4.3 Requirements to be met by the temperature limiter
The NGC-20-CL-E safety temperature limiter meets the requirements of IEC 60079-30-1 For applications installed in a hazardous area
Zone 1 (Zone 21) this means that the protective device shall de-energize the system to prevent exceeding the maximum permissible
surface temperature. In case of an error by, or damage to the sensor, the heating system shall be de-energized before replacing the
defective equipment. The protective device operates independently from the temperature controller.
4.3.1 Temperature limiter (schematic)
Reset
Set
Principle limiter analog circuit
Sensor
2
Sensor
1
Limiter sensor
Temperatue control
Alarm
R485
Alarm relay
..........
..........
..........
..........
..........
..........
L
N
PE
N-load L-load
limiter
relay
ground
fault relay
..........
– 12V
SPI
AND
ground fault
current sensor
load current
current sensor
Temperature -
controller
RTD check
Figure 10: Limiter block diagram.
4.3.2 Reset by hand only
The safety temperature limiter is designed such that after the temperature limiter has tripped the device needs to be reset by hand.
Resetting is possible only after the normal, safe operating conditions have returned.
4.3.3 Reset by hand via tool or keyed lock
In order to RESET the limiter after it has tripped, the user needs to press the internal Limiter Reset pushbutton as is shown in Figure 11.
The figure shows where the limiter RESET button is located inside the enclosure (lid removed). Alternatively the safety temperature
limiter can be reset via Supervisor, NGC-UIT2/TOUCH1500 or the handheld configuration and monitoring device NGDC-CMA2 and keying
a specific number on the keyboard. Refer to the operating manual of the specific units for more detailed instructions on how to use
these devices.
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