DE102007056917A1 - Method for tolerance compensation of electrical consumers - Google Patents

Abstract

The invention relates to a method for compensating for manufacturing tolerances of electrical consumers (2), which are supplied with electrical energy from a power supply (20) of a domestic appliance, comprising at least the following steps: a) measuring an actual value (10, RIst) of the resistance value of electrical consumer (2), b) determining a correction factor from the actual value (10, RIst) of the resistance value of the electrical load (2) and a resistance setpoint (30, Rnom) and c) taking into account the correction factor during operation of the domestic appliance.

Description

The The invention relates to a method for manufacturing tolerance compensation of electrical loads from a power supply of a household appliance be supplied with electrical energy.

modern Home appliances often have heaters as electrical Consumers on. These are currently used as heaters prefers thick film heaters instead of the previously used ones Bar heaters used. For the production of thick film heaters Trajectories of a suitable electrical resistivity having, thick layer on the surface of an electric printed on insulating substrate. While printing the length and width of the tracks set relatively accurately can be relatively large in thickness Variations that increase the total electrical resistance by about ± 15% to waver. Industry standards for manufactured thick film heaters confess resistance tolerances of the order of magnitude from about -5% to + 10% too.

At the Use of thick-film heaters in water-bearing devices, such as home appliances, form through contact with tap water on the sheets of thick film heaters limescale and other coverings. The thickness and the degree of area coverage of the coverings is called "area occupancy" designated.

With increasing area occupancy of the railways is worsening the heat transfer of the thick film heater the surrounding space. This increases locally under the Area occupation the temperature of the thick layer forming Resistance material. Because the usual resistance materials for thick film heaters due to their PTC property (Positive Temperature Coefficient) their specific electrical Increase resistance with increasing temperature increases also their specific electrical resistance in the places under the area occupation. Accelerates there the local Heating continues, the area occupancy also accelerates to. This uncontrollably accelerating heating may be abated a certain degree of surface occupancy within fractions of a second expire, leading to local destruction lead the thick film heater.

Around This can be prevented by increasing the total resistance of thick-film heating be detected during operation with relatively high accuracy. In time before reaching a limit value of the total resistance of the Assigned to boundary occupancy and at which the destruction process begins, the heating current is switched off and thus the heating operation is interrupted.

The relatively large tolerances of the heating resistance value of a thick-film heating therefore require a high measuring accuracy for detecting the limit value during operation of a thick film heater. After WO 96/17496 the resistance value in the production of thick-film heating is set to a desired value by printing compensating webs additionally and parallel to the actual thick-film webs provided for heating. Subsequently, they are connected in sections, electrically conductive with and parallel to the actual heating paths until the actual value of the total resistance of the thick-film heating has reached the desired value.

alternative may be a thick-film heater with its tolerance-related actual resistance value installed in the device to be heated and to the power supply be connected. Here, the tuned to the target value Control electronics circuit in a separate assembly step to the actual resistance value the thick film heater adjusted, which is a high technical and time required.

The Object of the present invention is a simpler and less Time-requiring method for manufacturing tolerance compensation of electrical To provide consumers.

• a) Messen eines Ist-Werts des Widerstandswerts des elektrischen Verbrauchers,
• b) Ermitteln eines Korrekturfaktors aus dem Ist-Wert des Widerstandswerts des elektrischen Verbrauchers und einem Widerstands-Sollwert, und
• c) Berücksichtigen des Korrekturfaktors bei Betrieb des Hausgeräts.

The object is achieved by a method for manufacturing tolerance compensation of electrical consumers which are supplied with electrical energy by a power supply of a household appliance, comprising at least the following steps:

• a) measuring an actual value of the resistance value of the electrical load,
• b) determining a correction factor from the actual value of the resistance value of the electrical load and a resistance setpoint, and
• c) Consideration of the correction factor when operating the household appliance.

there has the example. As a thick-film heater formed heating a dependent on a surface occupation resistance value on, and a control electronics circuit of the power supply is on adjusted the resistance setpoint and detects the achievement of a obtained at an interface occupancy of thick-film heating Range limit of the resistance value.

By taking into account the actual value of the resistance value in the control of the power supply, therefore, the resulting from the production of thick-film heating tolerances can be compensated and the limit or the shutdown of the Power supply can be adjusted as a resistance deviation with respect to the actual value of the resistor. The inventive method thus reduces the complexity of technical devices and required settings.

The Measurement accuracy when measuring the actual resistance value is as possible high, for example of the order of about 2%, more preferably about 1% and even more preferably about 0.5%. This reduces the possible tolerance regarding the actual value. In addition, the control electronics circuit determine the achievement of the resistance limit more accurately.

The Measure the actual value of the thick film heater resistance in step (a) may be advantageous before installing the thick film heater in the Household appliance already performed by the manufacturer become. Alternatively, the resistance measurement immediately before Installation of the thick film heater in a household appliance in a separate process step, approximately at the same time as assembly steps be executed before the installation of thick-film heating anyway done. So, when assembling the new home appliance Assembly time can be saved. In a repair of the household appliance can the measurement by the service technician in a special measuring device carried out on the exchange thick-film heating prior to their installation become.

It can be for each measured actual value of resistance Correction factor currently be determined. This results in a High accuracy of tuning the power supply to the thick film heater. But since the resistance values of the thick film heaters anyway a limited tolerance range can be used for Deviations within this framework alternatively already correction factors be stored in the controller. This reduces the calculation effort when tuning the power supply to the thick film heater.

The Procedure can be simplified if not for everyone measured deviation value between the actual and the desired value own correction factor must be determined. After another advantageous embodiment may be measured actual values associated with the resistance values of electrical load value intervals are each assigned a correction factor.

Preferably In this case, a mean value interval includes the resistance target value for thick film heating. Each interval becomes a suitable one Correction factor permanently assigned and stored in the controller. A measured actual value is then assigned to that value interval, which contains the measured actual value. This can be the control effort be significantly reduced because of a determination of the correction factor can be omitted.

Of the Set of contiguous value intervals may be an odd number of intervals whose average contains the setpoint. With an even number of intervals they can alternatively be symmetrical be arranged around a target value of the heating resistor around

The Value intervals can have a constant range width, which corresponds to the measurement accuracy required in step (a). The intervals and the associated correction values can Be numbered as well for easier discrimination. Thus, the correction factor of an actual value of resistance can be simpler Way specified by specifying the appropriate area number of the interval to which he is assigned. This simplifies the processing the measured actual value as well as the execution of the input required technical means.

In an alternative embodiment it is provided that the correction factor is transmitted to the household appliance so that the home appliance does not store memory for storage the correction factor associated with the value intervals, but according to the correction factor an adjustment of the supply the electrical consumer makes. It is preferably provided that the electrical consumer is an ohmic consumer, so that no reactive current losses are taken into account during the measurement be, which is preferably in the electrical consumer is a heater, in particular a thick-film heating.

The Principle of the invention will be described below with reference to a drawing by way of example explained in more detail. In the drawings show:

1 a diagram of the dependence of the electrical resistance R _{h of} a thick-film heating of their area occupation F;

2a , b circuit diagrams of a power supply unit with a connected thick film heater; and

3 a graphical representation of value intervals.

It will open 1 Referenced.

The 1 illustrates the dependence of the resistance value R _{h of} a thick film heater on the ordinate of their area _occupation F on the abscissa, a limit R _grenz for a resistance _deviation or an associated Boundary area _occupation F _limit of thick film _heating to protect against burn-through.

A power supply for a thick film heater is usually designed for a nominal or nominal value R _nom 30 of the total resistance. It is shown on the ordinate for an unused thick film heater without area occupation (F = 0). When in operation of the thick-film heating increasing area occupancy F, the resistance R _{h increases} approximately proportionally to the area occupancy. This relationship is the rising line 31 From the production thick film heaters come with a relatively large tolerance .DELTA.R with respect to the total resistance, wherein the ratio .DELTA.R / R _{nom is} in the order of 5% to 10%. Consequently, in the operation of such thick-film heaters, resistance values in the range of R _nom -ΔR to R _nom + ΔR are initially to be expected. With increasing surface occupancy, resistance values appear around the line 31 lie in a band with a width or height of 2ΔR. This band limit the lines 34 respectively. 36 ,

In order to prevent the process of uncontrolled local heating and destruction of the thick-film heating, which takes place in fractions of a second, an upper limit value R _grenz matched to the nominal value R _{nom of} the resistance of the thick-film _heating is stored in a control electronics _circuit as a threshold value. The threshold value is selected so that the thick film heater is reliably protected against destruction if the heating current is switched off when this limit value is reached. The associated switch-off point is in 1 marked with A _nom . About the dependence of the resistance R _h of the area _occupation F is the limit value R _limit, the boundary area _occupancy F _grenz or 38 assigned. If the limit _{Rlimit were used unchanged} in the control electronics _circuit as a threshold, then due to the manufacturing tolerance of -ΔR to + ΔR, shutdown points would occur in a wide range of surface occupancies, designated A and A +. A shutdown of the operation at the cut-off point A + would occur at a surface _{occupancy that} is smaller than the boundary area _occupancy F _grenz , and the service _life of thick-film _heating would be unnecessarily shortened. Conversely, if the shutdown occurs at the shutdown point A and thus at a surface _{occupancy that} is greater than the boundary area _occupancy F _grenz , then there is a high risk that the thick film _heater is destroyed by local overheating.

According to the invention is now as an example of an electrical load, the resistance R _is a thick-film heating before installation in a household appliance such. Example, a dishwashing or washing machine with a high accuracy δR measured, which is smaller than the tolerance .DELTA.R of the resistance from the manufacturing process. The measurement accuracy δR / R is on the order of less than 2%, z. B. 0.5%. The measured actual value R _is input to an evaluation circuit. Subsequently, the associated resistance _limit R _{grenz is} determined. The resistance limit value R limit (R _ist ), which is matched to the actual value, is calculated in such a way that its reaching, and therefore the switch-off, takes place at the same limit area _occupation F _{limit as} is provided for the nominal value R _nom . How out 1 As can be seen, the adjusted resistance _limit R _grenz (R _ist ) _{is calculated} on the basis of the resistance _limit R _grenz by an additive correction corresponding to the deviation (R _is -R _nom ) of the measured actual value R _ist from the target value R _nom for the heater resistance : R cross (R is ) = R cross (R nom ) + (R is - R nom ) (1)

The limit value R _limit (R _ist ) for the heater _resistance corrected taking into account the manufacturing _tolerance is reached at the same limit area _occupation F _limit (switch-off point A _is ( 40 )). Thus, for thick-film heating, a comparable protective effect against destruction is achieved, as provided for the nominal heating resistor R _nom . As in 1 shown, would for a thick film heater with the actual resistance R _is without correction of the shut-limit value of the extinction threshold R _is already in the _cross cut-off point A ', 40 ' achieved, ie at a smaller area _occupancy than the intended border area _occupation F _grenz .

It will be up now 2a and 2 B Referenced.

2a shows as a power supply 20 for a thick film heater 2 a voltage source 22 with a known with high accuracy output voltage for the supply of thick-film heating 2 with heating current, a measuring resistor 28 with a resistance R _m and a measuring circuit 24 for measuring the voltage across the measuring resistor 28 , The power supply 20 also has the connections 26 . 26 ' on, over which the heating current tapped and over supply lines of the thick film heater 2 is supplied. The thick film heater 2 includes a heating resistor track 4 Made of printable material, and at its outer ends connections 6 . 6 ' for passing the heating current. In the 2 B The circuit shown is schematically by the in 2a shown equivalent circuit diagram of the measuring circuit simplified. In the equivalent circuit diagram of 2 B is the thick film heater 2 as resistance 10 having a resistance value R _is represented (F).

In heating mode of thick film heating 2 the current gets through the measuring resistor 28 , whose Value is known with high accuracy, and the heating resistor 10 or thick-film heating 2 directed. The measuring circuit measures 24 the voltage drop across the measuring resistor 28 with a high accuracy, which is typically better than 0.5%, for example 0.1%. If, due to an increasing area occupation F, the value R _is (F) of the heating resistor 10 increases, the flowing heating current decreases. The change in the heating current causes a reduction in the voltage drop across the measuring resistor 28 , It is from the measuring circuit 24 detected and in a value R _h (F) for the heating resistor 10 or its change due to the area occupation F converted.

The measuring circuit 24 enters for the heating resistor 10 representative signal off. It can also generate a warning signal when the heater resistance 10 the limit value, in particular the limit R _grenz (R _ist ) associated with the limit area _occupation F _{grenz has been} reached. The warning signal can then be detected in a control logic circuit, whereupon the heating current is switched off.

It will be up now 3 Referenced.

In 3 are a resistance area on a number line 42 possible resistance values R _h applied. It ranges from a lower limit R _min 34 up to an upper limit R _max at 36 , It is around the nominal value R _nom 30 centered around and is placed in a set of contiguous and consecutive value intervals 44-1 to 44-5 divided by interval boundaries 48-1 to 48-6 are separated. The set of value intervals 44 is a set of consecutive integers or interval numbers 46 assigned. To indicate the actual value R _is the heater resistance 10 the value interval is specified in which the actual value lies. Thus, specifying the actual value R _is sufficient to specify the interval number 46 the value interval 44-4 (in the example the number 4), since it contains the actual value R _ist .

Each value interval is assigned a correction value that indicates the supply of heating current to that actually in the thick-film heating 2 present value R _is adjusted. Although this is done with an inaccuracy, because the heating current is not adjusted to the actual value but to an interval around the actual value R _is around. As a result, but the regulatory burden for the vote of thick-film heating 2 and the power supply 20 considerably simplified.

In an example typical of dishwashers, the nominal value is R _{nom of} the heater resistance 10 about 25 ohms and the required measurement accuracy δR _nom / R _nom ± 1%, corresponding to an interval of 24.75 ohms to 25.25 ohms. A standard production for thick film heaters has a tolerance of ΔR _nom / R _nom = 5% to the target value, so that resistance values R _min and R _max between a lower range limit 34 (R _min = R _nom ΔR = 23.75 ohms) and an upper range limit 36 (R _max = R _nom + ΔR = 26.25 ohms) may occur (see. 1 ). In order to use all thick film heaters from this production, the resistance range R _min to R _max in value intervals 44 divided. Their interval width is based on the measuring accuracy of ± 1%, so that between the lower range limit 34 and the upper range limit 36 a set of five intervals exists (cf. 3 ):

• Interval 1, 44-1 : 23.75 ohms-24.25 ohms
• Interval 2, 44-2 : 24.25 ohms-24.75 ohms
• Interval 3, 44-3 : 24.75 ohms-25.25 ohms
• Interval 4, 44-4 : 25.25 ohms-25.75 ohms
• Interval 5, 44-5 : 25.75 ohms-26.25 ohms.

The intervals with the interval numbers 46 from 1 to 5 are due to interval limits 48-1 to 48-6 separated. The outer interval limits 48-1 respectively. 48-6 set the lower range limit 34 or the upper range limit 36 dar. The other limits 48-2 to 48-5 result from the measuring accuracy of ± 1% relative to the nominal value R _{nom of} the heating resistor 10 (25 ohms). They thus satisfy equation (1) for their respective averages.

The interval limits 48-1 to 48-6 are stored in the factory in a controller. For thick layer heating, a measured value of, for example, R _ist = 25.634 ohms is now determined. It is assigned to the interval with the number "4". The thick film heater is thus without further to R _is based calculation from an occurring during operation resistance of 25.75 Ohm switched off because there is the danger of its overheating ensure that the control process is simplified. the thick-film heating considerably.

2

Thick film heating

4

Heizwiderstandsbahn

6 6 '

connection (the thick film heater)

10

Actual value _(R) of the heating resistor

12

lower measured value limit (R _is - δR) of the actual value

14

upper measured value limit (R _is + δR) of the actual value

20

power supply

22

power source

24

measuring circuit

26 26 '

connection (the power supply)

28

Current measuring resistor or shunt resistor (R _m )

30

Nominal value (R _nom ) of the heating resistor

32

tolerance range (2 × ΔR)

34

lower range limit (R _min = R _nom - ΔR)

36

upper range limit (R _min = R _nom + ΔR)

38

Border area _occupation F _grenz

40

Shutdown point with measured value input A _is

40 '

Switch-off point without measured value input A ' _is

42

Total resistance range (corresponds to tolerance width 32 )

44

Value interval ( 44-1 . 44-2 , ... 44-5 )

46

interval number

48

Interval limits ( 48-1 . 48-2 , ..., 48-6 )

A _nom

Target switch-off

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• WO 96/17496 [0006]

Claims (10)

Method for compensating production tolerances of electrical consumers ( 2 ), powered by a power supply ( 20 ) of a domestic appliance, at least comprising the following steps: a) measuring an actual value ( 10 , R _is ) of the resistance value of the electrical consumer ( 2 b) determining a correction factor from the actual value ( 10 , R _is ) of the resistance value of the electrical consumer ( 2 ) and a resistance setpoint ( 30 , R _nom ), and c) taking into account the correction factor when operating the household appliance. A method according to claim 1, characterized in that step (a) before installation of the electrical consumer ( 2 ) is carried out in a household appliance. Method according to claim 1 or 2, characterized that step (a) with a measurement accuracy (δR / R) of 1% or less. Method according to one of claims 1 to 3, characterized in that measured actual values ( 10 , R _is ) of the resistance value of an electrical consumer ( 2 ) Value intervals ( 44-1 . 44-2 , ... 44-5 ), to each of which a correction factor is assigned. Method according to claim 4, characterized in that a value interval ( 44-1 . 44-2 , ... 44-5 ) the resistance setpoint ( 30 , R _nom ). Method according to claim 4 or 5, characterized in that each value interval ( 44-1 , ... 44-5 ) an interval number ( 46 ), which is transmitted to the domestic appliance. Method according to one of claims 1 to 6, characterized in that the correction factor is transmitted to the domestic appliance becomes. Method according to one of claims 1 to 7, characterized in that the electrical consumer ( 2 ) is an ohmic consumer. Method according to one of claims 1 to 8, characterized in that the electrical consumer ( 2 ) is a heater, in particular a thick film heater. Method according to one of claims 1 to 9, characterized in that step (b) before installation of the electrical load ( 2 ) is carried out in a household appliance.