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.
Table 103: Limits for the mA/RTD inputs
mA/RTD input
Limit value
RTD temperature, high
> 200°C
RTD temperature, low
< –40°C
mA current, high
> 24 mA
mA current, low
< –24 mA
Resistance, high
> 4000 Ω
Resistance, low
Not defined
1
When necessary, the valid measuring range may be narrower than the default of the
selected measuring range. A narrower range can be defined with the
Value minimum
and
Value maximum settings.
RTD input supervision
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.
Delay for
SENSOR_FLT
activation depends on the connected sensor type,
amount of connected channels and RTD module type. The maximum
delay is 10 seconds.
mA input supervision
The current limit for mA input supervision is defined by parameter
Sensor fault
level. Value must be below Input minimum parameter.
SENSOR_FLT
is activated,
and measurement quality is set bad when measured current is below set limit. The
supervision is disabled if
Sensor fault level is set to 0 mA.
3.15.3.2
Output mode
A measurement value from another function, mA input or RTD input can be
represented by the mA output. The mA output scaling principle is otherwise similar
1
Low limit is not defined for the resistance input. In practice the low limit is 0 because the
resistance cannot be negative.
1MRS759142 F
Basic functions
REX640
Technical Manual
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