CN102384812A - Temperature compensation method and pressure transmitter digital display instrument adopting method - Google Patents

Abstract

The invention belongs to the technical field of industrial measurement and particularly relates to a temperature compensation method and a pressure transmitter digital display instrument adopting the method. Particularly, a power supply management system provides a power supply for a pressure transmitter, and a signal sampling module, an analog-to-digital conversion module and a main control chip are sequentially connected. The pressure transmitter digital display instrument also comprises a digital display module controlled by the main control chip. The main control chip adopts an MSP430F147 chip. The main control chip is also connected with a relay output module, a communication module, an external watchdog, an electrically erasable programmable read-only memory (EEPROM), a state indicating lamp and a press key input module. The pressure transmitter digital display instrument provided by the invention can be used for monitoring measurement signals in real time, can be used for operating and controlling the display data, has the advantages that the precision is high, the temperature drift is low, the stability is high, and the like, and the pressure transmitter digital display instrument can be widely applied to various fields of industry, scientific research, medical care and the like.

Description

Temperature compensation and adopt the pressure unit read out instrument of this method

Technical field

The invention belongs to the commercial measurement technical field, be specifically related to a kind of temperature compensation and adopt the pressure unit read out instrument of this method.

Background technology

Along with the development of electronic science and technology, it is more and more general that digitalized electron is measured, and aspects such as the precision measured and stability have been proposed increasingly high requirement.In the automatic measurement field, metering system becomes more diverse, and the traditional common type measurement instrument of function singleness can not satisfy user's actual demand under many circumstances.Usually after taking all factors into consideration the property easy to use and the market factor,, need development of new instrument targetedly for concrete application scenario.

The pressure unit working power of main flow mainly is divided into ± 15V and two types of ± 12V on the current market, and working current is output as the industrial signal 4～20mA or the 0～10V of standard below 100mA, and the precision aspect generally can reach ten thousand/, temperature drift is extremely low.Pressure unit needs the current measured value of real-time monitored when some industry spot are used; And the operator also hope displayed value have certain can be handling; Can carry out functions such as unit conversion as required, but traditional universal measurement instrument can't be realized above-mentioned functions.Simultaneously, the precision of pressure unit and stability are all very high, if adopt traditional supporting with it use of universal digital Displaying Meter, might cause the precision of measurement result to be affected and descend.

Summary of the invention

(1) goal of the invention

The object of the invention is to solve traditional universal measurement instrument and can't realizes the pressure transmitter measurement signal in real time is shown measured value, poor operability and might influence the stable problem of forepressure transmitter measuring-signal.

(2) technical scheme

For realizing above-mentioned purpose, the present invention provides a kind of read out instrument of supporting pressure unit work, and concrete technical scheme is following:

The temperature compensation that a kind of read out instrument adopted; With the output quantity AD0 of AD converter under room temperature, zero initial conditions as reference point; When the instrument operate as normal, at set intervals the once sampling Current Temperatures and with when calibration temperature relatively, through formula

$V=\left({\mathrm{AD}-\mathrm{AD}}_0\right)*\left(\frac{1}{\frac{1}{k_0}+{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="HSA00000248041700013.png,HSA00000248041700031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\mathrm{\&Delta;T}}\right)$

Calculate current actual signal voltage

A kind of pressure unit read out instrument that adopts the said temperature compensation method; To pressure unit power supply is provided by power-supply management system; Signal sampling module, AD modular converter are connected with main control chip successively, and its key is: also comprise the digital display module that is connected with main control chip.

Said main control chip adopts the MSP430F147 chip.Said main control chip also is connected with relay output module, communication module, outer watchdog, EEPROM, status indicator lamp and keyboard input module.

Said digital display module adopts red LED as display screen.

(3) beneficial effect

Pressure unit read out instrument provided by the invention can be monitored measuring-signal in real time; Can control video data; Have advantages such as precision height, temperature drift is low, stability is strong, can be used as the high precision electric measuring instrument and be widely used in various fields such as industry, scientific research, medical treatment.

Description of drawings

Fig. 1 is the entire system structural drawing of pressure unit read out instrument;

Fig. 2 connects synoptic diagram for power supply;

Fig. 3 is signal sample circuit figure;

Fig. 4 is digital display module circuit diagram;

Fig. 5 is relay output circuit figure;

Fig. 6 is the relation between sampled value and input signal and the temperature variation;

Fig. 7 is the process flow diagram of backoff algorithm.

Embodiment

Embodiment below in conjunction with concrete further specifies the present invention.

Present embodiment provides a kind of pressure unit read out instrument; Its entire system structure is as shown in Figure 1; To pressure unit power supply is provided by power-supply management system; Signal sampling module, AD modular converter are connected with main control chip successively, and its key is: comprise that also the number by main control chip control shows not module.

Main control chip is selected the MSP430F147 of TI company for use, and for strengthening vulnerability to jamming, system has adopted the outer watchdog mode.EEPROM (EEPROM) is used for storing the security parameter of some factory settings.Adopt the direct-connected mode of simple IO mouth to design four buttons, program is come the action of perception button through timing scan.

Adopt alternating current 220V to supply power to read out instrument in the present embodiment, and the working power of transmitter is provided, the power supply connected mode is as shown in Figure 2.For pressure unit, the shared one group of power supply in the power supply ground of the signal ground of output and input, if digital displaying meter inside is also same with one group of power supply, when signal source and signal ground reversal connection to instrument, danger will be short-circuited so.The function of measuring for the bipolarity that realizes instrument, with its output ± the 15V power supply effectively isolates with the working power of self inside.

Fig. 3 is signal sample circuit figure.AD7799 is a 24 modulus switching devices, and three groups of difference analogue passages are provided, and data transfer mode adopts the SPI mode.2.5V voltage reference adopts the REF5025 integrated chip of TI company, accuracy class is 0.05%, and temperature is floated only 3ppm/ ℃ of coefficient, and operating temperature range-40 ℃～125 ℃ has fully guaranteed the accuracy of AD sampling; In addition, REF5025 attaches temperature detecting function, can calculate environment temperature through measuring pin level.LM224 is the reinforcement version of operational amplifier LM324 commonly used, and working temperature is wideer, is applicable to industry spot.The analog quantity front end uses two 10V stabilivolt D1, D2 butt joint not to exceed the device tolerance range with the protection input voltage.Circuit that LM224 builds is realized the ratio addition, gets R1=R4=20K, and R2=R3=100K can realize the input voltage of-10V～10V is transformed to the signal of 0.5～4.5V.Transition function can be expressed as Vout=0.2Vin+2.5.At last, signal gets into a back level AD with the mode of pseudo-differential and is sampled effective like this noise of having avoided coming from signal ground.In the time of the circuit-board laying-out design, the circuit of analog part will be kept apart with other circuit, simulates ground and digitally adopts inductance or 0 Ohmage short circuit at AD7799 chip place.

Fig. 4 is digital display module circuit design.CH451 is a multifunction peripheral chip of having integrated charactron display driver and keyboard scan control and μ P monitoring.The built-in RC oscillatory circuit of CH451 can 8 charactrons of dynamic driving or 64 LED, have functions such as BCD decoding, flicker, displacement; Simultaneously can also carry out the keyboard scan of 64 keys; And monitoring functions such as electrification reset and house dog are provided.CH451 adopts the SPI mode to carry out exchanges data, and this programme uses its management charactron and the work of LED lamp.Because the WV of CH451 is 5V, main control chip IO mouth is the 3.3V level, can select for use the 74LVC4245 of TI company to carry out linking to each other with the CH451 communication interface after the level conversion.The display part comprises 5 charactrons, 1 negative sign pilot lamp, 4 measuring unit's pilot lamp and 4 alarm lamps.

Fig. 5 is the relay output circuit.Relay has been selected the G6B2114P two-way series of Omron Corp for use, and 12V drives, coil operating current 25mA.Because supply voltage is 15V, play the step-down effect so be connected in series 100 ohm resistance in the loop.The effect of electric capacity is to disappear to tremble, and prevents because the power supply instability causes the frequent adhesive of relay.That parallelly connected with 0.1u electric capacity is 1N4004, is fly-wheel diode, electric abrupt release induction electromotive force under coil.

Communication module adopts the communication interface of USB/485 or other modes.Under the indoor application environment, usb communication is more convenient, and hardware can be selected CP2102; A TTL changes the chip of USB, its inner self-powered management function, the stabilized power source of exportable 3.3V behind the connection main frame 5V power supply; Safe and reliable for guaranteeing, need the isolating chip of connecting between USB end and the MCU.As being applied in the industry control scene, 485 communications are reasonable selections, can select ADM2483 on the hardware, carry 485 communication integrated chips of isolation.

The temperature characterisitic of instrument is most important for this design.The temperature stability of forepressure transmitter is very high, if only because the design problem of secondary instrument finally causes the accuracy decline of measurement result not to be allowed to.In order to reach the setting index of expection, will its temperature characteristic parameter of special concern when each components and parts is selected for use.After the design moulding, also to do a net assessment to the temperature stability of complete machine.

Under room temperature condition, under zero input condition, the output quantity AD of the AD converter that the instrument sampling obtains ₀As reference point; Range of temperature is-25 ℃～85 ℃, and voltage signal input variation range is-12.500V～12.500V 5 ℃ at every interval, 0.500V; The output quantity AD of the AD converter that writing down once samples obtains and the difference of reference point are analyzed as the sample main body.

The three-dimensional plot that Fig. 6 constitutes for raw data, can get until what time important conclusion with this: 1) zero stability of instrument is very good.2) instrument is under isoperibol, and the linear relationship of input and output is fine.3) instrument temperature drift model can be that univariate linear function comes modeling in order to temperature value.

With the Δ AD deviation digital and reference point of representing to sample, T representes the residing environment temperature of instrument, and V representes to import the signal voltage of instrument.The relation of last figure can be shown by simple table:

ΔAD＝f(V，T) (1)

And following relation

is arranged

In the formula: d ₁, d ₂, d ₃, d ₄Be constant.

The digital AD=AD| of actual sampling _T=20+ Δ AD, so the function expression of AD value can be expressed as:

AD＝k ₁VT+k ₂V+k ₃T+k ₄ (2)

In the formula: k ₁, k ₂, k ₃, k ₄Be constant, wherein k ₀The sampled, digital amount that obtains when being calibration and the reduction coefficient of measured voltage values, k ₁The expression temperature variation is for the factor of influence of reduction coefficient.

Through checking, the zero point of instrument-25 ℃～85 ℃ constant basically, so can think k ₃=0, the further conversion of substitution (2) formula obtains

$V=\frac{{\mathrm{AD}-k}_4}{k_{1}T+k_2}---\left(3\right)$

K wherein ₄Practical significance promptly be the sampled value AD at zero point of instrument ₀

In the range calibration process, sampling storage environment temperature T at that time ₀, promptly obtain sampling sign indicating number and magnitude of voltage reduction coefficient k after calibration is accomplished ₀, can know the reduction formula of AD and voltage:

V＝(AD-AD ₀)*k ₀ (4)

When the instrument operate as normal, every certain interval of time once sampling Current Temperatures and with when calibration temperature T ₀Relatively get difference DELTA T, the computing formula of so current actual signal voltage can be expressed as

$V=\left({\mathrm{AD}-\mathrm{AD}}_0\right)*\left(\frac{1}{\frac{1}{k_0}+{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="HSA00000248041700013.png,HSA00000248041700031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\mathrm{\&Delta;T}}\right)---\left(5\right)$

The difference DELTA T of temperature can be through the pressure drop difference DELTA V under different temperatures of general-purpose diode or voltage stabilizing diode when Current Temperatures and calibration _TCharacterize promptly: at certain temperature range (20～80 degree) Δ T ∝ Δ V _T, then above-mentioned formula can be expressed as

$V=\left({\mathrm{AD}-\mathrm{AD}}_0\right)*\left(\frac{1}{\frac{1}{k_0}+k_T{\mathrm{\&Delta;V}}_T}\right)---\left(6\right)$

K wherein ₁As the performance parameter of instrument itself, in the preceding demarcation of dispatching from the factory.Above the error introduced successfully having compensated the error that temperature effect brings and having avoided of formula from voltage transitions to the absolute temperature process, directly be converted to the variation of temperature value from the change in voltage of temperature sensor, and then the k during to system calibration ₀Revise, thereby obtain real signal voltage value.Fig. 7 is given in the process flow diagram that embeds backoff algorithm in the master routine.

For manufacturer, k ₁Consistance extremely important, if because k ₁Widely different, all need before so every instrument is dispatched from the factory to investigate separately to demarcate, production cost will increase greatly.Through further theoretical analysis and experiment show, k ₁Value in fact only with employed 4 resistance R of amplifier LM224 ₁, R ₂, R ₃, R ₄Relevant.Like the unified 10ppm that uses, ± 1% or more high-grade resistance, k ₁Measured value be almost 0, promptly need not carry out temperature compensation; And inconsistent or to some extent during deviation when the temperature coefficient of resistance, k ₁Meaning then can manifest.In the experiment, picked at random some resistance, record k ₁Value reach 0.1728, by behind this model compensation with the compensation before do comparison, effect is quite obvious.Through measuring, behind this algorithm compensation, the operating ambient temperature of instrument changes between-20 ℃～80 ℃, and indicating value changes only 3mV of maximum, and the calibrating temperature is floated the predetermined value of coefficient far below 20ppm.

Through algorithm compensation, the temperature drift coefficient of instrument reduces greatly, uses this instrument to cooperate pressure unit work, and the high-quality signal of transmitter output can not receive indicator gauge fully and disturb.The input impedance of instrument is more than the 2M, measuring-signal to be exerted an influence hardly, therefore can be used as general voltage table and uses.For the pressure unit of current mode, can be at the prime parallel wire around precision resistance as sample resistance, convert voltage signal into and measure.

Above content is to combine preferred embodiment to specify what the present invention did, can not assert that embodiment of the present invention only limits to these explanations.Under the present invention, the those of ordinary skill of technical field, under the prerequisite that does not break away from the present invention's design, can also make some simple deductions and conversion, all should be regarded as belonging to protection scope of the present invention.

Claims (10)

1. temperature compensation that read out instrument adopted is with the output quantity AD of AD converter under room temperature, zero initial conditions ₀As reference point, when the instrument operate as normal, at set intervals the once sampling Current Temperatures and with when calibration temperature relatively, through formula

$V=\left({\mathrm{AD}-\mathrm{AD}}_0\right)*\left(\frac{1}{\frac{1}{k_0}+k_1\mathrm{\&Delta;T}}\right)$

Calculate current actual signal voltage.

2. a pressure unit read out instrument provides power supply by power-supply management system to pressure unit, it is characterized in that: signal sampling module, AD modular converter are connected with main control chip successively, also comprise the digital display module that is connected with main control chip;

Said signal sampling module is with the output quantity AD of AD converter under room temperature, zero initial conditions ₀As reference point, when the instrument operate as normal, at set intervals the once sampling Current Temperatures and with when calibration temperature relatively, through formula

$V=\left({\mathrm{AD}-\mathrm{AD}}_0\right)*\left(\frac{1}{\frac{1}{k_0}+k_1\mathrm{\&Delta;T}}\right)$

Calculate current actual signal voltage.

3. pressure unit read out instrument according to claim 2 is characterized in that: said main control chip adopts the MSP430F147 chip.

4. pressure unit read out instrument according to claim 2 is characterized in that: said main control chip also is connected with relay output module.

5. pressure unit read out instrument according to claim 2 is characterized in that: said main control chip also is connected with communication module.

6. pressure unit read out instrument according to claim 2 is characterized in that: said main control chip links to each other with outer watchdog.

7. pressure unit read out instrument according to claim 2 is characterized in that: said main control chip is connected with EEPROM.

8. pressure unit read out instrument according to claim 2 is characterized in that: said main control chip is connected with status indicator lamp.

9. pressure unit read out instrument according to claim 2 is characterized in that: said main control chip links to each other with keyboard input module.

10. pressure unit read out instrument according to claim 2 is characterized in that: said digital display module adopts red LED as display screen.

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