DD236994A1 - CIRCUIT ARRANGEMENT FOR PIEZORESISTIVE PRESSURE SENSORS WITH CORRECTIVE BEHAVIOR - Google Patents

Abstract

The invention relates to a circuit arrangement for a piezoresistive pressure sensor, which can be used to correct the Meßgasdruckeinflusses on the electrical output signal of gas analyzers. The aim of the invention is to correct the influenced by measuring gas pressure output of gas analyzers with little effort, the task is to provide a circuit by means of which the pressure-influenced output of a gas analyzer can be corrected by incorporating stretch-dependent resistors on a messgasdruckbeaufschlagten membrane. According to the invention, this object is achieved in that the voltage to be corrected is connected once to the input of an inverting operational amplifier, the output of which is connected to an input of an adder circuit of an output operation amplifier and is connected to another input of the adder circuit, wherein the strain-dependent resistor on Input of the non-inverting operational amplifier becomes larger with increasing pressure, while the expansion-dependent resistance between the output and the inverting input of the inverting operational amplifier decreases with increasing pressure. Fig. 1

Description

-2- 759 18

Origin signal relative enlargement of the correction effect is achieved. A dosage of this correction effect is possible by adjusting the input resistances of the adder circuit.

embodiment

The invention will be explained below using an exemplary embodiment. In the drawing show:

Fig. 1: electrical circuit of the piezoresistive pressure sensor

Fig. 2: Diaphragm of the piezoresistive pressure sensor with two strain-dependent resistors Fig.3: piezoresistive pressure sensor - overall view.

In Fig. 1, the signal path from the input of an optical gas analyzer 1 is shown to the output of a piezo-resistive pressure sensor 4 connected downstream of this. The optical gas analyzer 1 converts the gas concentration input с into an output signal U _{c; p} , which according to the laws of kinetic gas theory is proportional to the measuring gas pressure ρ prevailing in the measuring cuvette. Pressure deviations Λ ρ are caused by changes in the flow of the sample gas through the sample cell and by changes in the atmospheric pressure. The resulting measurement error can be eliminated by connecting a pressurized with the Meßgasdruck ρ piezoresistive pressure sensor 4. The transfer function of the electric circuit 2 (FIG. 1) is designed to cancel the pressure error of the optical gas analyzer 1. For this purpose, the voltage U _{c: p} to be corrected is connected once to the input of an inverting operational amplifier OV ₁ whose output is connected to an input of an adder circuit of the output operational amplifier OV ₂ and to another input of the adder circuit of the output operational amplifier OV _{2 is} switched. Here, the strain-dependent input resistance R _{1 of} the inverting operational amplifier OV ₁ is arranged on the membrane 3, that its resistance increases with increasing pressure on the membrane 3, while lying between the output and the inverting input of the inverting operational amplifier OV ₁ strain-dependent resistor R _2nd is arranged on the diaphragm 3, that its resistance value decreases with increasing pressure on the diaphragm 3, The resistors R ₃ , R ₄ and R ₅ determine the gain of the adder in the output operational amplifier OV _second In this case, the resistor R _{3 is connected} between the inverting input of the inverting output operational amplifier OV ₂ and the output of the inverting operational amplifier OV ₁ , the resistor R ₄ between the output of the gas analyzer 1 and the inverting input of the inverting operational amplifier OV ₂ . The resistor R ₅ is arranged between the inverting input and the output of the inverting operational amplifier OV ₂ . The connection points of the diaphragm 3 arranged on the strain-dependent resistors R ₁ and R ₂ are denoted by the letters A, B and C.

The following signal processing results from this circuit arrangement: The electrical output signal of the optical gas analyzer 1 is U _{c; p}

Po is the normal pressure in the measuring cell

The corrected output signal U _c is then

Γ : - \ - _: Jb 2 ι

The strain-dependent resistors R ₁ and R ₂ have the normal value p ₀ uniformly the value R ₀ . Taking into account that the strain-dependent resistors are stretched once by their different position on the pressurized vacuum-pressed membrane 3-R ₁ and once-upsetting-R ₂ , the relationship is obtained

= v

 ψ -> * K ^ -ß

-с

The piezoresistive coefficients α and β may vary depending on the location of the resistors on the membrane. The output signal U _c , _{p of} the optical gas analyzer 1 is pressure-proportional, that is to say:

А - Ό / T. 'j

-z-759

с ι

Neglecting the second-order A terms

) Π 1 -

j;

.eiin

is, results for

_ TT

Д)

i-Q

= σ.

With po = 1 bar is the correction

with a pressure deviation around 10m bar with an error of the order of 0.1%, with a pressure deviation around 30m bar with an error of the order of 10%, with a pressure deviation around 100 m bar with an error of the order of 1%.

Claims (1)

-1- 759 Invention claim. Circuit arrangement for piezoresistive pressure sensors with correction behavior in gas analyzers, in which two expansion-dependent resistors are mounted on a diaphragm loaded with the measuring gas pressure, characterized in that the voltage to be corrected (U _cp ) is switched once to the input of an inverting operational amplifier (OV ₁ ), whose output is connected to one input of an adder circuit of the output operational amplifier (OV ₂ ) and, on the other hand, to another input of the adder circuit of the output operational amplifier (OV ₂ ), the strain-dependent input resistance (R ₁ ) of the inverting operational amplifier (OV ₁ ) is arranged on the membrane (3) such that its resistance value increases with increasing pressure, while the strain-dependent resistance (R ₂ ) lying between the output and the inverting input of the inverting operational amplifier (OV ₁ ) is thus applied to the membrane (3 ) t is that its resistance value decreases with increasing pressure For this 1 page drawings Field of application of the invention The invention relates to a circuit arrangement for piezoresistive pressure sensors with correction behavior, which can be used to correct the Meßgasdruckeinflusses on the electrical output signal from gas analyzers. The circuit arrangement is particularly well in conjunction with piezoresistive elements in semiconductor and thick film technology Characteristic of the known technical solutions Means are known by means of which the output signal of optical gas analyzers is manually corrected via a potentiometer circuit after the barometric value has been determined on a barometer (US Pat. No. 4,069,420). Such a correction device is unsuitable for process monitoring because it is too large Maintenance required Furthermore, facilities are known in which the Meßgasdruck proportional influence on the output signal is eliminated in that the Meßgasdruck is detected by means of a pressure sensor and the pressure-proportional sensor signal is calculated in a divider with the output signal to be calibrated The device is particularly suitable the case is that a computing device is already present and is shared Otherwise, the effort is relatively large Furthermore, facilities are known in which the pressure sensor used for the correction of Meßgasdruckeinflusses pressure sensor and the correction circuit are connected to the reference voltage and thereby affect the reference voltage pressure proportional, during the The output of the reference voltage element is usually amplified and supplied to the output amplifier of a gas analyzer with control of the pilot signal (WP G 01 N / 254545 0). These devices are especially used in measuring devices with Re However, the application of the pilot signal is worthwhile only if several measuring systems have to be corrected at the same time. It is also known that variously the correction of the output signal is completely dispensed with and the gas analyzers have an additional error corresponding to the pressure fluctuations (Infralyt, VEB Junkalor , GDR, Uras, HuB, FRG) Object of the invention The aim of the invention is to correct the influenced by Meßgasdruck output of gas analyzers with little effort Explanation of the essence of the invention The rapid development of sensor technology in general, but especially the technologies used for pressure measurement technology for the production of piezoresistive elements (strain gages, thin-film, semiconductor and cover layer resistors) are constantly opening up new application possibilities Such a possibility is also a piezoresistive pressure sensor with correction behavior, which combines the hitherto customary pressure sensor and the logic circuit for the voltage to be calibrated. For the execution of a piezoresistive pressure sensor, the semiconductor and thick-film technology with the high k The invention has for its object to provide for a piezoresistive pressure sensor, a circuit by means of which by including strain-dependent resistors on a pressurized, printed against vacuum membrane of the pressure-influenced output of a Erfmdungsgemaß this task is solved by the fact that the voltage to be corrected is once switched to the input of an inverting operational amplifier whose output with a Input of an adding circuit of an Ausgangsoperversverstarkers is connected and connected to another input of the adding circuit of the Ausgangsoperversstarkstarkers, wherein the strain-dependent input resistance of the inverting operational amplifier is arranged on the membrane, that with increasing pressure, its resistance value is larger, while between the output and The expansion-dependent resistance lying on the membrane of the inverting input of the inverting operational amplifier is arranged so that with increasing pressure, the resistance is smaller With this circuit arrangement is achieved by the difference in the bestückten by strain-resistant resistors inverting operational amplifier signal too low and the to be fermented