Source: http://www.google.com/patents/US7658102?ie=ISO-8859-1
Timestamp: 2015-01-26 01:49:39
Document Index: 25000822

Matched Legal Cases: ['art 20', 'art 23', 'art 23', 'art 23', 'art 23', 'art 23', 'art 20', 'art 23', 'art 20', 'art 23']

Patent US7658102 - Thermal flow sensor having an amplifier section for adjusting the ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsA thermal flow sensor can adjust the temperature of a heating element in a highly precise and reliable manner with the use of simple circuits, devices and process steps. The sensor includes an amplifier section (7) that amplifies a voltage across opposite ends of at least one of resistors (3, 4, 5) that...http://www.google.com/patents/US7658102?utm_source=gb-gplus-sharePatent US7658102 - Thermal flow sensor having an amplifier section for adjusting the temperature of the heating elementAdvanced Patent SearchPublication numberUS7658102 B2Publication typeGrantApplication numberUS 12/209,792Publication dateFeb 9, 2010Filing dateSep 12, 2008Priority dateNov 22, 2005Fee statusLapsedAlso published asDE102006026890A1, DE102006026890B4, US7325449, US7487674, US7562569, US7568387, US7568388, US7574909, US20070113643, US20080178669, US20090007655, US20090007656, US20090007657, US20090007658, US20090013777Publication number12209792, 209792, US 7658102 B2, US 7658102B2, US-B2-7658102, US7658102 B2, US7658102B2InventorsKazuhiko Ohtsuka, Yuji AriyoshiOriginal AssigneeMitsubishi Denki Kabushiki KaishaExport CitationBiBTeX, EndNote, RefManPatent Citations (12), Non-Patent Citations (1), Referenced by (4), Classifications (9), Legal Events (4) External Links: USPTO, USPTO Assignment, EspacenetThermal flow sensor having an amplifier section for adjusting the temperature of the heating elementUS 7658102 B2Abstract A thermal flow sensor can adjust the temperature of a heating element in a highly precise and reliable manner with the use of simple circuits, devices and process steps. The sensor includes an amplifier section (7) that amplifies a voltage across opposite ends of at least one of resistors (3, 4, 5) that constitute a bridge circuit, a current control section (9) that is controlled based on an output voltage of the amplifier section (7), and an output terminal (14) that is connected to one end of a heating element (1) that is controlled to be energized by the current control section (9). The amplifier section (7) includes an amplification factor control section for controlling an amplification factor by an electric signal from a computer, and uses an output voltage which has been amplified and impressed to an input voltage to an operational amplifier (8).
said two heating elements and said two fluid temperature detection elements are arranged in fluid, and said two fluid temperature detection elements are arranged at a location free from the influence of heat from said two heating elements; and
an amplifier section that amplifies a voltage across opposite ends of a series circuit comprising at least one of said plurality of resistors and one of said two fluid temperature detection elements;
said amplification factor control part changes the amplification factor of said amplifier part by means of an electric signal so that the temperatures of said heating elements are adjusted to said control temperature. Description
In this case, the amplifier section 7 is designed to divide a voltage input thereto into a ratio of �x:1−x� and output the thus divided voltage. An output voltage of the operational amplifier 8 based on the output voltage of the amplifier section 7 is impressed to the base terminal of the transistor 9, whereby the transistor 9 controls a current supplied to the heating element 1 based on the voltage input to the base terminal thereof. As a result, the heating element 1 is controlled to be energized and deenergized through the transistor 9 that is current controlled by the operational amplifier 8 (i.e., operates in an active region).
FIG. 3 is a circuit configuration diagram that illustrates one example of the amplifier part 20, wherein there is illustrated an equivalent circuit in case where f or example, the resistors 2R1 through 2R3 are connected to the input terminal 18 by means of the switches S1 through S3, respectively, in FIG. 2, with only the resistor 2R4 being connected to the input terminal 17 by means of the switch S4. In FIG. 3, individual resistance values or combined resistance values are represented by �2R�.
V 19 = 2 R 4 R ( V 17 - V 18 ) + V 18 = 1 2 ( V 17 + V 18 ) ( 1 ) As can be seen from expression (1), the voltage division ratio x of the amplifier section 7 is decided by the ratio of resistance values (=2R/4R=�), so the absolute accuracy of the resistance values is not required, and voltage division with high precision can be made as long as the relative accuracy thereof is kept.
V 19 = V 17 - V 18 2 4 � N + V 18 ( 2 ) where N is a value which represents the connection states of the switches S1 through S4 by the digital value of a decimal number.
V16=(1−x)V13 (3)
V 13 = R 4 R 2 + R 3 + R 4 V 11 ( 4 ) where R2, R3 and R4 are the individual resistance values of the fluid temperature detection element 2 and the resistors 3, 4, respectively.
V 15 = R 5 R 1 + R 5 V 11 ( 5 ) where R1 and R5 are the individual resistance values of the heating element 1 and the resistor 5, respectively.
R 5 R 1 + R 5 V 11 = ( 1 - x ) R 4 R 2 + R 3 + R 4 V 11 ( 6 ) Accordingly, the resistance value R1 of the heating element 1 is represented by the following expression (7).
R 1 = ( R 2 + R 3 + xR 4 ) R 5 ( 1 - x ) R 4 ( 7 ) As can be seen from expression (7), by changing the voltage division ratio x of the amplifier section 7, the resistance value, i.e., the temperature, of the heating element 1 can be adjusted. The voltage division ratio x is changed by an electric signal Q input to the amplification factor control part 23 in FIG. 2.
V 19 = 8 C 16 C ( V 17 - V 18 ) + V 18 = 1 2 ( V 17 - V 18 ) + V 18 ( 8 ) As can be seen from expression (8), the voltage division ratio x of the amplifier section 7A is decided by the ratio of the capacitance values (=8C/16C=�), and the absolute accuracy of the capacitance values is not required, so voltage division with high precision can be made as long as the relative accuracy thereof is kept.
V 19 = V 17 - V 18 2 4 � N + V 18 ( 9 ) Thus, the voltage division ratio x of the amplifier section 7A can be changed by the electric signal Q.
V 27 = - 1 3 ( V 17 - V 18 ) + V 18 ( 11 ) In addition, from expression (11) above, an output voltage V19 of the amplifier section 7C is represented by the following expression (12).
V 19 = - ( V 27 - V 18 ) + V 18 = 1 3 ( V 17 - V 18 ) + V 18 ( 12 ) Here, note that the general formula of the output voltage V19 becomes, as shown by the following expression (13).
V 19 = 2 4 - N N ( V 17 - V 18 ) + V 18 ( 13 ) As can be seen from expression (13), the amplification factor of 1 or more can be obtained depending on the setting of the digital value N.
V 19 = 2 4 - 12 12 ( V 17 - V 18 ) + V 18 = 4 12 ( V 17 - V 18 ) + V 18 ( 14 ) Accordingly, the above-mentioned expression (12) is obtained from expression (14) above.
Here, as shown in FIG. 9 (corresponding to FIG. 1), assuming that the amplification factor of the amplifier section 7C is represented by G the output voltage V19 from the output terminal 19 of the amplifier section 7C is represented by the following expression (15).
V 19 = G � R 4 R 2 + R 3 + R 4 V 11 ( 16 ) Here, an input voltage V15 to a non-inverting input terminal 15 of the operational amplifier 8 is represented as shown in the above-mentioned expression (5), and the input voltage V15 and the output voltage V19 of the amplifier section 7C become equal to each other, so the relation of the following expression (17) holds.
R 5 R 1 + R 5 V 11 = G R 4 R 2 + R 3 + R 4 V 11 ( 17 ) Accordingly, the resistance value R1 of the heating element 1 is represented by the following expression (18).
R 1 = { R 2 + R 3 + ( 1 - G ) R 4 } R 5 G � R 4 ( 18 ) As can be seen from expression (18) above, by changing the amplification factor G of the amplifier section 7C, the resistance value, i.e., the temperature, of the heating element 1 can be adjusted. At this time, the amplification factor G is changed by the electric signal Q input to the amplification factor control part 23 (see FIG. 7).
Embodiment 7 Although in the above-mentioned sixth embodiment (see FIG. 11), no consideration has been given to the dielectric strength of switches that constitute the amplification factor control part 23 inside the IC 28D, in consideration of the case where a resistive circuit for over voltage protection is needed (i.e., the dielectric strength of the switches in the IC 28D is low), a switching circuit 30, which constitutes a partial function of an amplification factor control part 23E, may be provided besides the amplification factor control part 23E (outside an IC 28E), for example as shown in FIG. 12.
In general, in case where only the amplifier part 20 is formed on the circuit board outside of the IC 28E, it is necessary to connect between component parts from the amplification factor control part 23E in the IC 28E to the amplifier part 20 outside of the IC 28E by means of wiring. In addition, depending upon a method employed for manufacturing the IC 28E, there might be in some cases the need to connect the resistive circuit 31 to the switches S1 through S4 in the amplification factor control part 23E in order to protect them from overvoltage.
Similarly as stated above, when the amplifier section 7 divides an input voltage into a ratio of �x:1−x�, and outputs the thus divided voltage, an input voltage V16 to an inverting input terminal 16 of the operational amplifier 8 is represented by using a voltage V13 a at the junction 13A between the fluid temperature detection elements 2A, 2B, as shown by the following expression (19).
V 13 a = R 2 b + R 4 R 2 a + R 2 b + R 3 + R 4 V 11 ( 20 ) where R2 a and R2 b are the individual resistance values of the fluid temperature detection element 2A, 2B, respectively.
V 15 = R 1 b + R 5 R 1 a + R 1 b + R 5 V 11 ( 21 ) where R1 a and R1 b are the individual resistance values of the heating element 1A, 1B, respectively.
R 1 b + R 5 R 1 a + R 1 b + R 5 V 11 = ( 1 - x ) R 2 b + R 4 R 2 a + R 2 b + R 3 + R 4 V 11 ( 22 ) Accordingly, the resistance value R1 a of the heating element 1A is represented by the following expression (23) in association with the resistance value R1 b of the heating element 1B.
R 1 a = { R 3 + R 2 a + x ( R 2 b + R 4 ) } ( R 1 b + R 5 ) ( 1 - x ) ( R 2 b + R 4 ) ( 23 ) As can be seen from expression (23), by changing the voltage division ratio x of the amplifier section 7, the resistance value, i.e., the temperature, of the heating element 1A can be adjusted. Also, since the resistance value R1 b of the heating element 1B exists at the right-hand side of expression (23), the temperature of the heating element 1A is varied by the flow rate of fluid.
Here, similarly as stated above, when the amplifier section 7 divides an input voltage into a ratio of �x:1−x�, and outputs the thus divided voltage, an output voltage V19 of the amplifier section 7 is represented by the following expression (24).
V 19 = ( 1 - x ) R 2 b + R 4 R 2 a + R 2 b + R 3 + R 4 V 11 ( 24 ) The output voltage V19 of the amplifier section 7 is impressed to an inverting input terminal 16 of an operational amplifier 8. On the other hand, a voltage V15 (voltage at a junction 12A between heating elements 1A, 1B), being represented by the above-mentioned expression (21), is impressed to a non-inverting input terminal 15 of the operational amplifier 8.
R 1 a = ( R 3 + R 2 a + xR 2 b ) ( R 5 + R 1 b ) ( 1 - x ) R 2 b + R 4 ( 25 ) As can be seen from expression (25), by changing the voltage division ratio x of the amplifier section 7, the resistance value, i.e., the temperature, of the heating element 1A can be adjusted.
In FIG. 18, when the amplifier section 7F divides the input voltage into a ratio of �x:1−x� and outputs the thus divided voltage, and when the amplifier section 7G divides the input voltage into a ratio of �1−y:y� and outputs the thus divided voltage, an output voltage V19 f of the amplifier 7F at a ground side is represented by using the individual resistance values R2 through R4 of the resistors 2 through 4 and the voltage V11 at the junction 11, as shown by the following expression (26).
V 19 f = ( 1 - x ) R 4 R 2 + R 3 + R 4 V 11 ( 26 ) Also, an output voltage V19 g of the amplifier section 7G at the power supply 10 side is represented by the following expression (27).
V 19 g = R 2 + yR 3 + R 4 R 2 + R 3 + R 4 V 11 ( 27 ) Accordingly, an input voltage V15 to the non-inverting input terminal 15 of the operational amplifier 8 is represented by the following expression (28).
V 15 = V 19 f + R 5 R 1 + R 5 ( V 19 g - V 19 f ) = R 1 R 1 + R 5 V 19 f + R 5 R 1 + R 5 V 19 g = ( 1 - x ) R 1 R 1 + R 5 R 4 R 2 + R 3 + R 4 V 11 + R 5 R 1 + R 5 R 2 + yR 3 + R 4 R 2 + R 3 + R 4 V 11 ( 28 ) In addition, an input voltage V16 to the inverting input terminal 16 of the operational amplifier 8 is represented by the following expression (29).
V 16 = R 4 R 2 + R 3 + R 4 V 11 ( 29 ) Here, from V15=V16, a resistance value R1 of the heating element 1 is represented, as shown by the following expression (30).
R 1 = ( R 2 + yR 3 ) R 5 xR 4 ( 30 ) On the other hand, the resistance value R2 of the fluid temperature detection element 2 is changed in accordance with the temperature thereof, so it is replaced as shown by the following expression (31).
R 1 = ( R 20 + yR 3 ) R 5 xR 4 ( 1 + R 20 R 20 + yR 3 α 2 T 2 ) ( 32 ) In expression (32) above, the term R20/(R20+yR3)�α2 in the right-hand side parentheses represents the temperature coefficient of the resistance value R1, which can be adjusted by a voltage division ratio y. Also, the resistance value R1 can be adjusted by the voltage division ratio x. Accordingly, as can be seen from expression (32), the resistance value R1 and the temperature coefficient can be adjusted independently from each other.
In FIG. 19, each two of resistors 3A, 3B, and 4A, 4B are connected to the opposite ends, respectively, of the fluid temperature detection element 2. Specifically, in this case, the above-mentioned resistor 3 is divided into the resistor 3A and the resistor 3B, and the above-mentioned resistor 4 is divided into the resistor 4A and the resistor 4B. A voltage across the opposite ends of the resistor 3B is divided into a ratio of �1−w:w� by means of an amplifier section 7G, and a voltage across the opposite ends of the resistor 4B is divided into a ratio of �z:1−z� by means of an amplifier section 7F.
R 1 = ( R 2 + R 3 a + wR 3 b ) R 5 R 4 a + zR 4 b ( 33 ) When expression (33) above is compared with the aforementioned expression (30), the following expressions (34), (35) hold.
As shown in FIG. 20, when the amplifier section 7 divides the input voltage into a ratio of �x:1−x� and outputs the thus divided voltage, and when the amplifier section 7H divides the input voltage into a ratio of �1−y:y� and outputs the thus divided voltage, the resistance value R1 of the heating element 1 is represented, as shown by the following expression (36).
R 1 = ( R 2 + R 3 + xR 4 ) R 5 ( 1 - x ) R 4 - y ( R 2 + R 3 + R 4 ) ( 36 ) As can be seen from expression (36), by changing the voltage division ratios x, y of the amplifier sections 7, 7H, the resistance value, i.e., the temperature, of the heating element 1 can be adjusted.
R 1 = ( R 2 + R 3 + R 4 - G 2 R 4 ) R 5 G 2 R 4 - G 1 ( R 2 + R 3 + R 4 ) ( 37 ) As can be seen from expression (37), by changing the amplification factors G1, G2 of the amplifier sections 7′, 7H′, the resistance value, i.e., the temperature, of the heating element 1 can be adjusted. Accordingly, the temperature of the heating element 1 can be adjusted only by sending an electric signal for adjustment from an external computer, so the adjustment can be made in a short time by a simple arrangement or device. In addition, the amplification factors G1, G2 of the individual amplifier sections 7′, 7H′ are decided by the ratios of the resistance values of resistors, adjustment accuracy is not influenced by the absolute accuracies of the resistors, and adjustment with a high degree of precision can be made.
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