Solid-State Switching Devices for Resistive Loads 3RF29 Function Modules Load monitoring ■ Overview Partial load faults, "Basic" load monitoring If a deviation of at least 1/6 of the stored setpoint value is detected, a fault is signaled. The fault is indicated by a "Fault" LED and by activation of the fault signaling output. Load monitoring for 3RF2 single-phase solid-state switching devices 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 load elements (up to 6 in the basic version or up to 12 in the extended version), alloyed power semiconductors, a lack of voltage or a break in a load circuit. A fault is indicated by one or more LEDs and re- ported to the controller by way of a PLC-compatible output. 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 by the simple press of a button. In order to detect the failure of one of several loads, the current difference must be 1/6 (in the basic version) or 1/12 (in the extended version) of the reference value.
In the event of a fault, an output is actuated and one or more LEDs indicate the fault. ✓ LED is lit -- LED is not lit Partial load faults, "Extended" load monitoring ■ Design Depending on the setting of the "response time" potentiometer, a deviation of at least 1/12 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. 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 load monitoring module covers the lower main circuit connection. The cable to the load is simply pu- shed through and secured with the terminal screw. 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. ■ Function When settings are made on the right-hand side, the fault output is automatically reset after the deviation has been corrected.
The function module is activated when an "ON" signal is applied (IN terminal). The module constantly monitors the current level and compares this with the setpoint value. Voltage compensation, "Extended" load monitoring 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. Pressing the Teach button or actuating the input IN2 switches the device on; the current through the solid-state switching de- vice is detected and is stored as the setpoint value.
During this process the two lower (red 1) ) LEDs flash alternately; simultane- ous continuous light from the 3 (red 1) ) LEDs indicates the con- clusion of the teaching process. Startup 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. This means that the fault output is activated and the "Fault" ("Thyristor" 1) ) LED lights up. The Teach button can also be used to switch on the connected solid-state switching device briefly for test purposes. In this case the "ON" LED is switched on.
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. This means that the fault output is activated and the "Fault" ("Supply" 1) ) LED lights up. 1) Only "Extended" load monitoring. 47 Siemens · 2009 LEDs OK Fault Partial load failure/ load short- circuit Thyristor defect Mains failure/ Fuse rupture ON/OFF ✓ ✓ -- ✓ Current flowing ✓ ✓ ✓ -- Group fault -- ✓ ✓ ✓