CN100390515C - Intercept temperature difference tester - Google Patents

Abstract

The present invention relates to an instrument for testing temperature in an industrial automation production process, which comprises a testing circuit (1), a filter circuit (2), a CPU (3), a key board display circuit (4) and a memory (5), wherein the output end of the testing circuit (1) is connected with the input end of the filter circuit (2); the output end of the filter circuit (2) is connected with the input end of the CPU (3); the output end of the CPU (3) is connected with a temperature test control instrument. The testing circuit (1) comprises a signal collecting circuit (11) on the front end and a signal comparing amplifying circuit (12). Because the signal comparing amplifying circuit of the testing circuit of the present invention adopts an intercept form circuit, the present invention fundamentally realizes that the constant part of the input is subtracted by making use of a subtraction circuit for enlarging the enlargement proportion of the variable part; in this way, the high-precision temperature measurement can be ensured, the sensibility ratio is higher than that of a common amplifying circuit. The present invention is an intercept form temperature difference tester with high measure precision, smart design, convenience and practicability.

Description

Intercept temperature difference tester

1. Technical field:

The invention is an instrument for measuring temperature in the industrial automatic production process, in particular, it is used for measuring the temperature difference of the external cooler used in the sodium carbonate production process in the combined alkali production industry of chemical products.

2. Background technology:

In the industrial automation production process, temperature is one of the most important parameters, and its level and stability directly affect the production process and product quality. Especially in the temperature difference measurement of the external cooler used in the sodium carbonate production process in the combined alkali production industry of chemical products, the temperature has a great impact on production. According to the requirements of the soda making process, from the field operation experience and the characteristics of the mother liquor to be cooled, the mother liquor is cooled once in the external cooler, and the temperature drop is preferably 0.5°C. If the temperature difference between the inlet and outlet of the mother liquor is lower than 0.5°C, it indicates that the cooling effect has not been achieved, and it is necessary to add several more cooling devices of the same type in the subsequent operation process, which increases the investment in equipment; and if the temperature difference exceeds 0.5°C after cooling. ℃, it means that the temperature of the solution in the ring pipe drops suddenly, so that the mother liquid will solidify and scar, and some solids will solidify on the inner wall of the casing to block the pipe, damage the equipment, and greatly reduce the cooling effect. Therefore, it is an important link to guide the production process to accurately measure the temperature difference between the inlet and outlet of the loop pipe. , the measurement of the temperature of the external cooler must meet the accuracy requirements of at least 0.2°C (or even 0.1°C). Due to the high accuracy requirements, the measurement and control of this part of the temperature have not been well resolved in the industry. At present, although there are many high-precision temperature measuring instruments or measuring devices on the market, whether they are analog or digital, there is a certain error range. For example, for a 0.1-grade high-precision temperature measuring instrument with a measuring range of 150°C, its measurement error is ±0.15°C. If a thermometer is installed at the entrance and exit of the external cooler to measure the temperature difference, the maximum possible The error is 0.3°C, which does not include the error caused by the lead wire.

3. Contents of the invention:

The purpose of the present invention is to overcome the above-mentioned shortcomings and provide an intercept type temperature difference tester with high measurement accuracy. The present invention has ingenious design, simple structure and convenient operation.

The structure schematic diagram of the present invention is shown in accompanying drawing, comprises detection circuit (1), filter circuit (2), central processing unit (3), keyboard display circuit (4), memory (5), wherein detection circuit (1) The output end of the filter circuit (2) is connected to the input end of the filter circuit (2), the output end of the filter circuit (2) is connected to the input end of the central processing unit (3), and the output end of the central processing unit (3) is connected to the temperature measurement and control instrument.

The above-mentioned detection circuit (1) includes a front-end signal acquisition circuit (11), a signal comparison amplifier circuit (12), wherein the front-end signal acquisition circuit (11) includes a thermistor R _PT1 at the inlet of the outer cooler, and an outlet of the outer cooler The thermistor R _PT2 at the position, the setting resistance R _s corresponding to the intercept voltage, three three-terminal constant current source devices LM334-1, LM334-2, LM334-3, and three output currents of the constant current source LM334 that can be easily adjusted The adjustable resistors R1, R5, R11 of I _set , the signal comparison amplifier circuit (12) is an intercept type temperature measurement circuit, and this intercept type temperature measurement circuit is an operational amplifier P1, P2, wherein three constant current sources LM334 common voltage source V _cc , the output terminals of the three constant current sources LM334 are respectively grounded through the thermistor R _PT1 , thermistor R _PT2 , and the setting resistor R _s , and the output terminals of the constant current source LM334-1 are connected to each other through the diode D1 and the resistor R3 The positive input terminal of operational amplifier P1 is connected, the output terminal of constant current source LM334-2 is connected with the negative input terminals of operational amplifiers P1 and P2 through diode D2 and resistor R7, the output terminal of constant current source LM334-3 is connected through diode D3 and resistor R13 is connected to the positive input terminal of the operational amplifier P2, and the negative input terminals of the operational amplifiers P1 and P2 are respectively connected to their respective output terminals through resistors R9 and R10.

The central processing unit (3) is also connected with a keyboard display circuit (4) and a memory (5).

The above-mentioned central processing unit (3) is a 16-bit single-chip microcomputer 80C196KC, the memory (5) is two off-chip expansion memory chips PSD302 and AT24C02, and the keyboard display circuit (4) is an LCD display circuit.

Since the signal comparison and amplifying circuit in the detection circuit of the present invention have adopted an intercept type circuit, its basic realization idea is to use the subtraction circuit to subtract the constant part of the input in essence, so as to enlarge the amplification ratio of the changing part, so that it can ensure For high-precision temperature measurement, the sensitivity of the intercept circuit is higher than that of the general amplifier circuit. The invention is a convenient and practical intercept type temperature difference tester with high measurement precision, ingenious design.

4. Description of drawings:

Fig. 1 is a block diagram of the present invention;

Fig. 2 is the circuit schematic diagram of detection circuit (1) of the present invention;

Fig. 3 is a schematic circuit diagram of the present invention;

Fig. 4 is a schematic circuit diagram of the signal comparison and amplification circuit (12) in the detection circuit (1) of the present invention.

5. Specific implementation methods:

Example 1:

The principle block diagram of the present invention as shown in Figure 1, comprises detection circuit (1), filter circuit (2), central processing unit (3), keyboard display circuit (4), memory (5), wherein detection circuit (1) The output end of the filter circuit (2) is connected to the input end of the filter circuit (2), the output end of the filter circuit (2) is connected to the input end of the central processing unit (3), and the output end of the central processing unit (3) is connected to the temperature measurement and control instrument.

The above-mentioned detection circuit (1) includes a front-end signal acquisition circuit (11), a signal comparison amplifier circuit (12), wherein the front-end signal acquisition circuit (11) includes a thermistor R _PT1 at the inlet of the outer cooler, and an outlet of the outer cooler The thermistor R _PT2 at the position, the setting resistance R _s corresponding to the intercept voltage, three three-terminal constant current source devices LM334-1, LM334-2, LM334-3, and three output currents of the constant current source LM334 that can be easily adjusted The adjustable resistors R1, R5, R11 of I _set , the signal comparison amplifier circuit (12) is an intercept type temperature measurement circuit, and this intercept type temperature measurement circuit is an operational amplifier P1, P2, wherein three constant current sources LM334 common voltage source V _cc , the output terminals of the three constant current sources LM334 are respectively grounded through the thermistor R _PT1 , thermistor R _PT2 , and the setting resistor R _s , and the output terminals of the constant current source LM334-1 are connected to each other through the diode D1 and the resistor R3 The positive input terminal of operational amplifier P1 is connected, the output terminal of constant current source LM334-2 is connected with the negative input terminals of operational amplifiers P1 and P2 through diode D2 and resistor R7, the output terminal of constant current source LM334-3 is connected through diode D3 and resistor R13 is connected to the positive input terminal of the operational amplifier P2, and the negative input terminals of the operational amplifiers P1 and P2 are respectively connected to their respective output terminals through resistors R9 and R10. In this embodiment, the resistance values of the resistors R9 and R10 are the same, as shown in FIG. 2 .

In this embodiment, the signal comparison and amplification circuit (12) is actually an intercept circuit, and its basic realization idea is to use the subtraction circuit to subtract the constant part of the input in essence to enlarge the amplification ratio of the variable part, so that Guaranteed high-precision temperature measurement. The sensitivity of the intercept circuit is 1 or 2 units higher than that of the general amplifier circuit. Its principle is shown in Figure 4. U _i represents the input voltage corresponding to the thermistor at a certain temperature; U _s represents the voltage corresponding to the constant temperature part, which is the corresponding intercept; U ₀ represents the amplification The output voltage of the link; U is the voltage corresponding to the part that should be amplified after subtracting the intercept. When the fluctuation of temperature is not very large, U occupies a small share of U _i , and U _s basically reflects a value corresponding to the ambient temperature. After the subtraction circuit subtracts the fixed part (that is, the intercept U _s ), the variable part can be fully amplified, thereby greatly improving the measurement accuracy.

According to the operation formula of the addition and subtraction operation circuit, there is (U _i -U _s )R ₂ /R ₁ ＝U _o

In the actual circuit, the voltage drop of the current source on the resistance is used to replace the voltage source U _s , so that stepless intercept voltage setting can be realized by changing the variable resistance value.

The three constant current source devices in the front-end signal acquisition circuit (11) share a voltage source (V _cc ), and their common ground is also connected to the ground of the operational amplifier connected behind, which solves the potential caused by the non-common ground The phenomenon of floating and drifting eliminates the self-excited oscillation, which provides a strong guarantee for the stable acquisition of the subsequent single-chip digital acquisition system, and greatly reduces the burden of analog filtering and digital filtering.

Platinum resistors R _PT1 and R _PT2 are two corresponding temperatures, and changes in voltages U _pt1 and U _pt2 on them reflect changes in resistance (that is, changes in temperature). U _pt1 and U _pt2 correspond to U _i in Figure 4, and the corresponding calculation formula is:

(U _pt1 −U _s )R ₂ /R ₁ =ΔU ₀₁ , (U _pt2 −U _s )R ₂ /R ₁ =ΔU ₀₂

To ensure the accuracy of the circuit, R _PT1 , R _PT2 and R _s should be much smaller than R ₁ , so that the measurement accuracy will not be greatly affected by the shunt effect. Another point of attention to ensure the measurement accuracy is that before use, the current flowing through R _PT1 and R _PT2 must be adjusted to be consistent, otherwise the accuracy cannot be guaranteed, which is also the pre-commissioning work added by the common ground system. Connect the output voltage U ₀₁ and U ₀₂ to their respective low-pass filters, and then send the output signal of the filter to the A/D input terminal, and the signal acquisition task is completed.

In this embodiment, the operational amplifiers P1 and P2 are OPA627 chips, and the filter circuit (2) uses MAX7403 as the filter chip. After the input signal is compared, amplified and hardware filtered, it is sampled by the A/D channel of the MCU. In addition to sending the processed results to LCD display, the system also provides a 4-20mA current output signal.

The above-mentioned central processing unit (3) is also connected with a memory (5). In this embodiment, the above-mentioned central processing unit (3) is a 16-bit single-chip microcomputer 80C196KC, and the memory (5) is two off-chip expansion memory chips PSD302 and AT24C02, wherein the programmable peripheral logic device PSD302 is used as the main memory of the system, and also integrates ROM , RAM and logic decoding circuit and other functions, and at the same time complete the address signal latch and logic decoding. The use of this chip greatly simplifies the design of the hardware circuit, saves the space of the circuit board, and also improves the stability of the system. Significant enhancement. AT24C02 is a two-wire serial E ² PROM chip, which is used to store the corresponding relationship between temperature and resistance. As shown in Figure 3.

The above-mentioned central processing unit (3) is also connected with a keyboard display circuit (4), and the keyboard display circuit (4) is an LCD display circuit, which has LCD display and standard current output functions, and carries out online modification to some system parameters by means of identification, Can withstand large changes in the working environment of the system The system samples the input, and the temperature measurement display accuracy can reach 0.1°C; the outlet temperature measurement range is 4-15°C, and the temperature difference measurement range is 0-1.4°C; two-stage hardware filtering and The first-level software filtering ensures the stability and accuracy of the display, and can adapt to different work sites.

When the present invention is used, the temperature signal is converted into a corresponding power signal (signal acquisition part) by a platinum resistor, then the signal is compared and amplified, and then filtered, and the A/D channel of the MCS80C196/KC is used for sampling, and the processed result In addition to sending LCD display, the system also provides 4-20mA current output signal to drive the temperature measurement and control instrument. In this embodiment, the temperature measurement and control instrument is DDZIII type and other related instruments.

Claims (1)

1. An intercept type temperature difference tester includes a detection circuit (1), a filter circuit (2), a central processing unit (3), a keyboard display circuit (4), and a memory (5), wherein the detection circuit (1) The output end of the filter circuit (2) is connected to the input end of the filter circuit (2), the output end of the filter circuit (2) is connected to the input end of the central processing unit (3), and the output end of the central processing unit (3) is connected to the temperature measurement and control instrument, which It is characterized in that the detection circuit (1) includes a front-end signal acquisition circuit (11), a signal comparison amplifier circuit (12), wherein the front-end signal acquisition circuit (11) includes a thermistor R _PT1 at the entrance of the outer cooler, an outer cooler The thermistor R _PT2 at the outlet, the setting resistance R _s corresponding to the intercept voltage, three three-terminal constant current source devices LM334-1, LM334-2, LM334-3, and three output of the constant current source LM334 that can be easily adjusted The adjustable resistors R1, R5, R11 of the current I _set , the signal comparison amplifier circuit (12) is an intercept type temperature measurement circuit, the intercept type temperature measurement circuit is an operational amplifier P1, P2, and three constant current sources LM334 are shared The voltage source V _cc , the output terminals of the three constant current sources LM334 are grounded through the thermistor R _PT1 , thermistor R _PT2 , and the setting resistor R _s respectively, and the output terminals of the constant current source LM334-1 are grounded through the diode D1 and the resistor R3 It is connected with the positive input terminal of operational amplifier P1, the output terminal of constant current source LM334-2 is connected with the negative input terminals of operational amplifiers P1 and P2 through diode D2 and resistor R7, and the output terminal of constant current source LM334-3 is connected through diode D3 and The resistor R13 is connected to the positive input terminal of the operational amplifier P2, and the negative input terminals of the operational amplifiers P1 and P2 are respectively connected to their respective output terminals through the resistors R9 and R10.

Images