2 HARDWARE DESIGN
The P15D hardware comprises of following main components:-
• The housing, consisting of a front panel and connections at the rear
• Micro controller with DSP module
• Analogue input circuit
• Digital input circuit
• Digital output circuit
• Impulse output circuit
• Communication circuit
• Power supply unit
• Human machine Interface (HMI) module
• External battery backup circuit
Figure 1: P15D Hardware modules
2.1 Overview of Hardware design
The P15D hardware design overview is explained with the help of the schematic diagram. The P15D
hardware consists of three sets of internal Current Transformers (CTs). Each set consist of three
numbers of the CTs basically designed to cater to internal power supply requirements (5 V and 24 V)
with rectifier and MOSFET circuit and overcurrent protection requirements. Dedicated CT is available
for the earth fault protection requirements. The relay also has provision for the built-in SMPS unit
which accepts power supply input of 24-50 V DC or 100-230 V AC/DC from external source and
outputs of 12 V and 24 V DC for internal circuitry. The current signals acquired as analogue inputs get
processed through operational amplifier, filter circuit, multiplexer, ADC (analogue to digital circuit) and
finally fed to CPU.
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