Single Phase Zero Crossing Detector For PLC
Published on : Tuesday 12-04-2022
N Vinay Saketh explains how to check the circuit for detecting zero crossing in the input power source.
Detecting Zero crossing in an input power source gives us the advantage to control the timing of switching ‘On’ our high current load. In this article we can check the circuit for detecting zero crossing in the input power source, this circuit has been verified and tested practically.
Circuit and Simulation
We will be using PC817A for detecting the zero crossing; here the IR in the PC817A will not turn On until its Anode voltage is greater than the Cathode voltage and when the IR is On, then the GND is connected to the Input of the PC817A and making the higher values zero, hence we can easily observe the zero crossing of the Input signal.
Simulation is done in LT Spice software; Figure 1.1 is the actual zero crossing circuit for PLC and Figure 1.2 is the power supply circuit to the circuit.
Figure 1.3 shows the simulation results in LT Spice; in this figure you can see that zero crossings are clearly identified and max peak of the green wave is 24V.
We can also make full wave and half wave zero crossing detector by using a half wave rectifier and bridge rectifier. The result to be noted that the zero crossings are same in half wave and bridge wave rectifier.
Using Phoenix Contact PLC
Here let us use a Phoenix Contact ILC 131 ETH PLC shown in Figure 1.5, The ILC 131 ETH modular small-scale controller for the Inline I/O system is at the heart of easy automation. The ILC 1X1 series is characterised by its support for the Modbus/TCP and PROFINET Ethernet-based protocols. A new feature is the support for an optional SD card.
1. Memory extendable by up to 2 GB via plug-in SD card
2. Free engineering with PC Worx Express (IEC 61131-3)
3. Complete INTERBUS master (4096 I/O points)
4. PROFINET-Device
5. Modbus/TCP-Client
6. Integrated FTP and HTML5 web server
7. Numerous protocols supported such as: HTTP, FTP, SNTP, SNMP, SMTP, SQL, MySQL, etc.
We have used Ladder Logic to program the PLC to identify the Zero Crossings. If you take the output of the zero crossing detector circuit and connect it to a digital input of the PLC, and make the Ladder diagram as follows, you can easily identify the zero crossing and switch on the loads accordingly. Figure 1.6 shows the ladder logic in PC Worx software by Phoenix Contact.
Conclusion
Using PC817A we can easily identify the zero crossings in a 50Hz and 60Hz power frequency inputs for switching on heavy current loads.
N Vinay Saketh, Senior Electrical Engineer, M/s Entek Technical Services, Hyderabad, India. A self-taught PLC programmer and electrical engineer, Vinay is the inventor of NELVAC Cables, with interest in research and development of new electrical technologies. He is known for his wide knowledge in marketing strategies and customer relations. Vinay practiced marketing and got qualified leads for the company. He has also completed multiple research projects in Electrical Technology such as Gauss Meter and Magnetic Particle Inspector. Vinay is well versed with Energy Management System and Power Quality mitigation methods; he has also designed APFC panels and distribution boards.
https://orcid.org/0000-0002-3127-9281
