Method for manufacturing an electronic circuit for a field device in automation technology

Abstract

Method for manufacturing an electronic circuit for a field device of automation technology, wherein the electronic circuit comprises at least one printed circuit board with several electronic components, at least one of which exhibits a temperature dependence, wherein the method provides the following steps: - At least one local temperature change on the at least one electronic component of the at least one printed circuit board (S100), wherein the local temperature change is carried out in such a way that the at least one printed circuit board experiences the temperature change in a local area in which the at least one electronic component is located and preferably not the entire printed circuit board; Determining a temperature coefficient for the at least one electronic component (S200) based on the at least one local temperature change on the at least one electronic component.

Description

[0001] The invention relates to a method for manufacturing an electronic circuit for a field device in automation technology.

[0002] In automation systems, particularly process automation systems, field devices are frequently used to detect and / or control process variables. Sensors, such as those integrated into level gauges, flow meters, pressure and temperature gauges, pH / ORP meters, conductivity meters, etc., are used to detect process variables, measuring the corresponding process parameters of level, flow rate, pressure, temperature, pH value, and conductivity. Actuators, such as valves or pumps, are used to control process variables, changing the flow rate of a liquid in a pipe section or the fill level in a container. In principle, all devices used close to the process that provide or process process-relevant information are considered field devices.In connection with the invention, field devices also include remote I / Os, radio adapters or, more generally, devices that are arranged at the field level.

[0003] A large number of such field devices are manufactured and distributed by the company Endress+Hauser.

[0004] Such field devices typically comprise a sensor and / or actuator element and an electronic circuit that generates a measurement signal. The electronic circuit serves to control the sensor and / or actuator element and / or to process the sensor signal into the measurement signal.

[0005] Such electronic circuits for a field device often exhibit a temperature dependency that negatively affects the overall accuracy of the measurement result.

[0006] One approach to managing this temperature dependency is to reduce the need for temperature compensation or the temperature dependency itself through a careful selection of components or circuit parts. The disadvantage of this approach is that it doesn't always work, or doesn't work completely, across the entire electronic circuit.

[0007] Another approach is to use appropriate temperature-stable circuit components or parts. The disadvantage here is that the use of temperature-stable circuit components or parts is often not economically viable.

[0008] Often, the cost of a correspondingly temperature-stable circuit component or part is not justifiable. Therefore, in many systems, an error due to temperature changes remains, which is specified as measurement uncertainty over temperature (or simply: temperature error) in the field device's datasheet.

[0009] Another approach to further reduce the error is to temperature compensate the entire electronic circuit. This involves operating at various temperature points in a temperature chamber and comparing the output to a known target value. The measured error is then calculated and corrected using determined coefficients via an algorithm. The disadvantage of this method is that each individual electronic circuit must be compensated. This is a very time-consuming and, due to its high cost, not very economical approach. Furthermore, the limited number of temperature chambers typically restricts the throughput of electronic circuits in manufacturing.

[0010] The invention is therefore based on the objective of providing a remedy for this problem.

[0011] The problem is solved according to the invention by the method according to claim 1.

[0012] The inventive method for manufacturing an electronic circuit for a field device of automation technology, wherein the electronic circuit comprises at least one printed circuit board with several electronic components, at least one of which exhibits a temperature dependence, provides the following steps: - At least one local temperature change on the at least one electronic component of the at least one printed circuit board, wherein the local temperature change is carried out in such a way that the at least one printed circuit board experiences the temperature change in a local area in which the at least one electronic component is arranged, and preferably not the entire printed circuit board; - Determining a temperature coefficient for at least one electronic component based on at least one local temperature change at at least one electronic component.

[0013] According to the invention, a method for manufacturing an electronic circuit for a field device in automation technology is proposed, in which the temperature compensation of an electronic circuit is carried out at the component level by determining the temperature coefficient for the corresponding electronic component. Here, the temperature coefficient is understood to be a coefficient that describes the relative change of a specific physical quantity, in particular the resistance value, of the electronic component when the temperature changes relative to a defined reference temperature.

[0014] An advantageous embodiment of the method according to the invention can provide that the at least one local temperature change of the at least one electronic component is carried out by a heating device formed on the at least one printed circuit board.

[0015] A further advantageous embodiment of the method according to the invention can provide that the at least one local temperature change of the at least one electronic component is carried out by a heating wire or meander formed in the area, in particular in the area under the at least one electronic component on the circuit board.

[0016] A further advantageous embodiment of the method according to the invention can provide that, in order to determine the temperature coefficient, a local temperature change is carried out several times on at least one electronic component.

[0017] A further advantageous embodiment of the method according to the invention can provide that the at least one electronic component is a resistor.

[0018] A further advantageous embodiment of the method according to the invention may provide that a resistance measurement, in particular a 4-wire resistance measurement, is carried out to determine the temperature coefficient.

[0019] A further advantageous embodiment of the method according to the invention may provide that the method further includes the following step: - Temperature compensation of the electronic circuit using the determined temperature coefficient for at least one electronic component of the electronic circuit.

[0020] In particular, the embodiment can provide that the temperature compensation of the electronic circuit is carried out computationally using the determined temperature coefficient.

[0021] A further advantageous embodiment of the method according to the invention can provide that the determined temperature coefficient is stored.

[0022] A further advantageous embodiment of the method according to the invention can provide that, based on the determined temperature coefficients, at least one switching threshold of the electronic circuit for the field device is adjusted or set. In this context, the switching threshold is understood to be a response limit at which the electronic circuit for the field device performs a specific action. This could, for example, be the output of a warning when a supply voltage for the electronic circuit falls below the response limit. Another example is the switching of a switching output of the electronic circuit depending on the switching threshold.

[0023] The invention is explained in more detail with reference to the following drawing. It shows: Fig. 1: a schematic representation of the method according to the invention.

[0024] Fig.Figure 1 shows an exemplary representation of the inventive method for manufacturing an electronic circuit for a field device in automation technology. The method serves to determine the temperature dependence of an electronic component in an electronic circuit intended for use in a field device and, if necessary, to compensate for it. Since most temperature dependencies in electronic circuits are due to the tolerances of resistors, the method primarily relates to these. Besides resistors, which are frequently used in electronic circuits and are often key elements (e.g., in voltage dividers or amplifier circuits), the method is equally applicable to other electronic components that exhibit a temperature dependence, such as diodes, capacitors, or active references.

[0025] The method according to the invention provides, as a first process step S100, that a local temperature change is carried out at least once, but optionally several times, on the at least one electronic component of the at least one printed circuit board of the electronic circuit for the field device of automation technology. Preferably, a temperature profile specific for determining a temperature coefficient is followed. The local temperature change is carried out in such a way that the at least one printed circuit board experiences the temperature change in a local area in which the at least one electronic component is arranged, and preferably not the entire printed circuit board. In other words, this means that only the at least one electronic component experiences the temperature change and, in particular, not the entire printed circuit board or the other electronic components of the printed circuit board. For this purpose, for example,A heating element may be integrated on the printed circuit board in the area of ​​the at least one electronic component on the board. The heating element may, for example, be in the form of a heating wire or a heating coil located beneath the electronic component on the printed circuit board. Alternatively, the heating element may be in the form of a Peltier element, preferably integrated on the printed circuit board in the area of ​​the at least one electronic component. The local temperature change may also be achieved, additionally and / or alternatively, by a heating element that is separate from the electronic circuit, i.e., not integrated into it.

[0026] Furthermore, the method, in a second process step S200 following the first process step, provides for the determination of a temperature coefficient for the at least one electronic component, wherein the determination of the temperature coefficient is based on the local temperature change at the at least one electronic component. For example, the temperature-dependent change in the resistance value, and thus the temperature coefficient, can be determined by means of a precise resistance measurement. For example, the resistance measurement can be carried out in the form of a 4-wire measurement, in which a known electric current is passed through the electronic component via two wires during the local temperature change, and the voltage drop across the electronic component is tapped and measured via two further wires using a high-impedance connection.

[0027] Process steps one and two are preferably carried out for at least some of the electronic components of the electronic circuit that exhibit a temperature dependence, e.g., all resistors.

[0028] Furthermore, the procedure can include an optional third step (S300) following the second step, in which the electronic circuit for the automation field device is temperature-compensated using the previously determined temperature coefficient(s). For this purpose, the determined temperature coefficient(s) for the respective electronic components are stored. The stored temperature coefficient(s) can then be used, for example, to determine the temperature measurement uncertainty (temperature error) specified in the field device's datasheet.

[0029] Additionally or alternatively, the procedure can provide for adjusting or setting at least one switching threshold of the electronic circuit for the field device based on the determined temperature coefficients. For example, the electronic circuit can be designed to issue a warning message when a supply voltage drops below a specific value (switching threshold). Another example is switching a switching output of the electronic circuit depending on the switching threshold. By using the temperature coefficients specifically determined for the electronic circuit when adjusting or setting the switching thresholds, it is possible to position them even closer to the actual target value, as a higher level of confidence is achieved. Reference symbol list S100 Local temperature change at at least one electronic component S200 Determining a temperature coefficient for at least one electronic component S300 temperature compensation of the electronic circuit with at least one electronic component

Claims

[1] Method for manufacturing an electronic circuit for a field device of automation technology, wherein the electronic circuit comprises at least one printed circuit board with several electronic components, at least one of which exhibits a temperature dependence, wherein the method provides for the following steps: - At least one local temperature change on the at least one electronic component of the at least one printed circuit board (S100), wherein the local temperature change is carried out in such a way that the at least one printed circuit board experiences the temperature change in a local area in which the at least one electronic component is located and preferably not the entire printed circuit board; - Determining a temperature coefficient for the at least one electronic component (S200) based on the at least one local temperature change on the at least one electronic component. [2] Method according to claim 1, wherein the at least one local temperature change of the at least one electronic component is carried out by a heating device formed on the at least one printed circuit board. [3] Method according to one or more of the preceding claims, wherein the at least one local temperature change of the at least one electronic component is carried out by a heating wire or meander formed in the area, in particular in the area under the at least one electronic component on the printed circuit board. [4] Method according to one or more of the preceding claims, wherein to determine the temperature coefficient a local temperature change is carried out several times on the least one electronic component. [5] Method according to one or more of the preceding claims, wherein the at least one electronic component is a resistor. [6] Method according to one or more of the preceding claims, wherein a resistance measurement, in particular a 4-wire resistance measurement, is carried out to determine the temperature coefficient. [7] A method according to one or more of the preceding claims, wherein the method further provides the following step: - Temperature compensation of the electronic circuit (S300) using the determined temperature coefficient for at least one electronic component of the electronic circuit. [8] Method according to the preceding claim, wherein the temperature compensation of the electronic circuit is carried out computationally using the determined temperature coefficient. [9] Method according to one or more of the preceding claims, wherein the determined temperature coefficient is stored. [10] Method according to one or more of the preceding claims, wherein at least one switching threshold of the electronic circuit for the field device is adjusted or set based on the determined temperature coefficients.

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