#panel switch

Motor Stop Alarms

Panel frames get their mechanical power from duplex electric motors that are mounted at the base of the frames. Each frame is equipped with motor stop alarms. Here, I've removed the cover plate of the alarm governor and contact assembly to show how the alarm works: First, note the spinning governor, and the 3 relay contacts that it acts upon. When the motor is spinning, the arms of the governor are pulled out by centrifugal force, which pulls the top of the governor away from the center contact, allowing it to move into its normal "things are okay" position. When the motor is stopped, a spring forces the governor to elongate and strike the center relay contact. This closes ground to the front contact, which completes a circuit to trigger the alarm.

In the panel switch, the decoder frame is a type of translator. It takes an input from the sender, and provides output back to the sender. If it helps, you can think of it just like a database in a modern computer. 

When a subscriber dials a telephone number: 722-5678, the first three digits (722) is called the office code. The office code determines where the switch should send the call to reach the called station (the last four digits, or “5678″). The office code could refer to the local switch (an intraoffice call), or a distant switch (an interoffice call). In order to reach the desired office, the sender will need to set it’s internal registers in such a way that it can direct the selectors to a physical location on the switching fabric to advance the call. In addition, it will need to set additional registers that will tell it how to proceed once it connects to the desired set of terminals to reach the called office. All of the information the sender needs to complete a call comes from the decoder.

The decoder has its own framework, relay cabinets, and test equipment. For each call that the panel switch originates, the decoder is accessed once. On a busy day, the decoder could be accessed tens of thousands of times. Because of this, there could be up to six decoders in one office, that would be shared and load balanced as required by the senders. Since each decoder is accessed so frequently, a single fault could cause a great deal of calls to be mis-routed. In order to avoid this possibility as much as possible, there are a few things the decoder has at its disposal:

A decoder test frame, which can perform a number of tests on the decoder and decoder connector circuits.

A decoder trouble indicator, which lights lamps to display the state of the decoder upon failure.

Self-checking circuitry and alarms to proactively detect failure, and alert office staff. If trouble is detected, a bell rings, and the decoder instructs the sender to try again with a different decoder unit.

This week, we had several problems with the decoder, so I decided that I should finally get around to hooking up the decoder alarm bells and lamp indicators. Here’s a quick video showing the decoder test frame, decoder trouble indicator, and the two types of alarms that can be generated.