Why is signal amplification needed in instrumentation?

Signal amplification increases weak sensor signals to levels suitable for processing and transmission. Many sensors produce millivolt-level signals (thermocouples, strain gauges) that are susceptible to noise. Amplification improves signal-to-noise ratio by boosting the signal before noise can corrupt it. Amplifiers also provide impedance matching (high input impedance to not load sensor, low output impedance to drive cables), filtering, and level shifting. Instrumentation amplifiers with high common-mode rejection are commonly used.