DE102021100815B3 - Process automation field device - Google Patents

Abstract

The present invention relates to a field device (1) for process automation, having at least one first component (3) with a minimum operating temperature for proper operation of the field device (1), at least one first thermal switch, the first thermal switch (11) being arranged and connected in this way to carry out a first switching task when the temperature falls below a first limit temperature T1, the first thermal switch (11) having a mechanically acting temperature-sensitive element formed from a first shape-memory material.

Description

The present invention relates to a field device for process automation according to the preamble of patent claim 1.

Various field devices are known from the prior art.

The term field device is understood to mean various technical devices that are directly related to a production process. "Field" refers to the area outside of control rooms. Field devices can thus be actuators, sensors and measuring transducers in particular.

Field devices with corresponding sensors can, for example, be in the form of level, pressure, flow or density measuring devices.

Such field devices are used under a wide variety of environmental conditions. The ambient conditions also include the temperature, among other things. A field device always has an operating temperature range in which it can be operated properly and without danger or problems. The operating temperature range is the temperature range bounded by a minimum operating temperature and a maximum operating temperature in which the field device functions properly. If the minimum operating temperature is not reached, the field device can be heated, for example, and if the maximum operating temperature is exceeded, it can be cooled. If, for example, the field device cannot be heated, operation at ambient temperatures below the minimum operating temperature is also not possible and the field device must be switched off to avoid malfunctions or damage. In the same way, the field device without cooling must be protected above the maximum operating temperature, i.e. if the temperature is too high. Otherwise there is a risk that the field device will be damaged during operation, since not all electronic components are designed for the high temperatures under load. It can then make sense to disconnect the sensor from the power supply, thereby switching it off and thus protecting the electronics.

So-called over-temperature fuses are known from the prior art, in which components switch off when the temperature is too high. In most cases, the fuses then have to be switched on again manually.

In addition, temperature sensors are known from the prior art, which give a switching command to electronics, which then separates the power supply.

Furthermore, there are electrical components in the prior art which are destroyed when a temperature is exceeded, for example by melting, and thereby causing an emergency shutdown.

For low temperatures, heating elements that heat the field device are known from the prior art. However, this is only possible in such a way that the heating elements are either permanently activated, since this is the only way to ensure that the heating element is also activated at temperatures below the minimum operating temperature, for example of the electronics. Heating elements that are switched on and off under temperature control are controlled via a temperature sensor that is read by the electronics of the field device and can therefore only be operated within the operating temperature range of the electronics. At lower temperatures, for example, the effect can occur that in certain applications the field device, for example a sensor, does not start up when it is switched on, since a microcontroller used starts up in an undefined manner when the ambient temperature is too low and is therefore only operated unstably.

This is perceived as a disadvantage in the prior art.

Heating elements that are permanently in operation are also not optimal, since their heating effect increases the energy consumption of the field device on the one hand, and on the other hand reduces the operating temperature range upwards, i.e. the actual outside temperatures at which the field device can be operated are reduced , because the additional heating power of the heating elements acts on the components of the field device.

The present application also relates to self-sufficient field devices, in particular self-sufficient filling level or point level sensors. Self-sufficient field devices have an integrated power supply and can therefore be operated without an external power supply. For example, such self-sufficient field devices are completely supplied with energy by an integrated energy store, for example a battery. In addition, energy harvesting components can be installed, by means of which the smallest amounts of energy from the environment of the field device can be converted into electrical energy and stored. These can be, for example, photovoltaic cells for converting light, thermoelectric cells for converting temperature differences or antennas for converting electromagnetic radiation into electrical energy.

The self-sufficient filling level or point level sensors are preferably designed as radar sensors and, in order to ensure the self-sufficiency of the sensors, have, in addition to a sensor for acquiring measurement data, a transmission device for preferably wireless transmission of acquired measurement data or measurement values, and their own power supply. The transmission device can preferably be a radio module for narrowband radio technology (LoRa, Sigfox, LTE-M, NB-IOT), which transmits the measurement data or measurement values to a cloud, ie to a server on the World Wide Web. The energy supply is preferably designed as a battery or accumulator and can also include an energy harvesting module.

Typical application scenarios for such field devices include, in particular, inventory management or measurement tasks on mobile containers.

Known field devices of the aforementioned type previously made it possible to transmit measured values, so that a higher-level unit triggered a predetermined action based on the determined measured value. For example, based on the measured value of a fill level measuring device, an inlet can be closed or an outlet can be opened if a limit value is exceeded.

In the case of self-sufficient field devices, it is particularly important that as little energy as possible is consumed in order to enable the field devices to be operated for as long as possible. Therefore, here too, permanently activated heating elements are regarded as disadvantageous.

From the DE 10 2005 062 421 A1 a heating device for a field device display module is known, with an electronically acting thermostat. The temperature can be measured with a measuring device arranged on the display and the measured value can be forwarded to a heating element control device.

the DE 10 2013 114 736 A1 shows a field device with a heating element, a controller and a separate temperature measuring unit.

It is the object of the present invention to further develop a field device in such a way that it can be used in a larger temperature range, advantageously in a particularly energy-saving manner.

This problem is solved by a field device with the features of patent claim 1 .

Advantageous configurations and variants of the invention result from the dependent claims and the following description. The features listed individually in the subclaims can be combined with one another in any technically meaningful way, as well as with the features explained in more detail in the following description, and represent other advantageous embodiment variants of the invention.

A field device according to the invention for process automation with at least one component with a minimum operating temperature for proper operation of the field device, at least one first thermal switch, the first thermal switch being arranged and connected in such a way that a first switching task is carried out when the temperature falls below a first limit temperature T ₁ , is characterized in that from that the first thermal switch has a mechanically acting temperature-sensitive element.

A mechanically acting, temperature-sensitive element ensures that switching occurs independently of whether the electronics are in operation or whether the electronics are ready for operation, i. H. the switching task is also carried out if the electronics are not functional due to the ambient temperature.

The mechanically acting temperature-sensitive element is formed from a first shape-memory material.

A temperature-sensitive shape-memory material has two different structures depending on the temperature, with the conversion between the two structures being accompanied by a change in shape of the shape-memory material. As a result of the change in shape, temperature-dependent switching of the thermal switch can be implemented on a purely mechanical level.

The temperature-dependent phase transformation is usually a transformation between the crystal structures of martensite and austenite. The austenite crystal structure exists at higher temperatures and the martensite crystal structure at lower temperatures. The crystal structures or phases can change into one another as a result of temperature changes (two-way effect). The shape-memory material is able to deform back into a shape that was previously impressed—for example, by severe deformation. The phase transformation is reversible.

An alloy of the shape memory material is austenitic at high temperatures and martensitic at lower temperatures. Becomes a component of a martensitic shape memory alloy below deformed at a critical temperature, only a reversible change in shape takes place. Once the component is heated above the transformation temperature, austenite forms with the original orientation, so that the component returns to its original shape. The structural transformations during heating and cooling take place at different temperatures, which means that a hysteresis loop is run through.

By using a shape memory alloy as a temperature-sensitive element in the thermal switch, an embodiment can be achieved in which temperature-dependent switching takes place exclusively on the basis of the deformation.

In one embodiment, shape memory alloys that have a so-called one-way effect can be used as the shape memory material. If an element made of a shape memory alloy in the martensitic state is deformed in the martensitic range, only the highly mobile twin boundaries are shifted. When heated to the limit temperature for austenite, the transformation into the austenitic range takes place. This restores the element to its original shape. Since subsequent cooling of the material does not cause any further change in shape, this effect is referred to as a one-way effect. However, the element can be deformed again in the martensitic state by means of a suitable counterforce, which can be applied, for example, by a spring, for example a compression spring.

In this embodiment, the shape memory material and the counterforce can preferably be matched to one another in such a way that the material is deformed by the counterforce when it cools below the first limit temperature in such a way that a desired switching effect is achieved, in particular an electrical contact is closed, with heating of the Material achieved by the shape memory effect of the opposite switching effect, in particular the electrical contact is opened again.

In one configuration, the field device can have a second thermal switch, the second thermal switch having a mechanically acting, temperature-sensitive element, preferably made of a second shape-memory alloy, and being designed and connected in such a way as to carry out a second switching task when a second limit temperature T ₂ is exceeded.

The temperature-sensitive element of the second thermal switch can be designed in such a way that the shape memory alloy activates ventilation or de-energizes the field device and thereby protects it when the temperature rises above the second limit temperature. In this embodiment, too, resetting can be effected by means of a counterforce, with the shape-memory material and the counterforce also being matched to one another here such that the desired switching effect is achieved when the second limit temperature is exceeded.

The first limit temperature is preferably lower than the second limit temperature. In this way it can be achieved that an operating temperature window can be enlarged both downwards and upwards.

The field device can also have a third thermal switch, with the third thermal switch having a mechanically acting, temperature-sensitive element, preferably made of a third shape-memory material, and being designed and connected in such a way as to perform a third switching task when a third limit temperature T ₃ is exceeded, the third limit temperature preferably being higher is than the first limit temperature and can be lower than the second limit temperature.

A third thermal switch can be used to activate another switching task at another specified temperature.

Due to the hysteresis that occurs during the structural transformation of the shape-memory materials, further switching tasks can also take place when the respective second transformation temperature is reached.

In one configuration, the first thermal switch can also be activated manually at a temperature that is greater than the first limit temperature. This can ensure, for example, that a field device that is prepared and preconfigured at warmer temperatures, for example, is brought into the cold environment with the heating already activated.

In a preferred embodiment, the first thermal switch activates a heater for the field device when the temperature falls below the first limit temperature T ₁ . In this way it can be achieved that a heater for the field device is activated, for example when the temperature falls below a minimum operating temperature for electronics of the field device. In this way it can be achieved that the heating can be started independently of the electronics and the field device can be brought up to operating temperature.

In a further development it can be provided that the third thermal switch is designed and connected in such a way that the component, in particular the electronics and here in particular a microphone rocontroller of the field device, activated only above the minimum operating temperature, in particular supplied with energy.

In a further development it can be provided that at least one of the thermal switches, in particular the second thermal switch, is designed as an overtemperature protection. In this way it can be achieved that the field device is protected against damage caused by operation at excessively high temperatures.

Advantageously, at least two thermal switches are provided and designed and matched to one another in such a way that the electronics of the field device only attempt to start when a heater has reached a specific minimum temperature at which the electronics run reliably and stably. In addition, the thermal switch of the heating is designed in such a way that the heating is switched off as soon as stable sensor operation can be guaranteed and, for example, self-heating of the sensor is sufficient to keep the temperature above the minimum operating temperature. This also ensures that the upper end of the operating temperature range of the field device is not affected.

In one embodiment with further switching options, the first shape memory material and/or the second shape memory material and/or the third shape memory material can have a two-way effect.

Two-way effect devices remember both a high temperature form and a low temperature form. To set the two-way effect, a special pre-treatment is necessary, in which a dislocation movement occurs. During subsequent heating, only partial recovery then takes place. The effect of the dislocations is that preferred martensite variants are formed, which produce a specific low-temperature shape. With the two-way effect, however, smaller effect sizes can be set than with the one-way effect, but there is no restoring force.

Particularly good results are achieved when the shape memory material is in the form of a wire or a helical spring. Tensile forces can be applied very well by means of wires. Coil springs are good at generating compressive forces.

The materials mainly used as shape memory alloys are metallic alloys such as NiTi (nickel-titanium), NiTiCu (nickel-titanium-copper), CuZn (copper-zinc), CuZnAI (copper-zinc-aluminium), CuAINi (copper-aluminium-nickel) , FeMnSi (iron-manganese-silicon) or ZnAuCu (iron-gold-copper). Single-crystal alloys of nickel, manganese and gallium can also be used.

The decisive factor for the transformation temperature in the above nickel-containing alloys is usually the nickel content. With a nickel content of less than 50 atomic percent nickel, the transformation temperature is around 100 °C.

Furthermore, shape-memory plastics, such as shape-memory polymers, can also be used, which then do not themselves serve as conductors, but produce a conductive connection, for example through a coating, or the mechanical movement of an electrical conductor.

The thermal switches can be designed in such a way that the switch is opened and/or closed depending on the temperature. In this regard, either opening or closing or opening and closing can be accomplished by the shape memory material. If only one of the aforementioned processes is actively brought about by the structural transformation of the shape-memory material, then the counter-movement is brought about by a counter-force, for example by a compression or tension spring.

• 1 ein erstes Ausführungsbeispiel eines Feldgerätes mit drei Thermoschaltern zur Aktivierung von Zusatzfunktionen,
• 2 eine zweites, vereinfachtes Ausführungsbeispiel eines Feldgerät mit einem Thermoschalter als Übertemperatursicherung und
• 3 a) und 3 b) die Funktionsweise eines Thermoschalters wie er in den Feldgeräten der 1 und 2 zum Einsatz kommen kann.

The present invention is explained in detail below using exemplary embodiments with reference to the accompanying figures. Show it:

• 1 a first embodiment of a field device with three thermal switches for activating additional functions,
• 2 a second, simplified embodiment of a field device with a thermal switch as overtemperature protection and
• 3 a) and 3 b) the functionality of a thermal switch as it is in the field devices of the 1 and 2 can be used.

1 shows a first embodiment of a field device 1 with three thermal switches 11, 12, 13 for activating additional functions.

In the present exemplary embodiment, field device 1 is embodied as a radar level measuring device, radar level measuring device 1 having a radar sensor 31 for detecting a level, which emits electromagnetic waves via a horn antenna 33 for level measurement in the direction of a filling. Radar sensor 31 is coupled to a first component 3, which is embodied in the present case as electronics. The electronics 3 have a microprocessor for controlling the radar sensor and for processing the received radar signals. Furthermore, in the electronics, for example, a memory unit, various communication interfaces and other components for signal and/or data processing and/or measured value processing may be present.

In the present exemplary embodiment, a lower operating temperature range of the electronics 3 is limited by the operating temperature range of the built-in microprocessor. Below a minimum operating temperature, the microprocessor starts in an undefined state and is therefore not stable, so that reliable operation of the electronics 3 and thus of the entire field device 1 is not possible. In order to enable the field device 1 to be operated at outside temperatures below the minimum operating temperature of the microprocessor and thus of the electronics 3, it is necessary to ensure a sufficiently high operating temperature. For this purpose, the field device 1 has a heater 5 that is suitably designed and arranged to ensure a sufficient operating temperature for the electronics 3 and/or the sensor 31 and/or other components of the field device 1 . Since it is not possible to switch heating 5 on the basis of the measurement signal from a temperature sensor, since its signals would have to be evaluated by electronics 3 to generate a switching command, heating 5 is connected to a power supply 9 of field device 1 via a first thermal switch 11.

The first thermal switch 11 has a shape-memory material as a temperature-sensitive element and is designed in such a way that it activates the heater 5 when the temperature falls below a first limit T ₁ . The first limit temperature T ₁ is selected so that it is sufficiently above the minimum operating temperature of the electronics 3 and thus switching on the heater 5 in good time always ensures that activation of the field device 1 a sufficient operating temperature reliable operation of all components of the field device 1 is reached.

The first limit temperature T ₁ corresponds to the lower energy for the transition temperature, i.e. the temperature at which the shape memory material changes to the low-temperature phase and assumes the external shape associated with the low-temperature phase, or can be deformed by a force, for example by a compression spring, in the low-temperature phase. In the low-temperature phase, however, an electrical contact is closed in the first thermal switch 11, so that the heater 5 is supplied with energy and the field device 1 is heated up.

Since shape memory materials, in particular shape memory alloys, exhibit hysteresis during structural transformation, i. H. that the structural transition temperature in the low-temperature phase is lower than the structural transition temperature in the high-temperature phase of the shape-memory material, the material can be selected so that the heater 5 is exceeded when the minimum operating temperature of the electronics 3 is exceeded, for example when the field device 1 is running and by radiated operating heat from the individual components of the field device has a sufficient operating temperature, is deactivated again when the shape-memory material changes to the high-temperature phase.

In order to ensure reliable operation of the field device 1, the electronics 3 are coupled to the energy supply 9 via a second thermal switch 12, with the second thermal switch 12 likewise having a shape-memory material as a temperature-sensitive element. The second thermal switch 12 is designed such that the electronics 3 of the field device 1 is only conductively connected to the power supply 9 when the minimum operating temperature of the electronics has been reached, thus ensuring that it can be operated reliably. This can be achieved, for example, by the second thermal switch connecting the electronics 3 to the power supply 9 only when a second limit temperature T ₂ is exceeded, with the second limit temperature T ₂ corresponding to the minimum operating temperature of the electronics 3 or with a suitable safety margin slightly greater than this is chosen. The shape-memory material of the second thermal switch 12 can be configured, for example, in such a way that the electronics 3 are supplied with energy by the hysteresis during the structural transformation of the shape-memory material when the minimum operating temperature is exceeded and only when the minimum operating temperature is undershot up to the lower structural transformation temperature of the shape-memory material again is disconnected from the power supply.

The field device 1 also has a third thermal switch 13, which in the present exemplary embodiment is coupled to a third component 7, which in the present case is designed as a ventilation system. In the present exemplary embodiment, the third thermal switch 13 also has a shape memory material as a temperature-sensitive element and is designed and dimensioned in such a way that the ventilation 7 is switched on when a third limit temperature T ₃ is exceeded, which is selected at a suitable safety margin below a maximum operating temperature of the electronics 3 is to cool the electronics 3.

Because the heating 5 is already activated below a minimum operating temperature of the electronics 3, the heating 5 is switched off again in the operating temperature window of the electronics 3 and the ventilation 7 is activated when a maximum operating temperature of the electronics 3 is approached, the temperature window in which the field device 1 can be operated is increased both towards lower temperatures and towards higher temperatures. The individual limit temperatures T ₁ , T ₂ , T ₃ can be adapted to the needs of the respective field device 1 by a suitable selection of the respective shape memory material.

In this way it is possible to activate and/or deactivate various additional functions of the field device 1 reliably and temperature-controlled, even outside the operating temperature range of the electronics 3 .

2 shows a second, simplified exemplary embodiment of a field device 1.

The field device 1 according to 2 has only the third thermal switch 13, this being designed as an overtemperature fuse in the present exemplary embodiment. In order to ensure this, the electronics 13 of the field device 1 are connected to the power supply 9 via the third thermal switch 13 . The third thermal switch 13 is designed such that when the third limit temperature is exceeded, which in this case corresponds to a maximum operating temperature of the field device 1, it disconnects the electrical connection between the energy supply 9 and the electronics 3, so that the field device 1 is switched off. This can be necessary, for example, if individual components of the field device 1 would be damaged or destroyed in further operation above the maximum operating temperature.

If the field device 1 cools down to below the lower microstructural transformation temperature of the shape memory material of the third thermal switch 13, an electrical connection is established again between the power supply 9 and the electronics 3 and the field device 1 is thus restarted.

In the 3a and 3b is an embodiment of a thermal switch, as in the field devices 1 of 1 and 2 can be used, shown.

The thermal switch according to 3 is configured as the first thermal switch 11 in the embodiment according to 1 . This means that the first shape memory material 21 used is a material with a two-way effect, which assumes a different geometric shape at different temperatures θ. If the temperature θ falls below the first limit temperature T ₁ , the shape-memory material 21 assumes a predefined shape for the low-temperature range, and an electrical connection to a contact 23 is thereby established. This situation is in 3a) shown.

In 3b) the thermal switch is off 3a) shown, wherein the first shape memory material 21 is in the high-temperature phase, ie the temperature θ is above the upper microstructural transformation temperature of the first shape memory material. At this temperature θ, the shape memory material is in the form associated with the high-temperature phase and an electrical connection to the contact 23 is opened accordingly, so that the electronics 3 of the field device 1 are disconnected from the energy supply 9 .

At the in 3 In the thermal switch shown, the first shape-memory material 21 and the contact 23 are each arranged on a printed circuit board 25 .

Reference List

1

field device

3

Electronics / first component

5

heater / second component

7

ventilation / third component

9

power supply

11

first thermal switch

12

second thermal switch

13

third thermal switch

21

first shape memory material

23

Contact

25

circuit board

31

radar sensor

33

horn antenna

T1

first limit temperature

T2

second limit temperature

T3

third limit temperature

ϑ

temperature

Claims (13)

Field device (1) of the process automation with at least one first component (3) with a for proper operation of the field device (1) minimum operating temperature, at least a first thermal switch, the first thermal switch (11) being arranged and connected in such a way that it performs a first switching task when the temperature falls below a first limit T ₁ , characterized in that the first thermal switch (11) is a mechanically acting switch formed from a first shape-memory material (21). has temperature-sensitive element. Field device (1) according to claim 1 , characterized in that the field device (1) has a second thermal switch (12), the second thermal switch (12) having a mechanically acting temperature-sensitive element and being designed and connected in such a way that a second switching task is carried out when a second limit temperature T ₂ is exceeded. Field device (1) according to claim 1 , characterized in that the field device (1) has a second thermal switch (12), the second thermal switch (12) having a mechanically acting, temperature-sensitive element made of a second shape-memory alloy and being designed and connected in such a way that a second switching task occurs when a second limit temperature is exceeded T ₂ to execute. Field device (1) according to claim 2 or 3 , characterized in that the first limit temperature T ₁ is lower than the second limit temperature T ₂ . Field device (1) according to one of claims 2 until 4 , characterized in that the field device (1) has a third thermal switch (13), the third thermal switch (13) having a mechanically acting temperature-sensitive element and being designed and connected in such a way that a third switching task is carried out when a third limit temperature T ₃ is exceeded . Field device (1) according to one of claims 2 until 4 , characterized in that the field device (1) has a third thermal switch (13), the third thermal switch (13) having a mechanically acting temperature-sensitive element made of a third shape-memory alloy, and being designed and connected in such a way that a third switching task is exceeded when a third Run limit temperature T ₃ , wherein the third limit temperature T ₃ is higher than the second limit temperature T ₂ . Field device (1) according to one of claims 2 until 6 , characterized in that the first thermal switch (11) at a temperature T _A <T ₂ is manually activated. Field device (1) according to one of claims 2 until 7 , characterized in that the second thermal switch (12) is designed and connected in such a way that the first component (3) is only activated above the minimum operating temperature. Field device (1) according to one of claims 2 until 7 that the second thermal switch (12) is designed and connected in such a way that the first component (3) is only supplied with energy above the minimum operating temperature. Field device (1) according to one of the preceding claims, characterized in that at least one of the thermal switches (11, 12, 13) is designed as an excess temperature fuse. Field device (1) according to claim 5 or 6 or according to one of the Claims 7 - 10 , as far as this Claims 7 - 10 on claim 5 or 6 are referred back, characterized in that the third thermal switch (13) is designed as an excess temperature fuse. Field device (1) according to one of the preceding claims, characterized in that the first shape-memory material (21) and/or the second shape-memory material and/or the third shape-memory material has a two-way effect. Field device (1) according to one of the preceding claims, characterized in that the first thermal switch (11) activates a heater (5) of the field device (1) when the temperature falls below the first limit value T ₁ .

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