NGC-20 INSTALLATION MANUAL
17
4.3.4 Temperature setting secured and locked to prevent manipulation
The lock out temperature (set point) of the safety temperature limiter must be set in such
a way that maximum T-class temperature cannot be exceeded. The surface temperature
of the heat-tracing cables is limited to the temperature applicable in this T class -5 K
for temperatures below or equal to 200°C or -10 K for temperatures greater than 200°C.
Refer to section 4.4 below for the procedure to change the safety limiter set point.
Independence from control system
The safety temperature limiter operates totally independent from the temperature control
system and has an own temperature input (RTD Limiter) In case of a defect to any part of
the DigiTrace NGC-20 unit the device shall be de-energized before replacing the defective
equipment.
4.4 Changing limiter set point
Changing the set point of the limiter requires the combination of the internal limiter set
button and an external user interface.
4.4.1 Procedure to write new temperature set point to limiter
In order to write a new set point to the temperature limiter a safety procedure needs to
be followed. Changing the set point of the temperature limiter requires the combination
of the internal limiter set button as is shown in Figure 11 and a programming device. As
programming device one can use; DigiTrace Supervisor software, DigiTrace NGC-UIT
terminal or the handheld configuration and monitoring assistant DigiTrace NGC-CMA-EX
or DigiTrace NGC-CMA-NH.
The procedure to change the limiter set point is the same for all user interfaces. The
configuration tool will write the new set point to the input buffer of the DigiTrace NGC-
20-CL-E controller. Only when the internal temperature set button is pressed will the
new set point be forwarded to the internal memory of the temperature limiter. The limiter
set point button needs to be activated within a certain time after the buffer has been
loaded with the new set point. If the button has not been pressed before the programming
window is elapsed, the buffer will be emptied and the old value remains active. Once the
new set point has been written the new or in case the write procedure was not successful
the old set point will be read back by the programming device as confirmation to the user.
After changing the limiter set point the user shall verify whether the set point has been
updated correctly. The limiter set point can be shown on the DigiTrace NGC-20 hardware
by pressing and holding the black Limiter SET button. While the limiter set point is shown
the red LED indicator marked with LIMITER will blink. After the button is released the
display will show the controllers measured temperature again and the LIMITER LED
will go off. Each time after the limiter set point has been altered a functional test as per
paragraph 4.5.1 is to be performed.
Figure 11: Internal Limiter control buttons: Limiter (temperature) SET and Limiter RESET
pushbuttons.
HEATER
ALARM
LIMITER
RS485
BLUETOOTH
RESET
LIMITER
SET
Pentair Thermal Management DigiTrace NGC-20
Limiter reset button (rearm the limiter after it has tripped)
Limiter temperature set button to be pressed after
the polling process has been initiated
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