Indicator
Indicators are electromechanical display or signaling devices that can optically indicate two states: de-energized and energized (i.e. a voltage is present ).
Among other things, they were used in analog telephone technology as a call or busy indicator (e.g. in the A2 circuit ). Further applications are control rooms for plants and power plants as well as displays for landing flaps, landing gear or scrolling indicators in the cockpit of aircraft.
The advantage over signal lamps is that they can be controlled with very little power and (e.g. compared to incandescent lamps) have an almost unlimited service life. They can also be seen in bright lighting. In contrast to this, the related drop flap relays are triggered by a voltage pulse and remain in this position until manual reset. You can use this to report an event when it has occurred.
Today, indicators have mostly been replaced by other optical displays such as light-emitting diodes .
Types
There are essentially three different types in historical telephones and switching systems:
- Star indicators have a circular sector pattern, which is visible when spoken to by a rotatable, equally shaped disc (rotating anchor) behind it. Use as a single indicator, for example with the FeTAp 615 telephone .
- Similar to drop flap relays, throttle indicators have a surface ("flag") that is triggered by an anchor and appears behind a window.
- On such a flag, stripe or grid indicators have a stripe pattern that is quietly covered by a grid in front of it. They are often strung together to form multiple fields and were used in hand-operated telephone switching cabinets.
Switch position indicators have three positions and can be used as remote monitoring to display the states "Off", "On" and "Fault", for example of a circuit breaker .
Layout and function
All indicators work electromagnetically with magnetic coils .
Star indicators are cylindrical components with a diameter of 12 or 18 mm and a height of 30 mm. On the front side there is a star-shaped cut-out cover under which the mostly red or black viewing star, which is rotatably mounted on an axis, is located. In the non-excited state, it is held in the rest position by a small spiral spring and is thus covered. When current flows through, a magnetic field is built up, which turns the wing cross, which serves as an anchor, into the field of vision. When the current is switched off, it is reset by the spring.
Stripe indicators consist of a stripe pattern covered by a grid and moved by a hinged armature, which, when excited, shifts by exactly one grid spacing and thus emerges as a contrast.
As a rule, indicators are designed for direct current operation and, depending on the version, have an electrical resistance of 25 to 15000 Ω. In the highest resistance version they respond at a current of 0.75 mA , up to a current of 15 mA in the lowest resistance version. In telephone systems , they are often in series in the telephone line and react to the current flowing when they are picked up.
Switch position indicators are often equally suitable for direct and alternating voltage (e.g. 300 volts).
See also
Individual evidence
- ↑ a b c d e Handbook of Telecommunications Technology, Volume 10, Basics of Switching and Assembly Technology, as of spring 1980, p. 114
- ↑ Handbook of Telecommunications Technology, Volume 6, Telephones, Telephony Suppression, PABXs as of spring 1980, p. 19
- ↑ http://www.erel.de/ALLG/GLOSSAR/schauz.htm Private page on historical telephones
- ↑ Archived copy ( Memento of the original dated August 31, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Website of the Gossen company
- ↑ Archived copy ( memento of the original from January 12, 2011 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
