Final answer:
An accurate vacuum reading is obtained by placing the vacuum gauge close to the system being evacuated to measure negative pressure directly and avoid influences causing pressure drops. The gauge should measure gauge pressure, which is relative to atmospheric pressure, and it must be installed in a stable location for consistent readings, ensuring the observer's eye level is aligned with the gauge marker to avoid parallax error.
Step-by-step explanation:
To obtain an accurate vacuum reading during system evacuation, it is best to place the vacuum gauge as close to the system as possible, rather than on the vacuum pump itself. This positioning ensures that the gauge measures the vacuum pressure of the system directly, without the influence of factors like the length of the vacuum hose that can cause pressure drops and result in inaccurate readings.
When a pressure gauge is related to a vacuum system, it should be able to measure negative pressure, which occurs when the system pressure falls below the atmospheric pressure. Gauge pressure readings indicate pressure relative to the atmospheric pressure; for instance, a manometer connected to a vacuum system might show a negative value if it measures pressure that is less than the external atmospheric pressure.
To further ensure accuracy, the gauge should be installed where it is unaffected by the system's operations, such as temperature fluctuations and vibration. Having the gauge in an appropriate spot can reduce potential measurement errors and provide a more accurate reading of the vacuum conditions. Additionally, analog gauges need to be read with the eye level to the marker to avoid parallax error.