Differences Between Simplex, Duplex And Semiduplex Voice Communication
Industrial communication is one of the most vital types of voice communications as it is directly connected with the safety of sites, personnel and environment. The modern development level of industrial communication technologies allows creating flexible and reliable systems providing various functional capabilities depending on the customer’s requirements.Communication systems used for normal operation maintenance at production and transportation sites are usually referred as industrial intercom systems and PA/GA (Public Address and General Alarm).
The systems are used for timely managing of production processes in areas (where the technological equipment is installed) with harsh operating conditions and high requirements to their reliability. These systems shall establish quick and easy connection and reliable communication between the site personnel. Simplex communication meets these requirements most fully.
As for the terminology, simplex communication is a communication session with one-way transmission of data without sending answer messages. Simplex connection between subscribers is established only for the period of data (voice) transferring in one way and is terminated immediately after the session end. The other party shall establish a connection for the answer in the back direction. A group can be the recipient of the data as well as one subscriber.
In contrast to duplex communication, simplex can be one-way and two-way depending on requirements.
During a duplex connection, both receive and transmit channels are established; they are not connected between each other. It allows receiving and transmitting the information simultaneously. The most common type of duplex connection is a telephone conversation by means of a handset. The other example is a PC handset. Unfortunately, industrial intercom in the duplex mode is not possible as the microphone and speaker will have acoustic feedback. This term is referred to the effect which is created when a signal from the speaker is picked up by the microphone. As the speaker power in the loudspeaking mode is quite high, it can result in endless signal amplification and, as consequence, the impossibility of communication.
However, it doesn’t mean that simultaneous two-way communication of high quality can’t be established at industrial enterprises. Semiduplex (halfduplex) connection is used for this purpose. The peculiarity of this connection type is that data is transmitted only in one way at the current moment. During an active communication session, the data is being received or is being transmitted only. The communication direction can be controlled by the subscriber, for example, by pressing the special key Talk or by the special automatic system (for example, echocanceller or feedback suppression circuit). The telephone communication in the Hands-Free mode (“speakerphone”) can be the example of semiduplex mode. The built-in chip for acoustic feedback suppression controls automatically the connection of the subscriber device microphone and speaker making the subscriber which is speaking at the given moment of time active. Unfortunately, all the automatic duplex systems add some distortion to the wanted signal. The higher level of the ambient noise and the device volume are, the higher distortion is, so the automatic semiduplex is almost unusable in industrial environment.
So, the general peculiarities of all connection types are described here. The next part of the material will be devoted to simplex communication specifics in terms of industrial intercom systems functions.
See also:
Armtel intercom and PA/GA systems
Simplex In Industrial Intercom Systems. Part 2
