| 摘要 |
A system for monitoring the liquid level in containers such as boilers and tanks. An electrode inserted into the container completes a path through the liquid when the liquid is at or above a predetermined level. When the liquid falls below the level, the path is opened. If the open path persists uninterruptedly for a timed period, an output device such as a relay is energized (or deenergized, if desired) to signal the low fluid level. The circuit path is powered at a low AC level from an AC source which also powers the output device. The low level AC in the circuit path to the liquid minimizes electrolytic and other problems within the container. The low level AC periodically resets a timing device within a direct current monitoring circuit before the expiration of the timed period, as long as the circuit path through the liquid remains closed. The output device is an optical coupling device isolating the output device from the timing device and from the low level AC path.
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