ABB REF 54 Series Technical Reference Manual page 52

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Technical Reference Manual, General
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The value and the status (validity) of the input can be issued for each RTD/analogue
input by the attributes AI# (REAL type) and AI#IV (BOOL type), where # denotes
the number of the input. These attributes are available in the feeder terminal
configuration and can be used for different purposes.
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The AI# value represents the filtered absolute value of the physical input with the
unit according to the selected measuring mode, i.e. V, mA, Ω or °C.
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The AI#IV attribute represents the invalidity status of the input. The attribute is set
to FALSE when the value (AI#) is valid, and to TRUE when the value is invalid. The
input is invalid when one or more of the following conditions are true: the measured
value is outside the defined limits (see the parameters "Input high limit" and "Input
low limit"), an open-loop condition is detected (only possible on resistance and
temperature measuring modes) or the continuous recalibration of the module has
failed. The value (AI#) is not locked when the invalid attribute is set to TRUE, i.e.
the invalid value is available for inspection.
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The RTD/analogue inputs are supported in the Relay Configuration Tool by the
general measurement function blocks MEAI1...MEAI8. As an example, to monitor
temperature using a PT100 sensor, the measured value of the RTD/analogue input
is connected to the function block by connecting the value attribute RTD1_6_AI1 to
the RawAI input of the function block. The output HighAlarm is used to activate a
relay contact when the temperature exceeds a preset limit. The measured
temperature is displayed on the MIMIC view of the HMI by the connected
MMIDATA1 function block. To avoid unnecessary activation of the relay contact
in case of a fault, the corresponding invalid attribute of the RTD/analogue input
RTD1_6_AI1IV is connected to the IV input of the function block.
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