Op-amps are essential for signal conditioning. Without them, meters and inverters would not be able to accurately measure and process the voltage signals from the CT and burden resistor. Nor the high voltages from the busbars.
Operational Amplifier Circuit
💡 Op-Amp's Role in Signal Conditioning
Current → Voltage conversion happens at the burden resistor (V = I × R)
Op-amp then amplifies this small voltage to a usable level:
Example: 100mV from burden → 1V for ADC input
Gain of 10 needed (Rf/R1 = 10)
Differential measurement:
Measures voltage difference between V1 and V2
Rejects common-mode noise
Improves measurement accuracy
📶 Noise and Filtering
Op-amps amplify both signal and noise:
EMI from nearby power circuits
Switching noise from inverter operation
Grid harmonics and transients
Noise reduction methods:
Hardware: RC filters before op-amp input
Software: Nyquist sampling and digital filtering
PCB layout: Proper shielding and grounding
⚡ Signal Chain Example
CT outputs 1A secondary current
0.1Ω burden resistor creates 100mV (V = 1A × 0.1Ω)
Op-amp amplifies 100mV to 1V (Gain = 10)
ADC can now accurately read the signal
Signal Conditioning Best Practices
✅ Do
Use voltage dividers for high voltages
Include protection circuits
Buffer your inputs with op-amps
Filter noise before sampling
Consider temperature effects
❌ Don't
Connect high voltages directly
Ignore loading effects
Skip protection components
Forget about ground references
Neglect noise considerations
🌡️ Temperature Sensing Applications
Op-amps are crucial for temperature measurement circuits, working alongside specialized ICs:
Temperature sensors (like PT100, thermocouples) output small voltage changes
Specialized ICs (e.g., MAX31865) convert resistance to digital values