Author: PLC Play Ground
MQTT Shows a Value Before the Sensor Starts? Check the Retained Flag
A new subscriber can receive a retained value that was published before it connected.
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MQTT Counter Increments Twice? QoS Does Not Define Your Business Transaction
Message delivery guarantees do not automatically make an application action unique.
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MQTT Last Will Says Offline Too Late? Understand Detection Timing
A Last Will message is not an instantaneous physical failure detector.
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OPC UA Publishing Is Fast but Values Still Lag? Check Sampling
A fast subscription publishing interval does not guarantee equally fast source sampling.
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OPC UA Misses Intermediate Changes? Check Queue Size and Overflow
A subscription can deliver the newest value while omitting intermediate changes.
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OPC UA Deadband Changed After a Range Update? Percent Is Not Absolute
A percentage deadband depends on the engineering range, so changing that range changes the reporting threshold.
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Modbus TCP Works Until Replies Split? Treat TCP as a Stream
One network receive call does not necessarily contain one complete Modbus TCP reply.
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Modbus Gateway Replies but the Device Does Not? Check Unit Identifier
Reaching a Modbus TCP gateway is not the same as selecting the correct device behind it.
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Modbus Read Fails Only When You Add More Tags? Check Request Limits
Combining more tags into one request can exceed a protocol or device limit.
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A PROFINET Ring Still Trips on One Break? Check the Redundancy Design
A cable ring is not automatically a functioning redundancy system.
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