Method for operating a pirani pressure sensor, and device

Abstract

The invention relates to a method for operating a Pirani pressure sensor, comprising an electrically heated measuring resistor, wherein an electrical power is applied to the measuring resistor such that the measuring resistor has a constant operating temperature, wherein the electrical power required to maintain the constant operating temperature is a measure of the pressure to be measured in the measurement volume of the measuring resistor of the Pirani pressure sensor. The method is distinguished by the fact that, dependent on various predefined pressure ranges, the operating temperature is preset by means of a control unit to a target temperature value respectively applicable to the individual pressure range, wherein the application of power takes place within the respective pressure range in accordance with the respective target temperature value and the electrical power required in each case for this target temperature value is a respective measure of the pressure to be measured within the respective pressure range.

Description

[0001] Method for operating a Pirani pressure sensor and device

[0002] Description

[0003] The invention relates to a method for operating a Pirani pressure sensor having the features of claim 1 and a device for operating a Pirani pressure sensor having the features of claim 7.

[0004] Pirani-type pressure sensors are well known. A Pirani pressure sensor exploits the property that, within certain pressure ranges and under certain conditions, the thermal conductivity of gases depends on the gas pressure within the chamber. The higher the density of the surrounding gas, the higher the thermal conductivity of the gas. The lower the thermal conductivity, the lower the gas density. Because the gas pressure correlates with the gas density, the thermal conductivity of the gas depends on the gas pressure.

[0005] On a given hot surface, an equilibrium temperature is established at a given electrical power input, i.e., at a given heat input on the one hand, and through pressure-dependent heat conduction to the surrounding medium on the other. This equilibrium temperature forms the starting point for pressure measurement with a Pirani pressure sensor.

[0006] There are essentially two basic configurations commonly used for Pirani pressure sensors. In the first type of Pirani pressure sensor, the hot surface is realized, for example, by a filament whose equilibrium temperature is measured via a resistance measurement. Miniaturized versions using a so-called MEMS chip are also possible. MEMS stands for "micro electrical mechanical systems." In a MEMS chip, an electrical resistor is implemented on a chip substrate in the form of a conductive track surrounded by a cavity arranged on the chip. Under these conditions, the equilibrium temperature of the filament or the integrated resistor arranged on a MEMS chip, which occurs under a fixed electrical power application, depends on the thermal conductivity of the surrounding medium.

[0007] By measuring the temperature of the filament or the resistance, the pressure of the surrounding gas can be determined.

[0008] MEMS chips are typically installed in so-called TO packages, meaning they are welded, glazed, and bonded. TO stands for a package shape borrowed from transistor technology. MEMS chips for Pirani sensors typically contain a measuring resistor whose temperature is determined according to the Pirani measuring principle. A reference resistor may also be present on the MEMS chip. These types of MEMS chips are primarily suitable for use in medium vacuums.

[0009] A Pirani pressure sensor can be operated in two different ways. In the first mode, a fixed electrical power is applied to the measuring resistor, and the temperature of the measuring resistor is measured. The temperature is then the measured variable from which the gas pressure is determined using a calibration function.

[0010] However, it is also possible to specify a constant value for the temperature of the measuring resistor and then adjust the electrical power required to maintain the specified temperature at a given gas pressure. In this case, the adjusted power is the direct measured value.

[0011] For example, the documents GB 2105472 A, US 5,608,168 A1 and WO 2000 / 054018 A1 propose operating the Pirani sensor at a constant temperature, i.e. adjusting it to a constant temperature. To do this, the power applied to the sensor is actively adjusted so that the temperature in the filament remains constant. In this mode of operation, the power supplied during this control is a measure of the heat dissipated into the medium, and therefore of the thermal conductivity of the medium and ultimately of the pressure prevailing in the medium. Ultimately, this type of approach also determines the temperature of the filament or the electrical resistance. The applied electrical power is an indirect measure of how much a fixed temperature difference between the filament and the ambient medium needs to be adjusted.The strength of this adjustment is then a measure of the thermal conductivity of the gas and thus also of its pressure.

[0012] However, operating the Pirani sensor at a constant temperature and with power adjustment is also problematic. This method implicitly assumes that heat transfer between the filament or the hot electrical resistance of the Pirani pressure sensor to the surrounding medium is based on the same physical mechanisms, regardless of the gas pressure. Accordingly, at particularly low gas pressures or in areas of rough vacuum, the measurement accuracy of the measuring method becomes increasingly poor. In this case, either a sufficiently high signal swing that can be used by downstream evaluation electronics is no longer achieved, or the sensor can no longer be used outside of a specific intended measuring range because otherwise there is a risk of destroying the measuring resistor.

[0013] The task is therefore to provide a method for operating a Pirani pressure sensor with constant temperature and power adjustment that makes it possible to eliminate these disadvantages, significantly expand the measuring range of the Pirani pressure sensor, and take into account the dominant physical principles of action and adjust it to an optimal signal. Furthermore, the influence of a fluctuating ambient temperature is to be compensated for operationally and situationally, and the operation of the Pirani pressure sensor is to be adapted accordingly.

[0014] The object is achieved by a method for operating a Pirani pressure sensor having the features of claim 1 and by a device for operating a Pirani pressure sensor having the features of claim 7. The respective subclaims contain expedient and / or advantageous embodiments of the method and / or device.The method for operating a Pirani pressure sensor, comprising an electrically heated measuring resistor, wherein the measuring resistor is supplied with an electrical power such that the measuring resistor has a constant operating temperature and wherein the electrical power required to maintain the constant operating temperature is a measure of the pressure to be measured in the measuring volume of the measuring resistor of the Pirani pressure sensor, is characterized according to the invention in that the operating temperature is preset by means of a control unit as a function of various predefined pressure ranges to a temperature target value applicable to the individual pressure range.The power is applied within the respective pressure range according to the respective temperature target value and the electrical power required for this temperature target value is then a respective measure of the pressure to be measured within the respective pressure range.

[0015] This takes into account, in particular, that heat transfer from the Pirani pressure sensor to the surrounding medium occurs differently in different pressure ranges. At very low pressures, heat transfer occurs primarily via pressure-independent components, which, particularly in the case of IR radiation, increases nonlinearly at higher temperatures. This would cause the desired gas-type-dependent measurement signal to be proportionally smaller. For this reason, the operating temperature is preset to a rather low level.With the temperature values ​​now optimally adjusted for each pressure range, possibly taking the ambient temperature into account, the respective dominant physical effects (convection, IR radiation, heat conduction via solids, pressure-dependent heat conduction, and pressure-independent heat conduction) are taken into account in the control system, generating a strong signal that extends the measuring range and improves accuracy. In addition, this allows for an optimal balance between a high signal and an offset that is present on the signal and is not suitable for pressure determination. This offset can be set as low and constant as possible by reducing the respective interfering physical effects.

[0016] At medium vacuum pressures, where heat conduction to the surrounding medium plays a dominant role, the operating temperature is set to a higher value. Pressures in the receiver at higher vacuum pressures up to atmospheric pressure, where convection effects in the medium are to be expected, require a somewhat lower operating temperature to minimize convection effects compared to heat conduction.

[0017] In one embodiment, the control unit regulates the respective temperature target value within a ratio interval and / or within a difference interval with respect to an ambient temperature measured by a temperature sensor and / or a predetermined pressure range.

[0018] This means that the respective temperature target value and the ambient temperature are related to each other, with the value of this relationship lying within a predetermined interval, and / or that the temperature target value and the ambient temperature have a certain difference, with the value of this difference being set within a certain interval. Both conditions—i.e., the ratio and the difference—can be used simultaneously by the control unit to determine the temperature target value. Based on this, pressure-dependent control can be implemented, in which either a constant absolute temperature on the MEMS chip or a constant temperature difference to the ambient temperature is set.

[0019] In one embodiment of the method, the respective target temperature value is determined using a temperature sensor located in the immediate vicinity of the measuring resistor and designed as part of the Pirani pressure sensor. The control unit determines the target temperature value from an ambient temperature value determined by the temperature sensor as at least one additional input variable for the target temperature specification. This input parameter and / or the required power consumption can be used to calculate the actual pressure.

[0020] In this embodiment, the target temperature value is not specified invariably, but is adjusted to a specific ambient temperature and / or a pressure range established in the recipient within the range of the Pirani pressure sensor. To adjust the target temperature to the ambient temperature, the ambient temperature is determined via a temperature sensor. In this embodiment, the temperature sensor is designed as part of the Pirani pressure sensor. The determined ambient temperature value forms at least one input variable from which the target temperature is specified.

[0021] In combination or independently, the required power for setting the target temperature is used to determine the prevailing pressure range and adjust the target temperature.

[0022] In one embodiment of the method, a MEMS chip with at least one first conductor serving as a measuring resistor and a second conductor serving as a temperature sensor is used as the Pirani pressure sensor, with the ambient temperature being measured via the second conductor. The use of a MEMS chip offers the advantage that the Pirani pressure measurement and the ambient temperature measurement are structurally combined in a small space, thus allowing the ambient temperature to be measured practically directly at the location of the Pirani sensor.

[0023] In one embodiment, the control unit compares the respective temperature target value with the currently measured ambient temperature, with the ambient temperature serving as an upper limit for the respective temperature target value. The temperature target value is set based on the determined ambient temperature. In this first embodiment, the ambient temperature serves as an upper limit for the temperature target value. This means that the temperature target value is set by the control unit so that it does not exceed the ambient temperature.

[0024] In a further embodiment, the control unit compensates for offset drift due to ambient temperature changes. At a constant pressure, at least two different temperature values ​​are set, and their effects are measured. This determines at least two different Pirani and ambient temperatures, which generate a pressure signal that is independent of the offset. This allows, for example, temperature fluctuations during evacuation to be compensated. A device for operating a Pirani pressure sensor comprises an electrically heated measuring resistor and a control unit for applying electrical power to the measuring resistor to maintain a constant operating temperature.The control unit has a memory with a stored plurality of different pressure range-dependent target temperatures and a power control for applying power to the Pirani pressure sensor according to the respective target temperature.

[0025] In one embodiment, the power controller has a value input for a measuring unit of the ambient temperature of the Pirani pressure sensor and a comparison unit for comparing the ambient temperature with the target temperature to generate an adjusted target temperature and for applying power according to the adjusted target temperature.

[0026] In one embodiment, the Pirani pressure sensor is designed as a MEMS chip with a first conductor track as a measuring resistor and a second conductor track as a measuring unit of the ambient temperature.

[0027] The method and device will be explained in more detail below using exemplary embodiments. Figures 1 to 4 serve to illustrate this. The same reference numerals are used for identical or equivalent parts. It shows:

[0028] Fig. 1 shows an exemplary diagram with three different pressure ranges and three different operating temperatures assigned to the pressure ranges,

[0029] Fig. 2 shows the exemplary diagram from Fig. 1 with additional calibration functions assigned to the respective operating temperatures,

[0030] Fig. 3 is an exemplary block diagram of a device for carrying out the method,

[0031] Fig. 4 shows an example MEMS chip.

[0032] Fig. 1 shows an example diagram with three different pressure ranges and three different operating temperatures associated with the pressure ranges. All values ​​given in the following explanation are examples only and serve for illustrative purposes.

[0033] The basis of the method described below is the operation of a given Pirani sensor at a fixed operating temperature TO with power adjustment. The power P required to maintain the operating temperature TO is then a measure of the respective existing pressure. The power P represents the measured variable. This is converted into the pressure p using a calibration function. This is how the pressure is measured. In the method according to the invention and illustrated below as an example, the operating temperature TO changes depending on the pressure range. Each pressure range p1, p2, p3, pn is assigned its own operating temperature, i.e. the operating temperature T1, T2, T3, ... Tn. In principle, the maximum pressure interval to be measured can be divided into any number of individual pressure ranges, i.e. at least two individual ranges. A correspondingly large number of operating temperatures are provided.

[0034] In the example shown in Fig. 1, three pressure ranges are provided, namely a first pressure range pl from 10° to 10 3 mbar, a pressure range p2 of 10 -4 up to 10° mbar and a pressure range p3 of IO -6 up to 10 -4mbar. Each of the three pressure ranges is characterized by different mechanisms of heat transfer between the heated measuring resistor of the Pirani pressure sensor and the surrounding medium. In the pressure range p3, i.e. at very low pressures, heat transfer between the measuring resistor and the surrounding medium occurs primarily through the process of thermal radiation. The medium in a vacuum has such a low density in this pressure range that heat conduction is extremely limited and heat transfer to the surrounding medium via convection cannot occur and is excluded. Under these conditions, the measuring resistor is regulated by the control unit to an operating temperature T3. In this example, the temperature T3 is lower than 200°C.Under these conditions, the measuring resistor of the Pirani pressure sensor can be supplied with an electrical power P that generates a signal swing that is sufficiently large across the entire pressure range p3, while also preventing the measuring resistor from overheating due to the power application, thus avoiding damage to the measuring resistor. The operating range of the measuring resistor of the given Pirani pressure sensor can be extended beyond the limits of the pressure range p2 to lower pressures by adjusting it to the operating temperature T3 in the pressure range p3. The given Pirani pressure sensor can thus also register lower pressures than those for which it was initially designed.

[0035] In the pressure range p2, which is assumed here to be the optimal pressure range for the given Pirani pressure sensor and its measuring resistor, and for which the given Pirani pressure sensor and its measuring resistor are designed, the density of the surrounding medium is sufficiently high to ensure heat conduction between the heated measuring resistor and the surrounding medium, but on the other hand, no significant convection effects occur. The measuring resistor is regulated to a temperature T2, which in this example is more than 300 °C.

[0036] In the pressure range p2, the measuring resistor of the Pirani pressure sensor is operated at a maximum permissible operating temperature T2, which on the one hand ensures a correspondingly large signal with a corresponding power load, but on the other hand also protects the measuring resistor of the Pirani pressure sensor from damage according to the specific design of the pressure sensor.

[0037] In the pressure range pl, where there is approximately a rough vacuum and, at its upper limit, essentially atmospheric pressure, heat transfer from the heated measuring resistor to the surrounding medium now increasingly occurs via convection in addition to heat conduction. Pressure measurement with a conventional Pirani pressure sensor is problematic here because the measuring principle of the Pirani pressure sensor is normally based on heat transfer to the surrounding medium via heat conduction, and heat transfer via convection distorts the measurement result.

[0038] Under the conditions of the pressure range pl, a lower operating temperature TI is regulated. In this example, this lies below the operating temperature in T3 in the pressure range p3. The operating temperature TI in this example is approximately 100 °C. It is chosen so that the temperature gradient between the heated measuring resistor and the surrounding medium is so small that convective processes are avoided for a given design configuration of the Pirani pressure sensor. This means that the given design of a Pirani pressure sensor can also be used at pressures that are greater than the design-dependent pressure range of the given Pirani pressure sensor. In this example, the measurable pressure range p2 is therefore extended not only towards the lower pressure range p3, but also towards the higher pressure range pl.

[0039] It is understood that each of the operating temperatures TI, T2 and T3 is assigned its own calibration function, which assigns the power supply P required to maintain the operating temperature TI, T2 and T3 to the pressure p to be measured. Fig. 2 shows a corresponding example. Within the respective pressure ranges pl, p2 and p3, i.e. within the respectively applicable operating temperatures TI, T2 and T3 specified by the control unit, different calibration functions ml, m2 and m3 are valid, which assign the respective electrical power supplied to the measuring resistor to a pressure and thus make the pressure measurable. The numerical data shown in the example in Fig. 2 are also merely examples and serve to illustrate the method.

[0040] The illustration in Fig. 2 shows that the electrical power P supplied to maintain a certain operating temperature increases with increasing pressure p. This offers the possibility of automatic switching by the control unit between the individual operating temperatures and thus between the individual pressure ranges, without the pressure in the recipient having to be known. For this purpose, each of the operating temperatures TI, T2 and T3 is assigned an upper power limit Pl, P2 and P3 and a lower power limit Pl', P2' and P3'. The control unit switches between the individual operating temperatures TI, T2 and T3 precisely when either the upper power limit Pl, P2 or P3 for the respective operating temperature is exceeded, or when the lower power limit for the respective operating temperature is undershot.Exceeding the respective upper power limits occurs when the pressure in the receiver increases, and falling below the lower power limits occurs when the pressure in the receiver decreases. The lower and upper power limits are stored in advance in the control unit and can either be uniquely assigned to a given configuration of a Pirani pressure sensor or apply globally to all Pirani pressure sensors.

[0041] It is clear that passing through the pressure ranges from p1 to p3 or from p3 to p1 can be associated with switching hysteresis, where the limits of the individual pressure ranges can depend on the direction of their passage. In principle, these switching hysteresis do not pose a problem for the measurement process itself or for the switching processes described, provided the limit powers are preset in such a way that they do not impair the functionality of the Pirani sensor under any circumstances, even if the pressure in the vicinity of the Pirani sensor has already left the predefined pressure range.

[0042] As mentioned, the respective operating temperatures TI, T2,..., Tn can be set in various ways. They can be fixed and then controlled.

[0043] Another possibility is to first determine the operating temperature operationally within certain limits, depending on the specific measurement conditions, and then adjust it specifically. In this case, either no fixed operating temperature is specified or the operating temperature is selected and set from a specific predefined range.

[0044] To determine the operating temperature, the specific ambient temperature of the Pirani pressure sensor is determined. A temperature sensor can be used to determine the ambient temperature. This sensor is either structurally independent of the Pirani pressure sensor, is located near the Pirani pressure sensor, or is structurally integrated with the Pirani pressure sensor, for example, on a MEMS chip.

[0045] The control unit then adjusts the target value for the respective operating temperature as a temperature target value within a ratio interval and / or within a difference interval with respect to an ambient temperature measured by a temperature sensor and / or a specified pressure range. This adjustment process occurs continuously and thus also takes changes in the ambient temperature into account.

[0046] The operating temperature Tn to be controlled and the ambient temperature Tu are coupled with each other.

[0047] The criterion for this coupling can thus be a temperature difference ΔT = Tn - Tu or a specific ratio δ = Tn / Tu. Both ΔT and δ can lie within a predefined range for these values. This range is generally adjustable. Both ΔT and δ can be used individually or in combination to determine the operating temperature Tn.

[0048] Based on this, pressure-dependent control can then be realized, in which either a constant absolute temperature on the Pirani pressure sensor, in particular the MEMS chip, or a constant temperature difference or a specific temperature ratio of the pressure sensor to the ambient temperature is set.

[0049] During the measuring process, the prevailing pressure range can be determined based on the power required to set the target temperature, and the operating temperature can then be adjusted if necessary. If the power required to maintain a current target temperature suddenly drops significantly, i.e., particularly below a certain predefined minimum value, the control unit registers this as a drop in pressure in the recipient, and the operating temperature is set to a new, lower target value. At the same time, this is the signal that a lower pressure range has been reached. Analogously, an adjustment to a higher pressure range takes place. If the power supply exceeds a certain level, the target temperature is set to a new, lower value.

[0050] Such temperature adjustment can also be achieved under the influence of other environmental conditions, particularly the ambient temperature as mentioned above. By optimally adjusting temperature values ​​in the respective pressure range, the dominant physical effects (convection, IR radiation, heat conduction via solids, pressure-dependent heat conduction, and pressure-independent heat conduction) are regulated, thereby ensuring a strong signal to increase the measuring range and accuracy. In addition, this allows for an optimal ratio between high signal and offset (the offset that lies on the signal and is not suitable for pressure determination), whereby the offset can be set as low and constant as possible by reducing the respective interfering physical effects.

[0051] Fig. 3 shows an exemplary block diagram of a device for implementing the method. The method uses a measuring resistor 1, which is commonly used for typical Pirani configurations and is supplied with an electrical power P. A control unit is provided to operate the measuring resistor 1.

[0052] 2. This contains a memory 3 in which, in particular, the operating temperatures TI, T2, ..., Tn appropriate for the respective pressure ranges and for the respective measuring resistor are stored or in which these operating temperatures are operatively determined as target values.

[0053] The control unit 2 further contains a power controller 4, which controls and executes the power application P to the measuring resistor 1. A measuring sensor 5 for determining an ambient temperature is located in close proximity to the measuring resistor. The measuring sensor 5 is connected to a measuring unit 6. The measuring unit 6 is implemented as part of the control unit 2. The value for the ambient temperature determined by the measuring unit 6 is transferred to a comparison unit 7. This compares the determined ambient temperature Tu with the operating temperatures stored in the memory 3 and, depending on the comparison result, influences the power controller 4 as previously explained. This particularly applies to the comparisons between the ambient temperature and the operating and target temperatures described in each case.

[0054] The measuring resistor 1 is otherwise coupled as usual with a measuring temperature determination unit 8, which determines the actual temperature of the measuring resistor 1. This acts back on the power control 4, whereby the values ​​stored in the memory

[0055] The operating temperature TI, ...Tn stored in 3 serves as the setpoint. The electrical power P delivered by the power control 4 to the measuring resistor is determined and serves as a measured value for the pressure in an actual pressure measuring unit (not shown here) for determining the pressure in the recipient.

[0056] The measuring resistor 1 and the ambient temperature measuring unit 5 can, if desired, be structurally combined in a MEMS chip 9. An external input / output unit 10 enables the measured pressure value to be output, external operating temperature specifications, and external modifications to the process sequence. All components can be implemented both as hardware and, at least partially, in the form of signal processing software.

[0057] The control unit 2 is located away from the measuring resistor 1 and the temperature sensor 5 or the MEMS chip 9 outside the recipient.

[0058] Fig. 4 shows an exemplary MEMS chip 9 suitable for implementing the method. In this example, the measuring resistor 1 is embodied as a MEMS measuring resistor 11 surrounded by a series of cavities 12. These cavities are incorporated into the chip substrate such that the measuring resistor is suspended via a series of webs 13. These webs 13 also serve as the electrical supply for the MEMS measuring resistor 11. The cavities 12 are freely accessible to the ambient atmosphere in the volume of the recipient, and the temperature of the MEMS measuring resistor 11 is determined by the heat transfer between the measuring resistor and the surrounding cavities 12.

[0059] The MEMS chip also contains a MEMS temperature sensor 14 for measuring the ambient temperature of the MEMS measuring resistor 11. The MEMS temperature sensor 14 is located sufficiently close to the MEMS measuring resistor 11 to register the ambient temperature present in the medium to be measured, but it is also sufficiently removed from it so that the medium remains sufficiently unaffected by the heat emitted by it. Both the MEMS measuring resistor 11 and the MEMS temperature sensor 14 are electrically contacted with external components via conductor tracks and contact surfaces 15 (not shown here) running on the MEMS chip. The method has been explained in more detail using exemplary embodiments. Further embodiments can be found in the subclaims.

[0060] List of reference symbols

[0061] 1 measuring resistor

[0062] 2 control unit

[0063] 3 storage

[0064] 4 Power control

[0065] 5 Measuring sensor for ambient temperature

[0066] 6 measuring unit

[0067] 7 Comparison unit

[0068] 8 Measuring temperature determination unit

[0069] 9 MEMS chip

[0070] 10 Input / output unit

[0071] 11 MEMS measuring resistor

[0072] 12 Cavity

[0073] 13 jetty

[0074] 14 MEMS temperature sensor

[0075] 15 contact surfaces

Claims

Claims 1. A method for operating a Pirani pressure sensor, comprising an electrically heated measuring resistor, wherein the measuring resistor is supplied with an electrical power (P) such that the measuring resistor has a constant operating temperature (T0), wherein the electrical power (P) required to maintain the constant operating temperature (T0) is a measure of the pressure (p) to be measured in the measuring volume of the measuring resistor of the Pirani pressure sensor, characterized in that, by means of a control unit, the operating temperature (T0) is preset to a temperature target value (T1, T2, ..., Tn) applicable to the individual pressure range as a function of various predefined pressure ranges (P1, P2, ..., Pn), wherein the power supply within the respective pressure range (P1, P2, ..., Pn) corresponds to the respective temperature target value (T1, T2, ...,Tn) and the electrical power required for this temperature target value is a respective measure of the pressure to be measured within the respective pressure range (pl, p2, ..., pn).

2. Method according to one of claims 1 to 3, characterized in that the control unit regulates the respective temperature target value (TI, T2, ..., Tn) within a ratio interval and / or within a difference interval with respect to an ambient temperature (Tu) measured by a temperature sensor and / or a required power consumption and a back calculation to the existing pressure range.

3. Method according to claim 2, characterized in that when adjusting the temperature target value within a difference interval, the respective temperature target value (TI, T2, ..., Tn) is adjusted via a sensor located in the immediate vicinity of the measuring resistor. and is determined by a temperature sensor designed as part of the Pirani pressure sensor.

4. Method according to one of the preceding claims, characterized in that a MEMS chip with at least one first conductor track serving as a measuring resistor and a second conductor track serving as a temperature sensor is used as the Pirani pressure sensor, the ambient temperature being measured via the second conductor track.

5. Method according to one of claims 1 to 3, characterized in that a comparison between the respective temperature target value (TI, T2, ..., Tn) and the currently measured ambient temperature (Tu) is carried out in the control unit, wherein the ambient temperature and / or pressure range specifies an upper and lower limit for the respective temperature target value (TI, T2, ..., Tn).

6. Method according to one of claims 1 to 5, characterized in that in the control unit, compensation of the offset drift occurs in the event of an ambient temperature change, wherein at a constant pressure at least two different Pirani and ambient temperatures are determined by a temperature target value set.

7. Device for operating a Pirani pressure sensor, comprising an electrically heated measuring resistor (1), and a control unit (2) for applying an electrical power (P) to the measuring resistor (2) to maintain a constant operating temperature (TO), wherein the control unit (2) has a memory (3) with a stored plurality of different pressure range-dependent target temperatures (TI, T2, ..., Tn) and a power control (4) for applying power to the Pirani pressure sensor according to the respective target temperature.

8. Device according to claim 6, characterized in that the power controller (4) has a value input for a measuring unit (6) of the ambient temperature (Tu) of the Pirani pressure sensor and a comparison unit (7) for comparing the ambient temperature (Tu) with the target temperature (TI, T2, ..., Tn) to generate an adjusted target temperature and for applying power according to the adjusted target temperature.

9. Device according to one of claims 6 or 7, characterized in that the Pirani pressure sensor is designed as a MEMS chip (9) with a first conductor track as a measuring resistor and a second conductor track as a measuring unit for the ambient temperature.

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