Platinum resistor temperature measurement circuit of Coriolis mass flowmeter

Abstract

The utility model relates to the technical field of Coriolis mass flow meters, in particular to a platinum resistor temperature measurement circuit of a Coriolis mass flow meter, which comprises a reference constant current branch, a temperature measurement constant current branch, a differential amplification circuit and a platinum resistor temperature measurement branch, and the reference constant current branch and the temperature measurement constant current branch are respectively connected with reference voltage; the reference constant current branch is connected with the differential amplification circuit and the platinum resistor temperature measurement branch. The temperature measurement constant current branch is respectively connected with the differential amplification circuit and the platinum resistor temperature measurement branch; according to the constant current source driving circuit, a constant current source driving mode is adopted, deviation of measurement caused by the fact that wire resistance changes along with temperature is avoided, accuracy and stability of overall temperature measurement are improved, and the constant current source driving circuit is particularly suitable for a Coriolis mass flow meter system with the high requirement for measurement accuracy. The circuit is simple in structure, high in element universality and convenient to popularize and apply in actual industrial products.

Description

Technical Field

[0001] This utility model relates to the field of Coriolis mass flow meter technology, and in particular to a platinum resistance temperature measurement circuit for a Coriolis mass flow meter. Background Technology

[0002] Coriolis mass flow meters are widely used in high-precision scenarios such as process control and trade settlement because they can directly measure the mass flow rate, density, temperature, and pressure of fluids, and are not significantly affected by factors such as the type of medium or pressure fluctuations during the measurement process. They have no internal flow obstructions or moving parts, resulting in high reliability and long service life, making them particularly suitable for metering high-viscosity fluids and high-pressure gases. However, to ensure the overall measurement accuracy of the flow meter, high-precision temperature measurement must be achieved simultaneously. In existing technologies, temperature measurement is usually achieved indirectly by using a constant pressure source to drive a bridge circuit and reading the bridge's output voltage. This solution can meet general measurement needs under ideal conditions, but in practical applications, the long-distance wire connection between the sensor and the circuit board introduces errors due to changes in the resistance of these wires with ambient temperature, affecting measurement accuracy. Especially in high-precision applications, the temperature deviation caused by fluctuations in wire resistance further affects the final reading of the mass flow meter, becoming a major bottleneck for improving measurement accuracy. Therefore, how to reduce or eliminate the impact of wire resistance on temperature measurement accuracy has become a key problem that needs to be solved in current technology. Summary of the Invention

[0003] Based on the above problems, this utility model proposes a platinum resistance temperature measurement circuit for a Coriolis mass flow meter.

[0004] This utility model is achieved through the following technical solution:

[0005] A platinum resistance temperature measurement circuit for a Coriolis mass flow meter includes a reference constant current branch, a temperature measurement constant current branch, a differential amplifier circuit, and a platinum resistance temperature measurement branch. The reference constant current branch and the temperature measurement constant current branch are respectively connected to a reference voltage. The reference constant current branch is connected to both the differential amplifier circuit and the platinum resistance temperature measurement branch. The temperature measurement constant current branch is connected to both the differential amplifier circuit and the platinum resistance temperature measurement branch. A precision resistor is provided on the reference constant current branch.

[0006] Furthermore, the reference constant current branch includes a first operational amplifier, a first N-channel MOSFET, and a precision resistor R2. The non-inverting input of the first operational amplifier is connected to the reference voltage and the temperature measurement constant current branch, respectively. The inverting input of the first operational amplifier is connected to the source of the first N-channel MOSFET and then grounded. The output of the first operational amplifier is connected to the gate of the first N-channel MOSFET. The drain of the first N-channel MOSFET is connected to one end of the precision resistor R2 and the differential amplifier circuit, respectively. The other end of the precision resistor R2 is connected to the platinum resistance temperature measurement branch.

[0007] Furthermore, the temperature measurement constant current branch includes a second operational amplifier and a second N-channel MOSFET. The non-inverting input terminal of the second operational amplifier is connected to the reference voltage and the non-inverting input terminal of the first operational amplifier, respectively. The inverting input terminal of the second operational amplifier is connected to the source of the second N-channel MOSFET and then grounded. The output terminal of the second operational amplifier is connected to the gate of the second N-channel MOSFET, and the drain of the second N-channel MOSFET is connected to the platinum resistance temperature measurement branch and the differential amplifier circuit, respectively.

[0008] Furthermore, the differential amplifier circuit includes an instrumentation amplifier, the non-inverting input of which is connected to one end of a precision resistor R2 and the drain of a first N-channel MOS transistor; the inverting input of which is connected to a platinum resistance temperature measurement branch and the drain of a second N-channel MOS transistor; and the non-inverting input of which is connected to an MCU.

[0009] Furthermore, the platinum resistance temperature measurement branch includes a connector and a platinum resistance temperature sensor PT100. Pin 1 of the connector is connected to one end of resistor R1, and the other end of resistor R1 is connected to the VCC voltage terminal. The other end of precision resistor R2 is connected to pin 2 of the connector, and the drain of the second N-channel MOSFET is connected to pin 3 of the connector. The platinum resistance temperature sensor PT100 is connected to pins 1, 2, and 3 of the connector via three wires, and the three wires are of the same length and specifications.

[0010] Furthermore, the reference constant current branch also includes a resistor R3, one end of which is connected to the inverting input terminal of the first operational amplifier and the source of the first N-channel MOS transistor, and the other end of which is grounded.

[0011] Furthermore, the temperature measurement constant current branch also includes a resistor R4, one end of which is connected to the inverting input terminal of the second operational amplifier and the source of the second N-channel MOS transistor, and the other end of which is grounded.

[0012] Furthermore, the resistance of the precision resistor R2 is 100Ω.

[0013] Beneficial effects of the utility model:

[0014] This invention proposes a platinum resistance temperature measurement circuit for a Coriolis mass flow meter. By placing operational amplifiers, N-channel MOSFETs, and relevant precision resistors in the reference constant current branch and the temperature measurement constant current branch respectively, and utilizing the virtual short and virtual open characteristics of the operational amplifiers, the current consistency in the two branches is achieved, thus forming a stable and constant reference current and temperature measurement current. The voltage sampling signals from the two branches are then differentially amplified by an instrumentation amplifier, ultimately outputting the temperature signal. This circuit uses a precision 100Ω resistor as the zero-point temperature reference and eliminates the error introduced by the resistance of the lead wires from the three-wire platinum resistance meter through differential calculation, effectively suppressing interference from lead wire resistance during temperature measurement.

[0015] Compared to the traditional constant voltage source + bridge structure, this invention adopts a constant current source drive method, avoiding the deviation caused by the change in wire resistance with temperature, thus improving the accuracy and stability of the overall temperature measurement. It is particularly suitable for Coriolis mass flow meter systems with high measurement accuracy requirements, thereby improving the overall measurement accuracy and reliability of the instrument. At the same time, the circuit structure is simple and the components are highly versatile, making it easy to promote and apply in actual industrial products. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a circuit diagram of a platinum resistance temperature measurement circuit for a Coriolis mass flow meter proposed in this utility model. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of this utility model are only used to explain this utility model and are not intended to limit this utility model. Example

[0019] This embodiment presents a specific implementation of a platinum resistance temperature measurement circuit for a Coriolis mass flow meter.

[0020] like Figure 1 As shown, a platinum resistance temperature measurement circuit for a Coriolis mass flow meter includes a reference constant current branch, a temperature measurement constant current branch, a differential amplifier circuit, and a platinum resistance temperature measurement branch.

[0021] Both the reference constant current branch and the temperature measurement constant current branch are connected to the same reference voltage VREF to generate a constant current signal of equal amplitude. The two constant current branches are respectively connected to a differential amplifier circuit and the platinum resistance temperature measurement branch, thereby achieving dual-path voltage sampling input. A precision resistor R2 with a resistance of 100Ω is installed on the reference constant current branch to simulate the reference resistance of the platinum resistance PT100 at 0℃.

[0022] In a preferred embodiment, the reference constant current branch includes: a first operational amplifier U1, a first N-channel MOSFET Q1, a precision resistor R2, and a grounding resistor R3. The non-inverting input of the first operational amplifier U1 is connected to the reference voltage VREF, and shares a connection with the non-inverting input of the temperature measurement constant current branch to ensure the consistency of the reference voltage. The inverting input of U1 is connected to the source of the first MOSFET Q1 and grounded through R3. The output of operational amplifier U1 is connected to the gate of MOSFET Q1 to adjust the conduction state of the MOSFET. The drain of MOSFET Q1 is connected to one end of the precision resistor R2, and also to the non-inverting input of the differential amplifier circuit; the other end of R2 is connected to the platinum resistance temperature measurement branch to achieve current sampling output under the reference voltage path.

[0023] The temperature measurement constant current branch structure is similar to the reference constant current branch, including: a second operational amplifier U2, a second N-channel MOSFET Q2, and a resistor R4. The non-inverting input terminal of U2 is shared with the non-inverting input terminal of U1, i.e., both are connected to VREF; the inverting input terminal is connected to the source of Q2 and grounded through R4. The output terminal of U2 controls the gate of Q2, and the drain of Q2 is connected to the inverting input terminal of the platinum resistance temperature measurement branch and the differential amplifier circuit, realizing current output control under the PT100 path.

[0024] The differential amplifier circuit is preferably an instrumentation amplifier (AMP), with its non-inverting input connected to the drain of Q1 and one end of R2, and its inverting input connected to the drain of Q2 and the output of PT100. The output of the instrumentation amplifier is connected to the MCU input interface for subsequent signal acquisition and temperature conversion.

[0025] The platinum resistance temperature measurement branch specifically includes: connector X1, platinum resistance temperature sensor PT100, power supply current-limiting resistor R1, and three wires. Pin 1 of connector X1 is connected to one end of R1, and the other end of R1 is connected to VCC, forming the power supply path. Pin 2 of X1 is connected to the other end of R2, and pin 3 of X1 is connected to the drain of Q2, forming a sampling loop. PT100 is connected to pins 1, 2, and 3 of the connector via three wires of the same length and specification to eliminate the influence of wire resistance on the measurement, realizing a three-wire constant current sampling structure. This embodiment utilizes two independent constant current branches with the same reference voltage to control the current paths of the reference resistor and PT100, forming two sets of voltage sampling signals with the same amplitude but different temperature responses. The two signals are differentially amplified by an instrumentation amplifier before output, avoiding errors caused by changes in line resistance in the traditional bridge method. Since the reference branch uses a 100Ω high-precision resistor, which is equivalent to the resistance of PT100 at 0℃, the final differential voltage is linearly related to the temperature, which is convenient for subsequent MCU processing and calibration.

[0026] Furthermore, this utility model has a compact structure, and all the components used are conventional analog devices, which are easy to integrate into the existing flow meter motherboard without increasing the system complexity. At the same time, it greatly improves the temperature measurement accuracy and long-term stability, and is especially suitable for high-reliability mass flow meter products in industrial environments. Example

[0027] This embodiment further illustrates the functional principle of the platinum resistance temperature measurement circuit of the Coriolis mass flow meter described in this utility model, based on embodiment 1, in order to clarify the technical path for achieving high-precision temperature measurement.

[0028] This circuit constructs a constant current source based on the virtual short and virtual open characteristics of operational amplifiers. In the reference constant current branch and the temperature measurement constant current branch, operational amplifiers control the operating state of the N-channel MOSFETs, ensuring a constant drain current. A stable reference voltage VREF is connected to the non-inverting input of each operational amplifier. According to the virtual short principle, the voltage at the inverting input also remains at VREF. Since the input impedance of the operational amplifier approaches infinity, the input current can be considered zero. Therefore, the current across a precision resistor (such as a 100Ω resistor) or a PT100 platinum resistance thermometer can be simplified by Ohm's law as follows:

[0029] I = VREF / R;

[0030] Where R is a precision resistor or the current resistance value of PT100.

[0031] The constant current paths I1 (reference path) and I2 (temperature measurement path) have the same reference voltage and operational amplifier control structure, and their output currents are the same, i.e., I1 = I2 = I.

[0032] To reduce measurement errors introduced by the wires, the PT100 uses a three-wire connection, ensuring that the three wires are of the same length and specifications, and that their resistances Rw are equal. The sampling point voltages U1 and U2 are taken from the reference resistor branch and the PT100 branch, respectively. Considering the resistance of the wires and components, the following expressions can be derived:

[0033] U1 = VCC - 2I·R1 - 2I·Rw - I·Rw - I·100

[0034] U2 = VCC - 2I·R1 - 2I·Rw - I·Rw - I·(100 + 0.3851·T)

[0035] In the above expression: R1 is the current-limiting resistor; Rw is the resistance of each wire; T is the measured temperature (°C); 0.3851 is the temperature coefficient of resistance of PT100 (unit: Ω / °C); I·(100 + 0.3851·T) is the voltage change caused by the temperature change of PT100.

[0036] Since the voltage drops of U1 and U2 are completely identical except for the temperature-dependent portion of the PT100 circuit, after differential amplification, we can obtain: VOUT = U1 - U2 = 0.3851·T·I·a; where a is the gain of the instrumentation amplifier. The final differential voltage VOUT is linearly related to the temperature T and can be directly fed into the MCU for A / D conversion and temperature calculation.

[0037] In this embodiment, the influence of wire resistance is eliminated by making full use of the three-wire structure, current mirror characteristics and differential amplification structure. Even if the wire resistance fluctuates due to temperature rise or environmental changes, it will not affect the final temperature measurement result, thereby ensuring high accuracy and long-term stability of temperature measurement and meeting the high requirements of mass flow meter for temperature compensation calculation.

[0038] The foregoing has shown and described the basic principles, main features, and advantages of this utility model. Those skilled in the art should understand that this utility model is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this utility model. Various changes and modifications can be made to this utility model without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed utility model. The scope of protection of this utility model is defined by the appended claims and their equivalents.

Claims

1. A platinum resistance temperature measurement circuit for a Coriolis mass flow meter, characterized in that, The reference constant current branch, the temperature measurement constant current branch, the differential amplification circuit and the platinum resistance temperature measurement branch are connected with the reference voltage.

2. A platinum resistance temperature sensing circuit for a Coriolis mass flowmeter according to claim 1 wherein, The reference constant current branch comprises a first operational amplifier, a first N-channel MOS tube and a precision resistor R2.

3. A platinum resistance temperature sensing circuit for a Coriolis mass flowmeter according to claim 2 wherein, The temperature measurement constant current branch comprises a second operational amplifier and a second N-channel MOS tube.

4. A platinum resistance temperature measurement circuit for a Coriolis mass flowmeter according to claim 3 wherein, The differential amplification circuit comprises an instrument amplifier.

5. A platinum resistance temperature sensing circuit for a Coriolis mass flowmeter according to claim 4 wherein, The platinum resistance temperature measurement branch comprises a connector and a platinum resistance temperature sensor PT100. The platinum resistance temperature sensor PT100 is connected with the connector through three wires.

6. A platinum resistance temperature measurement circuit for a Coriolis mass flowmeter according to claim 2 wherein, The reference constant current branch further comprises a resistor R3.

7. A platinum resistance temperature measurement circuit for a Coriolis mass flowmeter according to claim 3 wherein, The temperature measurement constant current branch further comprises a resistor R4.

8. A platinum resistance temperature measurement circuit for a Coriolis mass flowmeter according to claim 2 wherein, The precision resistor R2 has a resistance of 100Ω.

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