2,
Title of the invention: Intelligent thermal current detection device 3, person making the amendment 5, detailed description of the invention in the specification to be amended. 6. Contents of the amendment (1) "Incandescent" on page 3, line 6 of the specification is corrected to "platinum." (2) "rI2s" on page 5, line 9 is corrected to "rIs2". (3) On page 6, line 4, "linear riser" is corrected to "linearizer."

Claims (1)

[Claims] A heating element made of a temperature-sensitive material such as platinum, a temperature compensation element made of a temperature-sensitive material such as platinum or a thermistor to detect the temperature of a flowing fluid, and an analog corresponding to the resistance value of the heating element and temperature compensation element. an A/D converter that converts a voltage value into a digital signal, and a digital signal output of the A/D converter that calculates a feedback power amount to be fed to the heating element according to the temperature of the flowing fluid; An arithmetic processing section consisting of a microprocessor that outputs a feedback power supply control signal, a D/A conversion section that converts the feedback power supply control signal of this arithmetic processing section into an analog signal, and a a power supply control section that controls the amount of power supplied to the heat generating element, and detects the flow rate of the flowing fluid, such as the flow rate, from the amount of heat transfer between the heat generating element and the flowing fluid. type flow rate detection device.