A gas detector includes a membrane configured to define a sensing chamber of the gas detector; a strain sensor operatively connected to the membrane, the strain sensor configured for generating output signals related to strain in the membrane; and a controller operatively connected to the strain sensor, the controller configured to: determine a strain in the membrane based on the output signals; and determine a condition of the membrane based on the determined strain, wherein the determined condition indicates whether the membrane is blocked.

A performance evaluation device of a membrane filtration device is a device for evaluating the performance of the membrane filtration device in pure water production equipment. The performance evaluation device includes branch lines that branch off at the inlet of the membrane filtration device from a line on which the membrane filtration device of the pure water production equipment is provided, and at least one evaluation filtration membrane device is connected to the branch lines. At least one of the evaluation filtration membrane devices has the same type of membrane as that of the membrane filtration device, and the membrane area of the membrane of at least one of the evaluation filtration membrane devices is smaller than the membrane area of the membrane of the membrane filtration device.