The Feeder That Delivered 228 V Instead of 240 V
A feeder calculation can miss half the resistance when it counts only the outgoing conductor and forgets the return path.
Subject: Electrical Computer
The Motor Load That Drew More Current Than the kW Suggested
A kW-only three-phase current calculation can look correct and still undersize a feeder when power factor is below unity.
The Op-Amp That Tried to Output -10 V on ยฑ5 V Rails
A correct inverting-gain calculation can still request an impossible output. Check the supply rails before accepting the result.
The Transistor That Refused to Amplify 100ร
An NPN switch has VCC = 5 V, Rc = 100 ฮฉ, ฮฒ = 100, and Ib = 1 mA. ฮฒIb predicts 100 mA, but with VCE(sat) โ 0.2 V the collector circuit can supply only about
The Protection Diode That Starved the 5 V Sensor
A 5 V source drives a forward-biased silicon diode and a 1 kฮฉ resistor in series. Using a 0.7 V silicon forward-drop model, the measured current is about 4
The Digital Filter That Lagged a Perfect Step
Unity DC gain does not mean instant response. Step through a recursive digital filter and see why its output rises gradually.
The 1 kHz Filter That Only Passed 70.7%
Cutoff does not mean fully passed. A first-order low-pass is already at 0.707 amplitude at fc.
The Vibration Sensor That Invented a 300 Hz Tone
A 900 Hz vibration can look like a clean 300 Hz signal when the ADC samples too slowly.
The Transfer Function That Settled at 5, Not 20
A transfer-function numerator is not automatically the steady-state gain. Diagnose why H(s) = 20/(s+4) gives a unit-step final value of 5.
The RLC Circuit That Peaked Instead of Filtering
An inductor and capacitor do not always add opposition. At series resonance, their reactances cancel and current can reach its maximum value.