A gauge is pegged when its reading sits at a range limit: a Pirani showing atmosphere, an ion gauge showing its overrange code, or a cap manometer stuck at full scale. The word comes from analogue needles resting against the end stop. It means either the pressure really is outside the gauge's range or the gauge or its cable has failed, and the next step is to cross-check against another gauge.
Foreline Pirani's pegged at atmosphere but the turbo's at speed, so it's the gauge, not the vacuum.
Also heard as
- railed
- pinned
- maxed out
Related terms
Pirani gauge
Thermal conductivity gauge that reads pressure from how quickly gas carries heat away from a hot wire.
Capacitance manometer
Diaphragm gauge that reads true pressure, regardless of gas type, from the capacitance of a flexing diaphragm.
Ionization gauge
Gauge that reads high and ultra-high vacuum by ionizing gas molecules and measuring the resulting ion current.