The weighing method is a classic method for preparing international and domestic standard gases. In the past, precision mechanical balances were usually used as standard gas preparation tools, and there has been a set of relatively mature methods for evaluating and calculating the uncertainty of the balance weighing process. In recent years, with the development of electronic balance technology, more and more precision electronic balances are used to prepare standard gases.

1. Scope of application

The weighing method is the method recommended by the International Organization for Standardization. It is only suitable for gases that do not react between the components, the components and the inner wall of the gas cylinder, and the condensable components that are completely in the gaseous state under experimental conditions.

2. Required equipment

The standard gas preparation equipment is composed of a gas filling device, a gas weighing device, a gas cylinder and a gas cylinder pretreatment device.

The gas filling device is composed of a vacuum unit, an ionization vacuum gauge, a pressure gauge, and a gas circuit system consisting of high-pressure, medium-pressure and low-pressure vacuum systems.

The weighing of the component gas is the key to preparing the standard gas. A high-precision balance with a large load (20kg) and a small sensing volume (10mg) is required.

Weighing precautions include: (1) Use reference gas cylinders of similar mass for weighing. (2) Add and subtract missing codes to eliminate unequal arm error. (3) Weigh after the cylinder is fully balanced. (4) Handle with care and keep the cylinder clean. (5) The weighing operation is performed three times, and the average value is taken.