ABB RELION REX640 Technical Manual page 168

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Basic functions

Platinum TCR 0.00385

Self-supervision

Each input contains functionality to monitor the input measurement chain. The

circuitry monitors the RTD channels continuously and reports a circuitry break of any

enabled input channel. If the measured input value is outside the limits, the minimum/

maximum value is shown in the corresponding output. The quality of the

corresponding output is set accordingly and the fault is reported at SENSOR_FLT to

indicate misbehavior in the mA/RTD input.

Limits for the mA/RTD inputs

mA/RTD input

RTD temperature, high

RTD temperature, low

mA current, high

mA current, low

Resistance, high

Resistance, low

1) Low limit is not defined for the resistance input. In practice the low limit is 0 because the resistance

cannot be negative.

RTD sensor currents are measured continuously at a fixed rate. The delay between the

RTD current/connectivity checks is about 10s at a maximum (if all 10 RTD channels

are active). If the RTD current is not within ±5% of the expected current, the

measurement is considered to be invalid and the channel is discarded until a valid

current is obtained.

The expected currents are 1 mA for RTD sensors and 0.21 mA for pure resistance.

While the quality of the invalid input is set accordingly, a warning is also provided on

the Relay Status page of LHMI/WHMI. The invalid signal is deactivated as soon as

the corresponding input signal is within the valid range.

Nickel TCR 0.00618

1MRS759142 C

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