Reklama

Requirements to sensors

Sensors used in the most severe operating conditions, therefore, the technical and engineering requirements to them are strictly controlled.

Various operational factors at influence on sensors measuring distort information about the status parameter. The degree of their influence depends largely on the principle of interaction with the object (sensors mounted - without introduction of the object of diagnosis or with the implementation in object; sensors embedded in the diagnostic object or the means of diagnosing) and from the principle of their interaction with controlled (contact and contactless) environment. The working conditions of the sensors, hung (or temporarily installed) and permanently embedded in the object of diagnosis, differ sharply.

 The most severe conditions characteristic of the embedded sensors in cars, tractors and other machines, since they should be operable under large temperature differences, for example in the engine compartment - from -50 to -100° C; in addition, there may be a temperature shock, for example, when cold water makes contact with the heated sensors. In addition to temperature factors on the built-in sensors constantly exposed to considerable shock loads during operation of the machine, dramatically increases the requirement for vibration and shock, but they can also be exposed to a corrosive environment (petrol fumes, diesel fuel, oil, all kinds of cleaning fluid and t. p.). In this regard, the reliability requirements to the embedded sensors must meet a more stringent, than hung.

To reduce or completely eliminate the influence on the sensors; influencing factors need to be constructive and technological measures in the design and manufacture of sensors.

Operating conditions measuring channel means of technical diagnostics can be divided into two parts: primary equipment and the secondary or measuring tract, since the sensor is mounted directly on the object of diagnosis, a secondary instrument is outside the object. Therefore, and a set of influencing factors to both parts of the measuring channel will be different.

Operational and technical requirements, requirements for sensors of means of technical diagnosing, can be represented in the form of three groups of signs, due: operating conditions; the type and nature of changes in the input (controlled) size; design features. Each of these signs has their own characteristics.

Let us consider briefly the main essence of these requirements

In the process of diagnosing the sensor from the object is influenced by a complex of operational factors, the main ones are the mechanical factors (vibration and shock load) and temperature (working environment temperature and facility in installation position of the sensor). In line with this, when developing a sensor to it requirements of mechanical strength; resistance to mechanical and thermal influences.

Depending on the mode of diagnosis, the position and mode of attachment to the object, the sensors must be done either in standard execution, when increased mechanical, temperature and other effects of the object are missing, or in a special performance (vibration, shockproof, vibration and t. D.).

Ordinary performance of the sensor - design, not intended for use in conditions of intensive mechanical and thermal influences, high concentrations of dust, spray, explosive atmospheres.

Vibration (shockproof) the sensor - design, able to resist the destructive action of vibration (shock) load and save upon exposure their efficiency. The sensors are vibration and impact resistant performances should be calculated taking into account the impact of vibration acceleration up to 10 in the frequency range from 10 to 300 Hz and shock loads of repeated action with acceleration up to 15″ and a pulse duration of 5-10. MS.

Temperatureprofile the sensor - design, able to resist the destructive action of high (low) temperature and retain their influence after their performance. Temperatureprofile the sensor should be designed for the temperatures of - 50 °C (when storing, transportation and t. p.) to +200°C (with engine running), and thermally stable performance - the effect of temperature of the object and the working environment during the measurements up to +100°C.

These features must be specified in the technical requirements for individual types of sensors depending on their purpose. In addition, when selecting a sensor, which is most effective must meet the requirements, it should be borne in mind, mechanical and thermal effects from the object of diagnosis can be reduced through the use of special damping devices, thermal insulation and t. p. The possibility of applying these measures should be considered in each specific case separately, as, for example, the use of shock absorbing devices (rubber tubes) for sensor dynamic processes often distorts the measurement information on the technical condition of the car.

Easy mounting and Dismounting. This is achieved through a simple form, small size (it is possible to install in hard to reach places) and design of the attachment method, t. e. connecting places. Sensor, set in the diagnosis, should not have any influence on his work, t. e. the element and node, to which are attached directly or indirectly interconnected, the sensor must remain functional and perform their functions while maintaining the specified technical characteristics.

The peculiarities of the environment. Operational factors, acting on the sensor from the environment when diagnosing cars, can be divided into three groups: climate (the temperature and humidity of the environment, precipitation and solar radiation); the contamination and aggressiveness of the environment; other (acoustic noise, external magnetic and electric fields). In accordance with these factors to the sensor special requirements.

Protection from environmental sensors to produce one of the performances: peltasticinae (splash-protected, waterproof) design, protected from ingress of dust Converter (water spray, moisture); hermetic design, protected from ingress of water sensor with full immersion in it; protected from aggressive environments - design, designed for use in the environment with the content of sulfur compounds and uglevodorodnykh, ammonia, nitrogen oxides, etc.

In terms of resistance to the effects of acoustic noise and solar radiation sensors are in each case requirements depending on the purpose and conditions of application Converter. Acoustic noise, characterized a maximum sound pressure level (dB) in the frequency range (Hz), act mainly on the design of the sensors large size. Their action is not dependent on depreciation and attachment of the sensor on the object. They cause devastating effects as well, as vibratory loads. Solar radiation causes chemical decomposition or oxidation of certain materials, the rapid ageing of plastics, the destruction of the rubber, and also degrades electrical and mechanical properties of the structure.

Protection against the effects of external magnetic and electric fields are requirements to sensors, which operate under conditions of magnetic or electric fields and are specified in the technical specification. The influence of external magnetic field for the sensor is "a hindrance" and can cause misrepresentation.

The sensors must be small and of low mass, protected from mechanical damage, water intake, dust, oil and other substances, which can cause corrosion or damage mechanism. They should have a simple and technological design. Electrical leads must be manufactured in the form of standard connectors, and connecting wires - securely protect the insulation and the braided shield. For sensors, operated under conditions of vibration of the object under the control of dynamic processes, should consider the phenomenon of resonance structural elements, which occurs when the coincidence of the natural frequencies of the sensor with frequencies of vibration from the object of diagnosis or frequency of a controlled environment in the case, when the sensor has an elastic mechanical system. To prevent the possibility of resonance in operation should be when designing the sensor to ensure no resonance of structural elements in the frequency range of vibration of the object and vibration controlled environment.

The reliability of the sensor - this property Converter, due to the dependability, durability and maintainability of its components and ensure the preservation of its performance within specified limits.

Since the majority of the sensors relates to systems, in case of occurrence of failure can not be restored in operation, the sensors can be regarded as non-restorable items.

In addition to the above General operational and technical requirements the sensor should take into account special requirements in the case:

1.               Contact or contactless mode of interaction of the sensor with a working (controlled) environment;

2.               Mounted on the object or built-in object sensors.

Special requirements should be taken into account in the case of sensors, built-in diagnostic object (car):

1.               Resource built-in sensors must meet the resource machine;

2.               Economic feasibility is seen as the primary factor, justifying the use of how do electronic diagnostics, and integrated sensors in particular. Economic feasibility is determined by the quality improvement, improved reliability, by reducing the complexity of diagnosing and t. p.;

3.               Health requirements and more stringent noise immunity, than looped sensors.

Because of limited volumes in the place of installation of sensors, their dimensions should be minimized as far as technically possible and economically viable. Such opportunities are currently available. So, for example, you can use temperature sensors to thermistors (semiconductor thermal resistance), and the pressure sensors strain gauge on semiconductor microwire or (maloletnye gauges).

There are specific requirements in terms of resistance to impact vibration and shock loads, since the operation can be aperiodic low-frequency shocks with acceleration 10 (when riding on the road with poor coverage) and high frequency resonant vibrations (with a wide range of frequencies), caused by the coincidence of the natural frequencies of the vibration sensor with the vibration frequency of one or another of the host machine (usually the engine). For the purpose of damping vibration oscillations, it is necessary to provide special fastening sensor (shock absorbing padding and t. p.).

Reklama