Instrumentation, Measurements and Spacecraft Electronics
Instrumentation, Measurements and Spacecraft Electronics tests transducers, bridge circuits, error analysis, electronic measurement, and the radiation and reliability constraints of space hardware.
Core rules
- Accuracy is closeness to truth; precision is repeatability. Systematic errors shift the mean; random errors set the spread.
- Wheatstone bridge balance: R1/R2 = R3/R4. For a single active strain gauge, ΔV/V ≈ (GF·ε)/4.
- Gauge factor GF = (ΔR/R)/ε; semiconductor gauges have higher GF but greater temperature sensitivity.
- Thermocouples need cold-junction compensation; RTDs are linear but suffer self-heating; thermistors are nonlinear.
- CRO: deflection sensitivity is in V/div and timebase in s/div; probes load the circuit under test.
- Spacecraft: TT&C links, telemetry, power bus, redundancy and radiation hardness. Single-event upsets are soft errors; latch-up can be destructive. Thermal vacuum and vibration are standard qualification tests.
Worked example
A 350 Ω strain gauge with GF = 2 is bonded to a member under 500 µε. ΔR/R = GF·ε = 2×500×10^−6 = 1×10^−3, so ΔR = 0.35 Ω. In a quarter-bridge with 5 V excitation, the differential output is approximately V·(ΔR/R)/4 = 5×0.001/4 = 1.25 mV. That small signal needs a high-gain instrumentation amplifier with good common-mode rejection; lead resistance and temperature drift can easily dominate if not compensated.
Traps
- Confusing accuracy with precision.
- Using the full-bridge formula for a quarter bridge.
- Ignoring cold-junction compensation.
- Forgetting probe loading in CRO measurements.
- Treating all radiation effects as destructive; SEUs are recoverable, but latch-up may not be.