Solid-State Switching Devices for Resistive Loads 3RF29 Function Modules Heating current monitoring ■ Overview ■ Function Heating current monitoring for 3RF2 single-phase solid- state switching devices The function module is activated when an "ON" signal is applied (IN1 terminal). The module constantly monitors the current level and compares this with the setpoint value. Many faults can be quickly detected by monitoring a load circuit connected to the solid-state switching device, as made possible with this module. Examples include the failure of up to 6 load ele- ments, alloyed power semiconductors, a lack of voltage or a break in a load circuit.
A fault is indicated by LEDs and reported to the controller by way of a relay output (NC contact). Startup Actuating the input IN2 switches the device on; the current through the solid-state switching device is detected and is sto- red as the setpoint value. During this process the two lower (red) LEDs flash alternately; simultaneous continuous light from the 3 (red) LEDs indicates the conclusion of the teaching process. The principle of operation is based on permanent monitoring of the current strength. This figure is continuously compared with the reference value stored once during commissioning.
In order to detect the failure of one of several loads, the current difference must be 1/6 of the reference value. In the event of a fault, an out- put is actuated and the LEDs indicate the fault. Partial load faults Depending on the setting of the "response time" potentiometer, a deviation of at least 1/6 of the stored setpoint value after a re- sponse time of between 100 ms and 3 s is signaled as a fault. The fault is indicated by a "Load" LED and by activation of the fault signaling output. The heating current monitoring has a teach input and therefore differs from the load monitoring. This remote teaching function enables simple adjustment to changing loads without manual intervention.
The potentiometer can also be used to determine the response behavior of the fault signaling output. When delay values are set in the left-hand half, the fault signal is stored. This can only be reset by switching on and off by means of the control supply voltage. ■ Design Mounting Easy snapping onto the 3RF21 solid-state relays or 3RF23 solid- state contactors establishes the connections to the solid-state switching devices. Because of the special design, the straight- through transformer of the heating current monitoring module covers the lower main circuit connection. The cable to the load is simply pushed through and secured with the terminal screw.
When settings are made on the right-hand side, the fault output is automatically reset after the deviation has been corrected. Voltage compensation In addition to the current, the load voltage is also detected. This makes it possible to compensate for influences on the current strength resulting from voltage fluctuations. Thyristor fault If a current greater than the leakage current of the controls is measured in the deenergized state, the device triggers a thyris- tor fault after the set delay time. The fault output is activated and the "Thyristor" LED lights up.
Power system fault If no current is measured in the energized state, the device trig- gers a power system fault after the set delay time. The fault out- put is activated and the "Supply" LED lights up. 48 Siemens · 2009