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Seira Elettronica S.r.l.

Via Ca’ del Bosco 1 - 37046 - MINERBE - VERONA - ITALY
Tel: +39 (0) 442 640955 | Fax: +39 (0) 442 640249
E-mail: seira@seiraelettronica.com


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Digital Control

NEW SELF-DIAGNOSIS SYSTEM   GENERAL CHARACTERISTICS

In 2001 -  2002 ,   SEIRA  completed the realization of a new static converter with 4 stages, and at the same time the study and construction of a new card “master”  SMD,  containing the  DSP  of  40MHz type TMS 320 LF 2407 APGES  of  Texas Instruments .  This card, the conception of which is strictly conforming to MIL norms, can carry out a precision regulation of the 4 above-quoted stages and also it can manage a new and very complex self-diagnosis system, because it is endowed with a “flash  memory of  2 Mbytes”  for the “Historical memory”.  The purpose of this self-diagnosis system is to simplify at the most the execution of the complete test of the converter and to realize the “blank tests”,  the search for damages or failures in a precise and detailed way and the after-sale assistance. To achieve these results, it is necessary to have a portable PC (correctly programmed) with a serial connection RS232; the screen points out a lot of analogical and digital signals and other appropriate indications to simplify the above-quoted operations. To achieve these purposes, our technicians had to face up to different problems, included the creation <ex novo> of a new management pattern, since there is no similar system on the market. The working of this system consists in using the card “master”  DSP, which can control also the good working of the other cards and of the static converter. In case of wrong working of the card “master” DSP, it is necessary to replace only this one; in case of wrong working of other parts of the converter (the other cards, blocks of power, etc.), the card DSP can point out not only the failure stage but also the area where the problem is present. The removable drawer, containing the failure stage, can be immediately replaced in few minutes by another of spare, to reduce to the minimum the drawback caused by the damage. Then, the drawer in which the breakdown took place, is repaired with precision and simplicity in laboratory, through a correct utilization of the self-diagnosis system.     METHOD OF TEST OF THE CONVERTER The card “master” SMD  and the card “interface” of all the input analogical signals are made with resistances of precision 0,5% and they are already calibrated “at the bench“ to assure that the outputs V-I have a precision better than 1,5% in comparison with the nominal working values and the environment temperatures varying between -25°C and +45°C. This characteristic is important to make the test of the static converter very simply, using an already programmed PC and a serial connection RS232.  Besides the strict respect of security norms ( it is not necessary to use the traditional measure instruments – testers, oscilloscopes, etc. – with the risk of working with high voltages); in this way, we realize an accurate test, complying with all the provided procedures, since it can be completely recorded. At the beginning of the test of the converter (the latter, endowed with all the components and electronic cards, has already been subjected to isolation tests through a megger and to the rigidity tests through the corresponding measures, following the technical specifications of the customer and the UIC norms), SEIRA’s technicians introduce (through an electronic key) the special identification data of the converter to be tested, that is to say, the registration number, the date of the beginning of the test, the customer’s name and/or the type of coach where the converter has to be installed, the type and the brand of the IGBT used in the different conversion stages, and, to conclude, they switch to zero the electronic timer, which from this moment will count the working hours of the converter, determined by the presence of the output three-phase voltage. Then, the test continues with the application from the outside, through an internal connector, of a feeding voltage of 110Vcc  ±25% with a power of about 120W. In this way, temporary excluding the Auto-starter device, we feed all the electronic cards and control all the connections, the appropriate working of the cards, etc.; all these data are visualized on the screen of the PC. Then, we prepare the software programme of the card DSP in the position “test at low voltage” and we apply, through a portable feeder, at the input of the converter, a voltage HT slowly variable between 0 and 360Vca. It is necessary to verify from the beginning the presence of a slow increase in the voltage (Switching HT) at the output of the first stage; to be sure that the signals of voltage and current at the input of the transformer are correctly connected between them and that the inverter begins to distribute its three-phase voltage. After the positive result of this phase, we prepare the software programme of the card DSP in the position “normal working” and the converter is directly fed by a voltage HT having an appropriate power between  360Vca  and  552Vca. If the voltage HT exceeds 360Vca, the card DSP, fed by the auto-starter device, begins the procedure for the starting of the converter, which shall regularly work within 5 seconds.    RE-STARTING OF THE CONVERTER DAMAGED In case of failure, the card DSP records in the 2  Mbytes “flash” memory all the logical and analogical signals of the 9 events that precede the moment of the failure (each event corresponds to the stage of the converter during 2 msec; so, a failure causes the recording of 10 events for a total of 20 msec). This fact is very important to carry out an efficient after-sale assistance. However, in case of failure, the card DSP turns on the red warning light of the bicoloured DEL to show the stage of failure on the synoptic panel. Now, the technician has only to substitute the removable drawer, which contains the failure stage with another drawer. For the failures of other components that are not included in the removable drawers (as for ex. the failure of the transformer, of the inductors and of the power capacitors, which are however very improbable), it is necessary to read the more detailed instructions on the screen of the PC.  REMOTE TRANSMISSION OF DATA  The card DSP has got some connectors for the connection to the other different  cards and a connector for the serial RS232,  and other 2 connectors for serial RS485. These serial connections can be used at the same time, the first for the connection to a local synoptic or to an optional card for the transmission of data via MVB Bus of the train, the other for the connection to the general table of control of the coach and/or for the transmission via GSM through another card at option.  Furthermore we have developed during the last few years other type of data transmission at distance without wires.

Please find below an example of Autodiagnosis through PC.