Industrial Electronics
This domain covers what sits between the wiring and the machine: rectification and smoothing, switching devices, sensing and signal conditioning, PLC input/output interfacing, variable-speed drives, and the protection and screening needed where electronics meets industrial noise.
Rectification and smoothing
Half-wave rectification gives roughly 0.45 Vrms; a full-wave bridge gives roughly 0.9 Vrms, minus two diode drops (about 1.4 V for silicon). Add a reservoir capacitor and the DC output rises towards Vpeak (√2 Vrms minus the diode drops), with a ripple of approximately I/(2fC) for a bridge on a 50 Hz supply.
Worked example
A 24 V AC secondary feeds a bridge rectifier with a 2200 µF reservoir and a 0.5 A load. Vpeak = 24 × 1.414 = 33.9 V; subtract two diode drops to give about 32.5 V. Ripple = 0.5/(2 × 50 × 0.0022) = 2.3 V, so the DC sits roughly between 30 V and 32.5 V. That is why a 24 V transformer can never be treated as a 24 V DC supply for a 24 V relay or sensor.
Interfacing and protection
- A PNP (sourcing) sensor needs a sinking input; an NPN sensor needs a sourcing input - a mismatch gives a permanently on or off signal.
- A 4–20 mA loop puts zero at 4 mA so a broken wire reads as a fault rather than a valid zero.
- Fit a freewheel diode across DC coils, and an RC snubber or varistor across AC coils, to protect the switching device.
- Screen signal cable and earth the screen at one end only to avoid circulating currents.
Traps
Using the 0.9 factor when a smoothing capacitor is fitted; forgetting diode drops; switching a DC inductive load with an AC-rated contactor; and forgetting that a TRIAC latches on and needs zero-crossing or commutation to turn off.