JPH04240532A - Differential pressure sensor and adjusting method of sensitivity thereof - Google Patents

Abstract

PURPOSE:To adjust the sensitivity characteristics of two strain detecting parts with high accuracy by providing two strain detecting parts with bridge circuits to detect the pressure, and providing at least one of the strain detecting parts with variable resistors which adjust the sensitivity of the bridge circuit. CONSTITUTION:Two diaphragm parts generate strains corresponding to the receiving pressure. Four strain gauges 3 of a strain detecting part of each diaphragm part change the resistance values corresponding to the strain, and bridge circuits 31, 32 generate outputs corresponding to the pressure. The sensitivity characteristic to pressure of each circuit 31, 32 is different because of the irregularity of the gauge ratio. Therefore, while the zero balance is secured by variable resistors 33-36, the pressure is changed, and the output is measured to obtain the respective sensitivity. The resistance values of the variable resistors 33, 34 of the one circuit 31 are changed while the zero balance is maintained, and the sensitivity of the circuit 31 coincides with that of the circuit 32.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a differential pressure sensor and a method for adjusting its sensitivity, and is particularly used for detecting the hydraulic status of various parts in hydraulic systems such as construction machinery, and for detecting distortions caused by hydraulic pressure. The present invention relates to a differential pressure sensor that detects the difference in fluid pressure and a method for adjusting its sensitivity.

0002

2. Description of the Related Art Differential pressure sensors typically include two diaphragms. Each diaphragm has a strain detection section on one surface and a pressure receiving surface on the other surface. The strain detection section includes, for example, four strain gauges arranged in a predetermined manner,
Four strain gauges form a Wheatstone bridge circuit. The other pressure-receiving surface is subjected to the pressure of pressurized oil or the like to be measured. When pressure is applied, the diaphragm deforms, creating strain within it. If the diaphragm deforms and distortion occurs, the balance of the bridge circuit described above will be lost, and
A bridge circuit output corresponding to the deformation, that is, the applied pressure can be extracted. By the way, in a differential pressure sensor, in order to obtain an accurate differential pressure output, it is necessary that the detection characteristics of the strain detection sections provided in each of the two diaphragms have the same sensitivity characteristics. Therefore, in each diaphragm, the detection characteristics of the distortion detection section and its related electric circuit section, which have separately manufactured electrical configurations, are electrically adjusted so that they have the same detection characteristics. . The electrical configuration associated with the strain detection section includes four strain gauges forming the bridge circuit described above and an amplifier that amplifies the output of the bridge circuit to a required level. The four strain gauges are formed as membranes deposited in predetermined positional relationships on the surface of the diaphragm, and the amplifier is formed as an external circuit. In the electrical configuration of such a differential pressure sensor, the detection characteristics of the distortion detection section have conventionally been adjusted by adjusting the gain of the amplifier.

0003

[Problems to be Solved by the Invention] In the conventional differential pressure sensor described above, the sensitivity characteristics of the two strain detection sections are adjusted using the gain of the amplifier, so the adjustment accuracy is low, and as a result, the sensitivity of the differential pressure sensor There was a problem that the sensing ability of the sensor could not be increased. An object of the present invention is to provide a differential pressure sensor that has two diaphragm parts and each diaphragm part is provided with a strain detection part, in which the sensitivity characteristics of the two strain detection parts can be adjusted with high precision. An object of the present invention is to provide a differential pressure sensor and a method for adjusting its sensitivity.

0004

[Means for Solving the Problems] A differential pressure sensor according to the present invention includes two diaphragm portions each having a strain detection portion on one surface and a pressure receiving surface on the other surface. , in a differential pressure sensor in which the pressure applied to the pressure receiving surface is detected by each strain detection section and the difference between the pressures detected by each strain detection section is determined, each of the two strain detection sections has a bridge for detecting pressure. At least one of the two distortion detection sections includes a variable resistor for adjusting the sensitivity of the bridge circuit. In the above configuration, the sensitivity characteristics of the distortion detection section including the variable resistor for sensitivity adjustment are made to match the sensitivity characteristics of the distortion detection section without the sensitivity adjustment function by adjusting the resistance value of the variable resistor. It is characterized by what it did. In the above configuration,
Each of the two distortion detection sections is characterized by having a variable resistor for sensitivity adjustment formed by trimming. A method for adjusting the sensitivity of a differential pressure sensor according to the present invention includes two diaphragm parts each having a strain detection section on one surface and a pressure receiving surface on the other surface, and at each of the diaphragm parts,
It is a differential pressure sensor in which the pressure applied to the pressure-receiving surface is detected by each strain detection section, and the difference between the pressures detected by each strain detection section is determined.The two strain detection sections each have a bridge for detecting pressure. circuit, and a variable resistor for sensitivity adjustment formed by trimming that is built into this bridge circuit to adjust its sensitivity, and the resistance value of the variable resistor for sensitivity adjustment is The present invention is characterized in that the sensitivity characteristics of the distortion detection section with high sensitivity are made to match the sensitivity characteristics of the distortion detection section with low sensitivity by adjusting.

[0005]

[Operation] In the differential pressure sensor and its sensitivity adjustment method according to the present invention, a strain detection section is provided on one surface of each of the two diaphragm sections, and at least one of the strain detection sections is provided with a sensitivity adjustment section. A variable resistor is provided,
By changing the resistance value of this variable resistor, the sensitivity of the strain detection section is adjusted, so the sensitivity characteristics of the two strain detection sections can be matched accurately, and the sensing accuracy as a differential pressure sensor is improved. can be increased. In particular, in the case where the two distortion detection sections are provided with variable resistors for adjusting the sensitivity and configured to adjust the resistance value by trimming, the resistance value can only be adjusted to be small. Adjustments are made so that the high sensitivity with a large resistance value matches the low sensitivity with a small resistance value.

[0006]

Embodiments Below, embodiments of the present invention will be explained based on FIGS. 1 to 5. Fig. 1 is a vertical cross-sectional view of the differential pressure sensor according to the present invention assembled at a mounting location, Fig. 2 is a plan view of the surface on which the strain detection section of the diaphragm is disposed, and Fig. 3 is the electrical diagram of the differential pressure sensor. The wiring diagram of the circuit section, FIG. 4 is a sensitivity characteristic diagram of the bridge circuit before sensitivity adjustment, and FIG. 5 is a sensitivity characteristic diagram after sensitivity adjustment. In FIG. 1, the differential pressure sensor is constructed by combining two diaphragm bases 1 and 2. The first diaphragm base 1 and the second diaphragm base 2 are formed of the same material and the same shape, and are each configured as a sensor half of a differential pressure sensor. The diaphragm base bodies 1 and 2 each consist of ring-shaped support parts 1a and 2a and diaphragm parts 1b and 2b, which are integrally formed. Support parts 1a, 2a are diaphragm parts 1b, 2b
It has the function of supporting. In this embodiment, the diaphragm parts 1b and 2b have a function as a pressure receiving part having a thin circular shape. Fluid pressure is applied to the diaphragm base 1 from above, and fluid pressure is applied to the diaphragm base 2 from below. In the diaphragm portion 1b of the diaphragm base 1, a strain detection portion 31 is provided on the back side of the pressure receiving surface, as shown in FIG. The strain detection section measures the strain that occurs in the diaphragm section 1b when the diaphragm section 1b is deformed by the pressure applied to the pressure receiving surface, and thereby detects the applied fluid pressure. In the strain detection section, a 4-layer film made of polysilicon, for example, is placed on the back side of the diaphragm section 1b.
Strain gauges 3 are arranged in a predetermined arrangement state. The four strain gauges 3 constitute a Wheatstone bridge circuit. Reference numeral 4 denotes an electrode made of gold that electrically connects the strain gauge 3, and the electrode 4 functions as a pad for bonding the wire 5 to the outside. Reference numeral 6 denotes, for example, a flexible printed circuit board, which has pads 7 on its surface to which the wires 5 are connected, and is used as a wiring member. The output of the bridge circuit taken out by the wire 5 is taken out to the outside by a lead wire 8 formed on the flexible printed circuit board 6. A plurality of lead wires 8 are formed on the flexible printed circuit board 6, and these lead wires 8 are drawn out in a collected state. Similarly to the above, a strain detection section having the same configuration is also provided on the back side of the pressure receiving surface of the diaphragm portion 2b of the diaphragm base 2.

In the differential pressure sensor according to the present invention, two diaphragm base bodies 1 and 2, each serving as a sensor half, are placed back-to-back in such a way that the surfaces of the diaphragm parts 1b and 2b, each provided with a strain detection part, face each other. The ring member 9 is interposed between the two diaphragm base bodies 1 and 2 and assembled. A space 10 is formed by the two diaphragm bases 1 and 2 and the ring member 9, and this space 10 is isolated from a location where a fluid exists, and is in a substantially sealed state except for the lead wire 8 lead-out portion. . The smaller the size of this space 10, the better. That is, the stress detecting sections disposed on the back surface opposite to the pressure receiving surface of each diaphragm section 1b, 2b are arranged as close as possible so that the temperature conditions are the same.

Reference numeral 11 at the periphery of the differential pressure sensor indicates a part of the housing in which the differential pressure sensor is accommodated. 12 is a circular hole formed in the housing 11 in which the differential pressure sensor is disposed;
13 is a first oil passage communicating with the hole 12, and 14 is a second oil passage communicating with the hole 12. Ring-shaped grooves 13a and 14a are formed all around the inner surface of the hole 12 corresponding to the outlet portions of the oil passages 13 and 14. Inside the hole 12, first, a ring-shaped spacer 15, a differential pressure sensor of the present invention, and a cover member 16 are arranged in this order from the bottom side. Spacer 1
5 is arranged corresponding to the oil passage 13 and the groove 13a, and the internal space and the oil passage 13 are in communication through the hole 15a formed in the spacer 15. diaphragm base 1,
On the outer periphery of 2, O
Rings 17 and 18 are provided to seal the pressure oil whose pressure is to be measured. The lower surface of the diaphragm portion 2b of the diaphragm base 2 is a pressure-receiving surface, and the pressure oil supplied from the oil passage 13 is guided to the pressure-receiving surface of the diaphragm portion 2b through the groove 13a and the hole 15a, and comes into contact with the pressure-receiving surface of the diaphragm portion 2b. Cover member 16
has the function of covering the differential pressure sensor from the outside. The cover member 16 has a hole 16a for guiding pressure oil from the oil passage 14 to the pressure receiving surface of the diaphragm base 1 of the differential pressure sensor.
is formed. With the differential pressure sensor, the diaphragm part 1b
, 2b, the lead wire 8 is drawn out from a strain detecting section consisting of a strain gauge or the like, and is passed through the horizontal hole 9a of the ring member 9 and the hole 19 formed in the housing 11 to the IC chip including the amplifier. It is pulled out to 20 places. 21 is a pin pulled out from the IC chip 20, and 22 is a cover that fixes the pin 21. The differential pressure sensor housed and installed in the hole 12 of the housing 11 is pressed down by the presser cover member 23 and fixed in the hole 12 . Further, the presser cover member 23 is fixed to the housing 11 with bolts, screws, or the like.

The electrical circuit system for detecting differential pressure is depicted in a circuit diagram as shown in FIG. As mentioned above, the strain gauge 3 forms a bridge circuit in the strain detection section formed on one surface of the diaphragm sections 1b and 2b.
When this is shown in a circuit diagram, it is shown as a bridge circuit using resistive elements. In FIG. 3, resistor 3 represents a strain gauge. Further, 31 is a bridge circuit of the distortion detection section of the diaphragm section 1b, and 32 is a bridge circuit of the distortion detection section of the diaphragm section 2b. Each bridge circuit 31, 32 has
A voltage V is applied. Sensitivity adjustment resistors 33, 34,
35 and 36 are connected. Bridge circuit 31, 32
The output of is amplified to a desired level by amplifiers 37 and 38 in the next stage. Thereafter, the outputs of each amplifier 37, 38 are input to a differential amplifier 39, where the voltage difference is amplified. The above three amplifiers 37 and 38 and the differential amplifier 3
9 are housed in the same IC chip 20 shown in FIG. 1 in terms of implementation.

Fluid pressure supplied from the outside through the oil passages 13 and 14 is applied to the diaphragm portions 1b and 2b of each diaphragm 1 and 2. When the diaphragm parts 1b and 2b receive pressure, they generate distortion corresponding to the pressure. The four strain gauges 3 formed on the strain detection section of the diaphragm section each cause a resistance value change corresponding to the strain, and each of the bridge circuits 31 and 32 generates a bridge circuit output proportional to the pressure. By the way, the sensitivity characteristics of the bridge circuits 31 and 32 with respect to pressure are different from each other due to variations in the gauge factor of each strain gauge or errors in the thickness of the diaphragm portions 1b and 2b. Therefore, in order to obtain an accurate differential pressure, it is necessary to adjust the sensitivity characteristics of the two bridge circuits 31 and 32 so that they have the same characteristics. FIG. 4 shows an example of the output characteristics of the bridge circuits 31 and 32 with respect to pressure. In FIG. 4, A is the output characteristic of the bridge circuit 31, and B is the output characteristic of the bridge circuit 32. The slopes of the two output characteristics A and B do not match. Therefore, by adjusting the resistance values of the four sensitivity adjustment variable resistors 33 to 36 added to each of the bridge circuits 31 and 32 shown in FIG. to match. Once the variable resistance values of the variable resistors 33 to 36 are set to a predetermined value, the resistance values are kept constant with respect to pressure. Variable resistor 33-3 for sensitivity adjustment
In this embodiment, 6 is an IC chip 2 as shown in FIG.
This is a trimmable chip resistor 20a provided at 0, and has an external structure. Since the resistance value of the trimmable chip resistor 20a can only be changed in the direction of increasing its resistance value, the sensitivity of the two bridge circuits 31 and 32 can be increased by increasing the resistance value and lowering the sensitivity of the bridge circuit. Match characteristics. Therefore, in this sensitivity adjustment, the sensitivity characteristics of the highly sensitive
This will match the sensitivity characteristics of something with low sensitivity. To explain the case of the example in FIG. 4, since the output characteristic A of the bridge circuit 31, that is, the sensitivity characteristic is higher, the variable resistor 3
The resistance value of either 3 or 34 is increased to match the output characteristic B of the bridge circuit 32. FIG. 5 shows output characteristics A and B after adjustment. By lowering the sensitivity (the slope of the straight line) of the output characteristic A, it is made to match the output characteristic B. Practical adjustment of the sensitivity characteristics of bridge circuits 31 and 32 will be explained. First, with a variable resistor for sensitivity adjustment,
Zero balance. Next, the output of each bridge circuit 31, 32 is measured while changing the pressure within a predetermined range, and the sensitivity of each is determined from the output characteristics. In order to match the sensitivity of the bridge circuit 31 with high sensitivity to the sensitivity of the bridge circuit 32 with low sensitivity, the resistance values of the two sensitivity adjustment variable resistors 33 and 34 of the bridge circuit 31 are increased while maintaining zero balance. to match the sensitivity of the bridge circuit 32. As an example, the resistance value of the strain gauge at no load is set to 3.
KΩ, and if a 100Ω sensitivity adjustment resistor is added when a bridge circuit is assembled, and this sensitivity adjustment resistor is further increased by 10%, the sensitivity of the bridge circuit is approximately 0.2%.
Decrease. In this way, the reduction in sensitivity of the bridge circuit can be adjusted to a very small level by the sensitivity adjustment resistor, thereby making it possible to accurately match the sensitivities of the two bridge circuits 31 and 32, and Fine adjustments can be made with high precision. Incidentally, when adjusting the gain of the amplifier as in the past, the resistance value of the adjustment resistor is set to 10
When increasing or decreasing the gain by 10%, the gain, that is, the sensitivity also changes by 10%. As described above, in the conventional adjustment method, the accuracy of the resistance value for adjustment and the accuracy of the gain are approximately the same, and are not suitable for adjusting the sensitivity.

In FIG. 3, each bridge circuit 31, 32
The voltage output from the first stage amplifier 37,
It is amplified by 38. In this case, since the amplifiers 37 and 38 are manufactured symmetrically on the same IC chip 20, they can be considered to have the same gain, and adjustments for gain matching can be made. There is no need to do so. The output voltages of each amplifier 37 and 38 are differenced by a differential amplifier 39, and an external gain adjustment resistor 40 is used.
The gain is adjusted to obtain a predetermined signal as the sensor output.

Note that the sensitivity adjustment resistors 33 to 3 mentioned above
When adjusting the sensitivity between the bridge circuits 31 and 32 according to No. 6, if the sensitivity is adjusted while maintaining the zero balance, there is a risk that the zero balance will be slightly distorted. In this case, the problem can be solved by providing the differential amplifier 39 with an offset adjustment function.

In the embodiment described above, two bridge circuits 3
Although the adjustment resistor for sensitivity adjustment No. 1 and 32 has been described as an example of a resistor whose resistance value is adjusted by trimming, it is also possible to use a small resistor whose resistance value can be freely increased or decreased. In this case as well, such a small resistor is externally attached near the IC chip 20. In particular, in the case of this embodiment, adjustment for sensitivity matching can be freely performed between a bridge circuit with high sensitivity and a bridge circuit with low sensitivity. That is, it can be matched with a bridge circuit with low sensitivity, or it can be matched with a bridge circuit with high sensitivity.

[0014]

[Effects of the Invention] As is clear from the above explanation, according to the present invention, there are two diaphragm parts, and therefore,
In a differential pressure sensor having two strain detection sections each including a bridge circuit composed of a strain gauge, the bridge circuit is provided with a variable resistor for sensitivity adjustment, so that the sensitivity of the two bridge circuits can be easily adjusted. And it can be adjusted accurately and with even higher precision. As a result,
According to the differential pressure sensor according to the present invention, it is possible to detect a differential pressure with little error between a high pressure region and a low pressure region.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a differential pressure sensor according to the present invention assembled at a location where it is to be mounted.

FIG. 2 is a plan view of a surface of a diaphragm on which a strain detection section is provided.

FIG. 3 is a wiring diagram of the electric circuit section of the differential pressure sensor.

FIG. 4 is a sensitivity characteristic diagram of the bridge circuit before sensitivity adjustment.

FIG. 5 is a sensitivity characteristic diagram after sensitivity adjustment of the bridge circuit.

[Explanation of symbols]

1, 2 Diaphragm base 1b, 2b
Diaphragm part 3 Strain gauge 6 Flexible printed circuit board 8
Lead wire 9 Ring member 11 Housing 13, 14 Oil passage 15 Spacer 16 Cover member 20 IC chip 31, 32 Bridge circuit 33-36 Sensitivity adjustment variable resistor 37, 38
Amplifier 39 Differential amplifier

Claims (4)

[Claims] 1. Two diaphragm portions each having a strain detection portion on one surface and a pressure receiving surface on the other surface, wherein the pressure applied to the pressure receiving surface of each of the diaphragm portions is applied to each of the strain detection portions. In the differential pressure sensor that determines the difference between the pressure detected at the strain detection section and the pressure detected at each strain detection section, each of the two strain detection sections has a bridge circuit for detecting pressure, and the two strain detection sections each have a bridge circuit for detecting pressure. A differential pressure sensor, wherein at least one of the parts includes a variable resistor for adjusting the sensitivity of the bridge circuit. 2. The differential pressure sensor according to claim 1,
The sensitivity characteristics of the distortion detection section equipped with a variable resistor for sensitivity adjustment are made to match the sensitivity characteristics of a distortion detection section without a sensitivity adjustment function by adjusting the resistance value of the variable resistor. Differential pressure sensor. 3. The differential pressure sensor according to claim 1,
The differential pressure sensor, wherein each of the two distortion detection sections has the variable resistor for sensitivity adjustment formed by trimming. 4. Two diaphragm portions each having a strain detection portion on one surface and a pressure receiving surface on the other surface, wherein the pressure applied to the pressure receiving surface of each of the diaphragm portions is applied to each of the strain detection portions. The sensor is a differential pressure sensor that calculates the difference between the pressure detected at the strain detection section and the pressure detected at each strain detection section, and each of the two strain detection sections includes a bridge circuit for detecting pressure, and a It has built-in variable resistors for sensitivity adjustment formed by trimming to adjust the sensitivity, and the resistance value of these variable resistors for sensitivity adjustment can be adjusted to create a highly sensitive distortion. A method for adjusting the sensitivity of a differential pressure sensor, characterized in that the sensitivity characteristics of the detection section are made to match the sensitivity characteristics of a strain detection section with low sensitivity.