Tuning fork level switch
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There is an alarm from a FEL54 fork-type level switch at the site; the wiring is fine, and there are no issues with the connection to ground. The automation system indicates that it’s a 24V signal – but isn’t it supposed to be an on/off signal? What does 24V mean? Does anyone have the manual for this device? Previously, it was connected using a DCS system, but now it’s connected via a SIS system. Are the wiring requirements the same for both?
A normal operation of the DCS alarm is indicated as 0 (no power), while a normal operation of the SIS interlock is indicated as 1 (with power). Underreporting connects to NC for low interlock, and overreporting connects to NO for high interlock. Since it is not possible to use a multimeter to determine continuity when there is a voltage present, the continuity of the terminals is determined by measuring the voltage between them; 24V indicates an open circuit, while 0V indicates a closed circuit. I understand; please refrain from commenting if you’re not interested.
In the left set of terminals, L1 and N provide 24VDC power to drive the internal circuits; the 6 terminals on the right consist of two sets of normally open and normally closed (DPDT) contact signals. The power supply is connected to the left side, while the DO signal outputs are connected to the right side. If the DCS and SIS share the same fork switch, it is sufficient to connect one set to each of the contact signals on the right side.