| 摘要 |
<p>The specification describes a system to indicate the position of the tongues, in a track installation where pivotal tongue switches are interposed between the main track and the tangent track to govern traffic, the system comprising two limit switches positionable on opposite sides of each tongue and having actuators separated by the included angle of tongue movement between the home positions of each tongue, each limit switch at one tongue being paired to a limit switch at the other tongue corresponding to a home position, the limit switches thus paired each having two pairs of normally closed contacts arranged in parallel to one another which open only when the tongues are in home position, the two pairs of parallel contacts of one limit switch being joined in series to the two pairs of parallel contacts of the other limit switch and the respective pairs being series-connected to a time delay relay which thereby starts to time out as the tongues are in transit, and the time delay relay having normally open contacts series-connected to an indicator which is energized by closure of the time delay relay contacts if the tongues are too long in transit.</p> |
