CN103278269A - Temperature compensation method for high accuracy pressure transmitter - Google Patents

Abstract

The invention belongs to a pressure sensing technology and relates to a temperature compensation method for high accuracy pressure transmitter. According to the invention, common temperature compensation components such as thermistors or diodes are not used, the temperature compensation of the pressure transmitter is realized by four groups of precise fixed resistors, and the error of the pressure transmitter is reduced; meanwhile, two independently-symmetric second order low-pass KRC active filters are designed by utilizing an operational amplifier of a differential amplifier circuit to filter out a differential mode interference signal from a pressure sensitive element, and the stability of the pressure transmitter on differentially outputting a voltage signal is guaranteed. The pressure transmitter manufactured by adopting the circuit design and the temperature compensation method is adapt to the temperature range of minus 55- 175 DEG C, and the output error in the whole temperature range is from minus 0.5 percent FS to plus 0.5 percent FS. The temperature compensation method for the high accuracy pressure transmitter has the advantages that the size is small, the weight is light, the anti-interference capacity is strong, the output is stable, and the technological process is simple and convenient, and the temperature compensation method is suitable for lager batch production.

Description

A kind of temperature compensation of high-precision pressure transmitter

Technical field

The invention belongs to the aviation pressure sensing technology, relate to a kind of temperature compensation and adjustment method of pressure unit.

Background technology

Pressure unit is that the various pressure signals that need to measure are converted into the electric signal of regulation, and electrical signal transfer is given the device of indicator or computing machine.Along with the development of aircraft industry, require pressure unit precision height, good stability, volume little, in light weight; Can adapt to bad working environment, be-55 ℃～175 ℃ as operating ambient temperature range.The realization key of high-precision pressure transmitter depends on circuit design and temperature compensation.At present, the high-precision pressure transmitter generally adopts the method for digital compensation to realize; And the maximum operating temperature of present domestic and international military digital device and special conditioning chip (as A/D conversion, microprocessor, D/A converter etc.) is 125 ℃, can't satisfy the request for utilization under the higher temperature condition.And analog temperature compensation adopts devices such as thermistor, diode to realize usually, adopts the temperature compensation by thermistor precision not high, adopts the diode temperature compensating circuit comparatively complicated; And common compensation method debug process complexity, temperature accommodation is narrower, and less stable is difficult to satisfy aircraft industry to the requirement of pressure unit.

Summary of the invention

The temperature compensation that the purpose of this invention is to provide a kind of high-precision pressure transmitter.

The technical scheme that the present invention takes is: a kind of high-precision pressure transmitter circuit, this circuit comprise constant current source (1), pressure resistance type SOI pressure-sensitive component (2), adjustable resistance Rp1～Rp4, double operational differential amplifier circuit (3,4); This steps on the quick electric bridge of four arm strengths to pressure resistance type SOI pressure-sensitive component (2) for favour, has 5 nodes, and wherein node d is positive power source terminal, and node b is negative power end, is connected with flowing into to hold with the outflow of constant current source respectively; Node a, c are respectively positive-negative output end, are connected with the positive and negative input end of differential amplifier circuit respectively; Adjustable resistance Rp3 one end links to each other with pressure resistance type SOI pressure-sensitive component (2) node d, and the other end links to each other with constant current source (1) outflow end; Adjustable resistance Rp2 is connected in parallel between pressure resistance type SOI pressure-sensitive component (2) positive power source terminal and the positive output end; Adjustable resistance Rp1 is connected in parallel between pressure resistance type SOI pressure-sensitive component (2) the positive-negative power end, links to each other by adjustable resistance Rp4 between two operational amplifier positive input terminals.

Rp1, Rp2, Rp3, Rp4 are adjustable resistance, and the effect of four debugging resistance is as follows respectively:

Rp1 is thermal sensitivity drift compensation debugging resistance, is used for compensation transmitter sensitivity temperature drift;

Rp2 is thermal zero drift compensation debugging resistance, is used for the temperature drift amount of compensation transmitter zero-bit output;

Rp3 is zero-bit output debugging resistance, is used for adjusting the output of transmitter zero-bit;

Rp4 is full scale output debugging resistance, is used for adjusting the output of transmitter full scale;

Value or the computing method of debugging resistance are as follows respectively:

(1) zero-bit output debugging resistance R p3:

The value of zero-bit debugging resistance R p3 requires to determine according to the zero-bit bias voltage that the zero-bit of pressure-sensitive component after the zero-bit temperature compensation exported and transmitter requires.Debugging is according to actual needs determined.

(2) full scale output debugging resistance R p4

The value of full scale output debugging resistance R p4 requires to determine according to the full scale output voltage that the full scale of pressure-sensitive component behind sensitivity compensation exported and transmitter requires; Its value depends primarily on enlargement factor.

If the transmitter output voltage is U _So, the pressure-sensitive component output signal is U _o, then according to the operational amplifier characteristic, have:

$\frac{U_o}{R_{p4}}=\frac{U_{\mathrm{so}}}{R_7+R_3+R_{p4}}$ ……………………………………………………①

Because R is arranged in the circuit ₇=R ₃, the computing formula that formula (1) can be put in order the enlargement factor A that can get differential amplifier:

$A=\frac{U_{\mathrm{so}}}{U_o}=1+\frac{{2R}_7}{R_{p4}}$ …………………………………………………②

(3) thermal sensitivity drift compensation debugging resistance R _P1

The thermal sensitivity drift of pressure unit also has the influence of amplifying circuit except from pressure-sensitive component; And R _P1Final value should make the output voltage thermal sensitivity drift of pressure unit minimum or be zero.So R _P1Actual value be:

$R_{p1}=-K_1\×\frac{\mathrm{\α}}{\mathrm{\α}+\mathrm{TCR}}\×R_{\left(T0\right)}$ ………………………………………③

Wherein:

K ₁Be the value coefficient, depend primarily on the temperature characterisitic of differential amplifier circuit; R _(T0)For in temperature T ₀Under the condition, the input impedance of pressure-sensitive component.

α is the heat sensitivity coefficient of pressure-sensitive component; TCR is that bridge is pressed temperature coefficient, and its numerical value calculates according to the nominal data of pressure-sensitive component.

When adopting the constant current source timing signal, in temperature T ₀Measure bridge and press U down, _{B (T0)}, electric current I _b, the zero-bit output voltage U _{Oz (T0)}, full scale output U _{Om (T0)}Under temperature T, measure bridge and press U _{B (T)}, the zero-bit output voltage U _{Oz (T)}, full scale output U _{Om (T)}, then have:

$R_{\left(T0\right)}=\frac{U_{b\left(T0\right)}}{I_b}$ …………………………………………………………④

$\mathrm{TCR}=\frac{U_{b\left(T\right)}-U_{b\left(T0\right)}}{U_{b\left(T0\right)}(T-T_0)}$ …………………………………………………⑤

$\mathrm{\α}=\frac{\frac{U_{\mathrm{om}\left(T\right)}-U_{\mathrm{oz}\left(T\right)}}{U_{b\left(T\right)}}-\frac{U_{\mathrm{om}\left(T0\right)}-U_{\mathrm{oz}\left(T0\right)}}{U_{b\left(T0\right)}}}{T-T0}$ ……………………………………⑥

4., 5., 6. through type calculates R respectively _(T0), α, TRC.3. through type calculates the sensitivity compensation resistance R again _P1

Generally, R _P1Span be (6～60) k Ω, and the input impedance of pressure-sensitive component is (3～6) k Ω.In order to reduce R _P1Adjustment to pressure unit initial temperature (T ₀) influence of (being generally normal temperature) output under the condition, should reduce R when temperature (T) as far as possible _P1Setting range, K generally ₁Span be (1.3～1.8).

In order to obtain higher compensation precision, need carry out the demarcation of a plurality of temperature spots to pressure-sensitive component; The quantity of bidding fixed temperature point is n, n 〉=2, and its obtaining value method is as follows:

When n=2, can by formula 3., 4., 5., 6. calculate R _P1, the method generally is used for the not high situation of sensitivity compensation accuracy requirement.In order to obtain higher compensation precision, answer value 3≤n≤8, the distribution of temperature spot is generally evenly chosen in the total temperature scope, also can select flexibly as required; This moment, the n value was more big, and the compensation precision of pressure unit is more high.When n＞8, increase the quantity of demarcating temperature, for the raising of pressure unit compensation precision and not obvious.

(4) thermal zero drift compensation debugging resistance R _P2

The hot zero compensation resistance R of pressure-sensitive component _P2Be in order to reduce temperature to the influence of output at zero point; Consider the influence of amplifying circuit, R in actual debug process _P2Initial value need adjust according to the output of the zero-bit of transmitter.Usually have:

R _p2=K ₂×R’p ₂……………………………………………………⑦

Wherein:

$R_{p2}^{\′}=\frac{(1+K)(\sqrt{1+K}+1)}{K}\≈\frac{2\×R}{K}$ ………………………………………⑧

Wherein K is determined by zero-bit output:

$K=\frac{4\×U_{\mathrm{oz}}}{U_b}$ …………………………………………………………⑨

7. calculate R according to formula _P2Theoretical span be (3～200) M Ω.And the arm resistance value of pressure-sensitive component is (3～6) k Ω; Work as R _P2During＞20M Ω, the variation of its resistance value to the influence of pressure-sensitive component zero-bit output be not more than ± 0.03%, can ignore.So R _P2Span can be defined as (3～20) M Ω.Because R _P2R _bAdjustment less for the output influence of initial temperature (T0) downforce zero-bit, therefore get K usually ₂=1.

The compensation method of a kind of high-precision pressure transmitter temperatures may further comprise the steps:

Step 1:SOI pressure-sensitive component is demarcated

In-55 ℃～175 ℃ temperature ranges, choose some temperature spot n, demarcate bridge pressure, electric bridge internal resistance and the output valve of SOI pressure-sensitive component;

Step 2: calculate intermediate parameters

According to the data that step 1 pressure-sensitive component is demarcated, obtain heat sensitivity factor alpha, bridge pressure temperature coefficient TCR with least square method;

Step 3: resistance R is repaid in supplement _P1, R _P2Initial value

Obtain compensating resistance R respectively according to hereinafter given computing formula _P1, R _P2Initial value.

Step 4: initial temperature T0 debugging;

Generally get T ₀=25 ° of C preset R _P1, R _P2Resistance, adjust R _P3, R _P4Make the pressure unit output voltage satisfy technical requirement.

Step 5: compensation temperature T debugging;

Keep R _P3, R _P4Constant, adjust R _P1, R _P2Make the pressure unit output voltage satisfy technical requirement.

Step 6: adjustable resistance R _P1～R _P4, the precision metallic film fixed resistance of resistance such as change into;

Step 7: the output error of verifying other temperature conditions downforce transmitter.

For better implement the present invention, in the above-mentioned steps 1, the number n that temperature spot is chosen is 3～8.

Resistance R is regulated in the output of pressure unit zero-bit _P3Adjustable resistance R with full scale output _P4, the normal temperature output characteristics according to pressure unit zero-bit and full scale calculates or actual measuring respectively; The sensitivity temperature drift compensating resistance R of pressure unit _P1With zero-bit temperature offset drift R _P2, calculate prevalue according to pressure unit zero-bit and full scale temperature drift characteristic.At initial temperature T ₀Under the condition, preset R _P1, R _P2, zero-bit output and the full scale output of adjusting pressure unit get final product R _P3And R _P4; Under compensation temperature T condition, keep R _P3And R _P4Constant, export drift value to R according to zero-bit output drift value and the full scale of pressure unit _P1, R _P2Finely tune.Owing to take initial value to calculate the method that presets, R _P1, R _P2Adjustment amount generally less, to initial temperature T ₀The output influence of condition downforce transmitter is very little, can ignore substantially.Therefore can avoid pressure unit under condition of different temperatures, to repeat debugging.

The present invention has beneficial effect: precision metallic film fixed resistance is only adopted in the output adjustment of pressure unit and temperature compensation, and do not use thermistor (precision is lower) and diode devices such as (circuit are comparatively complicated), can simplify compensating circuit, improve the compensation precision of pressure unit; The output adjustment of pressure unit is controlled with two groups of different resistance respectively with temperature compensation, the method that presets by initial resistance, can avoid influencing each other between two groups of resistance R p1, Rp2 and Rp3, the Rp4 preferably, namely independently carry out respectively in the debugging of initial temperature (T0) and compensation temperature (T1), avoid debugging repeatedly under different temperature points, simplified debug process.

This adjustment method overwhelming majority debugging step can both get off with computing machine and program Solidification thereof, can increase substantially production efficiency, thereby realizes production in enormous quantities of pressure unit.

Description of drawings

Fig. 1 is preferred embodiments connection diagram of the present invention, wherein 1: constant current source, 2: pressure resistance type SOI pressure-sensitive component, 3,4: the double operational differential amplifier circuit.

Embodiment

Below in conjunction with Figure of description the present invention is described in further detail.

Embodiment:

The compensation method of a kind of high-precision pressure transmitter temperatures may further comprise the steps:

Step 1:SOI pressure-sensitive component is demarcated;

Certain SOI presser sensor chip is at-55 ℃ ,-25 ℃, 0 ℃, 25 ℃, 75 ℃, 115 ℃, 150 ℃, 175 ℃ under totally 8 temperature spots, the output voltage U when testing input pressure respectively and being 0MPa _Oz(T)(unit is mV), the output voltage U when input pressure is 35MPa _Om(T)(unit is mV), electric bridge bridge are pressed U _B(T)(unit is V), data recording is as shown in table 1.

Table 1SOI pressure-sensitive component nominal data table

The temperature test point (℃)	-55	-25	0	25	75	115	150
								0MPa exports U oz（T）(mV)	-0.312	-0.193	-0.107	-0.036	0.044	0.035	0
35MPa exports U om（T）(mV)	85.676	86.863	87.691	88.524	90.016	91.196	92.182
								The electric bridge bridge is pressed U b(V)	2.891	3.034	3.154	3.282	3.542	3.764	3.965

Step 2: obtain α, TCR with least square method.

If probe temperature is T, then under this temperature conditions, the sensitivity coefficient of presser sensor assembly:

S _(T)=U _FS（T）/U _b（T）=[U _om（T）-U _oz（T）]/U _b（T）

The heat sensitivity factor alpha be S (T) to the first order derivative of temperature T, i.e. α=dS (T)/dT.

Under the general condition, sensitivity S (T) has linear relationship preferably to temperature T, and approximation relation formula: S (T)=α * T+ β is then arranged.

α, β can try to achieve with least square method, and wherein α is the heat sensitivity coefficient.

According to the test data of table 1, can calculate sensitivity temperature coefficient α, as shown in table 2.

Table 2 heat sensitivity factor alpha is calculated

The temperature coefficient TCR that bridge is pressed is U _B(T)To the first order derivative of temperature T, that is:

TCR=d?U _b（T）/dT

Under the general condition, bridge is pressed U _B(T)Temperature T is had linear relationship preferably, and TCR is that bridge is pressed U _B(T)To the slope value of temperature T, this is worth available least square fitting and obtains.

According to table 1 data, can calculate the temperature coefficient TCR that bridge is pressed.As shown in table 3.

Table 3 bridge is pressed U _B(T)Temperature coefficient TCR calculate

Step 3: heat sensitivity compensating resistance R _P1, R _P2Calculating

Under normal temperature (25 ℃) condition, heat sensitivity compensating resistance theoretical value R _P1Computing formula as follows:

R _p1=K ₁×（-α）/S _(25℃)×[α/S _(25℃)+TCR/U _b（25℃）]×U _b（25℃）/I _i。

K ₁Obtained by commissioning experience, get K generally speaking ₁=1.3.K ₁Usually span is (1.3～1.8), and its concrete value can be debugged needs adjustment according to reality.

Generally, R _P1Span be (6～60) k Ω.

By table 1, table 2, table 3 test data, according to above-mentioned computing formula (K ₁=1.3) can get: R _P1=11.9k Ω.

Under normal temperature (25 ℃) condition, the R of heat sensitivity compensating resistance theoretical value _P2Computing formula is as follows:

K ₂Obtained by commissioning experience, because R _P2Actual value is bigger, gets K generally speaking ₂=1.

Its concrete value can be debugged needs adjustment according to reality.

Work as R' _P2During＞20M Ω, the variation of its resistance value to the influence of pressure-sensitive component zero-bit output be not more than ± 0.03%, can ignore.So R' _P2Span can be defined as (3～20) M Ω.

By table 1 test data, can get R' according to above-mentioned computing formula _P2=299M Ω exceeds its value upper limit, desirable R' _P2=20M Ω.

Step: 4: initial temperature T0 debugging

Preset R _P1, R _P2Resistance, adjust R _P3, R _P4Make transmitter output satisfy technical requirement.

Under normal temperature (25 ℃) condition, the debugging output voltage values, requirement and step are as follows:

(1) insulation: the control temperature of sweat box is set to 25 ℃; Behind the temperature stabilization, keep 30min at least;

(2) preset resistance value R _PS, R _PL: according to the calculated value of 3.2 joints, regulate resistance box, make R _PS=R' _P1, R _PL=R' _P2

(3) debugging output: it is 0MPa that the debugging pressure controller makes input pressure, the debugging resistance box, and making output voltage values is 100mV; Debugging pressure controller then, to make input pressure be 35MPa, debugging electricity group case, and making output voltage values is 5000mV; Again input pressure is reduced to 0MPa, repeat above-mentioned debugging step 2～3 times; After debugging was finished, the corresponding output voltage values of debug component when input pressure is 0MPa and 35MPa was respectively 100mV and 5000mV;

(4) after debugging is finished, keep the resistance box resistance value to immobilize, and the resistance value of record resistance box.

Step 5: compensation temperature T debugging

Compensation temperature (T) debugging, this example is chosen T=115 ℃ of debugging, keeps R _P3, R _P4Constant, adjust R _P1, R _P2, make the output of transmitter satisfy technical requirement.

Under 115 ℃ hot conditions, the debug component output voltage values, requirement and step are as follows:

1) intensification and insulation: keep the resistance box resistance value to immobilize, keep assembly and commissioning device in running order; The control temperature of temperature test chamber is set to 115 ℃.Behind the temperature stabilization, keep 1h at least; In the temperature-rise period, making the assembly input pressure is 0MPa.

2) debugging output: it is 0MPa that the adjustment pressure controller makes input pressure, the debugging resistance box, and making output voltage values is 100mV; Adjusting pressure controller then, to make input pressure be 35MPa, debugging electricity group case, and making output voltage values is 5000mV; Again input pressure is reduced to 0MPa, repeat above-mentioned debugging step 2～3 times.After debugging was finished, the corresponding output voltage values of debug component when input pressure is 0MPa and 35MPa was respectively 100mV and 5000mV.

3) after debugging is finished, keep each resistance box resistance value to immobilize, and the resistance value of record resistance box.

Step 6: adjustable resistance Rp1～Rp4, the precision metallic film fixed resistance of resistance such as change into;

Step 7: the error of verifying other temperature conditions downforce transmitter.

Check that assembly is in the output error of-55 ℃, 25 ℃, 115 ℃, 150 ℃ temperature spots.Temperature spot-55 ℃ and 150 ℃ of temperature retention times are 2h, and 115 ℃ of temperature retention times of temperature spot are 1h.Assembly should satisfy table 1 requirement in the error of each temperature spot.

The error amount of table 4 pressure unit under each temperature test point

As shown in Table 4, the maximum error of pressure unit in-55 ℃～175 ℃ temperature ranges is ± 0.5%FS.

The present invention combines the temperature transmission characteristic of SOI pressure-sensing device and differential amplifier circuit, adopts four groups of minute adjustment resistance to finish the adjustment of pressure unit zero-bit output voltage, the adjustment of full scale output voltage, the temperature compensation of zero-bit output voltage and the compensation of sensitivity temperature respectively.The output adjustment of pressure unit is controlled with two groups of different resistance respectively with temperature compensation, the method that presets by initial resistance, can reduce influencing each other between two groups of resistance (Rp1, Rp2 and Rp3, Rp4), namely independently carry out respectively in the debugging of initial temperature (T0) and compensation temperature (T1), avoid debugging repeatedly under different temperature points, simplified debug process.

Claims (4)

1. the temperature compensation of a high-precision pressure transmitter is characterized in that: may further comprise the steps:

Step 1:SOI pressure-sensitive component is demarcated

In-55 ℃～175 ℃ temperature ranges, choose some temperature spot n, demarcate bridge pressure, electric bridge internal resistance and the output valve of SOI pressure-sensitive component;

Step 2: calculate intermediate parameters

According to the data that step 1 pressure-sensitive component is demarcated, obtain heat sensitivity factor alpha, bridge pressure temperature coefficient TCR with least square method;

Step 3: resistance R is repaid in supplement _P1, R _P2Initial value

Step 4: initial temperature TO debugging;

Generally get T ₀=25 ° of C preset R _P1, R _P2Resistance, adjust R _P3, R _P4Make the pressure unit output voltage satisfy technical requirement;

Step 5: compensation temperature T debugging;

Keep R _P3, R _P4Constant, adjust R _P1, R _P2Make the pressure unit output voltage satisfy technical requirement;

Step 6: adjustable resistance R _P1～R _P4, the precision metallic film fixed resistance of resistance such as change into;

Step 7: the output error of verifying other temperature conditions downforce transmitter.

2. the temperature compensation of high-precision pressure transmitter according to claim 1, it is characterized in that: in the step 1, the number n that temperature spot is chosen is 3～8.

3. the temperature compensation of high-precision pressure transmitter according to claim 1 is characterized in that: R _P1Span be (6～60) k Ω.

4. the temperature compensation of high-precision pressure transmitter according to claim 1 is characterized in that: R _P2Span can be defined as (3～2O) M Ω.