8
DESIGN AND OPERATING PRINCIPLE
Electric power output is regulated by proportional connection and disconnection of the full
load depending on the pre-set heating temperature.
For example, intermittent connection and disconnection of the load in 5 s intervals
generates 50 % of the maximum output.
The cycle length - i.e. the combined period of load connection and disconnection - is
adjustable within the 1 to 10 s range.
Reduction of the total cycle length increases the heating intensity and output temperature
variance amplitude.
The RNS-16 capabilities are limited to only one heating cascade.
Unlike the smaller model the RNS-25 is capable of controlling one or three heating
cascades with the power output equal or exceeding that of the controlled cascade.
The power output of the first cascade is controlled in a stepless manner by switching the full
load on and off.
The second and third cascades are controlled in steps.
For example, if the first cascade power output is insufficient for reaching the pre-set
temperature, the second cascade of the electric heater engages at 100 % capacity whereas
the first cascade output is dropped to 0 % and then increased to the required level to ensure
reaching the target temperature.
To connect two extra heating cascades install an electric contactor for activating each heater
cascade.
For overheating protection the electric heater must be equipped with two built-in thermal
contacts: TK50 with intervention temperature of +50 °C and automatic restarting and TK90 with
intervention temperature of +90 °C and manual restarting.
The air temperature is set by means of the integral pot resistor or an external control device
generating a 0-10 V control input signal for increasing the duct temperature proportionally in
the range from -30 to +30 °C.
The duct temperature sensor must be installed downstream of the heater in the direction of
the air stream travel at the minimum distance of 50 cm from the heater.
If the controller runs in the heating power output mode irrespective of the temperature
sensor feedback, no duct temperature sensor is necessary whereas the heating power output is
regulated in the 0 to 100% range by means of the 0-10 V control input signal.
CAUTION! Ensure a constant airow to the heating elements of the heater while the RNS
is operational.
The fan choice must account for the minimum air ow through the heater of 1.5 m/s.
The blowing fan of the heating element must operate for at least two minutes after
thesystem shutdown.
