JPH07117437B2 - Drift reduction device in measuring device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrical measuring device exposed to a fluid medium, and more particularly to a drift reducing device in an air mass flowmeter for an internal combustion engine, which measuring device is provided between two connecting portions. It has a temperature-dependent measuring resistance which is mounted on a support held in a holder.

[0002]

BACKGROUND OF THE INVENTION When an electrical measuring device is exposed to a flowing medium, for example air, for measuring the temperature of the flowing medium, the surface of the measuring device shows a dust layer over time. If a deposit layer of the shape is formed and the measuring device consists, for example, of a resistive layer arranged on a substrate, said deposit layer causes an offset (draft) of the characteristic curve of the measuring device. Especially in the case of high ohmic components, such a deposit layer causes parallel resistance. This is because, especially in the case of internal combustion engines, the majority of the constituents of the air pollutants consist of electrically conductive soot.

For this reason, various measures have been taken to prevent deposit layers which accumulate in the form of dust layers on such measuring devices.

As a typical example of such a countermeasure, an object facing in the flow direction is arranged in front of the air mass flow meter arranged in the measurement passage, and the object has an air flow of the air mass flow meter. The measurement area of the air mass flowmeter is substantially shielded in order to avoid direct impact on the. This prevents dust deposition at least partially.

As already mentioned, a parallel resistance is created by the deposit layer. This parallel resistance then changes in particular the resistance between the anode and the cathode of the measuring device.
Air moisture reinforces this effect. When the operation period is relatively long, or when the amount of dust (soot amount) is large, as in a diesel engine, electrolysis occurs between the connecting contacts (anode and cathode) based on the dust and air moisture, By electrolysis, especially when a platinum resistance is provided at the connection contact, the connection part of the platinum resistance is separated from the substrate and the functional reliability of the measuring device can no longer be guaranteed.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a device which at least significantly reduces the error of the measurement result due to the drift of the resistance value and prevents the peeling of the connection part from the support. is there.

[0007]

According to a further aspect of the invention, the drift-reducing device consists of an obstacle which is placed in front of the support on the side of the fluid medium which impinges on the measuring resistance. Moreover, the obstruction lies in that it is sized and arranged in front of the support so that the dust layer formed between the two connection sites is interrupted by the obstruction.

Advantageous embodiments of the invention are claimed in claims 2 and 3.
As described in.

[0009]

In order to obtain high response sensitivity, as is desired, for example, in the case of air mass flowmeters for internal combustion engines, the measuring device is generally exposed directly to the fluid medium. A durable measure to prevent electrolysis is to at least partially coat the protective lacquer layer. However, this method of forming a coating film is expensive because it cannot be automated, and there is a risk of misprocessing. The drift is reduced only when lacquering up to the next insulation, which in principle requires a special construction.

If the flow of the fluidized medium has a unique preferred direction, experiments have shown that it is sufficient if the dust coating layer is interrupted in one place. This interruption can be achieved in a very simple and inexpensive manner by prepositioning an obstacle on the support, as in the present invention.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings.

The cage 1 shown in the drawings can be made of a poorly heat conducting material such as plastic or glass. The cage 1 comprises a support 2 made of, for example, ceramic.
A temperature-dependent measurement resistance (not shown) is mounted on the support. The temperature-dependent measurement resistance is formed by a resistance element connected to a connection portion (not shown) arranged on the holder 1 via, for example, a wire. An obstacle 3 in the form of a thin sheet metal strip is arranged in the vicinity of the holder in front of the support 2 for the temperature-dependent measurement resistance, said obstacle being at least on the side of the measurement area. Over, and is narrower than the length of the measurement area.

The fluid medium impinging on the air mass flow meter is represented by the arrow labeled L. As can be seen from this figure, the obstacle 3 is arranged on the side of the support 2 facing the flowing medium.

By the way, when the air mass flowmeter is operated for a relatively long period of time, the support 2 is caused by contaminants in the fluid medium.
In addition, the dust layers 4 and 5 are deposited on the surface of the obstacle 3. Figure 2
As can be seen from the above, the dust layer 4 of the support 2 is interrupted in the region of the obstacle 3, so that the problem set at the beginning of this specification, that is, the occurrence of parallel resistance on the support 2 between the two connection sites. It is possible to solve the problem of preventing the occurrence of drift and thus preventing the drift.

[Brief description of drawings]

FIG. 1 is a schematic side view of a main part of an air mass flowmeter.

FIG. 2 is a schematic plan view of the air mass flow meter shown in FIG.

[Explanation of symbols]

1 cage, 2 supports, 3 obstacles,
4, 5 Dust layer, L Arrow indicating fluid medium

Claims (3)

[Claims] 1. A drift reduction device in an electrical measuring device exposed to a flowing medium, the measuring device having a temperature-dependent measuring resistance between two connection sites, the measuring resistance being retained. Of the type mounted on a support held in a vessel, the drift reduction device is an obstacle (3) in front of the support (2) on the side of the flowing medium impinging on the measuring resistance. And the obstacle (3) is dimensioned such that the dust layer (4) formed between the two connection sites is interrupted by the obstacle (3).
A drift reducing device in a measuring device, characterized in that it is arranged in front of. 2. Drift reduction device according to claim 1, wherein the obstacles (3) consist of sheet metal strips. 3. The drift reduction device according to claim 3, wherein the narrow side of the sheet metal strip is arranged substantially at right angles to the longitudinal side of the support (2) on the side exposed to the flowing medium.