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nVent.com/RAYCHEM RAYCHEM-OM-EU2032-NGCUIT3EX-EN-2203
The NGC-UIT3 monitors the control temperature and compares it to the setpoint. If the control temperature is above the setpoint
by more than the Dead Band value (see page 35) the relay output is turned off. If the control temperature falls below the setpoint
temperature, the output is turned on. The control temperature is defined as the lowest RTD temperature input value for that Circuit.
This algorithm monitors the control temperature of the Circuit and compares it to the setpoint temperature. If the control temperature
is at or below the setpoint temperature, then power is applied to the heater with a duty cycle of 100%. If the control temperature
is equal to or greater than the control setpoint temperature –15.5°C (+4°F), then the relay output will have a duty cycle of 0%. The
control temperature is constantly monitored, and the output duty cycle is adjusted proportionally once per second. See Appendix A for
additional information on Proportional Control.
This feature is a time-ramped soft start that reduces surge current produced by heaters at startup. When a solid state output relay is
first turned on, the duty cycle is ramped from 0 to 100% in 2.5% (25 millisecond) increments over a 40 second period. The update rate
for each step is fixed at 1 second.
This automatic feature is included only when using SSRs as an output device. It is incorporated into all control modes (On-Off,
Proportional, PASC, Always On). If an output has been off for more than 10 minutes, the soft-start algorithm will reset and be activated
the next time the SSR turns on. The soft-start algorithm will also reactivate whenever the NGC-30-CRMS boards loses power or is
reset.
(Proportional Ambient Sensing Control)
PASC takes advantage of the fact that the heat loss from a pipe is proportional to the temperature difference between the pipe and
the ambient air. This is true regardless of heater type, insulation type, or pipe size. Once the heat tracing and insulation on a pipe has
been designed to balance heat input with heat loss and maintain a particular temperature, the main variable in controlling the pipe
temperature becomes the ambient air temperature.
The NGC-30-CRM/-CRMS has a control algorithm that uses the measured ambient temperature, desired maintain temperature,
minimum ambient temperature assumption used during design, and size of the smallest pipe diameter to calculate how long the
heater should be on or off to maintain a near-constant pipe temperature.
The relay output is switched on (user override), turns on the power to the heater and leaves it on.
Monitor the pipe temperatures to avoid overheating. Alarms are still active.
The relay output is switched off (user override), turns off the power to the heater, and leaves it off.
Monitor the pipe temperatures for low temperature alarms. Alarms are still active.
Voltage
Voltage mode allows the NGC-UIT3 to monitor line voltage from the NGC-30-CRM/-CRMS boards. The NGC-30-CRM/-CRMS must
have an NGC-30-CVM connected to the line current sensor input when selecting voltage mode. As a result, this channel of the
NGC-30-CRM/-CRMS cannot be used to control an output device. But an RTD can be connected to this channel’s input to set up an
additional temperature monitoring Circuit. For an Elexant 5010i / NGC-20 controller, the voltage mode is not an option since this is a
standard feature.
This is the default mode that allows temperature monitoring for the Circuit. This means no output device has been selected.
The Fail Safe control button turns the power on or off to the heater if the Circuit loses all valid RTDs.
When the last remaining sensor for control fails (or communication with the sensor is lost), the NGC-UIT3:
• Signals an alarm for the failure of the sensor
• Changes control of the circuit to the fail safe control selected
• Changes the control status display to indicate that control of the circuit is in the fail safe state
• Records the events
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