Issues related to power distribution of S7-300 cards
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I’ve asked for advice. I’m facing a situation now: there are four cards of type 6ES7 331-1KF02-0AB0, with a value of 300 each. The other three cards are working properly, but one of these cards operates in a 3-point 2-wire configuration, with a 24V power supply provided via a cable from the cabinet; the remaining five points use a 4-wire configuration. Three two-wire meters are not functioning properly when connected to the main unit. When a signal generator is used to supply a 4–20mA signal, they work normally. However, once connected to the power supply in the cabinet, the signals sent back by these meters are only 3.5mA. The voltage of the field instruments is normal, and their displays also function correctly; it’s just the mA signals that are incorrect. It has been confirmed that the field instruments and wiring are in good condition. What could be the problem? Thank you!
Isolated and non-isolated instruments are connected to the module; it was mentioned in Liao Changchu’s book! I have also encountered the problem of second-tier and fourth-tier components being mixed together in one module. Suggestion: Connect several M points of the module to ground.
Connect the reference potential to the negative terminal of the instrument signal and give it a try
Is the reference potential the grounding mentioned on the second floor? Thank you
Does that mean the negative terminal of the instrument needs to be grounded? By doing so, it’s equivalent to grounding the negative terminal of the power supply – is that okay?
This post was last edited by xw712 on 2016-4-29 23:18. Yes. Here, the module operates at 24V, and the negative terminal of the 24V power supply for the instruments is connected to the \"instrument ground\", which serves as the common ground. Additionally, many four-wire instruments are not isolated; the signal negative terminal is connected to the instrument’s power negative terminal, meaning they are actually three-wire instruments. I’m afraid yours is one of those, and I used to have one as well.
The problem was resolved by identifying that there was an issue with a certain sensor on site; this caused the current signal from that sensor to become too high, resulting in problems in all the connection points of that component. By disconnecting that particular point, everything worked fine again. Thank you all – it’s been very informative!