SENSOR AND METHOD OF HEATING A SENSOR

Abstract

A sensor (10) is provided that has at least one sensor functional group (12), a heating device (14, 22), and a heating control (14, 20) to control a heating power (P.sub.heating) of the heating device (14, 22). In this respect, the heating control (20) is configured to adapt the heating power (P.sub.heating) to a power consumption (P.sub.sensor) of the sensor functional group (12).

Claims

1. A sensor that has at least one sensor functional group, a heating device, and a heating control to control a heating power of the heating device, with the heating control being configured to adapt the heating power to a power consumption of the sensor functional group.

2. The sensor in accordance with claim 1, wherein the sensor is an optoelectronic sensor.

3. The sensor in accordance with claim 1, wherein the heating control is configured to keep the sum of heating power and power consumption constant.

4. The sensor in accordance with claim 1, wherein the sensor functional group has at least one of the following components: a transmitter, a receiver, an analog circuit, a digital module, a motor.

5. The sensor in accordance with claim 1, wherein the heating device has a controllable electronic component as the heating element.

6. The sensor in accordance with claim 1, wherein the heating control is configured to heat at a high heating power in a starting phase and only then to switch the sensor functional group active.

7. The sensor in accordance with claim 1, wherein the heating control is configured to parameterize or teach the power consumption.

8. The sensor in accordance with claim 1, wherein the heating control is configured to measure the power consumption.

9. The sensor in accordance with claim 8, wherein the heating device has a current measurement unit for the current flowing in the sensor functional group in order thus to determine the power consumption.

10. The sensor in accordance with claim 1, wherein the heating control is configured to determine the power consumption only for some of the sensor functional group.

11. The sensor in accordance with claim 1, that has a temperature probe connected to the heating device.

12. The sensor in accordance with claim 1, wherein the heating device is accommodated in its own housing that is coupled to a housing of the sensor functional group.

13. The sensor in accordance with claim 1, wherein the heating device is accommodated in a housing that surrounds a housing of the sensor functional group.

14. The sensor in accordance with claim 1, that has at least one heat coupling element for conducting heat of the heating device and/or from thermally active sensor components to critical points of the sensor functional group.

15. A method of heating a sensor, the method comprising the steps of: heating at least one sensor functional group of the sensor by a heating device, controlling a heating power of the heating device by heating the at least one sensor functional group of the sensor, and adapting the heating power to a power consumption of the sensor functional group.

16. The method in accordance with claim 15, wherein the sensor is an optoelectronic sensor.

17. The method in accordance with claim 15, further comprising the step of: keeping the sum of heating power and power consumption constant.

Description

[0026] The invention will be explained in more detail in the following also with respect to further features and advantages by way of example with reference to embodiments and to the enclosed drawing. The Figures of the drawing show in:

[0027] FIG. 1 a block diagram of a heatable sensor;

[0028] FIG. 2 a time-dependent power observation with a conventional heating control;

[0029] FIG. 3 a block diagram of a heatable sensor with a heating control in accordance with the invention;

[0030] FIG. 4 a time-dependent power observation in an embodiment of the invention assuming a constant power consumption of a sensor functional group;

[0031] FIG. 5 a time-dependent power observation in a further embodiment in which the actual power consumption of the sensor functional group is measured, with the power consumption of the sensor functional group being subject to fluctuations here;

[0032] FIG. 6 a block diagram of an embodiment of a heatable sensor with a heating module coupled to the outside; and

[0033] FIG. 7 a block diagram of an embodiment of a heatable sensor with an inwardly disposed module.

[0034] FIG. 1 shows a block diagram of a heatable sensor 10. The representation is extremely simplified and combines the various elements for the sensor operation in a sensor functional group 12. The senor 10 can use any known sensor principle such as inductive, magnetic, capacitive, based on radiated or guided radar, light or ultrasound. Since optical elements are particularly sensitive to fogging at low temperatures, the sensor 10 is preferably an optoelectronic sensor, in particular a barcode scanner. The specific elements and arrangements of the sensor functional group 12 will not be looked at in any more detail here and are assumed as known.

[0035] A heating assembly 14 is furthermore provided in the sensor 10 and its design will be explained in more detail below in connection with FIG. 3. The heating assembly 14 provides that sufficiently high temperatures T.sub.int are present in the sensor 10 and thus allow the operation of the sensor 10 at low environmental temperatures T.sub.environment. A heat coupler 16 distributes the heat generated in the sensor 10 to the relative points. The sensor 10 is accommodated in a housing 18 that offers protection against the penetration of foreign bodies and that conversely provides protection for the user against dangers voltages or moving components. The housing 18 also serves at least to a certain extent for the maintenance of the temperature T.sub.int and can be additionally be configured as insulating for this purpose.

[0036] The sensor 10 is shown with only one sensor functional group 12. Further sensor functional groups can be provided that have their own heating assembly. It is, however, also conceivable that such further sensor functional groups are not cold-sensitive or are co-heated.

[0037] FIG. 2 shows a time-dependent power observation with a conventional heating control to illustrate its electrical operating behavior. In the upper part, the total power P.sub.total is shown by a solid line; the pure heating power P.sub.heating of the heating assembly 14 by a dotted line; the power consumption P.sub.sensor of the sensor functional group 12 by a chain-dotted line; and the mean power P.sub.total.sub._.sub.AVG by a dashed line. The lower part represents the temperature development of the temperature T.sub.int in the sensor 10.

[0038] In this example, a heating power of P.sub.total.sub._.sub.AVG=8 W is required for the operation of the sensor 10 at T.sub.environment=35° C. It is assumed that the sensor functional group 12 remains switched off at low temperatures so that the total heating power P.sub.total has to be applied via P.sub.heating on the switching on of the sensor. This status is maintained for so long until all the relevant internal sensor elements and components have reached the same minimum temperature. The electronics of the sensor functional group 12 can be released from then onward. The power loss P.sub.sensor of 5 W in this example hereby generated likewise makes an energetic contribution to the heating of the total device from this point in time onward.

[0039] Since the conventional heating assembly still continues to heat at an unchanged power P.sub.heating =8 W, the sensor 10 consumes a P.sub.total=13 W in this operating phase and converts it into heat. This produces unnecessarily high temperatures in the sensor interior so that, on reaching a maximum upper temperature threshold, the heating assembly 14 with the delivered thermal power P.sub.heating is completely switched off. The heating power now applied only over P.sub.sensor=5 W is no longer sufficient to cover the heating requirement of the sensor 10. This in turn has the result on or shortly before a reaching of a minimum temperature of a switching back on of the complete heating power P.sub.heating=8 W. These two states then alternate in the further course. To apply an average heating power of P.sub.total.sub._.sub.AVG=8 W, a supply for the peak of P.sub.heating+P.sub.sensor=13 W therefore has to be stored that is overdimensioned in principle. In addition, the temperature development is subject to unnecessary fluctuations.

[0040] FIG. 3 shows a block diagram of the sensor 10 with respect to which the design and function of the heating assembly 14 will be described in more detail. The heating assembly 14 comprises a heating control 20 that is connected to a heating element 22 and a switch 24 for activating and deactivating the sensor functional group 12.

[0041] The heating control 20 detects the current I.sub.sensor flowing in the sensor functional group 12, the total flowing current I.sub.total, and the supply voltage U.sub.total as the input values. A first current measurement unit 26 arid a second current measurement unit 28 as well as a voltage detection 30 are shown for this purpose. It is, however, also conceivable to detect these values in total or in part in another manner, for instance by an initial calibration or parameterization. A conceivable further input value is the temperature .sup.θ of an optional temperature probe 32. The heating control 20 derives a required heating power P.sub.heating from the input values and controls the heating element 22 accordingly. In addition, the sensor functional group 12 is activated, or not, by a switch 24 in dependence on the operating temperature. The operating temperature can be measured via the temperature probe 32, but can also be estimated independently, for example by the ending of specific heating durations.

[0042] The heating control 20 can be implemented as a purely open loop or as a closed loop. For the open-loop case, the heating control 20 preferably knows the transfer function of the heating element 22 to determine a correct variable P.sub.heating. From a technical circuit aspect, various embodiments of the heating control 20 can be considered, with this depending on demands such as speed, precision, required number of units, costs and available technologies. This ranges from purely analog circuits that determine the calculation operations for determining the required heating power P.sub.heating up to a purely digital implementation, for instance on a microprocessor or microcontroller, on an FPGA, an ASIC or mixed forms thereof with corresponding DACs and ADCs therebetween. The heating control 20 is furthermore admittedly clearly separate from the sensor functional group 12 in the Figures and description. It is, however, also possible in a manner deviating therefrom to at least partly combine the heating control 20 with electronics of the sensor functional group 12, whereby construction space and costs can be saved under certain circumstances.

[0043] The heating element 22 is preferably one or more electronic components that can be controlled directly or indirectly. They may be, non-exclusively, semiconductors such as transistors or integrated circuits, but also ohmic resistors.

[0044] The activation of the sensor functional group 12 takes place in the embodiment in accordance with FIG. 3 via switching in the supply voltage by means of the switch 24, for example a semiconductor switch or a mechanical relay. The voltage supply is alternatively constantly applied to the sensor functional group 12 and is activated in total or in part regions via a control input or via a plurality of control inputs.

[0045] The heating control 20 has the aim of keeping the total power consumption of the sensor 10 constant. In simplified terms, exactly so much heat should always be added such as does not anyway arise as waste heat at the sensor functional group 12.

[0046] A few basic considerations will now be presented for the understanding of the determination of the starting value P.sub.heating of the heating control 20 in dependence on its input values. It first applies

P.sub.total=P.sub.sensor+P.sub.heating=U.sub.sensor*I.sub.sensor+U.sub.heating*I.sub.heating.

[0047] The voltage in sensor 10 is frequently the same as the supply voltage everywhere. The currents then also add up to the total current, i.e.

P.sub.total=U.sub.total*I.sub.total=U.sub.total*(I.sub.sensor+I.sub.heating).

[0048] U.sub.total and I.sub.sensor are usually already predefined in practice. The required value of P.sub.total can then take place by a corresponding variation of I.sub.heating, with this naturally also directly changing I.sub.total. The simplified rule condition is therefore to select the heating current I.sub.heating such that it is added to the sensor current I.sub.sensor to form a desired total value I.sub.total. The rule deviation or the error of the input power then moves toward the target value of zero:

P.sub.error=P.sub.total.sub._.sub.set−P.sub.total.sub._.sub.actual.fwdarw.0.

[0049] The sensor current I.sub.sensor is measured in the embodiment in accordance with FIG. 3 by the heating control 20 via the first current measurement unit 26. A real time measurement ideally takes place to track any desired changes. Realistically, the measurement cycles must be selected in accordance with the demands, i.e. the degree to which the total power P.sub.total may fluctuate, but also the how strong the fluctuations are that are to be expected by influences such as supply voltage fluctuations, element tolerances or operating modes of the sensor 10, that is, for instance, the start-up phase, sensor activity, sensor parameterization, motor revolutions, and the like. The calculation cycles in the heating control 20 naturally also have to be designed in accordance with the demands on the control precision.

[0050] Alternatively to a current measurement, a parameterization or a teaching is conceivable, with this, however, assuming a work behavior of the sensor functional group 12 that is at least more or less predictable or requiring that the power consumption of the sensor functional group 12 rather plays a subordinate role. The resulting errors and power peaks that thereby occur can then be tolerated best.

[0051] A further alternative does not determine the sensor current I.sub.sensor for the total sensor functional group 12, but rather only some of them, preferably for the biggest consumers that can be sensible used as a heating source for heating the sensor 10 or for such elements whose activity is representative for the sensor functional group 12 and can be scaled up. It is conversely also conceivable to balance the heating control 20 itself as a consumer or heat source, i.e. to measure, to teach or to parameterize the current consumed there and to add it to the sensor current I.sub.sensor.

[0052] The simplification U.sub.sensor=U.sub.heating=U.sub.total is mostly sufficient in practice, but is not absolutely necessary. If the assumption is not correct in a specific sensor 10, these values only have to be determined, predefined or estimated, the variable I.sub.heating or P.sub.heating can then be determined in accordance with the described basic principle. The power is in this process, as generally customary, determined indirectly by ideally simultaneous voltage measurement and current measurement. Alternatives using thermal, photometric or calorific power measurements must only be mentioned for reasons of completeness.

[0053] The total heat requirement P.sub.total.sub._.sub.AVG of the sensor 10 that is constant and thus always the same as the instantaneous total power P.sub.total with an ideal control and that is intended to satisfy the heating control 20 is primarily determined by the environmental conditions, significantly the environmental temperature and air movements, as well as by sensor properties such as housing size, housing material and desired internal temperature. These all play an important role in the thermal design of the sensor 10 during the development phase. To remain flexible in this respect, the heating control 20 can provide the possibility of treating the standard parameter P.sub.total.sub._.sub.avg as a variable value. This, for example, allows a flexible adaptation to changed circumstances by parameterization or by cyclic measurement of the environmental temperature conditions.

[0054] FIGS. 4 and 5 each show a time-dependent power observation similar to FIG. 2, but now for the case of two embodiments of the heating control 20 in accordance with the invention. In this respect, FIG. 4 corresponds to the case in which the sensor power P.sub.sensor is considered as a constant. It then does not even have to be measured. It is an idealization since it only requires unnoticeable fluctuation influences by the operating state, operating mode, supply voltage and the like. Infringements of the assumption that the fluctuation influences can be neglected produce an imprecise temperature that can, however, possibly be tolerated.

[0055] As FIG. 4 shows, heating first takes place at full power P.sub.heating=8 W in this embodiment until a sufficient operating temperature is reached. On activation of the sensor functional group 12 or shortly beforehand, the desired value P.sub.heating is reduced by the known constant P.sub.sensor. In the further development, P.sub.heating=3 W and P.sub.sensor=5 W are added to form the total power P.sub.total=8 W and the goal of P.sub.total=P.sub.total.sub._.sub.AVG is already reached. The temperature still rises within its tolerance corridor and then stabilizes. There are no temperature fluctuations due to regulation cycles such as in FIG. 2.

[0056] FIG. 5 corresponds to the case in which the power consumption of the sensor functional group 12 is measured in real time in an idealized manner. Fluctuations in the power consumptions P.sub.sensor that occur in time are detected and are exactly compensated via P.sub.heating. The development in FIG. 5 is first similar to that in FIG. 4 up to the switching on of the sensor functional group 12 and for a little thereafter. From a point in time t.sub.1 selected randomly as an example, however, the power consumption P.sub.sensor of the sensor functional group 12 starts to fluctuate greatly. The heating control 20 provides an exactly compensating supplementation of the still missing heating power at any time by an adaptation of P.sub.heating to P.sub.sensor. Externally occurring power peaks are also avoided here despite greatly fluctuating P.sub.sensor, in this sense there are no corresponding peak values of P.sub.total as in FIG. 2, but rather P.sub.total=P.sub.total.sub._.sub.AVG constantly applies despite the variable P.sub.sensor. The power supplied for the device heating is correspondingly constant. In another respect, the fluctuations of the sensor power in the situation of FIG. 2 discussed here would even result in peak values P.sub.total considerably above 13 W.

[0057] The two power curves in accordance with FIGS. 4 and 5 illustrate the extreme cases of a completely constant P.sub.sensor or of a fluctuating P.sub.sensor measured in real time and error-free. Middle ways of both possibilities are naturally also conceivable, for instance with a slow cyclic measurement and corresponding constant intervals of P.sub.heating or with a modeling of a variable P.sub.sensor.

[0058] A comparison of FIGS. 4 and 5 with FIG. 2 underlines the advantages of the invention. Conventionally, a peak power of P.sub.total=13 W is required even without fluctuations of the power consumption of the sensor functional group 12. The supply, lines and securing have to be correspondingly designed for these peak powers and peak currents. In accordance with the invention, in contrast, the peak value P.sub.total=8 W is not exceeded and the supply and the elements associated therewith can be selected as correspondingly smaller. Furthermore, the temperature development T.sub.int in the device interior is practically no longer subject to any fluctuations in the steady state. The means less thermal stress at the elements and solder points in the device interior.

[0059] These advantageous effects can be further amplified if a heat coupler 16 is provided and preferably not only the heating element 22, but also the relative components of the sensor functional group 12 that generate power loss couple as well as possible thermally. The heat coupler 16 picks up the heat from the heat sources and distributes it to the critical points in the sensor 10. A large-area geometry of the heat coupler 16 can simultaneously serve for the temperature homogenization of the temperature T.sub.int in the device interior.

[0060] FIGS. 6 and 7 finally show two mechanical embodiments of the sensor 10 as alternatives to the basic structure of FIG. 1.

[0061] In the embodiment in accordance with FIG. 6, the heating assembly 14 is not accommodated in the actual housing 18 of the sensor 10, but a separate heating module having its own housing 34 is rather provided. The two housings 18, 34 contact one another over a large area at least one side and the thermal connection is even further assisted by heat couplers 16a-b at both sides.

[0062] In the embodiment in accordance with FIG. 7, the heating unit envelops the housing 18 of the sensor 10 with its own housing 36 and surrounds it completely (“housing-in-housing”). The demands on the heat coupling can in this respect possibly be a little less strict. Both heat couplers 16-b are nevertheless preferably also provided at both sides here.

[0063] The modularity in both variants in accordance with FIGS. 6 and 7 provide more flexibility as well as possibilities for expansion, retrofitting and combination. The principle with the heating control 20 explained with reference to FIG. 3 can be maintained. To still allow a current measurement and possibly also a voltage measurement of the sensor functional group 12, the electrical sensor connector can be looped over the heating module.