3BSE042236R2 PP865A Touch panel 15 inches

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During the renovation process of the heavy oil catalytic unit, the digital input card for the backup unit interlocking was a 16 point DI810 card with a total positive value. During system testing, it was found that the total fuse of the card was blown.

Cause analysis

Due to the 24v+power supply mode of the card, if one channel is grounded on site, it is equivalent to 24v+grounding, and the entire card power supply will be pulled down, which will inevitably cause the overall fuse of the DI810 card to melt and cause accidents, which will have very serious consequences for safety production.

Faced with the situation of about to drive, immediately organize personnel to solve the problem as soon as possible. There are several types of such cards, including commonality and grouping; At the same time, the common point type can be divided into two types: common positive and common negative, while the grouping type is further divided into four point groups and eight point groups based on the number of points; However, this type of card is not conducive to safety production. The possible reason is that the design institute made an error in the selection process, mistakenly using cards with a total of 24V+power supply mode for unit interlocking. The DI template model is DI810, with 16 channels for 24V+voltage signal input. The base model is TU810, with 24V+power supply. The DI input adopts a DI total of 24+V working mode, that is, which channel conducts, which channel receives a 24V+voltage, and that channel works. The 24V+input of DI and the 24V+card power supply are both supplied by a 1A, 24V+power supply, with a power fuse of 1A. The internal resistance of each channel of the card is 3.5K

Contact information: 15359213550

Contact person: He Gong

Email: geabbdcs@gmail.com   386353502@qq.com

Official website: https://www.gyamazon.com , http://www.geabb.com

processing method

After analysis and research, it is believed that there is not enough time to replace the card parts, and other solutions can only be taken. The method of adding a current limiting resistor to the card is currently a good way to eliminate hidden dangers. The conditions for ensuring the normal operation of the card are a DI channel input impedance of 3.5K and a logic "1" voltage of 15VDC to 30VDC. Taking into account the above factors, it is necessary to increase the input voltage as much as possible during normal operation of the channel, reduce the voltage division of R on it, and ensure that the voltage of logic "1" is greater than 15v+. At the same time, reduce the current flowing through R when the on-site circuit is short circuited. The calculation is as follows:

1) Ensure that the DI input voltage is greater than 15VDC and the maximum allowable value of R

R=3.5 × (24-15)/15

=2.1K

2) The value of R is 1.8-1.9K, with a power of 0.5W. Considering the actual value, the short-circuit current at 1.8K is 24/1.8=13mA, and the heating power of R is 13ma * 13mA * 1.8K=0.3W<0.5WDI. The input voltage is 24 * 3.5/(3.5+1.8)=15.5V. When a short circuit occurs, that is, the power supply is directly grounded through R, and the current value is 24v/2.1K=11.4ma, which has almost no effect on the power supply of 1A. The consideration is that 16 channels are grounded simultaneously, which only adds 11.4 for a 24+power supply × 16=182.8mA, the impact on a 1000mA power supply is also very small, and this situation is almost unlikely to occur in actual production.

Through multiple simulation tests on the improved DI card, there has been no further occurrence of the card's main fuse melting due to short circuits, which meets the requirements for use and meets the needs of device operation. And it has been verified in practice that the interlocking action is timely, ensuring the safe operation of the unit.

4 Conclusion

The signal alarm interlocking protection system, as an important component of device safety production, its reliability is crucial for safe and stable operation. It should be highly valued in all aspects of design, installation, commissioning, and maintenance. Firstly, in the design process, it is necessary to grasp the selection key to ensure the normal operation of the system and use the best components, and try not to use common positive 24V junction type cards as much as possible; The second is to determine the impact of control and safety functions, as well as the failure of primary components, on the system; The third is to establish good interlocking and parking modification and debugging records to ensure the safe operation of the system.