The interrupter is a 10Vac motorized device that has cams and contacts that deliver interrupted electricity as the cams turn. Steady generator and steady lamp battery are connected to the sets of contacts respectively, and the output leads deliver interrupted generator (1 second on/3 seconds off) for common bells, and interrupted lamp battery as follows:
60 ipm / 50% break for lamp flash ("LF"). Used to indicate an incoming call.
120 ipm / 5% break for lamp wink ("LW"). Used to indicate call Hold.
"Flutter" is a lamp supply that has an extremely rapid interruption rate (I seem to recall that it is 5 interruptions per second) that is not provided mechanically by standard interrupters. It is provided by an electronic timing circuit, and is used to indicate a call that has been placed on "I Hold" (pronounced "eye hold" -- the "I" stands for the person who placed the call on Hold, like "me").
I-Hold is a feature that is used in a large office (today they are called call centers) where it is is imperative that the person answering the call be the only one who can place it on Hold and retrieve it from Hold. This is important for a business that wants to ensure that an agent is the only one to talk to a caller, so that the caller is not inconvenienced by having to start his story all over again when the first agent places him on hold and goes to get some information.
Generally, I-Hold could only be offered on Call Director type telephones, with replaceable 598-type key strips. The first key strip usually has a red Hold key, and 5 clear (uncolored) line keys. Each successive key strip has 6 uncolored line keys. An 18-key Call Director (630 series) has three key strips, of 6 keys each, and a 30-key Call Director (631 series) has 5 key strips.
For I-Hold, the first key strip is replaced in the field with a special key strip that has a red Hold key, followed by a green I-Hold key, followed by 4 line keys.
To place a call on "regular" hold, the user presses the red Hold key as usual, and anyone who has access to the Held line can go back into the connection.
To place a call on I-Hold, the user presses the green key, and the line being placed on Hold can only be accessed by that person. The line lamp flutters at the "I" person's phone, and stays steady (or winks, depending upon the type of service requested by the customer) at all other appearances of the line.
This feature can be provided these days through software on electronic key systems. I am only vaguely familiar with electronic key systems, predominately the Samsung ones. On a Samsung Prostar system, if the user presses the red Hold key once, he puts the call on Hold. If he presses the Hold key twice in succession, he puts the call on "I-Hold." (I think they call it "priority Hold" or something like that.)
If you would like to chat about the various 1A, 1A1, and 1A2 systems and their oddities, feel free to email me to set up a phone call. It's easier to ramble on and on about this stuff by voice, rather than by teletype, like this.
