Will shorting the two circuits of a digital input card damage the card?
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It’s a digital input card; pins 5 and 6 provide feedback when active, while pins 7 and 8 provide feedback when inactive. A 24VDC voltage is present between these two wires. After making connections, it was found that shorting pins 7 and 8 results in a feedback signal, whereas shorting pins 5 and 6 does not produce any feedback signal, although there is still voltage between those two wires. I want to ask whether shorting any two of the pins 5, 6, 7, or 8 together could damage the circuit – for example, if pins 5 are shorted to pins 7 or 8, will the feedback signal be sent directly to this card?
5,6 and 7,8 are two separate channels; there is no such thing as a connection between them, and even if a connection were made, it wouldn’t form a circuit.
If shorting 5 and 6 doesn’t work, then the channel is damaged; just replace it with another channel and reconfigure it.
If the channel is damaged, how can we check whether there is still voltage?
The negative terminals of the DI signals in the DCS systems I’ve worked with are all shorted together. You can check the documentation provided by the manufacturer or use a multimeter to test whether there is a connection between those two negative terminals; the positive terminals, on the other hand, are not shorted.
May I ask, which DCS’ terminal board is this? Report the model number and check the manual
It’s quite difficult to burn the DI terminal board
1. Modern DI cards are generally opto-isolated; as long as the 24V terminal does not come into contact with ground (such as the enclosure of an on-site meter), there is no problem. If it does come into contact with ground, the fuse will definitely blow, but the issue can be resolved by replacing the fuse. 2. No response when short-circuited; either the fuse has blown or the configuration is incorrect. To check whether the configuration is correct, one can disconnect the two terminals that are shorted together and see if the indicator light on the card responds, for example by flashing on and off. That proves the channel is normal; it’s a configuration issue. If there is no response, then there is a problem with the channel. On some DI cards, the indicator light will turn on if the fuse is blown, or a yellow light will appear if there is a problem with the channel; in normal conditions it shows a green light (closed) or a red light (open), though this varies depending on the manufacturer. 3. When a card gets damaged, it is usually because 220V voltage gets into it. Pay special attention to the control signals sent to the electrical components; if 220V is applied to the DI terminals, the DI card will get damaged. In mild cases, only one card is affected, but in severe cases the entire circuit board can be damaged, which is very problematic.
I guess I accidentally grounded it, but I didn’t see any fuse on this board; if the fuse has burned out, how is there still voltage?
The voltage is virtual; it comes from the LED and the large resistor connected to the fuse, and the current is very small