RU2024097C1 - Method for accelerated tests of electrooptical transducer - Google Patents

Abstract

FIELD: vacuum-tube engineering. SUBSTANCE: method involves exposure of transducer to cyclic temperatures, to high temperature of 50 C, and to elevated humidity of 98% at 40 C for two days; number of scintillations is used as parameter under measurement; number of temperature cycles and time of exposure to elevated temperature are determined from relevant equations; transducer is held at elevated humidity in factory packing. EFFECT: provision for in-storage serviceability check of transducer. 5 dwg, 1 tbl

Description

 The invention relates to electrovacuum technology and can be used to accelerate the persistence tests of electron-optical converters (EOC).

 A known method of statistical forecasting of shelf life, which is based on predicting the shelf life of products according to the results of long-term storage during the test up to 30-40% of the specified minimum shelf life when changing shelf life parameters exceeding the measurement error. Based on the results of several measurements of the parameters at various monitoring times, the average value and the sample standard deviation of the measured value of the expiration parameter from its average value are calculated.

 This method requires a long storage time to obtain reliable results and further prediction of shelf life, and also does not allow to evaluate the shelf life of a particular device at the research and development stage.

A known method for predicting the temporal cross-section, which can be used to predict the shelf life of products based on the test results of the base product with two storage times: τ _o is the storage time for which storage is predicted, and τ _and is the storage time for which storage is predicted providing a meaningful estimate of the correlation coefficient.

 This method also requires a long storage time of products to obtain results and further forecasting retention.

The closest in technical essence to the invention is a method for rapid assessment of products on retentivity selected as a prototype in which the product is tested for retentivity in packaging manufacturer and is exposed to ambient temperature changes in the mode of low temperature - minus 55 ^{° C} for unheated and 5 ^C. for heated storage increased - 40 ^C. The storage conditions the product is exposed to high temperature + 40 ^{° C,} and exposed to high humidity of 98% at temp round 25 ^{° C} in a non-heated, to 80% at a temperature of 25 ^{° C} in heated storage conditions.

 The product is kept in normal climatic conditions in the dark for at least 24 hours and the parameters are measured before testing, after 6 months, 3 g, in the middle of the shelf life and after the shelf life tests. Shelf life is selected from the following series of 5, 8, 10, 12 years, and it is envisaged to store the product in an unheated and heated storage environment. Evaluation of test results is carried out in accordance with the technical specifications for a particular product.

 The disadvantages of this method are that it takes a lot of time to test products for shelf life and there is no way to predict suitability for a particular product.

 The purpose of the invention is to reduce the retention test time while making it possible to determine storage prospects for an individual product.

; (1)
t= [(N-1)/B]^2/3, (2) где n' - минимальное количество термоциклов преобразователя, вероятность отказа после которых не превышает ожидаемой вероятности отказа при длительном хранении;
Δ Т' - средний перепад температур в процессе хранения, определяемый местом и условиями хранения;
t' - продолжительность полусуточного цикла при хранении;
Δ Т - перепад температур термоцикла;
t - заданная продолжительность термоцикла;
N - относительное изменение количества сцинтилляций преобразователя при хранении;
В - экспериментальный коэффициент, зависящий от температуры и типа преобразователя (0,01-2), а повышенной влажностью воздействуют на преобразователь, размещенный в упаковке изготовителя.The object is achieved in that the method of accelerated testing image intensifiers comprising thermocycling converter speed to a normal climatic conditions in the dark for at least 24 hours exposure to an elevated temperature of 50 ^{° C,} repeated exposure to normal ambient conditions in the dark for at least 24 hours exposure to elevated humidity equal to 98% ^at 40 ° C for 2 days, additional exposure to normal environmental conditions in the dark for at least 24 hours, measuring the parameters of the converter and determining its validity, the quantity of scintillations is used as the measured parameter, the number n of thermal cycles and the time t of exposure to elevated temperature are determined from the relations
n =

; (1)
t = [(N-1) / B] ^2/3 , (2) where n 'is the minimum number of converter thermal cycles, the probability of failure after which does not exceed the expected probability of failure during long-term storage;
Δ T 'is the average temperature difference during storage, determined by the place and storage conditions;
t 'is the duration of the semi-daily cycle during storage;
Δ T is the temperature difference of the thermal cycle;
t is the specified duration of the thermal cycle;
N is the relative change in the number of scintillations of the transducer during storage;
B is an experimental coefficient depending on the temperature and type of the transducer (0.01–2), and they affect the transducer located in the manufacturer’s packaging with increased humidity.

The set of distinguishing features, namely the use, as the measured variable number of scintillations, determining the number of temperature cycles by the formula (1), as well as exposure to elevated temperature of 50 ^{° C,} for a time t = [(N-1) / B] ^{2 / 3} and the effect of increased humidity equal to 98% at 40 ^о С on the converter placed in the manufacturer’s packaging allows to achieve similar storage of the change in the state of the parameters of the image intensifier tube in terms much shorter than the shelf life specified for the product types th.

 When checking the patent documentation, no analogues were found with the specified set of distinctive features, which allows us to conclude that there are significant differences of the claimed method from previously known.

 The proposed method of accelerated testing of an image intensifier tube can be implemented as follows (the method was tested for a second generation image intensifier tube based on a metal-glass case, fiber optic plates (FOP), microchannel plates (MCP)).

 An example of a calculation by the method of accelerated persistence tests for EOPs of the type EP-10 and EP-16.

 When testing the image intensifier by long-term storage, it was found that short-term and time-consuming processes occur in them. Short-term ones are associated with latent manufacturing defects, such as a leak in the housing of the image intensifier tube, leakage and non-moisture resistance of the fiber optic tube and some others. Long-term temporary processes are associated with the properties of the material and the design of the image intensifier tube.

 The number of thermal cycles is determined.

For a tube with a MCP of type EP-10 and a three-module tube of type EP-16, failures associated with latent manufacturing defects are normally distributed during the first year of storage (Fig. 1). The expected probability of failure during long-term storage of data of types of image intensifier tubes is 0.2 ˙ 10 ^-3 . From figure 1 it is determined that this corresponds to 9 months of storage under conditions of an average temperature difference Δ T '= 3-5 ^o C.

 For 9 months (270 days) of long-term storage during which the state of the image intensifier tube is stabilized, the number of thermal cycles of accelerated tests is determined by the relation (1).

= 5 , т.е. пять термоциклов эквивалентны 9 мес длительного хранения.According to TU, the temperature in the cycle during thermal cycling tests varies from minus 60 to +50 ^о С (Δ Т = 110 ^о С), the cycle duration is 4 hours. The days during storage are divided into two cycles of temperature fluctuations: day-night, night-day ( cycle time 12 h), a total of 2,270 cycles. From here
n =

= 5, i.e. five thermal cycles are equivalent to 9 months of long-term storage.

Figure 2 is an experimental probability of failure distribution image intensifier type VC-10 and VC-16 thermal cycles at Δ T = 110 ^C. It is seen that after five cycles the probability of failure decreased to the expected failure during prolonged storage. The probability of thermal cycle failures for these types of image intensifier tubes is distributed in a similar way.

= 3 .To determine the structural margin and reliability, products of type EP-16 were tested by thermal cycling in the temperature mode from minus 60 to +100 ^о С (Δ Т = 160 ^о С), the cycle time is 4 hours. The temperature +100 ^о С is the limit for the tube with a similar design and manufacturing technology. For the specified 9 months of long-term storage, the number of accelerated thermal cycles is determined by the formula (1)
n =

= 3.

The experimental data are shown in figure 3. It can be seen that after three thermal cycles the probability of failure is close to the expected probability of failure during long-term storage. However, further thermal cycling in this mode leads to a mass failure of the products, since at a temperature of +100 ^о С the photocathode and the structural elements of the image intensifier tube begin to break down. The temperature difference during accelerated testing (Δ T) should not exceed the permissible temperatures for these types of image intensifier tubes.

Determine the EOF exposure time at an elevated temperature of 50 ° ^C.

For these types of EOF maximum allowable operating temperature is a temperature of 50 ° ^C. The most accurately determined EOC condition by changing the number of scintillations. Experimentally determined (Figures 4 and 5) that the relative change in the number N of scintillations on prolonged storage, and when exposed to the temperature 50 ^{° C} is described by the relation
N = 1 + B t ^2/3 .

From here
t = [(N-1) / B] ^2/3 .

It was found that for image intensifier type VC-10 B = 2 for long-term storage, B = 0.03 when subjected to a temperature of 50 ^° C for EOF type VC-16 V = 0.5 during prolonged storage, B = 0.01 when subjected to temperature 50 ^o C.

= 116 ,
для ЭОП типа ЭП-16
t =

= 108 .From the equality of the relative change amount of scintillations on prolonged storage for 8 years under the action of temperature and 50 ° ^C while the accelerated tests are:
for electronic tubes of type EP-10
t =

= 116,
for electronic tubes of type EP-16
t =

= 108.

 Therefore, the exposure for 116 and 108 hours for EOPs of the type EP-10 and EP-16, respectively, is equivalent to 8 g of long-term storage.

 Test conditions at high humidity are determined to verify the image intensifier tubes placed in the manufacturer's packaging.

It was experimentally found that the image intensifier has a non-moisture-resistant GP. The effect of moisture is of a relay nature, i.e. manifested at certain values of temperature and humidity. Moisture dissolves various inclusions in the pores between the fiber optic conductors of the GP and penetrates the EOP module, which leads to device failures. Packaging protects the product from this exposure during storage. To check the security of the image intensifier, it is exposed to moisture in the manufacturer's packaging. The test temperature of the EOP type EP-10 and EP-15 according to TU is +40 ^о С at a relative humidity of 98%. The minimum test time according to TU is 2 days.

 The order of the tests according to the method of accelerated testing of the image intensifier for persistence.

 Measure the parameters of the image intensifier tube and enter it into the table.

The product is placed in the installation type KSP chamber where temperature is maintained at ^-60 ° C, and held for 2 hours. Then, EOF is removed and placed in a KSP type installation chamber inside which the temperature is maintained 50 ^{° C} and held for 2 hours. Then the cycles are repeated.

 The product is maintained in normal climatic conditions in the dark for at least 24 hours.

The image intensifier tubes are placed in the chamber of the KSP installation, the temperature inside which is maintained at +50 ^о С, and they are kept for 116 hours with the ЭП-10 type intensifier tubes and 108 hours with the ЭП-16 type intensifier tubes without taking into account the thermal equilibrium time of 30 minutes

 The image intensifier is maintained in normal climatic conditions in the dark for at least 24 hours, the parameters are measured and entered into a table. The value of the parameters should not be lower than the TU standards.

EOC is packed into containers and placed in the installation chamber KSP type where support the following modes of testing: Temperature: 40 ^{° C,} relative humidity 98% and allowed to stand for 2 days.

 The product is taken out of the packaging chamber and kept in normal climatic conditions in the dark for at least 24 hours.

 Parameters are measured, data is entered into the table. The image intensifier is considered to have passed the test if the value of its parameters is not lower than the TU standards.

 The time of testing the image intensifier tube according to the specified method, taking into account the intermediate measurements of the parameters, is 22 days instead of 8 years.

 Technical appraisal and economic advantages consist in the fact that reducing the time of testing products for shelf life allows for operational monitoring of changes in shelf life parameters during storage, in addition, this method allows you to evaluate the shelf life of developed products, the calculated number of thermal cycles during accelerated testing allows you to identify hidden production defects and reduce the failure rate of products to the level of 0.02%, characteristic of long-term processes of natural aging, by dennoe ratio of high temperature exposure time is equivalent to storage time, which also reduces the manufacturing tests. This method allows to reduce the time of testing products for retention by 132 times. The time of testing the image intensifier tube according to the specified method, taking into account the intermediate measurements of the parameters, is 22 days instead of 8 years.

Claims (1)

METHOD FOR ACCELERATED TESTS OF ELECTRON-OPTICAL CONVERTER, including thermal cycling of the converter, exposure to normal climatic conditions in the dark for at least 24 hours, exposure to an elevated temperature of 50 ^o C, repeated exposure to normal climatic conditions in the dark for at least 24 hours, exposure to high humidity, equal to 98% at 40 ^o C for two days, additional exposure to normal environmental conditions in the dark for at least 24 hours, the measurement transducer parameters and determination of its validity from ichayuschiysya in that as the measured variable number is used scintillations number of thermal cycles and high temperature exposure time is determined from the relations
n =

,
t = [(N-1) / B] ^2/3,
where n 'is the minimum number of thermal cycles of the converter, the probability of failure after which does not exceed the expected probability of failure during long-term storage;
ΔT ′ is the average temperature difference during storage, determined by the place and storage conditions;
t 'is the duration of the semi-daily cycle during storage;
ΔT is the temperature difference of the thermal cycle;
t is the specified duration of the thermal cycle;
N is the relative change in the number of scintillations of the transducer during storage;
B - experimental coefficient, depending on the temperature and type of transducer (0,01 - 2),
and increased humidity affects the transducer located in the manufacturer’s packaging.

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