Circuits, Formulas and Tables Electrical Engineering - Basic vocational knowledge (Institut für Berufliche Entwicklung, 201 p.) 2. Bell Circuits (introduction...) 2.1. Direct-current Bell 2.2. Alternating-current Bell 2.3. House Bell Installation 2.4. Alarm Systems

Circuits, Formulas and Tables Electrical Engineering - Basic vocational knowledge (Institut für Berufliche Entwicklung, 201 p.)

2. Bell Circuits

The reference letters and numbers in the illustrations of bell circuits have the following meanings:

a	switch	E	voltage source
b	control switch	f	transducer
c	contactor	g	measuring instrument
d	auxiliary contactor, relay	h	visual and audio alarm
e	protective device	Tr	transformer

2.1. Direct-current Bell

Direct-current bell to be actuated from one place

Direct-current bell to be actuated from two places

Bell installation for reciprocal calls

Sell installation for reciprocal calls with key change-over switch

Bell installation for reciprocal calls with switch-on push-button, line-saving

Bell installation for reciprocal calls, line-saving

2.2. Alternating-current Bell

Alternating-current bell with bell transformer, simple circuit

Bell installation with change-over switch

2.3. House Bell Installation

Circuit of a house bell installation

Circuit of a house bell installation with electric door operator

2.4. Alarm Systems

Circuit of an alarm system with normally open contacts b₁ test key, 1 glass panel

Circuit of an alarm system with normally closed contacts b₂ test key, 1 glass panel